Download How do you test for simple sugars?

P IP in P A
D llS lL J tZ H
B io lo g ic ! molecules— proteins, carbohydrates, lipids, and nucleic
a c j£j s— interact to carry out activities necessary to living cells.
a bS taflny.
How do you test for
simple sugars?
Many different food sources supply the energy
that your body uses constantly. This energy is
stored in the bonds of molecules called simple
sugars. In this lab, you w ill test several mixtures
to determine if a simple sugar is present.
824
connectED.mcaraw-hill.com ;l
Skin cells— nucleic acids
Fats provide more than twice the energy per gram as carbohydrates
and proteins. Special lipids, callea phospholipids, make up the cellular
membranes of living cells.
SECTION 1
E s s e n tia l Q u e s tio n s
• How can the structures of amino
acids and proteins be described?
• What are the roles of proteins in
ceHS7
p o ly m e r: large molecules composed
of many repeating units called
monomers
N e w V o c a b u la r y
protein
amino acid
peptide bond
peptide
denaturation
enzyme
substrate
active site
Proteins
M A I N I D E A Proteins perform essential functions, including struc­
tu ral support, tran sp o rt o f m aterials, muscle contractions, and regulation
o f chem ical reactions.
_ „ „ _ —_
CHEM
4
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Some cleaning products, such as contact lens cleaning
solution, contain enzymes. Did you ever wonder w hat an
enzyme was?
Protein Structure
Enzymes form a class o f proteins. Proteins are organic polymers made
o f amino acids linked together in a specific order. Proteins are not just
large, randomly arranged chains of amino acids. To function properly,
each protein must be folded into a specific three-dimensional structure.
All living organisms, including the mountain goat and the plants shown
in Figure 1, are composed o f proteins. In this section, you will read
about how proteins are made from their amino-acid building blocks
and how different types o f proteins function.
A m in o a c id s As you read previously, many different functional
groups are found in organic compounds. Amino acids, as their name
implies, are organic molecules that have both an amino group and
an acidic carboxyl group. The general structure o f an amino acid is
shown below.
R
Amino group
Variable side chain
I
H?N— C — C — OH Carboxyl group
Hydrogen atom
I
H
II
O
Each amino acid has a central carbon atom around which four groups
are arranged: an amino group (—NH2), a carboxyl group (—COOH), a
hydrogen atom, and a variable side chain, R. The side chains range from
a single hydrogen atom to a complex double-ring structure.
■Figure 1 All living organisms contain
proteins. A goat's hair, hooves, and muscles
are made up of structural proteins, as are
the roots and leaves of plants.
826
C hapter 23 • The Chemistry of Life
Explore amino acids w ith an interactive table,
f
Am ino Acid Examples
T a b le 1
c h 2-
OH
SH
ch2
cn2
cn2
ch
I
H
I
H2N - C - C - O H
I
I
H2N - C - C - O H
II
H
I
0
H
Glycine
I
II
H
0
Serine
2
2
ch2
H2N - C - C - O H
II
nh
I
0
H2N - C - C - O H
I
Cysteine
II
H
0
Lysine
0
% /
OH
0
C
\
I
C
/
nh2
2
I
\
ch2
ch2
ch2
ch2
H2N - C - C - O H
H2N - C - C - O H
I
II
H
i j g
I
0
/
CH
i
I
CH2
H2N - C - C - O H
I
II
H
II
H
Glutamic acid
i
ch3 ch3
H2N - C - C - O H
0
I
Valine
0
H
II
0
Phenylalanine
Glutamine
Examine the different side chains o f the amino acids shown in
Table 1. Identify the nonpolar alkanes, polar hydroxyl groups, acidic
and basic groups such as carboxyl and amino groups, aromatic rings,
and sulfur-containing groups. This wide range o f side chains gives
the different amino acids a large variety o f chemical and physical
properties and is an important reason why proteins can perform so
many different functions.
T h e p e p t id e b o n d The amino and carboxyl groups provide conve­
nient bonding sites for linking amino acids together. Because an amino
acid is both an amine and a carboxylic acid, two amino acids can
combine to form an amide, releasing water in the process. This reaction
is a condensation reaction. As Figure 2 shows, the carboxyl group of
one amino acid reacts with the amino group of another amino acid to
form an amide functional group.
□ READING CHECK Explain how an amide functional group forms.
■Figure 2 The amino group of one amino acid bonds to the carboxyl group of
another amino acid to form a dipeptide and water. The organic functional group
formed is an amide linkage called a peptide bond.
Peptide bond
H
R
,
H
\ m- C - C - O H
/
H
I
H O
II
A m in o acid
+
R2
Rt
\l-C -C -O H
/
H
H
I
O
II
A m in o acid
^
H
R2
N - C - C - N - C - C - O H
/
H
I
H O
II
I
H O
+
H20
II
D ip e p tid e
W a te r
Section 1 • Proteins
827
The amide bond that join s two am ino acids, shown in F ig u re 3,
is referred to as a peptide bon d. A chain o f two or m ore am ino acids
linked together by peptide bonds is called a peptide. A m olecule that
consists o f two am ino acids bound together by a peptide bond is called
a dipeptide. F ig u re 4 a shows the structure o f a dipeptide that is formed
from the am ino acids glycine (Gly) and phenylalanine (Phe). F ig u re 4 b
shows a different dipeptide, also form ed by linking together glycine and
phenylalanine. Is G ly-Phe the same com pound as Phe-Gly? No, they’re
different. Exam ine these two dipeptides to see that the order in which
am ino acids are linked in a dipeptide is im portant.
Each end o f the tw o-am ino-acid unit in a dipeptide still has a free
group— one end has a free am ino group and the other end has a free
carboxyl group. Each o f those groups can be linked to the opposite end
o f yet another am ino acid, form ing m ore peptide bonds. Living cells
always build peptides by adding am ino acids to the carboxyl end o f a
growing chain.
H
I
— C — N—
P e p tid e b o n d
II
O
■ F ig u re 3 A peptide bond joins two
amino acids to form a dipeptide.
□ READING CHECK E xplain why Gly-Phe and Phe-Gly are different
dipeptides.
Polypeptides As peptide chains increase in length, other ways o f
referring to them becom e necessary. A chain o f ten or m ore am ino acids
joined by peptide bonds is referred to as a polypeptide. W hen a chain
reaches a length o f about 50 am ino acids, it is called a protein.
Because there are only 20 different am ino acids that form proteins, it
m ight seem reasonable to think that only a lim ited num ber o f different
protein structures are possible. However, a protein can have as few as 50
or m ore than a 1000 am ino acids, arranged in any possible sequence. To
calculate the num ber o f possible sequences these am ino acids can have,
consider that each position on the chain can have any o f 2 0 possible
am ino acids. For a peptide that contains n am ino acids, there are 2 0 ”
possible sequences o f the am ino acids. So a dipeptide, with only two
am ino acids, can have 2 0 2, or 400, different possible am ino acid
sequences. Even the smallest protein, containing only 50 amino acids,
has 2 0 50, or m ore than 1 x 1 0 65, possible arrangements o f am ino acids!
It is estim ated that hum an cells m ake between 80,000 and 100,000
different proteins. You can see that this is only a small fraction o f the
total num ber o f proteins possible.
□ READING CHECK C a lc u late the possible number of sequences for a
j peptide chain comprised of four amino acids.
■ F ig u re 4 Glycine (Gly) and
phenylalanine (Phe) can combine
in two configurations.
Describe the difference
betw een the configuration o f
the peptide bonds in these
two dipeptides.
©
A
i
Gly
H O
Phe
G ly c y lp h e n y la la n in e (G ly-P he)
828
C hapter 23 • The Chemistry of Life
N - C - C - NN - C —
- Cr -— On wH ,I
/
H O
H
I
N - C - C - N - C - C - O H
/
H
H
H
H
H
I
H
Phe
II
O
I
H O
II
Gly
P h e n yla la n y lg ly cin e (P he-G ly)
■Figure 5 The folding of polypeptide chains into both helices and sheets involves
amino acids in the chain held in position by hydrogen bonds. Other interactions among
the various side chains are not shown here but play an important role in determining the
three-dimensional shape of a polypeptide.
T h re e -d im e n s io n a l p ro te in s tru ctu re Long chains o f amino
acids start to fold into unique three-dimensional shapes before they are
fully synthesized. The three-dimensional shape is determined by the
interactions among the amino acids. Some areas o f a polypeptide might
twirl into helices, which are similar to the coils on a telephone cord.
Other areas might bend back and forth repeatedly into a pleated sheet
structure, like the folds o f an accordion. A polypeptide chain might also
fold back on itself and change direction. A given protein might have
several helices, sheets, and turns, or none at all. Figure 5 shows the
folding patterns o f a typical helix and a sheet. The overall three-dimen­
sional shape o f many proteins is globular— shaped like an irregular
sphere. Other proteins have a long, fibrous shape. The shape is impor­
tant to the function o f the protein. If the shape o f the protein changes, it
might not be able to carry out its function in the cell.
D enatu ration Changes in temperature, ionic strength, pH, and other
factors result in the unfolding and uncoiling o f a protein. D en atu ration
is the process in which a proteins natural three-dimensional structure is
disrupted. Cooking often denatures the proteins in foods. When an egg
is hard-boiled, the protein-rich egg white solidifies due to the denatur­
ation o f its protein. Because proteins function properly only when fold­
ed, denatured proteins are generally inactive.
The M any Functions o f Proteins
Proteins play many roles in living cells. They are involved in speeding
up chemical reactions, transport o f substances, regulation of cellular
processes, structural support o f cells, communication within cells and
among cells, cellular motion, and even serving as an energy source
when other sources are scarce.
S p e e d in g u p re a ctio n s In most organisms, the largest number of
proteins function as enzymes, catalyzing the many reactions that occur
in living cells. An enzym e is a biological catalyst. You read previously
that a catalyst speeds up a chemical reaction without being consumed in
the reaction. A catalyst usually lowers the activation energy o f a reaction
by stabilizing the transition state.
RealWorld IHEMISTRY
Enzymes
PAPAIN A n e x a m p le o f an e n zym e
you m ig h t have used is p ap ain , fo u n d
in papayas, pineapples, and o th e r
p la n t sources. This e n zy m e catalyzes a
re ac tio n th a t breaks d o w n p ro tein
m olecules in to fre e a m in o acids.
P apain is th e active in g re d ie n t in
m an y m e a t ten d e rize rs . W h e n you
sprinkle th e d rie d fo rm o f papain
o n to m oist m ea t, th e p ap ain fo rm s a
s olu tion th a t breaks d o w n th e to u g h
p ro te in fibers in th e m ea t, m aking
th e m e a t m o re ten d er.
Watch a video about surfactants
and enzymes.
Section 1 • Proteins
829
Complex sugar
Enzymes act on specific substrates,
such as a complex sugar.
Active
sites
Each substrate fits into the active site.
The enzyme changes shape slightly to fit
more tightly with the substrate.
+ H 20
After the reaction, the enzyme released
is in its original shape and can carry
out the same reaction repeatedly.
The products are released; in this case
the complex sugar is divided into less
complex sugars.
Enzyme
■ F ig u re 6 Enzymes lower the activation energy needed for a reaction to occur.
Enzymes change the speed at which chemical reactions occur without being altered
themselves in the reaction.
■ F ig u re 7 Hemoglobin is a globular
protein with four polypeptide chains, each
containing an iron group (called a heme) to I
which oxygen binds.
Heme
How do enzymes function? The term su b strate refers to a reactant
in an enzyme-catalyzed reaction, as shown in F ig u re 6 . Substrates bind
to specific sites on enzyme molecules, usually pockets or crevices. The
spot to which the substrates bind is called the active site of the enzyme.
After the substrates bind to the active site, the active site changes shape
slightly to fit more tightly around the substrates. This recognition
process is called induced fit. The shapes o f the substrates must fit the
shape o f the active site, in the same way that puzzle pieces or a lock and
key fit together. A molecule that is only slightly different in shape from
an enzyme’s normal substrate will not bind as well to the active site and
might not undergo the catalyzed reaction.
The structure that forms when substrates are bound to an enzyme is
called an enzyme-substrate complex. The large size o f enzyme mol­
ecules allows them to form multiple bonds with their substrates, and the
large variety of amino acid side chains in the enzyme allows a number
of different intermolecular forces to form. These intermolecular forces
lower the activation energy needed for the reaction in which bonds are
broken and the substrates are converted to product.
□ READING CHECK Describe in your own words how an enzyme works.
T r a n s p o r t p r o t e in s Some proteins are involved in transporting
smaller particles throughout the body. F ig u re 7 shows the protein
hemoglobin, which carries oxygen in the blood from the lungs to the
rest of the body. Other proteins combine with biological molecules
called lipids to transport them from one part of the body to another
through the bloodstream. You will learn about lipids later in this chapter.
830
C hapter 23 • The Chemistry of Life
■ F ig u r e 8 Human hair
is made up of a fibrous structural j
protein called keratin.
SEM magnification: 500x
S t r u c t u r a l s u p p o r t The sole function o f certain proteins is to form
structures vital to organisms. These molecules are known as structural
proteins. The most abundant structural protein in most animals is
collagen, which is part o f skin, ligaments, tendons, and bones. Other
structural proteins make up feathers, fur, wool, hooves, fingernails,
cocoons, and hair, as shown in F ig u r e 8 .
C o m m u n ic a t io n H orm ones are m essenger m olecules that carry
signals from one part o f the body to another. Som e horm ones are
proteins. Insulin, a fam iliar example, is a sm all (51 am ino acids) protein
h orm one m ade by pancreas cells. W h en insulin is released into the
bloodstream , it signals body cells that blood sugar is abundant and
should be stored. A lack o f insulin often results in diabetes, a disease
that results w hen there is too m uch sugar in the bloodstream .
Because m odern technology has m ade possible the laboratory
synthesis o f proteins, som e protein horm ones are being synthetically
produced for use as m edicines. Insulin, thyroid horm ones, and growth
horm ones are som e examples. B oth natural and synthetic proteins
are used in a variety o f products—-from m eat tenderizer to cleaning
< S B ;
Incorporate information
from this section into
your Foldable.
solutions to health and beauty aids.
s e c tio n 1
REVIEW.
S e c tio n S u m m a r y
1. M A IN ID E A Describe three proteins and identify their functions.
• Proteins are biological polymers
m ade o f amino acids th at are linked
by peptide bonds.
2. Com pare the structures of amino acids, dipeptides, polypeptides, and proteins.
Which has the largest molecular mass? The smallest?
3. D ra w the structure of the dipeptide Gly-Ser, circling the peptide bond.
• Protein chains fold into intricate
three-dim ensional structures.
4. Evaluate How do the properties of proteins make them such useful catalysts?
• Proteins have many functions in the
human body, including functions
w ithin cells, functions betw een cells,
and functions of structural support.
5. Explain how a change in tem perature m ight affect a protein's function.
How do they differ from other catalysts you have studied?
6 . C ategorize Identify an amino acid from T a b le 1 th at can be classified
into each of the categories in the following pairs.
a. nonpolar side chain v. polar side chain
b. aromatic v. aliphatic
c. acidic v. basic
Section 1 • Proteins
831
M A IN IDEA
Essential Questions
• How can the structures of
monosaccharides, disaccharides, and
polysaccharides be described?
• What are the functions of
carbohydrates in living things?
N e w V o c a b u la r y
carbohydrate
monosaccharide
disaccharide
polysaccharide
Carbohydrates provide energy and structural m aterial
fo r living things.
CH EM
4
v n
, -
R e v ie w V o c a b u la r y
stereoisomers: a class of isomers
whose atoms are bonded in the same
order but are arranged differently in
space
es
A lot of media attention has been focused on carbohydrates.
Some recommend low-carb diets as a w ay of controlling
weight. However, carbohydrates are an important energy
source for the body.
Kinds o f Carbohydrates
Analyzing the term c a r b o h y d r a te offers a hint about the structure o f this
group o f m olecules. Early observations that these compounds have the
general chem ical form ula C „(H 2 0 ) „ and appear to be hydrates of
carbon led to their being called carbohydrates. Although scientists now
know that there are no full water m olecules attached to carbohydrates,
the nam e has stayed.
T he m ain function o f carbohydrates in living organisms is as a
source o f energy, both im m ediate and stored. Foods rich in carbo­
hydrates include pasta, m ilk, fruit, bread, and potatoes. Carbohydrates
are com pounds that contain multiple hydroxyl groups (— O H) as well as
a carbonyl functional group ( C = 0 ) . These m olecules range in size from
single m onom ers to polym ers made o f hundreds or even thousands of
m onom er units.
M o n o s a c c h a r id e s The simplest carbohydrates, often called simple
sugars, are monosaccharides. The m ost com m on monosaccharides
have either five or six carbon atoms. Examples o f m onosaccharides are
shown in Figure 9. Notice that they have a carbonyl group on one
carbon and hydroxyl groups on m ost o f the other carbons. The presence
o f a carbonyl group makes these compounds either aldehydes or ketones,
depending on the location o f the carbonyl group. Multiple polar groups
make m onosaccharides water-soluble and give them high melting points.
■Figure 9 Glucose, galactose, and fructose are monosaccharides. In aqueous
solutions, they exist in an equilibrium between their open-chain and cyclic forms.
H
c=o
I
H—C— OH
H /Ic-
I
HO- C - H
I
0
H- C OH
l/H
l\?H
HO c —
I
H
H -C -O H
H
,/ l
I
■C OH
H - C - OH
I
OH
Cyclic form
H
Open-chain form
G lucose
832
C hapter 23 • The Chemistry of Life
I
I
c=o
c h 2o h
H
H
I
H -C -O H
I
I
CH2OH
HO £
I
r /H
&
HO
Ov
h
VI
V/
■c OH
I
H
c=o
H -C -O H
I
I
HO- C - H
I
H -C -O H
I
H -C — OH
I
OH
Cyclic form
I
C- H
H
Open-chain form
G a la cto se
I
HO- C - H
CH2OH
Ov
4
)\ y
a t i i
h?
HO c _ _ c
I
OH
I
H
/ i
«
CH2OH
I
H -C -O H
I
H -C -O H
I
I
H
H
Cyclic form
H - C - OH
Open-chain form
Fructose
Glucose
Fructose
Sucrose
Water
■Figure 10 When glucose and fructose bond, the disaccharide sucrose forms.
Note that water is also a product of this condensation reaction. Remember that
each ring structure is made of carbon atoms, which are not shown for simplicity.
Glucose is a six-carbon sugar that has an aldehyde structure. Glucose
is present in high concentration in blood because it serves as the major
source o f immediate energy for the body. For this reason, glucose is
often called blood sugar. Closely related to glucose is galactose, which
differs only in how a hydrogen and a hydroxyl group are oriented in
space around one o f the six carbon atoms. Recall that this relationship
makes glucose and galactose stereoisomers. Fructose, also known as
fruit sugar because it is the major carbohydrate in most fruits, is a
six-carbon monosaccharide that has a ketone structure. Fructose is a
structural isomer o f glucose.
W hen monosaccharides are in aqueous solution, they exist in both
open-chain and cyclic structures, but they rapidly interconvert forms.
The cyclic structures are more stable and are the predominant form of
monosaccharides at equilibrium. Note in Figure 9 that the carbonyl
groups are present only in the open-chain structures. In the cyclic
structures, they are converted to hydroxyl groups.
D is a c c h a r id e s Like amino acids, monosaccharides can be linked
together by a condensation reaction in which water is released. When
two monosaccharides bond together, a d isacch arid e is formed, as
shown in Figure 10. The new bond formed is an ether functional
group (C -O -C ).
One common disaccharide is sucrose, also known as table sugar
because sucrose is used mainly as a sweetener. Sucrose is formed by the
linking o f glucose and fructose. Another common disaccharide is
lactose, the most important carbohydrate in milk. It is often called milk
sugar. Lactose is formed when glucose and galactose bond.
V o c a b u l a r y ..................................
W o rd origin
Polysaccharide
comes from the Greek word polys,
which means m a n y and the ancient
Sanskrit word s a rka ra , which means
s u g a r .....................................................
■Figure 11 The glycogen found in
the muscle and liver of animals is a
polysaccharide made of glucose.
P o ly s a c c h a r id e s Complex carbohydrate is a term used in some
nutrition books and journal articles. Another name for a complex
carbohydrate is p olysacch arid e, which is a polymer o f simple sugars
that contains 1 2 or more monomers, or subunits. The same type of
bond that joins two monosaccharides in a disaccharide also links the
monomers in a polysaccharide. Glycogen, shown in Figure 11, is a
polysaccharide. It is composed o f glucose subunits. It stores energy and
is found mostly in the liver and muscles of humans and other animals.
It is also found in some species of microorganisms including bacteria
Glucose
subunit
and fungi.
□ READING CHECK Explain the differences among a monosaccharide, a
T disaccharide, and a polysaccharide.
Section 2 • Carbohydrates
833
Cellulose
Cross-link bond
Glucose subunit
■ F ig u re 12 Two important polysaccharides are starch and cellulose,
a . Starch molecules can be branched or unbranched, b . Cellulose has a
linear, unbranched structure that resembles a chain-link fence.
Glucose
subunit
€m an m
Incorporate information
from this section into
your Foldable.
Two other important polysaccharides are starch and cellulose, shown
in F ig u re 1 2 . Starch and cellulose are also composed solely of glucose
subunits. However, that is the only similarity among the three poly­
saccharides, as all three have different properties and functions. Plants
make both starch and cellulose. Starch is a soft, water-insoluble
molecule used to store energy, whereas cellulose is a water-insoluble
polymer that forms rigid plant-cell walls, such as those found in wood.
Glycogen, starch, and cellulose are composed o f glucose subunits,
but they have different properties. The bonds that link the subunits
together are oriented differently in space. Because o f this difference in
,
, ,
,
,
,
, ,
„ ,
bond shape, hum ans can digest glycogen and starch but not cellulose.
Digestive enzymes cannot fit cellulose into their active sites. The
cellulose in the fruits, vegetables, and grains that we eat is called
d ie ta ry f ib e r because it passes through the digestive system largely
unchanged.
s e c tio n
z
REVIEW
S e c tio n S u m m a r y
7. MAINIDEA Explain the functions of carbohydrates in living things.
• Carbohydrates are compounds that
contain multiple hydroxyl groups
(-0H) and a carbonyl functional
group (C=0).
8 . Describe the structures of monosaccharides, disaccharides, and polysaccharides.
• Carbohydrates range in size from
single monomers to polymers
composed of hundreds or thousands
of monomers.
• Monosaccharides in aqueous solution
exist in both open-chain and cyclic
structures.
Which has the largest molecular mass? The smallest?
9. Com pare and contrast the structures of starch and cellulose. How do the
structural differences affect our ability to digest these two polysaccharides?
10. Calculate If a carbohydrate has 2 n possible isomers, where n is equal to the
number of chiral carbon atoms in the structure, calculate the number of possible
isomers for the following monosaccharides: galactose, glucose, and fructose.
11. In te rp re t Scientific Illustrations Copy the illustration of sucrose on a
separate sheet of paper, and circle the ether functional group that bonds the
monomer sugars together.
CH2OH
.0 .
HO
CH,OH
OH
834
C hapter 23 • The Chemistry of Life
Lipids
SECTION 3
M A IN IDEA Lipids m ake cell m em branes, store energy, and regulate
cellular processes.
E s s e n tia l Q u e s tio n s
• How can the structures of fatty acids,
triglycerides, phospholipids, and
steroids be described?
CH EM
• What are the functions of lipids in
living organisms?
4
• What are some reactions that fatty
acids undergo?
U
The w ax used to polish cars, the fat that drips out of hamburgers, and the vitamin D that fortifies the milk people drink— what
do Ihese things have in common? They are all lipids.
What is a lipid?
• How are the structure and function of
cell membranes related?
A lip id is a large, nonpolar biological m olecule. Because lipids are
nonpolar, they are insoluble in water. Lipids have two m ajor functions
in living organism s. They store energy efficiently, and they make up
m ost o f the structure o f cell m em branes. Unlike proteins and carbohy­
drates, lipids are n ot polymers with repeated m onom er subunits.
R e v ie w V o c a b u la r y
n o n p o la r: without separate positive
and negative areas or dipoles
N e w V o c a b u la r y
F a t t y a c id s Although lipids are not polymers, many lipids have a
m ajor building block in com m on. This building block is the fa tty acid,
a long-chain carboxylic acid. M ost naturally occurring fatty acids
contain between 12 and 24 carbon atoms. T h eir structure can be
represented by the following formula.
lipid
fatty acid
triglyceride
saponification
phospholipid
wax
steroid
C H 3 (C H 2 )hCO OH
M ost fatty acids have an even num ber o f carbon atoms, which is a result
o f being constructed two carbons at a tim e in enzymatic reactions.
Fatty acids can be grouped into two m ain categories, depending on
the presence or absence o f double bonds between carbon atoms. Fatty
acids that contain no double bonds are referred to as saturated. Those
that have one or m ore double bonds are called unsaturated. The struc­
tures o f two com m on fatty acids are shown in Figure 13.
E? READING CHECK Explain why oleic acid is described as unsaturated.
■Fig u re 13 Two fatty acids, which are found in many foods, including butter,
are the 18-carbon unsaturated oleic acid and the 18-carbon saturated stearic acid.
Explain how the structure o f the molecule is affected by the presence o f
a double bond.
Oleic acid
O,
t C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H = . C H C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 3
HO'
Stearic acid
O,
t C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 2C H 3
HO'
Section 3 • Lipids
835
■ F ig u re 1 4 Ester bonds in
a triglyceride are formed when
the hydroxyl groups of glycerol
combine with the carboxyl groups
of the fatty acids.
O
O
II
H O C (C H 2)14C H 3
c h 2o h
I
CHOH
C H ,O H
o
o
II
+ H O C (C H 2)16C H 3
II
C H - 0 - C - ( C H 2)16- C H 3 + 3 H 20
o
o
H O C (C H 2)18C H 3
Glycerol
II
C H 2 - 0 - C - ( C H 2)14- C H 3
ch
3 Fatty acids
2—
o
—
II
c — (CH2)18— c h 3
Triglyceride
Water
An unsaturated fatty acid can become saturated if it reacts with
hydrogen. As you read previously, hydrogenation is an addition reaction
in which hydrogen gas reacts with carbon atoms that are linked by
multiple bonds. Each unsaturated carbon atom can pick up one
hydrogen atom to become saturated. For example, oleic acid, shown
in F ig u re 1 3 , can be hydrogenated to form stearic acid.
The double bonds in naturally occurring fatty acids are almost all in
the cis geometric isomer form. Recall that the cis isomer has identical
groups oriented on the same side o f the molecule around a double bond.
Because o f the cis orientation, unsaturated fatty acids have a kink, or
bend, in their structure that prevents them from packing together. They
do not form as many intermolecular attractions as saturated fatty acid
molecules. As a result, unsaturated fatty acids have lower melting points.
V
ocabulary
.....................................
S c ie n c e u s a g e v . C o m m o n u s a g e
Saturate
S cience usage: to add something to
the point that no more can be
absorbed, dissolved, or retained
The s a lt w a te r s o lu tio n w as s a tu ra te d
w ith salt.
C o m m o n usage: to furnish a market
with a product or products to its full
purchasing capacity
T r ig ly c e r id e s Although fatty acids are abundant in living organisms,
they are rarely found alone. They are most often found bonded to
glycerol, a molecule with three carbons, each containing a hydroxyl
group. When three fatty acids are bonded to a glycerol backbone
through ester bonds, a trig ly c e r id e is formed. The formation of a
triglyceride is shown in F ig u re 1 4 . Triglycerides can be either solids or
liquids at room temperature, as shown in F ig u re 1 5. If liquid, they are
usually called oils. If solid at room temperature, they are called fats.
□ READING CHECK D e s c rib e the difference between fatty acids and
triglycerides.
The shops in the coa sta l to w n are
sa tu ra te d w ith sea shell c ra ft ite m s .. .
■ F ig u re 1 5 Most mixtures of
triglycerides from plant sources are
liquids because the triglycerides
contain unsaturated fatty acids.
Animal fats contain a larger
proportion of saturated fatty acids.
They are usually solids at room
temperature.
836
C hapter 23 • The Chemistry of Life
o
II
CH2- 0 - C - ( C H 2)14CH3
■Figure 16 Soap forms
by the reaction of a triglyceride
and a strong base.
CH2OH
o
O
II
CH - O - C - (CH2)14CH3 + 3NaOH
CHOH + 3CH3(CH2)14 - C - O-Na
O
II
c h 2-
0 -
c
-(
c h 2)14c h 3
Triglyceride
CH2OH
Base
Glycerol
Soap
Fatty acids are stored in the fat cells o f your body as triglycerides.
W hen energy is abundant, fat cells store the excess energy in the fatty
acids o f triglycerides. W hen energy is scarce, the cells break down the
triglycerides, releasing the energy used to form them.
Although enzymes break down triglycerides in living cells, the
reaction can be duplicated outside o f cells by using a strong base, such
as sodium hydroxide. This reaction—the hydrolysis o f a triglyceride
using an aqueous solution o f a strong base to form carboxylate salts and
glycerol— is sa p o n ificatio n , as shown in Figure 16. Saponification is
used to make soaps, which are usually the sodium salts o f fatty acids.
A soap molecule has both a polar end and a nonpolar end. Soaps are
used with water to clean nonpolar dirt and oil because the nonpolar dirt
and oil bond to the nonpolar end o f the soap molecules, and the polar
end o f the soap molecules is soluble in water. Thus, the dirt-laden soap
molecules can be rinsed away with the water.
MiniLAB
O b s e rv e a S a p o n ific a tio n
R e a ctio n
How is soap made? The reaction between a
triglyceride and a strong base is called saponifica­
tion. A sample chemical reaction is shown in
Fig u re 16.
P ro c e d u re
1. Read and com plete the lab safety form.
2 . Place a 2 5 0 -m L b e a k e r on a h o t p la te . Add 2 5 g
s o lid v e g e t a b le s h o r te n in g to the beaker. Turn
on the hot plate to a medium setting.
3 . As the vegetable shortening melts, use a 2 5 -m L
g r a d u a te d c y lin d e r to slowly add 12 mL e th a n o l
and then 5 mL 6 .0 M N a O H to the beaker.
W A R N IN G : E th a n o l is fla m m a b le . N a O H cau ses s k in
b u rn s . W e a r g lo v e s .
4. Heat the m ixture fo r about 15 min. Use a
s tir rin g ro d to occasionally stir the mixture.
Do not allow it to boil.
5 . W hen the mixture begins to thicken, use to n g s
to remove the beaker from the heat. A llo w the
beaker to cool fo r 5 min, then place it in a cold
w a t e r b a th in a 6 0 0 -m L b e a k e r.
6 . Add 2 5 mL s a tu ra te d N aC I s o lu tio n to the mix­
ture in the beaker. The soap is not very soluble
and will appear as small clumps.
7. Collect the solid soap clumps by filtering them
through a c h e e s e c lo th -lin e d fu n n e l.
8 . Using gloved hands, press the soap into an
e v a p o r a tin g d is h . Remove your gloves and wash
your hands.
A n a ly s is
1. Explain W hat type o f bonds present in the
triglycerides are broken during the saponification
reaction?
2. Identify the type o f salt form ed in this
chemical reaction.
3. Determ ine which is the polar end and which is
the nonpolar end o f the soap molecule.
Section 3 • Lipids
837
■ Figure 1 7 A phospholipid
has a polar head and two
nonpolar tails. The membranes
of living cells are formed by a
double layer of lipids, called a
bilayer. The polar heads are on
the outer and inner perimeter of
the membrane and the tails are
on the inside of the bilayer.
Outside the cell
"
Inside the cell
Polar heads
1
hT°S^°
a^er
Nonpolar tails
P h o s p h o lip id s Another important type o f triglyceride, a phos­
pholipid, is found in greatest abundance in cellular membranes. A
phospholipid is a triglyceride in which one o f the fatty acids is replaced
by a polar phosphate group. As shown in Figure 17, the polar part of
the molecule forms a head and the nonpolar fatty acids look like tails. A
typical cell membrane has two layers o f phospholipids, which are
arranged with their nonpolar tails pointing inward and their polar heads
pointing outward. This arrangement is called a lipid bilayer. Because the
lipid bilayer structure acts as a barrier, the cell is able to regulate the
materials that enter and leave through the membrane.
■ Figure 1 8 Plants produce a wax
that coats their leaves. The wax protects
the leaves from drying out.
ItiVU11iWtWHJ>M1fc
Vt The venom o f poisonous snakes contains a class
of enzymes known as phospholipases. These enzymes catalyze the
breakdown o f phospholipids. The venom of the eastern diamond-back
rattlesnake contains a phospholipase that hydrolyzes the ester bond at
the middle carbon o f phospholipids. If the larger o f the two breakdown
products o f this reaction gets into the bloodstream, it dissolves the
membranes o f red blood cells, causing them to rupture. Because the
venom destroys the blood cells, it is referred to as a hemotoxic venom.
(The prefix hemo- indicates blood.) A bite from the eastern diamondback can lead to death if it is not treated immediately.
W a x e s Another type of lipid, wax, also contains fatty acids. A w ax
is a lipid that is formed by combining a fatty acid with a long-chain
alcohol. The general structure of these soft, solid fats with low melting
points is shown below, with x and y representing variable numbers of
CH 2 groups.
O
II
CH3(CH2)x - C - O - (CH2)yCH3
Both plants and animals make waxes. Plant leaves are often coated
with wax, which prevents water loss. Notice in Figure 18 how raindrops
bead up on the leaves o f a plant, indicating the presence o f the waxy
layer. The honeycombs that bees make are also made o f a wax, com ­
m only called beeswax. Com bining the 16-carbon fatty acid palmitic
acid and a 30-carbon alcohol chain makes a com m on form o f beeswax.
Candles are sometim es made o f beeswax because it tends to burn slowly
and evenly.
838
C hapter 23 • The Chemistry of Life
S te r o id s Not all lipids contain fatty acid chains. Steroids are lipids that
have multiple cyclic rings in their structures. All steroids are built from
the basic four-ring steroid structure shown below.
<i JiU m anH
Incorporate information
yr°™ foldable'00
Some hormones, such as many sex hormones, are steroids that function
to regulate metabolic processes. Cholesterol, another steroid, is an
important structural component o f cell membranes. Vitamin D also
contains the four-ring steroid structure and plays a role in the formation
o f bones. The Giant Marine toad, Bufo marinus, shown in F ig u re 19
uses a steroid called bufotoxin as a defense mechanism. The toad
secretes the toxin from warts on its back and from glands just behind
the eye. The toxin is only an irritant for humans, but in small animals
the toxin causes drooling, loss o f coordination, convulsions, and death.
sFcnoN i
REVIEW
-I
jy
S e c t io n S u m m a r y
12. MAIIMIDEA Describe the function of lipids.
• Fatty acids are long-chain carboxylic
acids that usually have between
12 and 24 carbon atoms.
13. Describe the structures of fatty acids, triglycerides, phospholipids, and steroids.
• Saturated fatty acids have no double
bonds; unsaturated fatty acids have
one or more double bonds.
• Fatty acids can be linked to glycerol
backbones to form triglycerides.
• Steroids are lipids that have multiplering structures.
14. List an important function of each of these types of lipids.
a. triglycerides
b. phospholipids
c. waxes
d. steroids
15. Id e n tify two reactions that fatty acids undergo.
16. Describe the structure and function of cell membranes.
17. Com pare and contrast the structures of a steroid, a phospholipid, and a wax.
18. W rite the equation for the complete hydrogenation of the polyunsaturated fatty
acid linoleic acid, CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH.
19. In te rp re t Scientific Illustrations Draw the general structure of a
phospholipid. Label the polar and nonpolar portions of the structure.
Section 3 • Lipids
839
Nucleic Acids
SECTION 4
E s s e n tia l Q u e s tio n s
M A IN ID E A
• What are the structural components
of nucleic acids?
• How is the function of DNA related to
its structure?
• What are the structure and function
of RNA?
Nucleic acids store and transm it genetic inform ation.
DNA testing is becoming more routine in medicine, forensic
science, genealogy, and identification of victims in disasters.
Modern techniques have m ade it possible to get a useful DNA
sample from surprising sources, such as a strand of hair or dried
saliva on a postage stamp.
R e v ie w V o c a b u la r y
genetic inform ation: an inherited
Structure o f Nucleic Acids
sequence of RNA or DNA that causes
traits or characteristics to pass from one
generation to the next
Nucleic acids comprise a fourth class o f biological molecules. They are
the information-storage molecules of the cell. This group o f molecules
got its name from the cellular location in which the molecules are
primarily found—the nucleus. It is from this control center o f cells that
nucleic acids carry out their major functions. A n u c le ic a c id is a
nitrogen-containing biological polymer that is involved in the storage
and transmission of genetic information. The monomer that makes up a
nucleic acid is called a n u c le o tid e . Each nucleotide has three parts: an
inorganic phosphate group, a five-carbon monosaccharide sugar, and a
nitrogen-containing structure called a nitrogenous base. Examine each
part of F ig u re 2 0 a . Although the phosphate group is the same in all
nucleotides, the sugar and the nitrogen base vary.
In a nucleic acid, the sugar o f one nucleotide is bonded to the
phosphate o f another nucleotide, as shown in F ig u re 2 0 b . Thus, the
nucleotides are strung together in a chain, or strand, containing
alternating sugar and phosphate groups. Each sugar is also bonded to a
nitrogen base that sticks out from the chain. The nitrogen bases on
adjoining nucleotide units are stacked one above the other in a slightly
askew position, much like the steps in a staircase. This orientation is
shown in F ig u re 2 0 b . Intermolecular forces hold each nitrogen base
close to the nitrogen bases above and below it.
N e w V o c a b u la r y
nucleic acid
nucleotide
■ F ig u re 2 0 Nucleotides are the monomers from which nucleic acid polymers are formed.
o
HI I
o
ii
H O - P - O ---- CH?
Hi
H
H
VC /iH
m C— ■
I
OH
I
N itro g e n -c o n ta in in g
base
OH
Sugar
N u c le o tid e
Each nucleotide contains a nitrogen-containing base,
a five-carbon sugar, and a phosphate group.
840
b- L
I
H
C hapter 23 • The Chemistry of Life
o
Phosphate
1
-i
HO
P hosphate g ro u p
NH,
-
Sugar
—
Base
Sugar f l - 1
Base
Phosphate
i
I
Phosphate
aSugar
sp
Base
N u c le ic a cid
Nucleic acids are linear chains of alternating sugars and phos­
phates. Attached to every sugar is a nitrogen base. Because the
nucleotides are offset, the chains resemble steps in a staircase.
DNA: The Double Helix
You might have heard o f DNA (deoxyribonucleic acid), one o f the two
types o f nucleic acids found in living cells. DNA contains the master
plans for building all the proteins in an organisms body.
View an animation about the
structure of DNA.
T h e S t r u c t u r e o f D N A DNA consists of two long chains of
nucleotides wound together to form a spiral structure, as shown in
F ig u r e 2 1 . Each nucleotide in DNA contains a phosphate group, the
five-carbon sugar deoxyribose, and a nitrogenous base. The alternating
sugar and phosphate groups in each chain make up the outside, or
backbone, o f the spiral structure. The nitrogen bases are on the inside
o f the structure. Because the spiral structure is composed o f two chains,
it is known as a double helix.
DNA contains four different nitrogenous bases: adenine (A),
thymine (T), cytosine (C), and guanine (G). As F ig u r e 2 2 shows, both
adenine and guanine contain a double ring. Thymine and cytosine are
single-ring structures. Looking again at F ig u r e 2 2 , notice that each
nitrogen base on one strand o f the helix is oriented next to a nitrogen
base on the opposite strand, in the same way that the teeth o f a zipper
are oriented. The side-by-side base pairs are close enough so that
hydrogen bonds form between them. Because each nitrogen base has a
unique arrangement o f organic functional groups that can form
hydrogen bonds, the nitrogen bases always pair in a specific way so that
the optimum number o f hydrogen bonds form. As F ig u r e 2 2 shows,
guanine always binds to cytosine, and adenine always binds to thymine.
The G -C and A -T pairs are called complementary base pairs.
■ F ig u r e 2 1 The structure of DNA is
a double helix that resembles a twisted
zipper. The two sugar-phosphate backbones
form the outsides of the zipper.
H READING CHECK D e s c rib e what forms the teeth of the DNA zipper.
Because o f complementary base pairing, the amount of adenine in a
molecule o f DNA always equals the amount of thymine, and the amount
o f cytosine always equals the amount o f guanine. In 1953, James Watson
and Francis Crick used this observation to make one o f the greatest
scientific discoveries o f the twentieth century when they determined the
double-helix structure o f DNA. They accomplished this feat without
performing many laboratory experiments themselves. Instead, they
analyzed and synthesized the work o f numerous scientists who had
carefully carried out studies on DNA.
■ F ig u r e 2 2 In DNA, base pairing exists between a double-ringed base and a single­
ringed base. Adenine and thymine always pair, forming two hydrogen bonds between them.
Guanine and cytosine always form three hydrogen bonds when they pair.
Thymine
Adenine
Cytosine
Guanine
Section 4 • Nucleic Acids
841
T h e f u n c t io n o f D N A Watson and Crick used their model to
predict how DNA’s chemical structure enables it to function. DNA
stores the genetic information o f a cell in the cell’s nucleus. Before the
cell divides, the DNA is copied so that the new generation o f cells gets
the same genetic information. Having determined that the two chains of
the DNA helix are complementary, Watson and Crick realized that
complementary base pairing provides a mechanism by which the
genetic material o f a cell is copied.
The four nitrogenous bases o f DNA serve as the letters o f the
alphabet in the information-storage language of living cells. The specific
sequence o f these letters represents an organisms master instructions,
just as the sequence o f letters in the words of this sentence convey
special meaning. The sequence o f bases is different in every species o f
organism, allowing for an enormous diversity o f life-forms—all from a
language that uses only four letters. It is estimated that the DNA in a
human cell has about three billion complementary base pairs, arranged
in a sequence unique to humans.
Problem-Solving LAB
Formulate a M odel
H o w d o e s D N A re p lic a te ? DNA replicates
before a cell divides so that each of the tw o
newly form ed cells has a complete set of
genetic instructions. W hen DNA begins to
replicate, the tw o nucleotide strands start to
unzip. An enzyme breaks the hydrogen bonds
between the nitrogenous bases, and the strands
separate. Other enzymes deliver free nucleo­
tides from the surrounding medium to the
exposed nitrogenous bases, adenine hydrogenbonding w ith thymine, and cytosine bonding
w ith guanine. Thus, each strand builds a com­
plementary strand by base-pairing with free
nucleotides. This process is shown in the top
diagram at the right. W hen the free nucleotides
have been hydrogen-bonded into place, their
sugars and phosphates bond covalently to those
on adjacent nucleotides to form the new
backbone. Each strand of the original DNA
molecule is now bonded to a new strand.
A n a ly s is
The bottom diagram shows a small segment of
a DNA molecule. Copy the base sequence onto
a clean sheet o f paper, being careful not to
make copying errors. Show the steps of replica­
tion to produce tw o segments of the DNA.
T h in k C ritic a lly
1. D e s c rib e how the base sequence of a newly
synthesized strand compares with the
original strand to which it is bonded.
842
C hapter 23 • The Chemistry of Life
A T
C G G T T
A A A C G
T A G C C A A T T T G C
1
1
2. E x p la in If the original DNA segment is colored
red and the free nucleotides are colored blue,
w hat pattern of colors w ill the newly replicated
DNA segments have? W ill all new segments have
the same color pattern?
3. E x p la in how an organism m ight be affected if an
error occurs during replication of its DNA. Are the
effects permanent? Explain.
a.
DNA
b. RNA
O
HsC^
V
H ^N
H
.H
H
0
N'
H
I
hr
H
D e o x y rib o s e
T h y m in e
O
I
H
Ribose
Uracil
■Fig u re 23 DNA and RNA differ in their components. The two structures
on the left are found in DNA. The two structures on the right are found in RNA.
Identify tw o differences in the structures o f RNA and DNA.
RNA
RNA (ribonucleic acid) is also a nucleic acid. Its general structure differs
from that o f DNA in three important ways, as shown in Figure 23.
First, as you have read, DNA contains the nitrogen bases adenine,
.
.
,
cytosine, guanine, and thymine. RNA contains adenine, cytosine,
guanine, and uracil. Thymine is never found in RNA. Second, RNA
contains the sugar ribose. DNA contains the sugar deoxyribose, which
has a hydrogen atom in place o f a hydroxyl group at one position.
The third difference between DNA and RNA is a result o f these
structural differences. DNA is normally arranged in a double helix in
which hydrogen bonding links the two chains together through their
bases. RNA is usually single-stranded, with no such hydrogen bonds
forming among the bases.
Whereas DNA functions to store genetic information, RNA allows
cells to use the information found in DNA. You have read that the genetic
information o f a cell is contained in the sequence o f nitrogen bases in the
DNA molecule. Cells use this base sequence to make RNA with a corre­
sponding sequence. The RNA is then used to make proteins, each with
an amino-acid sequence that is determined by the order of nitrogen bases
in RNA. The sequences o f bases are referred to as the genetic code.
Because proteins are the molecular tools that carry out most activities in
a cell, the DNA double helix is ultimately responsible for controlling the
thousands o f chemical reactions that take place in cells.
s f c t io n
4
dAlliM:lljLM
Incorporate information
s®[:t'on 'nt0
your Foldable,
REVIEW
.......M
S e c tio n S u m m a r y
20. MAINIDEA Explain the primary function of RNA and DNA.
• Nucleic acids are polymers of
nucleotides, which consist of a
nitrogen base, a phosphate group,
and a sugar.
21. Id e n tify the specific structural components of both RNA and DNA.
• DNA and RNA are the informationstorage molecules of a cell.
• DNA is double stranded, and RNA is
single stranded.
22. R elate the function of DNA to its structure.
23. R elate the function of RNA to its structure.
24. A nalyze the structure of nucleic acids to determine what structural feature
makes them acidic.
25. Predict what might happen if the DNA that coded for a protein contained the
wrong base sequence.
Section 4 • Nucleic Acids
843
SECTION 5
Metabolism
M A IN ID E A
E s s e n tia l Q u e s tio n s
• How do anabolism and catabolism
compare?
• What is the role of ATP in
metabolism?
• How can the processes of
photosynthesis, cellular respiration,
and fermentation be compared and
contrasted?
R e v ie w V o c a b u la r y
redox process: a chemical reaction
in which electrons are transferred from
one atom to another
N e w V o c a b u la r y
metabolism
catabolism
anabolism
ATP
photosynthesis
cellular respiration
fermentation
M etabolism involves m any thousands o f reactions in
living cells.
4 YOU
You have studied the four major kinds of biological molecules
and learned that they are all present in the food you eat. What
happens to these molecules after they enter your body?
A n a b o lis m a n d C a ta b o lis m
Many thousands o f chemical reactions take place in the cells o f a
living organism. The set o f chemical reactions that occur within an
organism is its m etabolism . Why are so many reactions involved in
metabolism? Living organisms must accomplish two major functions in
order to survive. They have to extract energy from nutrients in forms
that they can use immediately as well as store for future use. In addition,
they have to use nutrients to make building blocks for synthesizing all of
the molecules needed to perform their life functions. These processes
are summarized in Figure 24.
The term catab olism refers to the metabolic reactions that break
down complex biological molecules such as proteins, polysaccharides,
triglycerides, and nucleic acids for the purposes o f forming smaller
building blocks and extracting energy. After you eat a meal o f spaghetti
and meatballs, your body immediately begins to break down the starch
polymer in the pasta into glucose. The glucose is then broken down into
smaller molecules in a series o f energy-releasing catabolic reactions.
Meanwhile, the protein polymers in the meatballs are catabolized into
amino acids.
The term anabolism refers to the metabolic reactions that use
energy and small building blocks to synthesize the complex molecules
needed by an organism. After your body has extracted the energy from
the starch in the pasta, it uses that energy and the amino-acid building
blocks produced from the meat proteins to synthesize the specific
proteins that allow your muscles to contract, catalyze metabolic
reactions, and perform many other functions in your body.
■Figure 24 A large number of different metabolic reactions take place
in living cells. Some involve breaking down nutrients to extract energy; these are
catabolic processes. Others involve using energy to build large biological molecules;
these reactions are anabolic processes.
Describe Choose one food that you ate recently, and describe how it
was metabolized.
Carbohydrates
Fats
Proteins
844
Complex cellular
molecules
Interm ediate products
Nutrients ingested
Catabolism
(nutrients broken
down)
C h a p te r 23 • The Chemistry of Life
Amino acids
Simple sugars
Fatty acids
Nucleotides
ATP
V.________________________
Anabolism
(new molecules
/
synthesized)
Proteins
Polysaccharides
Triglycerides
Nucleic acids
ADP + P
Adenine
Triphosphate
group
h 2o
Ribose
Adenine
Diphosphate
group
+
Ribose
A
+ -Energy'
Phosphate
ADP
■ F ig u re 2 5 The breakdown of ATP provides energy for cellular processes in
living organisms.
E x p la in w here the energy is stored in ATP.
F ig u re 2 4 shows the relationship between catabolism and
anabolism . T h e nutrients listed on the left side o f the diagram are
broken down into interm ediate products. These interm ediate products
are used as building blocks for the products listed on the right side o f
the diagram . A nother way o f conceptualizing this process is to view the
nutrients ingested as the raw m aterials for the com plex cellular
m olecules form ed in a living organism.
V
o cabulary
.....................................
A c a d e m ic v o c a b u l a r y
Conceptualize
visualizing or conceiving an abstract
idea in the mind
The a to m ic c lo u d m o d e l is h a rd to
con cep tu alize ........................................
□ READING CHECK E x p la in how the terms m eta b o lism , cata b o lism , and
! a n a b o lism are related.
A T P C atabolism and anabolism are linked by com m on building blocks
that catabolic reactions produce and anabolic reactions use. A com m on
form o f potential chem ical energy also links the two processes, as shown
in F ig u re 2 5 . A T P (adenosine triphosphate) is a nucleotide that func­
tions as the universal energy-storage m olecule in living cells. During
catabolic reactions, cells harness the chem ical energy o f foods and store
it in the bonds o f ATP. W h en these bonds are broken, the chem ical
energy is released and used by cells to drive anabolic reactions that
m ight not otherw ise occur. M ost cellular reactions have an efficiency o f
only about 40% at best; the rem aining 60% o f the energy in food is lost
as heat, which your body uses to keep warm.
D uring catabolic reactions, cells produce ATP by adding an inor­
ganic phosphate group to the nucleotide adenosine diphosphate (ADP)
in an endotherm ic reaction. O ne m ole o f ATP stores approximately
30.5 k j o f energy under norm al cellular conditions. D uring anabolism,
the reverse reaction occurs. ATP is broken down to form ADP and
inorganic phosphate in an exotherm ic reaction. Approximately 30.5 k j
o f energy is released from each m ole o f ATP.
Q READING CHECK D escribe what occurs when ATP becomes ADP.
Section 5 • Metabolism
845
P h o to s y n th e s is
What is the source of energy that fuels metabolism? For most living
things, including the grass shown in F ig u r e 2 6 , certain wavelengths of
sunlight provide this energy. Some bacteria and the cells o f all plants
and algae are able to capture light energy and convert some o f it into
chemical energy. Animals cannot capture light energy, so they get
energy by eating plants or by eating other animals that eat plants. The
process that converts energy from sunlight to chemical energy in the
bonds o f carbohydrates is called photosynthesis. During the complex
process o f photosynthesis, carbon dioxide and water yield a carbohy­
drate (glucose) and oxygen gas. The following net reaction takes place
during photosynthesis.
6C 02 +
Carbon
dioxide
6H 20
Water
+
light energy
—>
C 6 H 120 6
Glucose
+
602
Oxygen
Photosynthesis results in the reduction o f the carbon atoms in carbon
dioxide as glucose is formed. During this redox process, oxygen atoms
in water are oxidized to oxygen gas.
■ F ig u r e 2 6 Grass and other green
plants use certain wavelengths of sunlight
as an energy source. Other living organ­
isms, such as cows, obtain energy by
eating plants or eating other organisms
that eat plants.
Get help with photosynthesis and
respiration.
C e llu la r R e s p ira tio n
Most organisms need oxygen to live. Oxygen that is produced during
photosynthesis is used by living things during cellular resp iration , the
process in which glucose is broken down to form carbon dioxide, water,
and large amounts o f energy. Cellular respiration is the major energyproducing process in living organisms. F ig u r e 2 7 shows one use of
energy in the body. This energy is stored in the bonds o f ATP. Cellular
respiration is a redox process; the carbon atoms in glucose are oxidized
while oxygen atoms in oxygen gas are reduced to the oxygen in water.
The net reaction that takes place during cellular respiration is as follows.
C 6H i 20 6
Glucose
+
602
->
Oxygen
6C 02
Carbon
dioxide
+
6H 20
Water
+
energy
■ F ig u r e 2 7 Swimmers need large amounts of energy when they compete in a
(t)DLILLC/CORBlS, (b)AP Photo/Joe Cavaretta
race. This energy is stored in the bonds of ATP in their cells.
846
C hapter 23 • The Chemistry of Life
■Figure 28 Carbon dioxide formed
during fermentation, leaves holes in the
bread. These holes give bread a light, lessdense texture.
Ferm entation
D uring cellular respiration, glucose is com pletely oxidized, and oxygen
gas is required to act as the oxidizing agent. Cells can extract energy
from glucose in the absence o f oxygen, but not nearly as efficiently.
W ith ou t oxygen, only a fraction o f the chem ical energy o f glucose can
be released. W hereas cellular respiration produces 38 m ol o f ATP for
every 1 m ol o f glucose catabolized in the presence o f oxygen, only 2 m ol
o f A TP are produced per m ole o f glucose that is catabolized in the
absence o f oxygen. T h is provides enough energy for oxygen-deprived
cells so that they do n ot die. T h e process by which glucose is broken
down in the absence o f oxygen is known as fe rm e n ta tio n . There are
two com m on kinds o f ferm entation. In one, ethanol and carbon dioxide
are produced. In the other, lactic acid is produced.
A lc o h o lic f e r m e n t a t i o n Yeast and som e bacteria can ferm ent
glucose to produce the alcohol ethanol.
c 6H12o6
2 C H 3 C H 2OH
G lucose
Ethanol
+
2C 02
+
C arbon dioxide
CAREERS
IN
rCHEMISTRY-------Baker Using a variety of chemical
processes to create tasty and often
beautiful creations is the job of a
baker. Not only do breads and
doughnuts undergo fermentation
processes, but cakes and other
pastries are often acid-base
reactions.
energy
T h is reaction, called alcoholic ferm entation, is im portant in producing
som e foods, as shown in Figure 28. A lcoholic ferm entation is needed to
m ake bread dough rise, form tofu from soybeans, and produce the
ethanol in alcoholic beverages. A nother use o f the ethanol is as an
additive to gasoline, as shown in Figure 29.
■Figure 29 Ethanol is often added to
gasoline and used as a fuel in some cars and
trucks. Ethanol is made from grain.
Explain how the use o f ethanol can
reduce the dependence on fossil fuels.
N O T G ASO LINE
E -85 for use in Flexil
Fuel Vehicles (F FV s) <
Please consult your ve
owner’s manual or store
if you need assistan
TO SEE IF YOUR VEHI
Section 5 • Metabolism
847
■ F ig u re 3 0 During strenuous activity,
oxygen can be depleted in cells. Then,
energy is produced without oxygen and
lactic acid is produced. Soreness in muscles
a day or two after the activity is a sign of
lactic acid formation.
L a c tic a c id f e r m e n t a t i o n Have you ever experienced muscle
fatigue while running a race, like the person shown in F ig u re 3 0?
D uring strenuous activity, m uscle cells often use oxygen faster than it
can be supplied by the blood. W hen the supply o f oxygen is depleted,
cellular respiration stops. Although anim al cells cannot undergo alco­
holic ferm entation, they can produce lactic acid and a small amount
o f energy from glucose through lactic acid ferm entation.
C 6 H 120 6
Glucose
->
2C H 3 C H (O H )C O O H
Lactic acid
+
energy
T he lactic acid that is produced is moved from the muscles through
the blood to the liver. There, it is converted back into glucose that can
be used in catabolic processes to yield m ore energy once oxygen
becom es available. However, if lactic acid builds up in muscle cells at
a faster rate than the blood can remove it, muscle fatigue results. An
im m ediate burning sensation and soreness a few days later is an indica­
tion that lactic acid was produced in the muscles during exercise.
s e c t io n s
REVIEW
S e c tio n S u m m a r y
26. MAINIDEA Explain why metabolism is important to living cells.
• Living organisms undergo catabolism
and anabolism.
27. Com pare and contrast the processes of anabolism and catabolism.
• Photosynthesis directly or indirectly
provides almost all living things with
energy.
29. Com pare and contrast the processes of photosynthesis, cellular respiration,
and fermentation.
• The net equation for cellular
respiration is the reverse of the net
equation for photosynthesis.
28. Explain the role of ATP in the metabolism of living organisms.
30. D e te rm in e whether each process is anabolic or catabolic.
a. photosynthesis
b. cellular respiration
c. fermentation
31. E valuate Why is it necessary to use sealed casks when making wine?
32. Calculate How many moles of ATP would a yeast cell produce if 6 mol of
glucose were oxidized completely in the presence of oxygen? How many moles
of ATP would the yeast cell produce from 6 mol of glucose if the cell were
deprived of oxygen?
848
C hapter 23 • The Chemistry of Life
careers
Career: Molecular Paleontologist
Acid Test Reveals Surprise
"N o righ t-th in kin g paleontologist w ould do
w h a t M ary did. W e d o n 't go to all this effort to
dig this stu ff ou t o f the ground and then destroy
it in acid." So says a colleague about Mary
Schweitzer, the scientist w ho used the tech­
niques o f m olecular biology to discover soft
tissue w here none should be— in the thighbone
o f a 68-m illion-year-old T y ra n n o s a u ru s re x.
Figure 2 Scientists also found blood vessels and individual cells
in the soft tissue of the T. rex.
M o th e r B ob W hen the fossilized T. re x,
The a cid te s t To study the m edullary bone
nicknam ed Bob, was recovered by paleontolo­
gists in 2003 from a rem ote section o f M ontana,
the bones w ere encased in plaster fo r protection
during transport. However, the bones and
plaster w eighed more than the helicopter could
lift. So the paleontologists w ere forced to break
the intact thig h b on e to move the dinosaur out
o f the rem ote area. Schweitzer to o k small
fragm ents from the broken thighbone fo r
fu rth er study.
more closely, Schweitzer dissolved fragments
o f the bone in dilute acid to remove calcium
phosphate— a technique norm ally used to
examine fresh tissue. Because a fossilized bone
has usually m ineralized, it was assumed that the
bone w ould com pletely dissolve in dilute acid.
Yet this step yielded astonishing results— w ithin
the bone was soft tissue. Under the microscope,
the tissue showed w hat looked like preserved
blood vessels and even individual cells, as shown
in F ig u re 2. But how could soft tissue have
survived 68 m illion years in the ground?
The first surprise came quickly. "B ob " was a
fem ale, and she had been producing eggs at the
tim e o f her death. The bone Schweitzer studied
is called m edullary bone. Previously, this bone
tissue was know n only in birds, as shown in
F ig u re 1. O vulating hens produce m edullary
bone, then later use the calcium stored in the
bone to make eggshells. A fte r egg production,
the bone disappears. F ig u re 1 shows the m edul­
lary bone fo u n d in the T. rex thighbone.
Figure 1 The hen bone and T. rex bone both have a hard outer
bone called cortical bone (CB) and softer medullary bone (MB).
M o re w o r k Schweitzer has since subjected
other bones to the same acid test, and found
sim ilar soft tissue and fine structures. No one
knows yet just w hat these fine structures are
showing, but, says a colleague, "there may be
a lot o f things out there that we've missed
because of our assumption of how preservation
works." Clearly, more research is needed.
W R ITIN G iN ^C hem istry
Persuasive W ritin g It is u n lik e ly th a t d in o s au r D N A
w ill be fo u n d in th es e s o ft tissues. Even so, th e discovery
brings u p th e q u estio n : S hould e x tin c t anim als be cloned
fro m recovered D N A ? W rite a persuasive essay expressing
y o u r o p in io n .
39
Chemistry & Careers
849
ChemLAB
Observe Temperature and Enzyme Action
B a c k g ro u n d : Enzymes are natural catalysts used by
living things to speed reactions. These proteins have
specialized structures that enable them to interact
with specific substances.
Q u e s tio n : How does temperature affect the action of
enzymes?
D ata Table
Water Bath
Temperature
(°C)
Height of
Foam (cm)
Potato
Ice water
Room-temperature water
M aterials
red-skin potato pulp
hydrogen peroxide
(3% H 2 O 2 )
water
250-m L beaker (4)
test tubes (4)
test-tube rack
test-tube clamp
25-m L graduated cylinder
therm om eter
ice
ruler
clock
hot plate
raw fresh liver pulp
Safety Precautions
Procedure
i t Read and complete the lab safety form.
2. Write a hypothesis that identifies the temperature
at which the enzymes are the m ost active.
3. Copy the data table on a separate sheet o f paper.
4. Place the four test tubes in the test-tube rack.
5. Measure and place 2.0 mL o f red-skin potato pulp
into each test tube.
6 . Using the hot plate and ice, prepare water baths in
the beakers at four different temperatures: ice water,
room-temperature water, body-temperature water,
and gently boiling water at or near 100°C.
7. Place one test tube in each water bath using
a test-tube clamp.
8 . Measure and record the temperature o f each
water bath.
9. After 5 min in the water baths, measure and place
5.0 mL of 3% H 2O 2 in each test tube.
10. Allow the reaction to proceed for 5 min.
11. Measure the height o f the foam produced in each
test tube.
12. Dispose o f the contents of the test tubes as directed
by your teacher and wash the test tubes.
13. Repeat Steps 4 -1 2 using 2.0 mL of beef liver pulp
instead o f potato pulp.
850
C h a p te r 23 • The Chemistry of Life
Body-temperature water
Boiling water (near 100°C)
Liver
Ice water
Room-temperature water
Body-temperature water
Boiling water (near 100°C)
14. Cleanup and Disposal Dispose o f the remaining
solutions as directed by your teacher. Wash and
return all lab equipment to its designated location.
Analyze and Conclude
1. Make and Use Graphs Make a line graph with
temperature on the x-axis and height o f foam on
the y-axis. Use a different color for the potato and
liver data points and lines.
2. Summarize How does temperature affect the action
o f enzymes? Infer why the maximum reaction
occurred at the temperature in which it did for the
potato and liver.
3. Recognize Cause and Effect W hich water bath
produced the least amount o f foam for each mate­
rial? Propose explanations for why this happened.
4. Com pare and Contrast Did the experimental data
support your hypothesis in Step 2? Explain.
5. Model Write a balanced reaction for the decompo­
sition o f hydrogen peroxide for each reaction. How
are the reactions similar? Infer why they are similar.
6. E rro r Analysis Identify potential sources o f errors
for this investigation and suggest methods to correct
them.
INQUIRY EXTENSION
Design an Experiment Would a change in pH affect
the results? Design an experiment to find out.
BIGIDEA
Biological molecules— proteins, carbohydrates, lipids, and nucleic acids— interact
to carry out activities necessary to living cells.
MAIIMIDEA Proteins perform essential functions, including regulation of chemical reactions,
structural support, transport of materials, and muscle contractions.
• Proteins are biological polymers made of amino acids that are linked by peptide bonds.
• Protein chains fold into intricate three-dimensional structures.
• Proteins have many functions in the human body, including functions within cells,
functions between cells, and functions of structural support.
sectio n
2
VOCABULARY
•
•
•
•
•
•
•
•
protein
amino acid
peptide bond
peptide
denaturation
enzyme
substrate
active site
C arb o h y d rate s
MAIIMIDEA Carbohydrates provide energy and structural material for living things.
VOCABULARY
• Carbohydrates are compounds that contain multiple hydroxyl groups (-OH) and
a carbonyl functional group (C = 0 ).
•
•
•
•
• Carbohydrates range in size from single monomers to polymers composed of hundreds
or thousands of monomers.
carbohydrate
monosaccharide
disaccharide
polysaccharide
• Monosaccharides in aqueous solution exist in both open-chain and cyclic structures.
lipids______
SECTION 3
MAIIMIDEA Lipids make cell membranes, store energy, and regulate cellular processes.
• Fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms,
• Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more
double bonds.
• Fatty acids can be linked to glycerol backbones to form triglycerides.
• Steroids are lipids that have multiple-ring structures.
MAIIMIDEA Nucleic acids store and transmit genetic information.
• Nucleic acids are polymers of nucleotides, which consist of a nitrogen base,
a phosphate group, and a sugar.
. DNA and RNA are the information-storage molecules of a cell.
VOCABULARY
•
•
•
•
•
•
•
lipid
fa tty acid
triglyceride
saponification
phospholipid
wax
steroid
VOCABULARY
• nucleic acid
• nucleotide
. DNA is double stranded, and RNA is single stranded.
s f c t i o n 5 M e ta b o lism--------MAIIMIDEA Metabolism involves many thousands of reactions in living cells.
VOCABULARY
• Living organisms undergo catabolism and anabolism.
. Photosynthesis directly or indirectly provides almost all living things with energy.
• metabolism
• catabolism
• anabolism
. The net equation for cellular respiration is the reverse of the net equation for photosynthesis.
• ATP
• photosynthesis
• cellular respiration
• ferm entation
C h a p te r 23 • Study Guide
SECTION 1_____
M astering Concepts
33. What should you call a chain of eight amino acids?
A chain of 200 amino acids?
34. Name the two types of functional groups that react
together to form a peptide bond, and name the
functional group in the peptide bond itself.
35. Using the symbols below to represent four amino acids,
draw peptide structures for four-member chains that
link them together in different orders.
Amino acid 1 :B
Amino acid 3: ♦
Amino acid 2: A
Amino acid 4: •
36. Human Anatomy Name five parts of the body that
contain structural proteins.
37. List four major functions of proteins, and give one
example of a protein that carries out each function.
46. Cellular Chemistry Most proteins with a globular
shape are oriented so that they have mostly amino acids
with nonpolar side chains located on the inside and
amino acids with polar side chains located on the outer
surface. Does this make sense in terms of the nature of
the cellular environment? Explain.
M astering Problems
47. How many different ways can you arrange three
different amino acids in a peptide? Four amino acids?
Five amino acids?
48. How many peptide bonds are present in a peptide that
has five amino acids?
4 9 . Proteins The average molecular weight of an amino
acid residue in a polypeptide is 110 amu. What is the
approximate molecular weight of the following proteins?
a. Insulin (51 amino acids)
b. Myosin (1750 amino acids)
OH
38. Describe two common shapes found in the threedimensional folding of proteins.
39. Name the organic functional groups in the side chains
of the following amino acids.
a. glutamine
c. glutamic acid
b. serine
d. lysine
40. Explain how the active site of an enzyme functions.
4 1 . Name an example of an amino acid that has an aromatic
ring in its side chain.
42. Name two amino acids with nonpolar side chains and
two amino acids with polar side chains.
Q
I
NH
I
OH
h 3c
I
CH,
\
/
CH
3
H
H
I
I
-N- -C - -C- -N - C — C I II
I II
H
o
SH
ch3
H
I
CH2
CH,
H
H
O
H
II
-N -C -C -O H
N -C -C
I
O
I
O
I
H
■ Figure 32
50. Determine how many amino acids and peptide bonds
are in the peptide shown in Figure 32.
51. The average molar mass of an amino acid is llOg/mol.
Calculate the approximate number of amino acids in a
protein that has a molar mass of 36,500 g/mol.
c = ^
I
SECTION 2
ch,
h 2n
- c- c- oh
I
H
II
O
■ Figure 31
43. The structure shown in Figure 31 is tryptophan.
Describe some of the properties you would expect
tryptophan to have, based on its structure. In what class
of large molecules is tryptophan a member? Explain.
44. Is the dipeptide lysine-valine the same compound as the
dipeptide valine-lysine? Explain.
45. Enzymes How do enzymes lower the activation energy
for a reaction?
852
C h a p te r 23 • The Chemistry of Life
M astering Concepts
52. Carbohydrates Classify the following carbohydrates as
monosaccharides, disaccharides, or polysaccharides.
a. starch
d. ribose
g. fructose
b. glucose
e. cellulose
h. lactose
c. sucrose
f. glycogen
53. Name two isomers of glucose.
54. What kind of bond is formed when two monosaccha­
rides combine to form a disaccharide?
55. Sugars Give a scientific term for each of the following.
a. blood sugar
c. table sugar
b. fruit sugar
d. milk sugar
SECTION 3_________
M astering Concepts
66 . Compare and contrast the structures of a triglyceride
Cellulose
and a phospholipid.
Starch
67. Predict whether a triglyceride from beef fat or a
triglyceride from olive oil will have a higher melting
point. Explain your reasoning.
68. Soaps and Detergents Explain how the structure of
soaps makes them effective cleaning agents.
69. Draw a portion of a lipid bilayer membrane, labeling the
polar and nonpolar parts of the membrane.
■ F ig u re 33
56. Cellulose and Starch The molecular structures of
cellulose and starch are shown in Figure 33. Compare
and contrast their molecular structures.
57. Chemistry in Plants Compare and contrast the func­
tions of starch and cellulose in plants. Explain why their
molecular structures are important to their functions.
58. Infer how the different bonding arrangements in
cellulose and starch give them such different properties.
59. The disaccharide maltose is formed from two glucose
monomers. Draw its structure.
70. Where and in what form are fatty acids stored in the
human body?
71. What type of lipid does not contain fatty acid chains?
Why are these molecules classified as lipids?
72. Soap Draw the structure of the soap sodium palmitate
(palmitate is the conjugate base of the 16-carbon
saturated fatty acid, palmitic acid). Label its polar and
nonpolar ends.
73. Determine whether each structure is a fatty acid,
triglyceride, phospholipid, steroid, or wax. Explain
your reasoning.
60. The hydrolysis of cellulose, glycogen, and starch
produces only one monosaccharide. Why is this so?
What monosaccharide is produced?
61. Digestion Disaccharides and polysaccharides cannot
be broken down in the absence of water. Why do you
think this is so? Include an equation in your answer.
62. Draw the structure of the open-chain form of fructose.
Circle all chiral carbons, and then calculate the number
of stereoisomers with the same formula as fructose.
63. Sugars Compare and contrast the molecular formula,
molecular weight, and functional groups found in
glucose and fructose.
64. Historical Perspective Carbohydrates are not hydrates
of carbon as the name suggests. Explain how this
misconception occurred.
M astering Problems
65. Complex Carbohydrates Stachyose is a tetrasaccharide
that contains two D-galactose units, one D-glucose unit,
and one D-fructose unit. Each sugar unit has a molecular
weight of 180 g/mol before it is linked together in this
tetrasaccharide, and one water molecule is released for
each two sugar units that come together. What is the
molecular weight of stachyose?
0
b - O - P11 - O — c h 2
1
O
o
I
II
CH — O — C - CH2
o
h 2c
II
- o - c-
ch2
M astering Problems
74. The fatty acid palmitic acid has a density of 0.853 g/mL
at 62°C. What will be the mass of a 0.886-L sample of
palmitic acid at that temperature?
75. Polyunsaturated Fats How many moles of hydrogen
gas are required for complete hydrogenation of 1 mol of
linolenic acid, whose structure is shown below? Write a
balanced equation for the hydrogenation reaction.
CH3CH2CH = (CHCH2CH) 2 = CH(CH2)7COOH
C h a p te r 23 • Assessment
853
SECTION 4____
87. How many grams of glucose can be oxidized completely
by 2.0 L of O 2 gas at STP during cellular respiration?
M astering Concepts
76. What three structures make up a nucleotide?
77. Name two nucleic acids found in organisms.
78. Explain the roles of DNA and RNA in the production
of proteins.
79. Where in living cells is DNA found?
80. Describe the types of bonds and attractions that link the
monomers together in a DNA molecule.
88. Life Processes Compare the net reactions for photo­
synthesis and cellular respiration with respect to
reactants, products, and energy.
MIXED REVIEW_________
89. Draw the carbonyl functional groups present in glucose
and fructose. How are the groups similar? How are the
groups different?
9 0. List the names of the monomers that make up proteins,
complex carbohydrates, and nucleic acids.
9 1. Describe the functions of proteins, carbohydrates, lipids,
and nucleic acids in living cells.
A Adenine Q Cytosine
U Uracil
Q Guanine
9 2. Write balanced equations for photosynthesis, cellular
respiration, and the hydrolysis of lactose.
9 3. Write a balanced equation for the synthesis of sucrose
■ Figure 34
from glucose and fructose.
81. Classify the nucleic acid structure shown in Figure 34
as DNA or RNA and explain your reasoning.
82. In the double-helical structure of DNA, the base
guanine is always bonded to cytosine, and adenine is
always bonded to thymine. What do you expect to be
the relative proportional amounts of A, T, C, and G in a
given length of DNA?
83. DNA Replication One strand in a DNA molecule has
the following base sequence. What is the base sequence
of the other strand in the DNA molecule?
C-C-G-T-G-G-A-C-A-T-T-A
Mastering Problems
84. A triplet code is a sequence of three bases in RNA that
codes for one amino acid in a peptide chain or protein.
How many RNA bases are required to code for a protein
that contains 577 amino acids?
85. DNA Comparisons A cell of the bacterium E sch erichia
c o li has about 4.2 x 106 base pairs of DNA, whereas
each human cell has about 3 X 109 base pairs of DNA.
What percentage of the size of the human genome does
the E. c o li DNA represent?
SECTION 5______________
Mastering Problems
86. Energy Calculate and compare the total energy in kj
that is converted to ATP during the processes of cellular
respiration and fermentation.
854
C h a p te r 23 • The Chemistry of Life
THINK CRITICALLY
9 4. Make and Use Graphs A number of saturated fatty
acids and values for some of their physical properties
are listed in Table 2.
a. Make a graph plotting melting point versus number
of carbon atoms.
b. Graph density versus the number of carbon atoms.
c. Draw conclusions about the relationships between the
number of carbon atoms in a saturated fatty acid and
its density and melting point values.
d. Predict the approximate melting point of a saturated
fatty acid that has 24 carbon atoms.
T a b le 2 Physical Properties of Saturated Fatty Acids
Number of
Carbon
Atoms
Melting
Point (°C)
Density (g/mL)
(values at
60-80°C )
Palmitic acid
16
63
0.853
Myristic acid
14
58
0.862
Arachidic acid
20
77
0.824
Caprylic acid
8
16
0.910
Docosanoic acid j
22
80
0.822
Stearic acid
18
70
0.847
Laurie acid
12
44
0.868
Name
9 5. Calculate Approximately 38 mol of ATP are formed
when glucose is completely oxidized during cellular
respiration. If the heat of combustion for 1 mol of
glucose is 2.82 x 103 kJ/mol and each mole of ATP
stores 30.5 kJ of energy, what is the efficiency of cellular
respiration in terms of the percentage of available energy
that is stored in the chemical bonds of ATP?
9 6. Recognize Cause and Effect Some diets suggest
severely restricting the intake of lipids. Why is it not
a good idea to eliminate all lipids from the diet?
I/VRITINGin ^ Chem istry
103. Cholesterol Use the library or the Internet to
research cholesterol. Write a newspaper article about
cholesterol that is written for a teenage audience.
Make sure the following questions are answered in
the article. Where is this molecule used in your body?
What is its function? Why is too much dietary
cholesterol considered to be bad for you? Is genetics
a factor in high cholesterol?
E Q a Document-Based Questions
Fatty Acids O m ega-3 a n d o m ega-6 f a t t y acids are f a t t y acids
th a t g e t th e ir nam es f r o m th e ir structures. T hey c o n ta in a
d o u b le b o n d e ith e r three o r s ix carbo n ato m s f r o m the end o f
the f a t t y a c id cha in. These f a t t y acids have a b e n e fic ia l effect
on h e a lth because the y lo w e r b a d cholesterol levels a n d raise
g o o d cholesterol levels in the blood. Levels o f om ega-3 a n d
o m ega-6 f a t t y acids w ere s tu d ie d in sa lm o n fr o m three d iffe r­
e n t sources as w e ll as in the fe e d used in sa lm o n fa rm in g .
■ F ig u re 35
9 7. Analyze Insulin is a protein that functions as an
important hormone in the human body. People who are
diabetic often do not produce enough insulin, and must
inject themselves with an insulin solution to maintain
their health. Use Figure 35 to infer how a person should
care for a bottle of insulin.
Figure 36 shows the p e rc e n t o f om ega-3 a n d o m eg a-6 f a t t y
a cids c o m p a re d to the to ta l a m o u n t o f lip id s in the samples.
Data obtained from: Hamilton, M.C. et al. 2005. Environmental Science
Technology 39:8622-8629.
Concentration of Fatty Acids
A
0m ega-3 acid
9 8. Calculate If a double-stranded section of DNA has
adenine as 2 0 % of its bases, what percent of the other
three bases are present in the DNA strand?
CHALLENGE PROBLEM
9 9. Calculate how many moles of ATP a human body can
produce from the sugar in a bushel of medium-sized
Red Delicious apples. Use the Internet to find the
information you need to solve this problem.
10
CIIMIII ATIVE R E V I E W ______
100 . a. Write the balanced equation for the synthesis of
ethanol from ethene and water,
b. If 448 L of ethene gas reacts with excess water at STP,
how many grams of ethanol will be produced?
101. Identify whether each of the reactants in these reactions
is acting as an acid or a base.
a. HBr + H20 —» H 30 + + Br~
b. NH 3 + HCOOH —» NH4+ + HCOCT
c. h c o 3_ + H20 —> c o 32 - + H 30 +
20
30
Percent lipids
■ Figure 36
104. Which type of fish had the most omega fatty acids?
105. Based on this study, which type of salmon would
you recommend to people who want to maximize the
amounts of omega-3 and omega-6 fatty acids in their
diets?
106. Infer from the graph why the farm-raised and
supermarket salmon contains more omega-3 and
omega-6 fatty acids than wild salmon.
1 02 . What is a voltaic cell?
C h a p te r 23 • Assessment
855
1. W hich is N O T true o f carbohydrates?
4.
A. Monosaccharides in aqueous solutions convert
continuously between an open-chain structure
How much NaOH, in grams, is required to
completely neutralize 50.0 mL o f 0.100M HCl?
A. 0.200 g
B. 5.00 g
and a cyclic structure.
B. The monosaccharides in starch are linked
together by the same kind o f bond that links the
C. 0.125 g
D. 2 0 0 g
m onosaccharides in lactose.
C. All carbohydrates have the general chemical
formula C „(H 20 )„ .
D. Cellulose, made only by plants, is easily digestible
Use th e ta b le b e lo w to a n s w e r Q u e s tio n s 5 to 7.
Nucleotide Data for Samples of Double-Stranded DNA
by humans.
7
165
231
D
7
2. W hich is N O T a difference between RNA and DNA?
number
A. DNA contains the sugar deoxyribose, while RNA
percent
20.8
7
29.2
7
contains the sugar ribose.
B. RNA contains the nitrogen base uracil, while
number
?
402
7
7
percent
?
32.5
?
7
number
7
7
194
234
percent
?
7
22.7
27.3
203
7
7
7
7
DNA does not.
C. RNA is usually single-stranded, while DNA is
usually double-stranded.
D. DNA contains the nitrogen base adenine, while
RNA does not.
number
percent
266
28.4
21.6
U se th e g r a p h b e lo w to a n s w e r Q u e s tio n 3.
50.0 mL 0.100M HCl Titrated
with 0.100M NaOH
5.
W hat is the % T o f Sample IV?
A. 28.4%
C. 71.6%
B. 78.4%
D. 21.6%
6 . Every nitrogen base found in a DNA molecule is part
o f a nucleotide o f that molecule. The A nucleotide,
C nucleotide, G nucleotide, and T nucleotide have
molar masses o f 347.22 g/mol, 323.20 g/mol,
363.23 g/mol, and 338.21 g/mol respectively. What
is the mass o f 1 mol o f Sample I?
A. 2.79
X
10 5 g
C. 2.6390 X 10 5 g
B. 2.7001 X 105 g
D. 2.72 X 105 g
7. How many molecules o f adenine are in one molecule
Volum e NaOH added (mL)
3.
W hich chemical indicator would be most effective
in identifying the equivalence point of this
titration?
A. methyl orange, pH range o f 3.2—4.4
B. phenolphthalein, pH range o f 8 .2 -1 0
C. thymol blue, pH range o f 8 .0 - 9 .6
D. bromothymol blue, pH range of 6.0—7.6
856
C h a p te r 23 • The Chemistry of Life
o f Sample II?
A. 402
B. 434
C. 216
D. 175
8 . W hich is not a structural isomer of
C H 2 = C H C H 2C H = C H C H 3?
A. C H 2 = C H C H 2C H 2C H = C H 2
B. C H 3C H = C H C H 2C H = C H 2
C. c h 3c h = c h c h = c h c h 3
d.
c h 2 = c = c h c h 2c h 2c h 3
SAT SUBJECT TEST: CHEMISTRY
9.
The sequence o f bases in RNA determ ines the
U se th e ta b le b e lo w to a n s w e r Q u e s tio n s 1 5 -1 7 .
sequence o f am ino acids in a protein. Three bases
D ata fo r Elem ents in th e Redox Reaction
code for a single am ino acid; for example, CAG is
Zn + H N 0 3 - > Z n (N 0 3)2 + N 0 2 + H20
the code for glutamine. How many am ino acids are
coded for in a strand o f RNA 2.73 x 10 4 bases long?
U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 10.
Zn
O
II
ChUChUCH, -C- -H
0
none
Zn in Zn(N03)2
+ 2
none
H in HN03
+1
none
H in H20
10. W hich type o f functional group is in this
none
N in HN03
compound?
N in N02
U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 11.
?
no 3-
+4
none
N in Zn(N03)2
H
H Br H H
I
I I
I
0 in HN03
I
F—C —C —C —C—C —H
I
I I
H
I
n ° 3-
I
Cl H Br H
—2
no 3-
0 in N02
?
none
0 in Zn(N03)2
7
no 3-
0 in H20
11. Give the IUPAC nam e for this organic compound.
12. W hat is the condensed structural formula of
none
- 2
15. W hich element forms a monatomic ion that is a
spectator in the redox reaction?
heptane?
A.
EXTENDED RESPONSE
Zn
D. H
B. O
C. N
U se th e d ia g r a m b e lo w to a n s w e r Q u e s tio n 13.
E. 0 2
16. W hat is the oxidation number o f N in Zn(N 0 3) 2 ?
c —
A.
B.
c — c — c — c
c
+1
+2
D. + 5
E. + 6
C. + 3
c—c
13. A student records the name o f the alkane represented
17. W hat is the element that is oxidized in this
reaction?
by this carbon skeleton as 2 -ethyl 3 ,3 -dimethyl
pentane. Evaluate whether this is the correct name
A.
B.
C.
D.
E.
for the compound.
14. Compare and contrast aliphatic and aromatic
compounds.
Zn
O
N
H
o 3
NEED EXTRA HELP?
If You Missed
Q uestion. . .
Review Section . . .
1
2
3
4
5
6
23.2
23.4
19.4
19.4
23.4
23.4
23.4
8
9
10
11
12
13
14
15
16
17
21.4
23.4
22.1
23.1
21.2
21.2
21.5
9.3
19.1
19.1
C h a p te r 23 • Assessment
857
R IP in F A
Nuclear chemistry has a vast range of applications, from the production of
electricity to the diagnosis and treatment of diseases.
1 Nuclear Radiation
2 Radioactive Decay
3 Nuclear Reactions
4 A pplications and Effects o f
Nuclear Reactions
How do chain reactions
occur?
When the products of one nuclear reaction
cause additional nuclear reactions to occur, the
resulting chain reaction can release large
amounts of energy in a short period of tim e. In
this lab, you w ill explore chain reactions by
modeling them w ith dominoes.
There's a good chance that you or someone you know
has been helped by nuclear chemistry. From the magnetic
properties of protons that enable MRIs, to the radiation
used in X-rays, PET scans, and hundreds of other tests and
treatments, research in nuclear chemistry has resulted in some
of the most powerful tools available to modern medicine.
ypes of Radiation
lake a layered-look book. Label it as shown,
se it to help you organize inform ation about
le different types of radiation.
i l S R ! ■if'"'■
' , ‘t
■*’>
'
’^1
connectED.nicaraw-hill.com
SECTION 1
E s s e n tia l Q u e s tio n s
• How was radioactivity discovered
and studied?
• What are the key properties of alpha,
beta, and gamma radiations?
R e v ie w V o c a b u la r y
nucleus: the extremely small, posi­
tively charged, dense center of an atom
that contains positively charged
protons, neutral neutrons, and is
surrounded by empty space through
which one or more negatively charged
electrons move
N e w V o c a b u la r y
radioisotope
X-ray
penetrating power
T a b le
Nuclear Radiation
M A I N I D E A Under certain conditions, some nuclei can e m it alpha,
beta, or gam m a radiation.
CH EM
4 YOU
T h e D is c o v e ry o f R a d io a c tiv ity
You have studied various form s o f chem ical reactions. Atoms can gain,
lose, or share valence electrons, but the identity o f the atoms does not
change. Nuclear reactions, which you will study in this chapter, are
different. Nuclear chem istry is concerned with the structure o f atomic
nuclei and the changes they undergo. W hereas chem ical reactions
involve only small energy changes, nuclear reactions involve much
larger energy changes. T a b le 1 offers a com parison o f chem ical
reactions and nuclear reactions.
In 1895, Germ an physicist W ilhelm Roentgen (1 8 4 5 -1 9 2 3 ) found
that invisible rays were emitted when electrons bom barded the surface
o f certain materials. These invisible rays caused photographic plates to
darken, and Roentgen named these high-energy emissions X - r a y s . At
that time, French physicist H enri Becquerel (1 8 5 2 -1 9 0 8 ) was studying
m inerals that emit light after being exposed to sunlight, a phenomenon
called phosphorescence. Building on Roentgens work, Becquerel wanted
to determ ine whether phosphorescent m inerals also emitted X-rays.
i Comparison of Chemical and Nuclear Reactions
Chemical Reactions
Occur when bonds are broken
and formed
Involve only valence electrons
Associated with small energy
changes
Atoms keep the same identity
although they might gain,
lose, or share electrons, and
form new substances
Temperature, pressure,
concentration, and catalysts
affect reaction rates
860
If you w ake up while it is still dark, the glowing numbers on your
dock let you know w hat time it is. M any docks use a type of
radiation to m ake the numbers glow. The word ra d iatio n might
cause you to think about nudear power plants or dangerous,
highly radioactive substances. However, less dangerous forms
of radiation are often used in everyday objects, such as clocks.
C h a p te r 24 • Nuclear Chemistry
Nuclear Reactions
Occur when nuclei combine,
split, and emit radiation
Can involve protons, neutrons,
and electrons
Associated with large energy
changes
Atoms of one element are
often converted into atoms
of another element
Temperature, pressure, and
catalysts do not normally
affect reaction rates
Becquerel discovered by chance that phosphorescent uranium salts
produced spontaneous emissions that darkened photographic plates.
He observed this phenomenon even when the uranium salts were not
exposed to light. Chemist Marie Curie (1867-1934) and her husband
Pierre Curie (1859—1906) took Becquerel’s mineral sample, called
pitchblende, and isolated the components emitting the rays. They
concluded that the darkening o f the photographic plates was due to rays
emitted from the uranium atoms present in the mineral sample. Marie
Curie named the process by which materials give off such rays radioac­
tivity; the rays and particles emitted by a radioactive source are called
radiation. F ig u re 1 shows the darkening o f photographic film that is
exposed to radiation emitted by radium salts.
The work o f Marie and Pierre Curie was extremely important in
establishing the origin o f radioactivity and developing the field of
nuclear chemistry. In 1898, the Curies identified two new elements,
polonium and radium, on the basis o f their radioactivity. Henri
Becquerel and the Curies shared the 1903 Nobel Prize in Physics for
their work. Marie Curie also received the 1911 Nobel Prize in
Chemistry for her work with polonium and radium.
□ READING CHECK E x p la in what Marie and Pierre Curie concluded about
I the darkening of the photographic plates.
■ F ig u re 1 Radium salts are placed on
a special emulsion on a photographic plate.
After the plate is developed, the emulsion
shows the dark tracks left by radiation
emitted by the radium salts.
Types o f Radiation
After reading about the discovery o f radioactivity, you might wonder
what types o f radiation are emitted by radioactive nuclei or which nuclei
are radioactive.
Recall that isotopes are atoms o f the same element that have different
numbers of neutrons. Isotopes o f atoms with unstable nuclei are called
rad ioisotop es. These unstable nuclei emit radiation to attain more
stable atomic configurations in a process called radioactive decay.
During radioactive decay, unstable atoms lose energy by emitting
radiation. The three most common types o f radiation are alpha (a ),
beta ((3), and gamma (7 ). Table 2 summarizes some o f their important
properties. Later in this chapter, you will learn about other types of
radiation that can be emitted in a nuclear reaction.
T a b le 2
Properties of Alpha, Beta, and Gamma Radiation
Property
Symbol
Composition
Description of radiation
Charge
Mass
Approximate Energy
Relative penetrating power
Alpha Radiation
Beta Radiation
Gamma Radiation
a
(3
K
alpha particles
beta particles
high-energy electromagnetic radiation
helium nuclei, ^He
electrons
photons
2+
1-
0
6.64 x 10-27 kg
9.11 x 10-31 kg
0
5 MeV
0.05 to 1 MeV
1 MeV
blocked by paper
blocked by metal foil
not completely blocked by lead or concrete
Section 1 • Nuclear Radiation
861
Zinc-sulfidecoated screen
■ F ig u re 2 The effect of an electric field depends on the charge and mass of the radiation.
Positively charged alpha particles deflect toward the negative plate. Negatively charged beta
particles deflect toward the positive plate. The lighter beta particles undergo the larger
deflection. Gamma rays have no charge and are not affected by an electric field.
E rnest Rutherford (1 8 7 1 -1 9 3 7 ), who perform ed the famous gold
foil experim ent that helped define m odern atom ic structure, identified
alpha, beta, and gamma radiation when studying the effects o f an
electric field on the em issions from a radioactive source. As you can see
in F ig u re 2, gamm a rays carry no charge and are not affected by the
electric field. Alpha particles carry a 2 + charge and are deflected toward
the negatively charged plate. Beta particles carry a 1 — charge and are
deflected toward the positively charged plate. Because beta particles are
less massive than alpha particles, they undergo a larger deflection.
□ READING CHECK Explain how Rutherford determined whether each of
1 the three types of radiation had a positive or negative charge or was
i unchanged.
j
Incorporate information
from this^sectionjnto
A lp h a p a r tic le s A n alpha particle ( a ) has the same com position as
a helium nucleus— two protons and two neutrons—and is therefore
given the symbol jH e. T he charge o f an alpha particle is 2 + due to the
presence o f the two protons. Alpha radiation consists o f a stream o f
alpha particles. Because o f their mass and charge, alpha particles are
relatively slow-moving compared with other types o f radiation. Thus,
alpha particles are not very penetrating— a single sheet o f paper stops
alpha particles. As you can see in F ig u re 3 , radium -226, an atom whose
nucleus contains 8 8 protons and 138 neutrons, undergoes alpha decay
by em itting an alpha particle.
■ F ig u re 3 A radium-226 nucleus
undergoes alpha decay to form radon-222
and an alpha particle.
Evaluate What is the number o f
protons and neutrons in radium-226
and radon-222?
+
226
3
88 R
rxa
Radium-226
862
C h a p te r 24 • Nuclear Chemistry
2I I Rn
Radon-222
m
2 He
Alpha particle
■ F ig u re 4 An iodine-131 nucleus
undergoes beta decay to form xenon-131
and a beta particle.
w
E xplain How d oes b eta decay affect
the mass number o f the decaying
nucleus?
131,
53 >
Iodine-131
In examining F ig u re 3 , note that the reaction is balanced. That is,
the sum o f the mass numbers (superscripts) and the sum o f the atomic
numbers (subscripts) on each side o f the arrow are equal. Also note that
when a radioactive nucleus emits an alpha particle, the product nucleus
has an atomic number that is lower by 2 and a mass number that is
lower by 4.
B e ta p a r t ic le s A beta particle is a very fast-moving electron that is
emitted when a neutron in an unstable nucleus converts into a proton.
Beta particles are represented by the symbol (3 or e- . They have a
1 — charge. Their mass is so small compared with the mass o f nuclei
involved in nuclear reactions that it can be approximated to zero. Beta
radiation consists o f a stream o f fast-moving electrons. An example o f
the beta decay process is the decay o f iodine-131 into xenon-131 by
beta-particle emission, as shown in F ig u re 4 . Note that the mass
number o f the product nucleus is the same as that of the original
nucleus (they are both 131), but its atomic number has increased by 1
(54 instead o f 53). This change in atomic number occurs because a
neutron is converted into a proton, as shown by the following equation.
V
ocabulary
..................................
W o r d o r ig in
Radiation
comes from the Latin word ra d ia re
which means to r a d ia t e ...................
n —»p + (3
As you might recall, the number o f protons in an atom determines its
identity. Thus, the formation o f an additional proton results in the
transformation from iodine-131 to xenon-131. Also, note that the
electric charge in the equation above is conserved. The neutron is
neutral. The proton has a 1+ charge and the beta particle has a 1 —
charge. Because beta particles are both lightweight and fast-moving,
they have greater penetrating power than alpha particles. A thin sheet of
metal foil is required to stop beta particles.
G a m m a r a y s Gamma rays are photons, which are high-energy
(short wavelength) electromagnetic radiation. They are denoted by the
symbol -y. Because photons have no mass and no charge, the emission of
gamma rays does not change the atomic number or mass number o f a
nucleus. Gamma rays almost always accompany alpha and beta radia­
tion, as they account for most of the energy loss that occurs as a nucleus
decays. For example, gamma rays accompany the alpha-decay reaction
of uranium-238.
29 2 U ~ > 29 o T h + 2 H e
+
2 ^
The 2 in front o f the 'y symbol indicates that two gamma rays of
different frequencies are emitted. Because gamma rays have no effect
on mass number or atomic number, it is customary to omit them from
nuclear equations.
Section 1 • Nuclear Radiation
863
■ F ig u re 5 The Chandra
Observatory, launched in July 1999,
photographed X-rays emitted from a
cool gas cloud surrounding the black
hole at the center of a neighboring
galaxy.
As you have learned, the discovery o f X-rays helped set the stage for
the discovery o f radioactivity. X-rays, like gamma rays, are a form of
high-energy electromagnetic radiation. However, X-rays are not pro­
duced by radioactive sources and their energy is lower than that o f
gamma rays. They are emitted when inner electrons are knocked out
and electrons from higher energy levels drop down to fill the vacancy.
F ig u re 5 shows an X-ray image taken in space. It allows astronomers to
observe objects not visible in optical images. The presence of X-rays
indicates phenomena such as exploding stars or black holes. Hospitals
and dentists have machines that produce X-rays when a beam of
electrons strikes a metal target. The familiar X-ray images are produced
as the beam o f X-rays passes easily through soft tissue but is partly
blocked by hard tissue, such as bone.
Q READING CHECK C o m p are and c o n tra s t X-rays and gamma rays.
P e n e t r a t in g p o w e r The ability o f radiation to pass through matter
is called penetrating power. Alpha particles have a low penetrating
power because they move slowly due to their large mass, and their 2 +
charge causes them to lose energy quickly through interactions with
other particles. The penetrating power o f beta particles is higher
because they are smaller and faster than alpha particles. However, they
can still interact with particles and can be stopped by thin shielding.
Gamma rays are highly penetrating. Because they have no charge and
no mass, the probability o f matter stopping them is low.
s ectio n 1
REVIEW
S e c tio n S u m m a r y
1. MAINIDEA List the different types of radiation and their charges.
• Wilhelm Roentgen discovered X-rays
in 1895.
2. Compare the subatomic particles involved in nuclear and chemical reactions.
• Henri Becquerel, Marie Curie, and
Pierre Curie pioneered the fields of
radioactivity and nuclear chemistry.
• Radioisotopes emit radiation
to attain more stable atomic
configurations.
864
C h a p te r 24 • Nuclear Chemistry
3. Explain how you know whether the reaction is chemical or nuclear when an
atom undergoes a reaction and attains a more-stable form.
4. Calculate Table 2 gives approximate energy values in units of MeV. Convert
each value into joules using the following conversion factor:
1MeV = 1.6 x 10~13J.
5. Summarize Make a time line that summarizes the major events that led to the
understanding of alpha, beta, and gamma radiation.
s e c t io n
2
E s s e n tia l Q u e s tio n s
Why are certain nuclei radioactive?
How are nuclear equations balanced?
How can you use radioactive decay
rates to analyze samples of
radioisotopes?
R e v ie w V o c a b u la r y
r a d io a c tiv it y : the process by which
some substances spontaneously emit
radiation
N e w V o c a b u la r y
transmutation
nucleon
strong nuclear force
band of stability
positron emission
positron
electron capture
radioactive decay series
half-life
radiochemical dating
Radioartive Decay
M A I N I D E A Unstable nuclei can break apart spontaneously,
changing the identity of atoms.
CHEM
4 YOU
To m ake sure that containers have the correct amount of fluid,
some manufacturing processes use radioactivity. Detectors
measure the number of particles produced by radioactive decay
after they pass through the containers. For instance, a half-full
bottle of juice would allow too much radiation to pass through
and would not pass inspection.
N u c le a r S t a b ility
Except for the emission o f gamma radiation, radioactive decay involves
the conversion o f an element into another element. Such a reaction, in
which an atom’s atomic number is altered, is called tran sm u tatio n .
W hether an atom spontaneously decays and what type o f radiation it
emits depends on its neutron-to-proton ratio.
An atom’s nucleus contains positively charged protons and neutral
neutrons. Protons and neutrons are referred to as nucleons. Despite the
strong electrostatic repulsion forces among protons, all nucleons remain
bound in the dense nucleus because o f the strong nuclear force. The
stro n g n u clear force acts on subatomic particles that are extremely
close together and overcomes the electrostatic repulsion among protons.
The fact that the strong nuclear force acts on both protons and
neutrons is important. Two protons repel each other, but because neu­
trons are neutral, a neutron that is adjacent to a positively charged
proton creates no repulsive electrostatic force. Yet these two adjacent
particles are held together by the strong nuclear force. Likewise, two
adjacent neutrons create no electrostatic force, but they, too, are held
together by the strong nuclear force. Thus, the presence of neutrons adds
an attractive force within the nucleus, as illustrated in F ig u re 6 . The
number o f neutrons in a nucleus is important because nuclear stability
is related to the balance between electrostatic and strong nuclear forces.
■Figure 6 The electrostatic force,
represented by the purple arrows, acts
between two charged particles. It is
repulsive between two protons. The strong
nuclear force, represented by the green
arrows, acts between any two or more
nucleons and is always attractive.
In f e r W hat is th e e ffe c t o f the
e le c tro s ta tic fo rce b e tw e e n tw o
n eu tro n s? B e tw e e n a p ro to n a n d
an e le ctro n ?
Proton
Proton
Neutron
Neutron
Proton
Neutron
Section 2 • Radioactive Decay
865
The Band of Stability
130
120
110
100
90
c
o
■§
80
h-
70
-Q
60
Z
50
0
o
i_
V
E
N e u t r o n - t o - p r o t o n r a t i o To a certain degree, the
stability o f a nucleus can be correlated to its neutron-toproton (n/p) ratio. For atoms with low atomic numbers
( < 2 0 ), the m ost stable nuclei are those with neutron-toproton ratios o f 1:1. For example, helium (^He) has two
neutrons and two protons, and a neutron-to-proton
ratio o f 1:1. As atomic num ber increases, m ore and
more neutrons are needed to produce a strong nuclear
force that is sufficient to balance the electrostatic repul­
sion force between protons. Therefore, the neutron-toproton ratio for stable atoms gradually increases,
reaching a m axim um o f approximately 1.5:1 for the
largest atoms. An example o f this is lead ( 2^ P b ). W ith
124 neutrons and 82 protons, lead has a neutron-toproton ratio o f 1.51:1.
Cp READING CHECK E xplain why the neutron-to-proton
ratio of stable nuclei increases as the atomic number
increases.
40
30
T h e b a n d o f s t a b i l i t y Exam ine the plot o f the
20
10
0
Number of protons
■Figure 7 The band of stability is the region where all
stable nuclei fall when plotting the number of neutrons versus
the number of protons. As the atomic number increases, the
neutron-to-proton ratio (n/p) increases from 1:1 to 1.5:1.
□ GRAPH CHECK
Find the number of protons above which the neutron-toproton ratio starts to differ from 1:1.
num ber o f neutrons versus the num ber o f protons for
all known stable nuclei shown in Figure 7. N otice that
the slope o f the plot indicates that the num ber of
neutrons required for a nucleus to be stable increases as
the num ber o f protons increases. This correlates with
the increase in the neutron-to-proton ratio o f stable
nuclei with increasing atom ic number. The area on the
graph w ithin which all stable nuclei are found is known
as the band of stability. As shown in Figure 7, jHe
and ^ P b are both positioned within the band o f
stability although they have a different neutron-toproton ratio. All nuclei outside the band o f stability—
either above or below— are radioactive and undergo
decay in order to gain stability. After decay, the new
atom is positioned m ore closely to, if not within, the
band o f stability. The band o f stability ends at lead-208;
all elem ents with atom ic numbers greater than 82 are
radioactive.
E^l READING CHECK D e fin e the band of stability and relate
it to the value of the neutron-to-proton ratio.
T y p e s o f R a d io a c tiv e D e c a y
The type o f radioactive decay a particular radioisotope
undergoes depends to a large degree on the underlying
causes for its instability. Atoms lying above the band o f
stability generally have too many neutrons to be stable,
whereas atoms lying below the band o f stability tend to
have too many protons to be stable. Depending on the
relative num ber o f neutrons and protons, atoms can
undergo different types o f decay—beta decay, alpha
decay, positron emission, or electron capturefeto gain
stability.
866
C h a p te r 24 • Nuclear Chemistry
B e ta d e c a y A radioisotope that lies above the band o f stability is
unstable because it has too many neutrons relative to its number o f pro­
tons. For example, unstable *gC has a neutron-to-proton ratio o f 1.33:1,
whereas stable elements o f similar mass, such as l\(Z and ^N, have
neutron-to-proton ratios o f approximately 1:1. It is not surprising, then,
that 6C undergoes beta decay, as this type o f decay decreases the num­
ber o f neutrons in the nucleus.
14C ^ 14N + (3
V
ocabulary
................................
S c ie n c e u s a g e v. C o m m o n u s a g e
Unstable
S cience usage: spontaneously
radioactive
U nstab le a to m s decay to reach a m ore
sta b le state.
C o m m o n usage: not firm or fixed in
F ig u re 8 a shows the beta decay o f carbon-14 into nitrogen-14. Note
that the atomic number o f the product nucleus, 'yN, has increased by
one. The nitrogen-14 atom now has a stable neutron-to-proton ratio of
1:1. Thus, beta emission has the effect of increasing the stability o f a
neutron-rich atom by increasing its atomic number, that is by lowering
its neutron-to-proton ratio. The resulting atom is closer to, if not within,
the band o f stability.
one place
Th e c h a ir is u nsta b le because one o f its
legs is s h o rte r th a n the o th e r . ...............
□ READING CHECK E x p la in why radioisotopes above the band of stability
are unstable.
A lp h a d e c a y All nuclei with more than 82 protons are radioactive
and decay spontaneously. Both the number o f neutrons and the number
o f protons must be reduced in order to make these radioisotopes stable.
These very heavy nuclei often decay by emitting alpha particles. For
example, polonium -210 spontaneously decays into lead-206 by emitting
an alpha particle.
“ “P o - ^ P b + ^He
F ig u re 8 b shows the alpha decay of polonium-210 into lead-206.
The atomic number o f ^ P o decreases by 2 and the mass number
decreases by 4 as the nucleus decays into 82Pb.
H READING CHECK C a lc u la te how the neutron-to-proton ratio changes
j when polonium-210 decays into lead-206.
■ F ig u re 8 Depending on where nuclei lie on the band of stability, they can emit a
beta particle or an alpha particle.
C o m p a re a n d c o n tra s t b eta decay and alpha decay in terms o f the atomic
number o f the nuclei involved in the reaction.
14
N
Nitrogen-14
14/
Polonium-210
Carbon-14
Beta particle
Beta decay
Alpha particle
Alpha decay
Section 2 • Radioactive Decay
867
P o s itr o n e m is s io n a n d e le c t r o n c a p tu r e For nuclei with low
neu tron-to-proton ratios, two com m on radioactive decay processes
occur: positron em ission and electron capture. These two processes
tend to increase the neutron-to-proton ratio o f the neutron-poor atom,
bringing the atom closer to, if not within, the band o f stability.
P o sitro n em ission is a radioactive decay process that involves the
em ission o f a positron from a nucleus. A p o sitro n is a particle with the
same mass as an electron but opposite charge; thus, it is represented by
the symbol |3+ or e +. During positron emission, a proton in the nucleus
is converted into a neutron and a positron, and then the positron is emitted.
Boron-
Carbon-11
Positron
F ig u re 9 shows the positron em ission o f a carb o n -11 nucleus.
C a rb o n -11 lies below the band o f stability and has a low neutron-toproton ratio o f approximately 0.8:1. C arb o n -11 undergoes positron
em ission to form b o ro n -11. Positron em ission decreases the num ber of
protons from six to five, and increases the num ber o f neutrons from five
to six. The resulting atom, ^ B , has a neutron-to-proton ratio o f 1 .2 : 1 ,
which is within the band o f stability.
Electron capture is the other com m on radioactive-decay process that
decreases the num ber o f protons in unstable nuclei lying below the band
o f stability. E lectro n cap tu re occurs when the nucleus o f an atom draws
in a surrounding electron, usually one from the lowest energy level. This
captured electron com bines with a proton to form a neutron.
Positron emission
o
•
+
Electron
§7 Rb
Rubidium-81
X-ray
photon
Electron capture
■ F ig u re 9 When a nucleus under­
goes positron emission or captures an
electron, the number of protons
decreases by one.
p + e ~ —>n
T he atomic num ber o f the nucleus decreases by 1 as a consequence o f
electron capture. The form ation o f the neutron also results in an X -ray
photon being emitted. These two characteristics o f electron capture are
shown in the electron capture o f rubidium -81 in F ig u re 9 . The bal­
anced nuclear equation for the reaction is shown below.
C o m p are and c o n tra s t h o w
th e n u m b e r o f p ro to n s a n d n e u tro n s
c h a n g e d u rin g p o s itr o n e m is s io n a n d
e le c tro n c a p tu re .
+ a’Rb
K r + X -ray photon
The five types o f radioactive decay you have read about in this
chapter are sum marized in T a b le 3.
□ READING CHECK List the decay processes that result in an increased
neutron-to-proton ratio and a decreased neutron-to-proton ratio.
T a b le
3 Summary of Radioactive Decay Processes
Type o f Radioactive Decay
Particle Em itted
Change in Mass Num ber
Change in Atom ic Num ber
decreases by 4
decreases by 2
Alpha decay
jH e
Beta decay
|3 or e-
no change
increases by 1
Positron emission
3+ or e+
no change
decreases by 1
Electron capture
X-ray photon
no change
decreases by 1
Gamma emission
1
no change
no change
868
C h a p te r 24 • Nuclear Chemistry
W riting and Balancing Nuclear Equations
The radioactive decay processes you have just read about are all exam ­
ples o f nuclear reactions. N uclear reactions are expressed by balanced
nuclear equations ju st as chem ical reactions are expressed by balanced
chem ical equations. However, in balanced chem ical equations, numbers
and types o f atom s are conserved; in balanced nuclear equations, mass
num bers and charges are conserved.
BALANCING A NUCLEAR EQUATION NASA uses the alpha decay o f plutonium - 238
(294^u) as a heat source on spacecraft. W rite a balanced equation fo r this decay.
A N A LY ZE THE PROBLEM
You are given that a plutonium atom undergoes alpha decay and forms an unknown
product. Plutonium-238 is the initial reactant, while the alpha particle is one of the products
of the reaction. The reaction is summarized below.
238
9 4 Pu
u
?Z X + 2^He
You must determine the unknown product of the reaction, X.
□
Known
Unknow n
reactant: plutonium-238 C^Pu]
decay type: alpha particle emission C^He)
mass number of the product A = ?
atomic number of the product Z = ?
reaction product X = ?
SOLVE FOR THE UNKNOW N
238 = A + 4
A = 238 — 4 = 234
Apply th e conservation of m ass num ber.
Solve for A.
Thus, the mass number of X is 234.
94 = Z + 2
Z = 94 - 2 = 92
Apply th e conservation of charges.
Solve for Z.
Thus, the atomic number of Y is 92.
The periodic table identifies the element as uranium [U],
238
94Pu & 239a2U + 2He
□
W rite the balanced nuclear equation.
EVALUATE THE ANSW ER
The correct formula for an alpha particle is used. The sums of the superscripts and
subscripts on each side of the equation are equal. Therefore, the charge and the
mass number are conserved. The nuclear equation is balanced.
PRACTICE Problem
6 . Write a balanced nuclear equation for the reaction in which oxygen-15
undergoes positron emission.
7. Thorium-229 is used to increase the lifetime of fluorescent bulbs. What
type of decay occurs when thorium-229 decays to form radium-225?
8. Challenge The figure at right shows one way that bismuth-212 can decay,
producing isotopes A and B.
a. Write a balanced nuclear equation for this decay.
b. Identify the isotopes A and B that are produced.
212 R:
83 Bl
Bismuth-212
Section 2 • Radioactive Decay
869
■ F ig u re 1 0 Uranium-238
undergoes 14 different radioactive
decay steps before forming stable
lead-206.
...
92
“
I
Uranium-238 Decay Series
!
Alpha decay
Mb
91
y
ft*
r
% W— — 1 ft
90
/
14
/
a
.a
V ft
E
/
87
E
o
<
p&
86
85
p
84
/
83
82
0
/
W
St able isotope
1
r
U
200 202 204 206 208 210 212 214 216 218 220 222 224 226 228 230 232 234 236 238
M ass n u m b e r
R a d io a c tiv e S e rie s
A ra d io a c tiv e d e ca y series is a series o f nuclear reactions that begins
with an unstable nucleus and results in the form ation o f a stable nucleus.
As F ig u re 1 0 shows, uranium -238 first decays to thorium -234, which in
turn decays to protactinium -234. Decay reactions continue until a stable
nucleus, lead-206, is formed.
□ GRAPH CHECK List each step in the decay of uranium-238. Include the
type of decay and the resulting product.
R a d io a c tiv e D e c a y R a te s
Explore half-life.
You m ight wonder how there could be any naturally occurring radioiso­
topes found on Earth. After all, if radioisotopes undergo continuous
radioactive decay, won’t they eventually disappear? Furthermore,
radioisotopes have been decaying for about 4.6 billion years— the span
o f Earths existence. Yet, naturally occurring radioisotopes are not
u ncom m on on Earth. Som e radioisotopes, such as carb on -14, are
continuously form ed in the upper atm osphere o f Earth. O thers are
formed in the universe, during stellar nucleosynthesis for instance.
Radioisotopes can also be synthesized in laboratories. The differing
decay rates o f isotopes also contribute to their presence on Earth.
Radioactive decay rates are measured in half-lives. A h a lf- life is
the tim e required for on e-h alf o f a radioisotopes nuclei to decay into its
products. For example, the half-life o f the radioisotope strontium -90 is
29 years. I f you had 10.0 g o f strontium -90 today, 29 years from now
you would have 5.0 g left. T a b le 4 shows how this decay continues
through four half-lives o f strontium -90. F ig u re 11 presents the data
from the table in term s o f the percent o f strontium -90 remaining after
each half-life. The decay continues until a negligible amount o f stron­
tium -90 remains.
□ READING CHECK D e fin e the term half-life.
870
C h a p te r 24 • Nuclear Chemistry
The Decay of Strontium-90
Table 4
Number of
Half-Lives
Elapsed
Time
Decay of Strontium
Amount of Strontium-90 Present
0
Oy
1 0 .0 g
1
29 y
1 0 .0 g x (1) = 5 .0 0 g
2
58 y
3
87 y
10.0 g x (y )(y )(y ) = 1 -25 g
4
116 y
10.0 g x (y)(-j)(4-)(y) = 0-625 g
=2.50 g
10.0 g x (y )(y )
T h e data in Table 4 can be sum m arized in a simple equation represent­
ing the decay o f any radioactive elem ent.
=
N
„
|
■Figure 11 The graph shows how the
amount of strontium in a sample changes
as a function of the number of half-lives.
Get help with exponential graphing.
Rem aining A m o un t of Radioactive Element
N
Number of half-lives
(1 half-life = 29 years)
N is th e rem aining am ount.
N 0 is th e inital am ount.
n is th e n u m ber o f h alf-lives th a t have passed.
The amount remaining is equal to the initial amount times one-half raised the number
of half-lives that have passed.
The exponent n can also be replaced with the equivalent quantity t / T ,
w here t is the elapsed tim e and T is the duration o f the half-life. Note
that t and T m ust have the sam e units o f tim e.
N = N „ ( i) ',r
T his type o f expression is know n as an exponential decay function.
Figure 11 shows the graph o f a typical exponential decay function— in
this case, the decay curve for strontium -90.
Cp GRAPH CHECK Infer how much strontium remains after 1.5 half-lives.
Each radioisotope has its own characteristic half-life. Half-lives for
several radioisotopes are given in Table 5. N otice the large range o f
values for half-lives, from m illionths o f a second to billions o f years!
Table
5 Half-Lives of Several Radioisotopes
Radioisotope
Polonium-214
Symbol
Half-Life
214Po
84ro
163.7 /zs
Cobalt-60
S P
Radon-222
J I Ra
5.272 y
3.8 d
Phosphorus-32
n
14.28 d
Carbon-14
146c
5730 y
Uranium-238
23982u
4.46 x 109y
Section 2 • Radioactive Decay
871
CALCULATING THE AM O UN T OF REMAINING ISOTOPE Krypton-85 is used in
indicator lights o f appliances. The half-life of krypton-85 is 11 y. How much of
a 2.000-mg sample remains after 33 y?
□
AN A LYZE THE PROBLEM
You are given a known mass of a radioisotope with a known half-life. You must first
determine the number of half-lives that passed during the 33-year period. Then, use
the exponential decay equation to calculate the amount of the sample remaining.
Known
Unknown
Initial amount = 2.000 mg
A m o u n t re m a in in g = ? m g
Elapsed time CO = 33 y
Half-life [T] = 11 y
□
SOLVE FOR THE UNKNOW N
Number of half-lives [n] S
elapsed tim e(f)
haif-life[7]
33 v
n B f g i = 3.0 half-lives
S ubstitute t = 3 3 y and T = 11 y.
A m o u n t re m a in in g = [initial amount] (■
=•
W rite th e exponential decay equation.
■
■
y
A m o u n t re m a in in g Ej (2000 mg] l^A m o u n t re m a in in g = [2.000 mg]
E3
D eterm in e the num ber of half-lives
passed during the 33 y.
S ubstitute initial am ount = 2 .0 0 0 mg
3.0
and n = 3.
= 0 .2 5 0 0 m g
EVALUATE THE ANSW ER
Three half-lives are equivalent to
>or (gj- The answer [0.25 mg] is equal to
(■Tj of the initial amount. The answer has two significant figures because the number of
years has two significant figures, n does not affect the number of significant figures.
PRACTICE Problems
Do additional problems J ^ S
9 . Bandages can be sterilized by exposure to gamma radiation from cobalt-60, which has a
half-life of 5.27 y. How much of a 10.0-mg sample of cobalt-60 is left after one half-life?
Two half-lives? Three half-lives?
10. If the passing of five half-lives leaves 25.0 mg of a strontium-90 sample, how much was
present in the beginning?
11. C h alle n g e The table shows the amounts of radioisotopes in three different samples.
To the nearest gram, how much will be in Sample B and Sample C when Sample A
has 16.2 g remaining?
Sample
872
Radioisotope
Half-life
Amount (g)
A
cobalt-60
5.27 y
64.8
B
tritium
12.32 y
58.4
C
strontium-90
28.79 y
37.6
C h a p te r 24 • Nuclear Chemistry
S
g |
MiniLAB
M o del Radioactive Decay
How do radioactive isotopes decay?
P ro c e d u re S
7. Place all o f the tails-up pennies back in the
plastic cup.
8 . Repeat Steps 3 through 7 as many times as
needed until no pennies remain.
ife
1. Read and com plete the lab safety form.
2. Place 100 pennies in a plastic cup.
3. Place your hand over the top o f the cup and
shake the cup several times.
4. Pour the pennies into a shoebox. Remove all
the pennies that land heads-up. These pennies
represent atom s o f the radioisotope that have
undergone radioactive decay.
5. Prepare a data table to record the num ber of
rem aining pennies (tails-up pennies).
6 . Count the num ber o f pennies that remain, and
record this num ber in your data table.
A n a ly s is
1. Construct a graph of T ria l N u m b e r v. N u m b e r o f
P e n n ie s R e m a in in g from your data table. Draw
a curve through the plotted points.
2. Calculate how many trials it took for 50%,
75%, and 90% o f the sample to decay.
3. Evaluate the half-life o f the radioisotope if the
tim e between each trial is 1 min.
4. Determ ine how the results w ould change if you
used 100 dice instead of pennies. In this case,
you w ould assume that any dice that lands with
the six side facing up represents a decayed atom
and is removed.
R a d io c h e m ic a l d a t i n g C hem ical reaction rates are greatly affected
by changes in tem perature, pressure, and concentration, and by the
presence o f a catalyst. In contrast, nuclear reaction rates rem ain con ­
stant regardless o f such changes. In fact, the half-life o f any particular
radioisotope is constant. Because o f this, radioisotopes can be used to
determ ine the age o f an object. T h e process o f determ ining the age o f an
ob ject by m easuring the am ount o f a certain radioisotope rem aining in
that ob ject is called ra d io c h e m ic a l d atin g.
C o n n e c t io n s Biology A type o f radiochem ical dating known as car­
bon dating is used to m easure the age o f artifacts that were once part o f
a living organism . C arbon dating m akes use o f the radioactive decay o f
ca rb o n -14, w hich is form ed by cosm ic rays in the upper atm osphere at a
fairly constant rate. These ca rb o n -14 atoms becom e evenly spread
throughout E arth s biosphere, where they m ix with stable carb o n -12 and
ca rb o n -13 atom s. Plants use carbon dioxide from the environment,
w hich contains all carbon isotopes, to build m ore com plex molecules
through the process o f photosynthesis. W hen animals eat plants, the
ca rb o n -14 atom s that were part o f the plant becom e part o f the animal.
Because organism s are constantly taking in carbon com pounds, they
contain the sam e ratio o f ca rb o n -14 to carb o n -12 and carb o n -13 found
in the atm osphere. However, after they die, organisms no longer ingest
new carbon com pounds, and the ca rb o n -14 they already contain con ­
tinues to decay. T h e ca rb o n -14 undergoes beta decay to form
n itro g en -14.
“C
- ^
+ p
C a rb o n -14 has a half-life o f 5730 years. Because the amount o f stable
carbon in the dead organism rem ains constant while the carb o n -14
continues to decay, the ratio o f unstable carbon-14 to stable carbon-12
and ca rb o n -13 decreases.
Section 2 • Radioactive Decay
873
■ F ig u re 1 2 Using the radiocarbon dating
method on organic materials, such as ash and
charcoal found at the Great Pyramid of Giza,
scientists estimate the pyramid to be more than
4000 years old.
By measuring this ratio and com paring it to the nearly constant
ratio present in the atmosphere, the age o f an object can be estimated.
For example, if an o b jects C -14 to (C -12 + C -13) ratio is one-quarter of
the ratio measured in the atmosphere, the object is approximately two
half-lives, or 11,460 years old. C arbon-14 dating is lim ited to accurately
dating objects up to approximately 45,000 years o f age. This m ethod was
used to date the Great Pyramid o f Giza, shown in F ig u re 12.
The decay process o f a different radio­
isotope, uranium -238 to lead-206, is com m only used to date objects
such as rocks. Because the half-life o f uranium -238 is 4.5 x 10 9 years, it
can be used to estimate the age o f objects that are too old to be dated
using carb o n -14. By radiochem ical dating o f m eteorites, the age o f the
solar system has been estimated at 4.6 X 10 9 years.
REVIEW
S e c tio n S u m m a r y
12. MAINIDEA Describe what happens to unstable nuclei.
• The conversion of an atom of one
element to an atom of another by
radioactive decay processes is called
transmutation.
13. Explain how you can predict whether or not an isotope is likely to be stable if
you know its number of neutrons and protons.
• Atomic number and mass number are
conserved in nuclear reactions.
15. Predict the nuclear equation for the alpha decay of radium-226 used on the tips
of older lightning rods.
• A half-life is the time required for half
of the atoms in a radioactive sample
to decay.
16. Calculate how much of a 10.0-g sample of americium-241 remains after four
half-lives. Americium-241 is a radioisotope commonly used in smoke detectors
and has a half-life of 430 y.
• Radiochemical dating is a technique
for determining the age of an object
by measuring the amount of certain
radioisotopes remaining in the object.
17. Calculate After 2.00 y, 1.986 g of a radioisotope remains from a sample that
had an original mass of 2.000 g.
a. Calculate the half-life.
b. How much of the radioisotope remains after 10.00 y?
14. Describe the forces acting on the particles within a nucleus and explain why
neutrons are the glue holding the nucleus together.
18. Graph A sample of polonium-214 originally has a mass of 1.0 g. Express
the mass remaining as a percent of the original sample after a period of one,
two, and three half-lives. Graph the percent remaining versus the number of
half-lives. Approximately how much time has elapsed when 20% of the original
sample remains?
874
C h a p te r 24 • Nuclear Chemistry
Pixtal/SuperStock
SECTION 2
SECTION 3
Nuclear Reactions
• How are mass and energy related?
M A I N ID E A Fission, the splitting of nuclei, and fusion, the combining
of nuclei, release tremendous amounts of energy.
• How do nuclear fission and nuclear
fusion compare and contrast?
CH EM
E s s e n tia l Q u e s tio n s
• What is the process by which nuclear
reactors generate electricity?
4 YOU
R e v ie w V o c a b u la r y
mass number: the number after an
element's name, representing the sum
of its protons and neutrons
N e w V o c a b u la r y
induced transmutation
transuranium element
mass defect
nuclear fission
critical mass
breeder reactor
nuclear fusion
thermonuclear reaction
On a hot summer day, you step outside and feel the intense
heat of the Sun. Nuclear reactions within the Sun release
enough energy to w arm Earth and other planets in the solar
system for billions of years. It is no surprise, then, that scientists
are trying to use this same type of nuclear reaction to produce
electricity.
Induced Transmutation
All nuclear reactions, or transm utations, that have been described thus
far are examples o f radioactive decay, where one elem ent is converted
into another elem ent by the spontaneous em ission o f radiation. How­
ever, transm utations can also be forced, or induced, by bom barding a
stable nucleus with a neutron or with high-energy alpha, beta, or
gam m a radiation. In 1919, Ernest Rutherford perform ed the first
laboratory conversion o f one elem ent into another element. By b om ­
barding n itrog en -14 with high-speed alpha particles, oxygen-17 and
hydrogen-1 were form ed. This transm utation reaction is illustrated
in F ig u re 1 3 and the reaction is shown below.
XyN + ^He—>
+ }H
As Rutherford dem onstrated, nuclear reactions can be induced, in
other words, produced artificially. The process, which involves striking
nuclei with high-velocity particles, is called ind u ced tra n sm u ta tio n .
In the case o f charged particles, such as the alpha particles used by
Rutherford, the incident particles must be moving at extrem ely high
speeds to overcom e the electrostatic repulsion between themselves and
the target nucleus. Because o f this, scientists have developed methods
to accelerate charged particles to extrem e speeds by using very strong
electrostatic fields and m agnetic fields. Particle accelerators are
m achines built to produce the high-speed particles needed to induce
transm utation. Since Rutherfords first experim ents involving induced
transm utation, scientists have used the technique to synthesize
hundreds o f new isotopes in the laboratory.
■ F ig u re 1 3 When an alpha particle bombards a nitrogen-14 atom, an atom of
oxygen-17 and an atom of hydrogen-1 are produced.
+
* He
Bombarding
alpha particle
1?N
Target
nitrogen atom
’ SO
Oxygen
atom
?H
Hydrogen
atom
Section 3 • Nuclear Reactions
875
T r a n s u r a n iu m e le m e n t s The elem ents immediately following
uranium in the periodic table— elem ents with atom ic num bers 9 3 and
greater— are known as the tra n su ra n iu m elem en ts. All transuranium
elem ents have been produced in the laboratory by induced transm uta­
tion and are radioactive. M any transuranium elem ents have been
nam ed in honor o f their discoverers or the laboratories at which they
were created. Scientists continue their ongoing efforts to synthesize
new transuranium elem ents and study their properties.
EXAMPLE Problem
IN D U C E D T R A N S M U T A T IO N R E A C TIO N E Q U A T IO N S W rite a balanced nuclear
equation fo r the induced transm utation o f oxygen-16 into nitrogen-13 by proton
bombardment. An alpha particle is em itted from the nitrogen atom in the reaction.
□
□
ANALYZE THE PROBLEM
You are given all of the particles involved in an induced transmutation reaction. Because
the proton bombards the oxygen atom, they are reactants and must appear on the reactant
side of the reaction arrow.
Known
Unknow n
reactants: oxygen-16 and a proton
products: nitrogen-13 and an a-particle
n u c le a r e q u a tio n fo r th e re a c ta n t = ?
SOLVE FOR THE UNKNOW N
Nuclear formula for oxygen-16: ’ gO
Use the periodic tab le to obtain the atom ic
num ber of oxygen.
Nuclear formula for nitrogen-13: 12N
Use th e periodic ta b le to obtain th e atom ic
num ber of nitrogen.
Nuclear formula for proton: p
Nuclear formula for alpha particle: ^He
’ JjO + p - ^ ’ yN + jH e
W rite th e balanced nuclear equation.
EVALUATE THE ANSW ER
A proton has a charge of 1+ and a mass number of 1. Therefore, both charge and mass
number are conserved. The formula for each participant in the reaction is also correct. The
nuclear equation is written correctly.
19. Write the balanced nuclear equation for the induced transmutation of
aluminum-27 into sodium-24 by neutron bombardment. An alpha particle
is released in the reaction.
5
20 . Write the balanced nuclear equation for the alpha-particle bombardment
of 2g®Pu. One of the reaction products is a neutron.
2 1 . C h alle n g e Archeologists sometimes use a procedure called neutron
activation analysis to identify elements in artifacts. The figure at right
shows one type of reaction that can occur when an artifact is bombarded
with neutrons. If the product of the process is cadmium-110, what was
the target and unstable isotope? Write balanced nuclear equations
for the process to support your answer.
876
C h a p te r 24 • Nuclear Chemistry
Neutron
'
Target
p
U n s ta b le ^ *,
isotope
Product
Binding Energy Variation
o
x
■ Figure 1 4 The binding energy per
nucleon is a function of the mass number.
Light nuclei gain stability by undergoing
nuclear fusion. Heavy nuclei gain stability by
undergoing nuclear fission.
3li
0
01
3
C
>i
31
h.
01
e
01
3»
JC
.e
3
Mass number
□ GRAPH CHECK
; Describe how the binding energy varies
as a function of the mass number.
Nuclear Reactions and Energy
In your study o f chem ical reactions, you read that mass is conserved.
For m ost practical situations this is true—but, it is n ot accurate.
E in s te in 's e q u a t i o n A lbert E insteins equation relates mass and
energy. It states that any reaction produces or consum es energy due to a
loss or gain in m ass. Energy and mass are equivalent. Note that because
c 2 is large, a sm all change in m ass results in a large change in energy.
E n e rg y E q u iv a le n t o f M ass
A
E
=
A m c2
A E is th e change in energy, in Joules. Am is the
change in m ass, in kg. c is th e speed of light.
The change in energy is equal to the change in mass times the square of the speed of light.
M a s s d e f e c t a n d b in d in g e n e r g y Scientists have determ ined
that the m ass o f the nucleus is always less than the sum o f the masses
o f the individual protons and neutrons that com prise it. This difference
in mass betw een a nucleus and its com ponent nucleons is called the
m ass defect.
W h en nucleons com bine together to form an atom, the energy
corresponding to the mass defect is released. Conversely, energy is
needed to break apart a nucleus into its nucleons. T he nuclear binding
energy can be defined as the am ount o f energy needed to break one
m ole o f nuclei into individual nucleons. The larger the binding energy
per nucleon, the m ore strongly the nucleons are held together, and the
m ore stable the nucleus is. Less-stable atoms have lower binding ener­
gies per nucleon. In other words, it is harder to break apart a nucleus
with a high binding energy than a nucleus with a low binding energy.
Figure 14 shows the average binding energy per nucleon versus the
mass num ber. Note that the binding energy per nucleon reaches a
m axim um around a mass num ber o f 60. Elem ents with a mass num ber
near 60 are the m ost stable.
Section 3 • Nuclear Reactions
877
C a lcu la tin g M a s s D efect
You can calculate the mass defect o f an isotope if you know the
mass of the isotope and the num ber and masses o f its components.
Applying the equation A £ = A m e 2, you can then derive the
equivalent binding energy.
Mass defect = m nuc|eus - [N pm p + /Vnm n]
where m nuc|eus is the mass of the nucleus, m p is the mass o f a proton,
m n is the mass o f a neutron, N p is the num ber of protons, and /Vn is
the num ber o f neutrons.
If you start w ith the mass o f the atom, you have to take into
account the mass o f the electrons. To do so, the mass of a hydrogen
atom, which is composed of a proton and an electron, is used
instead o f the mass of a proton. The equation is then:
Mass defect = m isotope - [N pm H - A/nm n]
Use the fo llo w in g values fo r the calculations: m H m 1.007825 amu
and m n = 1.008665 amu. The accepted value fo r c is 3.00 x 108 m/s.
To calculate the energy in Joules, you can convert the masses into
kilograms using 1 amu = 1.660540 x 10~27 kg.
Apply the Strategy
Calculate the mass defect and binding energy o f lithium-7.
The mass o f lithium-7 is 7.016003 amu.
In typical chem ical reactions, the energy produced or consumed
is so small that the accom panying changes in mass are negligible. In
contrast, the mass changes and associated energy changes in nuclear
reactions are significant. For example, the energy released from the
nuclear reaction o f 1 kg o f uranium is equivalent to the energy
released during the chem ical com bustion o f about four billion
kilogram s o f coal.
Nuclear Fission
V o c a b u l a r y .........................
A c a d e m ic v o c a b u la r y
Generate
to bring into existence, to originate
by a physical or chemical process
F ire generates a lo t o f h e a t ................
Binding energies in Figure 14 indicate that heavy nuclei tend to be
unstable. To gain stability, they can fragm ent into several smaller nuclei.
Because atoms with mass numbers around 60 are the m ost stable, heavy
atoms (those with mass num bers greater than 60) tend to fragment into
smaller atoms in order to increase their stability. The splitting o f a
nucleus into fragments is known as nuclear fission. The fission o f a
nucleus is accompanied by a very large release o f energy.
Nuclear power plants use nuclear fission to generate power. The first
nuclear fission reaction discovered involved uranium -235. As you can
see in Figure 15, when a neutron strikes a uranium -235 nucleus, it
undergoes fission. B ariu m -141 and krypton-92 are just two o f the many
possible products o f this fission reaction. In fact, scientists have identi­
fied more than 2 0 0 different product isotopes from the fission o f a
uranium -235 nucleus.
□ READING CHECK Explain why heavy atoms undergo nuclear fission.
878
C hapter 24 • Nuclear Chemistry
■Figure 15 When bombarded with a
neutron, uranium-235 forms unstable
uranium-236, which then splits into two lighter
nuclei and additional neutrons. The fission of
uranium-235 is accompanied by a large release
of energy.
+
(Unstable nucleus)
C h a in r e a c t io n s E ach fission o f uranium -235 releases additional
neutrons, as shown in Figure 15. I f one fission reaction produces two
neutrons, these two neutrons can cause two additional fissions. I f those
two fissions release four neutrons, those four neutrons could then
produce four m ore fissions, and so on, as shown in Figure 16. This
self-sustaining process in w hich one reaction initiates the next is called
a chain reaction. As you m ight im agine, the num ber o f fissions and the
am ount o f energy released can increase rapidly. T h e explosion from an
atom ic bom b is an exam ple o f an uncontrolled chain reaction.
■Figure 16 When uranium nuclei undergo fission, they release neutrons,
which trigger more fission reactions. The ongoing reactions are characteristics
of a nuclear chain reaction.
View an animation about chain reactions.
#
Q
n (neutron)
Fission
fragment
m
2! i u nucleus
#
Section 3 • Nuclear Reactions
879
■ F ig u re 17 Whether a nuclear reaction
can be sustained depends on the amount of
matter present. In a subcritical mass, the
chain reaction does not start because
neutrons escape before causing enough
fission to sustain the chain reaction. In a
supercritical mass, neutrons cause more and
more fissions and the chain reaction
accelerates.
View an animation about critical mass.
Subcritical mass
Supercriticalmass
A sample o f fissionable m aterial must have sufficient mass in order
for a chain reaction to occur. I f it does not, neutrons escape from the
sample before they can start the chain reaction by striking other nuclei.
A sample that is not massive enough to sustain a chain reaction is said
to have subcritical mass. A sample that is massive enough to sustain a
chain reaction has c ritic a l m ass. W hen a critical mass is present, the
neutrons released in one fission cause other fissions to occur. I f much
m ore mass than the critical mass is present, the chain reaction rapidly
escalates. This can lead to a violent nuclear explosion. A sample o f
fissionable m aterial with a mass greater than the critical mass is said to
have supercritical mass. F ig u re 17 shows the effect o f mass on the
initiation and progression o f a fission reaction.
□ READING CHECK C o m p are subcritical mass and critical mass.
nuclear power plant are the reactor under
the dome and the cooling tower.
880
C h a p te r 24 • Nuclear Chemistry
N u c le a r R e a c to rs
Nuclear fission produces the energy generated by nuclear reactors. This
energy is prim arily used to generate electricity at nuclear power plants,
such as the one shown in F ig u re 18. A com m on fuel is fissionable
uranium (IV ) oxide (U O 2 ) encased in corrosion-resistant rods. U -238 is
the m ost abundant isotope (99% ) o f uranium. U -235, which makes up
0.7% o f the natural uranium, has the rare property o f being able to
undergo induced fission; U -235 atoms undergo fission when hit by a
neutron. T he fuel used in nuclear power plants is enriched to contain
3% uranium -235, the am ount required to sustain a chain reaction, and
is called enriched uranium. Additional rods, often made o f cadmium or
boron, control the fission process inside the reactor by absorbing
neutrons released during the reaction.
Keeping the chain reaction going while preventing it from racing out
o f control requires precise m onitoring and continual adjusting o f the
control rods. Much o f the concern about nuclear power plants focuses
on the risk o f losing control o f the nuclear reactor, possibly resulting in
the accidental release o f harm ful levels o f radiation. The Three Mile
Island accident in the United States in 1979 and the Chernobyl accident
in Ukraine in 1986 provide examples o f why controlling the reactor is
critical. F ig u re 1 9 shows the city o f Pripyat, located 3 km from
Chernobyl. The city was completely abandoned after the accident.
vario images GmbH & Co.KG/Alamy
■ F ig u re 1 8 The main parts of a
■ F ig u re 1 9 The city
of Pripyat was deserted
after the accident at the
Chernobyl power plant.
The fission within a nuclear reactor is started by a neutron-emitting
source and is stopped by positioning the control rods to absorb all o f the
neutrons produced in the reaction. The reactor core contains a reflector
that acts to reflect neutrons back into the core, where they will react
with the fuel elements, also called fuel rods. A coolant, usually water,
circulates through the reactor core, to carry off the heat generated by
the nuclear fission reactions. The hot coolant heats water that is used to
power steam-driven turbines, which produce electric power.
Nuclear power plants and fossil-fuel burning power plants are
similar; heat from a reaction—nuclear fission or chemical combustion
o f coal is used to generate steam. The steam then drives turbines that
produce electricity, as shown in the nuclear power plant illustrated in
F ig u re 2 0 . The other major components o f a nuclear power plant are
also illustrated in F ig u re 2 0 .
View an
animationaboutnuclear
power plants.
■ F ig u re 2 0 A nuclear reactor produces heat that drives the formation of steam.
The energy from the steam spins a turbine which produces electricity. The steam is
eventually cooled and recycled. The water used to cool the steam enters the cooling
tower where steam is released to the atmosphere.
— Containment
structure
Control
rods
Hot coolant
Steam
Steam
generator
Steam turbine
(high-energy
steam spins
turbines and
generates
electricity)
Warm water
Fuel
elements
Cool water
Reactor
coolant
not to scale
-Carbon
moderators
Large body
of water
Section 3 • Nuclear Reactions
881
Because o f the hazardous radioactive fuels and fission products
present at nuclear power plants, a dense concrete structure is usually
built to enclose the reactor. T he m ain purpose o f the containm ent
structure is to shield personnel and nearby residents from harmful
radiation.
As the reactor operates, the fuel rods are gradually depleted and
products from the fission reactions accumulate. Because o f this, the
reactor must be serviced periodically. Spent fuel rods are extracted from
the reactor, as shown in F ig u re 2 1 , and can be reprocessed and repack­
aged to m ake new fuel rods. Som e fission products, however, are
extrem ely radioactive and cannot be used again. These products must
be stored as nuclear waste.
Risks o f accidents, such as the ones m entioned in F ig u re 2 2 , have to
be taken into account when operating nuclear power plants. However,
the storage o f highly radioactive nuclear waste is still one o f the m ajor
issues surrounding the debate over the use o f nuclear power. Approxi­
mately 2 0 half-lives are required for the radioactivity o f nuclear waste
m aterials to reach levels acceptable for biological exposure. For some
types o f nuclear fuels, the wastes rem ain substantially radioactive for
thousands o f years. A considerable am ount o f scientific research is
devoted to the disposal o f radioactive wastes. Highly radioactive m ateri­
als from the reactor core are first treated with advanced technologies
that ensure the materials will not deteriorate over a very long period o f
tim e. Treated wastes are then stored in sealed containers that are buried
deep underground.
A nother issue is the lim ited supply o f the uranium -235 used in the
fuel rods. O ne option is to build reactors that produce new quantities o f
fissionable fuels. Reactors able to produce m ore fuel than they use are
called breed er reacto rs. Although the design o f breeder reactors poses
many difficult technical problems, they are currently in operation in
several countries.
■ F ig u re 21 The interior of a reactor is
filled with water. A crane is used to extract
and replace fuel rods.
Q READING CHECK In fe r how the storage of nuclear wastes affects the
I environment.
■ F ig u re 22
T h e N u cle a r A g e
The discovery of X-rays in 1895 initiated a
series of breakthroughs in understanding
atomic nuclei. Today, nuclear chemistry
applications involving medicine, weaponry, and
energy affect the lives of people worldwide.
1919
J
The first artificially
induced nuclear reaction
causes the transmutation
of nitrogen into an iso­
tope o f oxygen by bom­
barding nitrogen gas
w ith alpha particles.
1934
Enrico Fermi's
experiments result in
the world's first nuclear
fission reaction. Fermi's
subsequent research
will pioneer nuclear
power generation.
1900
^1 1895
The first
X-ray photographs
fuel intense inter­
est among the sci­
entific community.
882
C hapter 24 • Nuclear Chemistry
1898 Marie and Pierre Curie
discover the radioactive
elements polonium and
radium. Their work establishes
the early fram ework for the
study of nuclear chemistry.
1941—45
Manhattan Project
scientists develop uranium and
plutonium bombs, which were
dropped on Hiroshima and
Nagasaki, Japan, in 1945 and
ended World War II.
Nuclear Fusion
Recall fro m th e binding en erg y d iag ram in F ig u re 1 4 th at a m ass
RealWorld CHEMIS
Nuclear Fusion
n u m b er o f abou t 6 0 has the m o st stable atom ic configuration. Thus, it is
possible to bin d to g eth er tw o o r m o re light (m ass n u m b er less than 6 0 )
■ and less-stable nuclei to fo rm a single m ore-stable nucleus. T h e com b ining o f a to m ic nuclei is called nuclear fusion. N uclear fusion reactions,
w hich are responsible for the p ro d u ctio n o f the heaviest elem ents, are
■ capable o f releasing v e ry large am o u n ts o f energy. You already have
som e everyd ay know ledge o f this fact— th e Sun is pow ered by a series
o f fusion reactio n s as h ydrogen atom s fuse to form helium atom s.
4 }H —> 2(3 + jH e + en ergy
Scientists have spent several decades research in g nuclear fusion. It is
a p rom isin g so u rce o f en erg y and has several advantages co m p ared to
SOLAR FUSION Nuclear fusion
nu clear fission. Lightw eight isotopes used to fuel the reaction s, such as
reactions are responsible for the
glow and heat from stars such as the
Sun. The temperature of the Sun's
core is about 15,000,000 K. It is so
hot and dense that hydrogen nuclei
fuse to produce helium. After
billions of years, the Sun's hydrogen
w ill be mostly depleted. Its
temperature will rise to about
100,000,000 K, and the fusion
process will then change helium
into carbon.
hydrogen, are ab u ndant. Fusion reaction p ro d u cts are n ot generally
rad ioactive. N u clear fusion p rod u ces large am ou nts o f energy. Fusion
reaction s p ro d u ce m o re en erg y p er unit o f m ass o f fuel than fission
reaction s. T h is cou ld solve th e problem o f the increasing needs for
electricity in the w o rld s societies.
U nfortunately, th ere are m ajor problem s th at m u st be o vercom e on a
co m m ercially viable scale. O ne su ch p roblem is that fusion requires
extrem ely h igh energies to initiate and sustain a reaction . T h e required
energy, w hich is achieved only at extrem ely high tem peratures, is
need ed to o v erco m e th e electrostatic repulsion betw een the nuclei in the
reaction . B ecau se o f the en ergy requirem ents, fusion reaction s are also
k now n as thermonuclear reactions. A tem p erature o f 5 ,0 0 0 ,0 0 0 K is
required to fuse h ydrogen atom s. T his tem p eratu re— and even higher
tem p eratu res— have been achieved using an atom ic explosion to initiate
the fusion p rocess, but this ap p roach is n o t p ractical for controlled
electric p ow er generation.
t 1 9 4 9 Radiocarbon dat­
ing allows scientists to
determine the age of
artifacts made from
plant-based materials
as old as 45,000 years.
•
1960s Scientists research
using high-energy radiation to
treat cancer. Clinical trials
bring dramatic improvement
in the treatment and cure of
malignant tumors.
2 0 0 6 The Cassini spacecraft
explores the Saturn system. Cassini
is powered by technology that
converts heat from the radioactive
decay of plutonium into electricity.
1 9 7 9 , 1 9 8 6 Nuclear power
plant accidents at Three Mile
Island, Pennsylvania, and
Chernobyl, Ukraine, focus world
attention on the dangers asso­
ciated with nuclear power.
• 2 0 1 0 Scientists using NASA's Fermi Gamma-
ray Space Telescope discover two massive
bubbles, one above and one below the core of
the Milky Way. They are thought to be the
result of activity from either a black hole or
star formation.
S e c tio n 3 • Nuclear Reactions
883
Poloidal field
magnet
Toroidal field
magnet
Vacuum
chamber
■Figure 23 A tokamak reactor, a ring-shaped reactor, uses strong magnetic
fields to contain the intensely hot fusion reaction and keep it from direct contact
with the reactor interior walls. The poloidal magnets follow the shape of the reactor
and the toroidal magnets wrap around the reactor.
Obviously, m an y problem s m u st be resolved before fusion becom es a
practical en ergy source. A n o th er significant problem is confinem ent o f
the reaction . T here are cu rren tly n o m aterials capable o f w ithstanding
the trem en d ou s tem peratures th at are required by a fusion reaction.
M uch o f the cu rren t research centers arou nd an apparatus called a
tokam ak reactor. Th e nam e tokamak com es from Russian and m eans
toroidal ch a m ber with an axial m agnetic field. A tokam ak reactor, shown
in Figure 23, is a donut-shaped device that uses strong m agn etic fields
to con tain the fusion reaction . W h ile significant progress has been
m ade in the field o f fusion, tem peratures high enough for continuous
fusion have n ot yet been sustained for long periods o f time.
SECTION 3
REVIEW
S e c tio n S u m m a r y
• Induced transmutation is the
bombardment of nuclei with particles
in order to create new elements.
• In a chain reaction, one reaction
induces others to occur. A sufficient
mass of fissionable material is
necessary to initiate the chain
reaction.
• Fission and fusion reactions release
large amounts of energy.
22. M AINIDEA Com pare and contrast nuclear fission and nuclear fusion
reactions. Describe the particles that are involved in each type of reaction and the
changes they undergo.
23. Describe the process that occurs during a nuclear chain reaction and explain
how to monitor a chain reaction in a nuclear reactor.
24. Explain how nuclear fission can be used to generate electric power.
25. Form ulate an argument supporting or opposing nuclear power as your state's
primary power source. Assume the primary source of power currently is the
burning of fossil fuels.
26. Calculate What is the energy change (AE) associated with a change in mass
{Am) of 1.00 mg?
27. In te rp re t Graphs Use the graph in F ig u re 1 4 to answer the following
questions.
a. Why is the isotope ^Fe highest on the curve?
b. Are more stable isotopes located higher or lower on the curve?
c. Compare the stability of Li-6 and He-4.
884
C h a p te r 24 • Nuclear Chemistry
SECTION 4
Applications and Effects
ofjsluclear Reactions
M A I N I D E A N uclear reactions have m any useful applications, but
th e y also have harm ful biological effects.
E s s e n tia l Q u e s tio n s
• What are several methods used to
detect and measure radiation?
CH EM
• How is radiation used in the
treatment of disease?
4
• What are some of the damaging
effects of radiation on biological
systems?
R e v ie w V o c a b u la r y
isotope: an atom of the same element
with the same number of protons but
different number of neutrons
v n . ,
| U U
Almost everyone gets cuts or scrapes from lime to time. Usually,
the first thing you do is dean the injury and cover it with a
bandage to keep out germs. One of the many uses of radiation
is to sterilize medical bandages.
Detecting Radioactivity
You read earlier th at Becquerel discovered radioactivity because o f the
effect o f radiation on photograp h ic plates. Since this discovery, several
o th er m eth od s have b een devised to d etect radiation. People w ho w ork
N e w V o c a b u la r y
n ear radioactive sources, for exam ple, m igh t be required to w ear a
ionizing radiation
radiotracer
th erm olu m in escen t d osim eter (T L D ) badge, w hich contains a tiny
crystal. R adiation excites electrons w ithin the crystal. To determ ine the
rad iation dose, the crystal is heated, and the electrons retu rn to their
grou n d states, em itting light. R adioactivity readers d etect this light as a
m easure o f the radiation dose to w hich a w orker has been exposed.
M onitorin g the radiation dose received by people w ho w ork near
rad ioactive sources is im p ortan t to ensure th eir safety.
R adiation energetic enough to ionize m atter w ith w hich it collides is
called ionizing radiation. Th e G eiger co u n ter is an ionizing radiation
d etection device. As show n in Figure 24, a G eiger cou n ter consists o f
a m etal tube filled w ith a gas. In the cen ter o f the tube is a wire that is
co n n ected to a pow er supply. W h en ionizing radiation penetrates the end
o f the tube, the gas inside the tube absorbs the radiation and form s ions
and free electrons. T h e free electrons are attracted to the wire, causing
an electric cu rren t. A m eter built into the Geiger cou n ter m easures the
cu rren t flow through the ionized gas. This cu rren t m easurem ent is used
to determ in e the am ou nt o f ionizing radiation present.
■Figure 24 A Geiger
counter is used to detect and
measure radiation levels.
Ionizing radiation produces an
electric current in the counter.
The current is displayed on a
scaled meter, whereas a speaker
produces audible sounds.
Gas molecules
are ionized by
the radiation
Counter and audio device
Electrode
(positively charged)
Metal tube
(negatively
charged)
Nonionized
gas molecules
Window
Ionizing
radiation
S e c tio n 4 • Applications and Effects of Nuclear Reactions
885
■Figure 25 Scintillation counters are used to detect the presence of ionizing radia­
tion. An ionizing radiation excites the electrons in the phosphors. As the electrons return to
their ground states, they emit photons, which are then detected by the photodetector.
A n o th er d etection device is a scintillation counter. Scintillations
are b rief flashes o f light p rodu ced w hen ionizing radiation excites the
electrons in certain types o f atom s o r m olecules called phosphors. A
scintillation co u n ter contains a base m aterial— often a plastic, a crystal,
o r a liquid— con tain ing phosphors, as shown in Figure 25. Ionizing
radiation that strikes the scintillation cou n ter can transfer energy either
directly to the phosphors o r to the base m aterial, w hich then transfers
the en ergy to the phosphors. This energy excites electrons in the ph os­
■Figure 26 Gauges such as the one
phors. As these electrons retu rn to their grou n d states, they release
pictured use beta emission from krypton,
promethium, or strontium. The radioactive
source is placed on one side of the paper,
and a detector is on the other side. Most
beta particles are absorbed by the paper,
but the percentage that are able to travel
through to the detector indicates the
thickness of the paper.
energy in the form o f light. This light is transm itted through the base
m aterial to a p h otod etector that con vert the light to an electrical signal.
The n u m ber and brightness o f the scintillations give a m easure o f the
am ou nt o f ionizing radiation.
□ READING CHECK S u m m a rize how a scintillation detector works.
Uses o f Radiation
W ith p roper safety procedures, radiation can be useful in m any scien ­
tific exp erim ents and industrial applications. F or instance, neutron
activation analysis is used to detect trace am ounts o f elem ents present in
a sample. C om p u ter-ch ip m anufacturers use this technique to analyze
the com position o f highly purified silicon wafers. In the process, the
sam ple is bom barded with a beam o f neutrons from a radioactive
source, causing som e o f the atom s in the sam ple to becom e radioactive.
T h e type and am ount o f radiation em itted by the sam ple is used to
determ ine the types and quantities o f elem ents present. N eutron activa­
tion analysis is a highly sensitive m easurem ent technique capable o f
detecting quantities o f less than 1 x 1 0 ~ 9 atom s in a sample. Beta
em ission is another application o f radiation. It is used to m easure paper
thickness, as shown in Figure 26.
886
C h a p te r 24 • Nuclear Chemistry
U s in g r a d io is o t o p e s R adioisotopes can also be used to follow the
cou rse o f an elem en t th rou g h a ch em ical reaction . F o r exam ple, C O 2
gas co n tain in g rad ioactive c a r b o n -14 isotopes has been used to study
glucose fo rm atio n in photosynthesis.
6 C 0 2 + 6 H 20 - nhght> C 6 H 120 6 + 6 0 2
B ecau se the C O 2 co n tain ing c a r b o n -14 is used to trace the progress
o f ca rb o n th ro u g h th e reactio n , it is referred to as a rad iotracer. A
radiotracer is a rad ioiso to p e th at em its n on -ion izing radiation and is
used to signal th e p resen ce o f an elem ent o r specific substance. Th e fact
that all o f an elem en ts isotopes have the sam e ch em ical properties
m akes th e use o f radioisotopes possible. Thus, replacing a stable atom
o f an elem en t in a reactio n w ith one o f its isotopes does n ot alter the
^ v . n t l V I I 3 I l \ T ------------------- -n
R adiatio n Therapist Under the
supervision of a physician, a
radiation therapist administers
radiation treatment to patients.
Radiation therapists work closely
with patients and must be compas­
sionate and supportive. Training
programs prepare radiation thera­
pists to use particle accelerators and
other forms of technology.
Knowledge of radiation hazards is an
important part of this job.
reaction . R ad io tracers are im p o rtan t in a n u m b er o f areas o f chem ical
research , p articu larly in analyzing the reactio n m echan ism s o f com plex,
m ultistep reaction s.
R ad io tracers also have im p o rtan t uses in m edicine. Io d in e -1 3 1 , for
exam ple, is co m m o n ly used to d etect diseases associated w ith the
thyroid gland. If a p roblem is suspected, the patient will drink a solution
con tain in g a sm all am o u n t o f io d in e -131. A fter the iodine is absorbed,
the a m o u n t o f iod ine taken up by the thyroid is m easured and used to
m o n ito r th e fu n ction in g o f th e thyroid gland.
□ READING CHECK D e fin e rad iotracer.
T r e a t in g c a n c e r R adiation can pose serious health problem s for
h u m an s b ecau se it can dam age o r destroy healthy cells. However,
rad iation can also d estroy unhealthy cells, such as can cer cells. All
can cers are ch aracterized by the rapid grow th o f abnorm al cells. This
grow th ca n p ro d u ce m asses o f ab n orm al tissue, called m alignant
tu m ors. R adiation th erapy is used to treat can cer b y destroying the
ca n ce r cells. In fact, ca n ce r cells are m o re susceptible to d estru ction by
rad iation than healthy ones. Figure 27 shows a brain scan with a
m align an t tum or. A fter rad iation treatm en t, the baseline returns to
n orm al. U nfortunately, in the p rocess o f destroying unhealthy cells,
rad iation also destroys som e healthy cells. D espite this m ajor draw back,
■Figure 27 Radiation can be used to treat
rad iation th erapy has b eco m e one o f the m o st effective treatm ent
cancer. MRI images taken before treatment and
after 4 and 10 months of treatment show the
decrease in the size of the tumor.
options in the fight against cancer.
S e c tio n 4 • Applications and Effects of Nuclear Reactions
887
■Figure 28 Gamma rays emitted by the
radiotracers absorbed by the patients are mea­
sured with this detector. The image on the right
shows different areas of the brain emitting
gamma rays. These images might help doctors
locate a tumor or observe a brain function.
U s in g p o s it r o n e m is s io n A n o th er radiation-based m edical
diagnostic tool is called p ositron em ission transaxial tom ograph y
(P E T ). In this proced u re, a rad io tracer that decays by positron em ission
is injected into the p atien ts b loodstream . Positrons em itted by the
rad io tracer cause g am m a -ra y em issions that are then detected by an
array o f sensors surrou n d in g the patient, as show n in Figure 28. P E T
scans can be used to diagnose diseases o r study the parts o f the brain
that are activated un d er given circu m stan ces, also shown in Figure 28.
Biological Effects o f Radiation
A lthough radiation has a n u m b er o f m edical and scientific applications,
it can be v ery harm ful. T h e dam age p rodu ced from ionizing radiation
absorbed by the b od y depends on several factors, such as the type of
radiation, its energy, the type o f tissue absorbing the radiation, the
p enetrating power, and the distance from the source. Figure 29 shows
an exam ple o f such dam age.
Connection¥9 Biology H igh-energy ionizing radiation is dangerous
because it can fragm ent and ionize m olecules w ithin biological tissue.
A free radical is an atom o r m olecule that contains one or m ore unpaired
electrons and is one exam ple o f the highly reactive products o f ionizing
radiation. In a biological system, free radicals can affect a large num ber
o f oth er m olecules and ultimately disrupt the operation o f norm al cells.
Ionizing radiation dam age to living systems can be classified as either
som atic o r genetic. Som atic dam age affects only nonreproductive body
tissue. It includes burns and can cer caused by dam age to the cell’s
grow th m echanism . G enetic dam age can affect offspring by dam aging
reproductive tissue. Such dam age is difficult to study because it m ight
n ot b ecom e apparent for several generations.
■Figure 29 Radiation can disrupt cell
processes and damage skin.
Infer Is the lesion pictured here
somatic or genetic?
| j|
\ ■VVv.
1 1 1 1 1 8 8
888
C h a p te r 24 • Nuclear Chemistry
D o s e o f r a d i a t i o n A dose o f radiation refers to the am ou nt
o f rad iation a b od y absorbs fro m a rad ioactive source. Two
units, th e rad an d th e rem , are co m m o n ly used to m easure
doses. T h e rad , w hich stands for rad iation -ab sorb ed dose, is a
Table 6 Effects o f S hort-term
R adiation Exposure
Dose (rem)
Effects on Humans
m easu re o f th e am o u n t o f rad iation that results in the ab so rp ­
tion o f 0 .0 1 J o f en erg y p er k ilogram o f tissue. T he dose in rads,
0-25
how ever, d oes n o t acco u n t for the en erg y o f the radiation, the
type o f living tissue absorbing the rad iation , o r the tim e o f the
25-50
exp osu re. To a cc o u n t for these factors, the dose in rads is
m ultiplied by a n u m erical facto r th at is related to the radiations
effect on the tissue involved. T h e result o f this m ultiplication is
100-200
a unit called the rem . T h e rem , w hich stands for roentgen
equivalent for m an , is n am ed after W ilhelm R oentgen, who
d iscovered X -ra y s in 1 895. T a b le 6 su m m arizes the sh o rt-te rm
500
no detectable effects
temporary decrease in
white-blood-cell population
nausea, substantial decrease
in white-blood-cell population
50% chance of death within
30 days of exposure
effects o f rad iation on h u m an s, depending o n the dose.
A v ariety o f so u rces con stan tly b om b ard you r b od y with
rad iation . Y o u r exp o su re to these sou rces results in an average
annual rad iatio n exp o su re o f 1 0 0 - 3 0 0 m illirem s o f h igh -en ergy
rad iation o r 0 .1 - 0 .3 rem s. T a b le 7 shows y ou r annual exposure
to co m m o n rad iation sources.
I n t e n s i t y a n d d is t a n c e T h e intensity o f radiation depends
Watch a video about radioisotopes.
on th e d istan ce fro m the so u rce as show n by the equation
below. T h e farth er aw ay the so u rce, the low er the intensity.
T h e intensity o f rad iation is m easu red in am ou nt o f radiation
p er u n it o f tim e a n d /o r surface, su ch as m re m /s -m 2.
Radiation Intensity and Distance
_ , 2
M ** 1
t j 2
and d 2 a re tw o distances from the source.
^ 2 “ 2 / , is th e intensity a t </lf and l 2 is the intensity a t d 2.
The intensity of a radiation at a distance d, from the source multiplied by the
square of the distance equals the intensity of the radiation at a distance dj
multiplied by the square of the distance.
Table 7
Average Annual
Radiation Exposure
Source
Average Exposure (mrem/y)
Cosmic radiation
20-50
Radiation from the ground
25-175
Radiation from buildings
10-160
Radiation from air
20-260
Human body (internal)
Medical and dental X-rays
Nuclear weapon testing
Air travel
Total average
-20
50-75
<1
5
100-300
S e c tio n 4 • Applications and Effects of Nuclear Reactions
889
oblem-Solvinq LAB
Interpret Graphs
How does distance affect radiation
exposure? W hen one of the reactors at the
Chernobyl nuclear pow er plant exploded, the
im m ediate vicinity o f the pow er plant was
highly contam inated and declared a dead zone.
The radiation spread over thousands o f kilome­
ters. However, th e intensity o f the radiation
decreased w ith th e distance from the reactor.
Radiation Intensity
Versus Distance
From Source
A n a ly s is
The graph to the right shows the intensity of a
radioactive source versus the distance from the
source. Note how the intensity of the radiation
varies w ith th e distance from the source. The
unit o f radiation intensity is millirems per
second per square meter. This is the am ount of
radiation striking a square m eter o f area each
second.
Distance from source (m)
T h in k C ritic a lly
1. Evaluate How does the radiation exposure
change as the distance doubles from 0.1 m
to 0.2 m? How does it change as the
distance quadruples from 0.1 m to 0.4 m?
2. Formulate in words th e mathematical
relationship described in your answer to
Question 1.
SECTION 4
REVIEW
S e c tio n S u m m a r y
• Different types of counters are used
to detect and measure radiation.
• Radiotracers are used to diagnose
disease and to analyze chemical
reactions.
• Short-term and long-term radiation
exposure can cause damage to living
cells.
3. Interpret Graphs Determ ine the distance from
the source at which the radiation decreased to
0.69 mrem/s*m2. This intensity is the maximum
radiation exposure intensity considered safe.
{Hint: Use the equation kfjn = c/22/c/12.)
Section Self-Check
28. MAINIDEA Explain one way in which nuclear chemistry is used to diagnose or
treat disease.
29. Describe several methods used to detect and measure radiation.
30. Com pare and contrast somatic and genetic biological damage.
31. Explain why it is safe to use radioisotopes to diagnose medical problems.
32. Calculate A lab worker receives an average radiation dose of 21 mrem each
month. Her allowed dose is 5,000 mrem/y. On average, what fraction of her
yearly dose does she receive?
33. In te rp re t D ata Look at the data in T a b le 7. Suppose someone is exposed to
the maximum values listed for average annual radiation from the ground, from
buildings, and from the air. What fraction would the person receive of the
minimum short-term dose (25 rem) that causes a temporary decrease in white
blood cell population?
890
C h a p te r 24 • Nuclear Chemistry
c a r e e r s
Career: Archaeologist
N e u tr o n A c t iv a t io n A n a ly s is
In th e Andes m ountain range, m ore than 500
years ago, a young girl was sacrificed to appease
th e gods. As was th e custom o f th e ancient
Incas, pottery and other artifacts w ere buried
w ith her. Neutron activation analysis perform ed
on pottery such as th e vessel in F ig u re 1
allow ed archaeologists to determ ine the origin
o f th e soil from which th e pottery was made.
Concentration of Elements
Sample ID = CPA1260
Irrad. tim e = 5 s
Decay tim e = 25 min
Counting tim e = 12 min
100,000
10,000
1000
100
10
1
0
800
1600
2400
3200
Energy (keV)
Figure 2 A gamma-ray spectrum indicates the concentration
of different elements in a sample.
Figure 1 Neutron activation analysis allowed comparison of
soil and pottery to determine where this Incan vessel was made.
D e te c tin g e le m e n ts Neutron activation
analysis is a m ethod o f detecting elements in
a m aterial. A small sample o f th e material is first
exposed to a strong neutron source. Neutron
bom bardm ent produces radioisotopes in about
three-fourths o f th e elements. W hen the radio­
isotopes decay, they em it gam m a rays w ith
energies th a t are characteristic o f the elem ent.
A gam m a detector is used to measure the
sample's radiation output. Gamma rays of
d iffe re n t energies produce peaks at different
places on graphs, such as the one in F ig u re 2.
Each peak corresponds to a specific elem ent.
Some elem ents have more than one peak
because they em it gam ma rays o f different
energies. The height o f the peak, or the area
under the peak, indicates the concentration of
the elem ent in th e sample.
This m ethod can be used to search for just
one elem ent or many elements in a sample. The
process can detect extrem ely low concentrations
of elements, as low as parts per billion.
A d v a n ta g e s Most forms o f chemical analysis
require vaporization, dissolution, or alteration
o f the analyzed sample in some way. Neutron
activation analysis is a nondestructive process
th a t can be used to study liquid, solid, or gas­
eous samples. Sensitive items, such as forensic
evidence, meteorites, or artifacts, can be ana­
lyzed w ith o u t harm.
Uses Analyzing the composition o f artifacts
such as pottery allow ed scientists to establish
the origin of the clay used to make the objects
th a t w ere buried w ith the young, sacrificed
girl. Astonishingly, the clay did not come from
local soil but from the Incan capital and other
religious centers. Representatives from the
Incan Empire traveled to remote places, bringing
pottery and other artifacts w ith them , to
perform rituals.
WRITINGiNKhemistry
A n a ly z e Look at the graph in F igure 2. Write an
explanation about how a technician could use the graph
to determine the elements present in the irradiated
sample. Is the height of the peaks important? Which
element is found in the greatest concentration in the
sample? What are the approximate energies of
gamma rays emitted by this element?
Chemistry & Careers
891
C h e m L A B ______
(L —
Investigate Radiation Dosage
Background: Radiation is a term that causes
fearful responses in people. However, not all radiation
is dangerous. We are surrounded by radiation from
space and from natural radioactivity on Earth.
Radiation can also be used in a safe and controlled
way for medical purposes.
Question: What methods are effective in minimizing
exposure to radiation?
8
. Place the alpha source on the 10-cm m ark, and place
a heavy piece o f cardboard between the source and
the Geiger counter.
9 . M easure and record the highest reading.
10. Place the source on the 3 0 -cm m ark, and place the
piece o f cardboard on the 10 -cm m ark. M easure and
record the radiation.
1 1 . Place the piece o f cardboard on the 2 0 -cm mark, and
repeat the m easurem ent.
Materials
alpha source
beta source
gam m a source
Geiger counter
piece o f cardboard
piece o f plastic
m eterstick
1 2 . Place the piece o f plastic between the source, and
counter and record the highest reading.
13. Repeat Steps 8 - 1 2 with the beta source and the
gam m a source.
14. Cleanup and Disposal Return all lab equipment
and radiation sources to the designated location.
R em em ber to wash your hands with soap and water
after com pleting the lab.
clock
Safety Precautions
WARNING: Radioactive sources can be harmful.
Wash hands and arms thoroughly before handling
objects which go to the mouth, nose, or eyes. Do not
eat or drink in laboratories where radioactive sources
are used. Do not handle radioactive sources if you
have a break in the skin below the wrist. Do not
use—and immediately report to your teacher—any
sealed disc containing a radioactive source which
is damaged.
Procedure
1. Read and com plete the lab safety form.
2 . Using what you know about types o f radiation, write
a hypothesis about how pieces of cardboard and
plastic will affect the radiation dose.
3. Create a table to record your data.
Analyze and Conclude
1. Summarize How does distance affect the am ount
o f radiation from a source?
2. Compare and Contrast Does the experim ental
data support your hypothesis?
3. Explain Based on the data, explain why you were
required to w ear goggles and a lab apron in this lab.
4. Recognize Cause and Effect W hich radiation
source was least affected by the cardboard and
plastic shields? Explain why this source is different
from the other two sources.
5 . Infer Did the position o f the piece o f cardboard
influence the results? Explain why or why not.
6. Observe and Infer W h at can you say about the
penetrating power o f X -rays based on the fact that
you have to wear a lead shield at the dentist to
p rotect your body from the radiation?
4 . Place the m eterstick on the lab station with the
Geiger counter at the zero-end.
5. Place the alpha source at the 10-cm m ark, and
record the highest reading on the Geiger counter.
6
. Repeat the m easurem ent with the source at 20 cm
and 30 cm.
7 . Repeat Steps 5 and 6 with the beta source and
gam m a source.
892
C h a p te r 24 • Nuclear Chemistry
INQUIRY EXTENSION
Research
Find references that list and quantify the
exposure to radiation that we receive in everyday
life. Calculate your average annual exposure, and
describe m ethods that could reduce this dosage.
B IG ID E A
Nuclear chemistry has a vast range of applications, from the production of
electricity to the diagnosis and treatment of diseases.
MAIIMIDEA Under certain conditions, some nuclei can emit alpha, beta, or gamma radiation.
• Wilhelm Roentgen discovered X-rays in 1895.
• Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and
nuclear chemistry.
VOCABULARY
• radioisotope
• X-ray
• penetrating power
• Radioisotopes emit radiation to attain more-stable atomic configurations.
s e c tio n 2
Radioactive Decay
MAIIMIDEA Unstable nuclei can break apart spontaneously, changing the identity of atoms.
• The conversion of an atom of one element to an atom of another by radioactive decay
processes is called transmutation.
• Atomic number and mass number are conserved in nuclear reactions.
• A half-life is the time required for half of the atoms in a radioactive sample to decay.
N = N ^ i ) 'o r N = N ^ ) "
• Radiochemical dating is a technique for determining the age of an object by measuring the
amount of certain radioisotopes remaining in the object.
s e c tio n 3
VOCABULARY
• transmutation
• nucleon
• strong nuclear force
• band of stability
• positron emission
• positron
• electron capture
• radioactive decay series
• half-life
• radiochemical dating
Nuclear Reactions__
MAIIMIDEA Fission, the splitting of nuclei, and fusion, the combining of nuclei, release tremendous
amounts of energy.
• Induced transmutation is the bombardment of nuclei with particles in order to create new
elements.
• In a chain reaction, one reaction induces others to occur. A sufficient mass of fissionable
material is necessary to initiate the chain reaction.
• Fission and fusion reactions release large amounts of energy.
VOCABULARY
• induced transmutation
• transuranium element
• mass defect
• nuclear fission
• critical mass
• breeder reactor
• nuclear fusion
• thermonuclear reaction
E = m e2
« rn n M i
Applications and Effects of Nuclear Reactions
MAIIMIDEA Nuclear reactions have many useful applications, but they also have harmful biological
effects.
• Different types of counters are used to detect and measure radiation.
VOCABULARY
• ionizing radiation
• radiotracer
• Radiotracers are used to diagnose disease and to analyze chemical reactions.
• Short-term and long-term radiation exposure can cause damage to living cells.
Il4 l = ^2^2
C h a p te r 24 • Study Guide
SECTION 1_______
SECTION 2
M astering Concepts
M astering Concepts
34. Compare and contrast chemical reactions and nuclear
reactions in terms of energy changes and the particles
involved.
35. Match each numbered choice on the right with the
correct radiation type on the left.
1 . high-speed electrons
a. alpha
2 . 2 + charge, blocked easily
b. beta
3. no charge, electromagnetic
c. gamma
radiation
42. What is the strong nuclear force? On which particles
does it act?
43. Explain the difference between positron emission and
electron capture.
44. Categorize each type of radioactive decay.
a. Mass number and atomic number are unchanged.
b. Mass number remains the same and atomic number
decreases.
45. What is the significance of the band of stability?
46. What is a radioactive decay series? When does it end?
O
+
1—
Radioactive
source
—
y
47. Radioisotopes What are the factors that determine the
amount of a given radioisotope in nature?
Band of
Stability
^
A
Charged plates
Q)
E
■ Figure 30
36. Figure 30 shows alpha particles, beta particles, and
gamma rays passing through a screen and between two
charged plates. What can you infer about the identity of
a, b, and c? Explain your answer.
3 7. What is the difference between X-rays and gamma rays?
M astering Problems
38. Dental crown Uranium-234 is used to make dental
crowns appear brighter. The alpha decay of uranium-234
produces what isotope?
39. Detecting Material Flaws Flaws in welded metal parts
of airplanes can be identified by placing the isotope
iridium-192 on one side of the weld and photographic
film on the other side to detect gamma rays that pass
through. How does the gamma ray emission affect the
atomic number and mass number of the iridium?
40. Colored Glass Thorium-230 can be used to provide
coloring in glass objects. One method of producing
thorium-230 is through the radioactive decay of
actinium-230. Is this an example of alpha decay or
beta decay? How do you know?
41. Plastic Bags Thin sheets of plastic are used to make
items such as grocery bags. The sheets move under a
source of promethium-147, emitting beta particles. The
radiation intensity, measured under the plastic sheets, is
used to monitor the thickness of the plastic. During this
process, promethium changes into which element?
894
C h a p te r 24 • Nuclear Chemistry
Number of protons
■ Figure 31
48. In which region(s) in Figure 31 are you likely to find
a. stable nuclei?
b. nuclei that undergo alpha decay?
c. nuclei that undergo beta decay?
d. nuclei that undergo positron emission?
49. Carbon-14 Dating Carbon-14 dating makes use of
a specific ratio of two different radioisotopes. Define
the ratio used in carbon-14 dating. Why is this ratio
constant in living organisms?
Mastering Problems
50. Calculate the neutron-to-proton ratio for each atom.
a. tin-134
c.carbon-12
b. silver-107
d.carbon-14
51. Complete the following equations.
,B i- 2r
,He
b. 2f 3Np-931',F239
83^*
it +
T ' ?:
•**
7 94PaU + ?
52. Write a balanced nuclear equation for the alpha decay of
americium-241.
53. Write a balanced nuclear equation for the beta decay of
cesium-137.
54. Bone Formation The electron capture of strontium-85
can be used by physicians to study bone formation.
Write a balanced nuclear equation for this reaction.
55. Nuclear Safety The half-life of tritium (JH) is 12.3 y.
If 48.0 mg of tritium is released from a nuclear power
plant during the course of a mishap, what mass of the
nuclide will remain after 49.2 y? After 98.4 y?
56. Static Charge Static charge can interfere with the
production of plastic products by attracting dust and dirt.
To reduce it, manufacturers expose the area to poloni­
um-210, which has a half-life of 138 days. How much of
a 25.0-g sample will remain after one year (365 days)?
57. The half-life of polonium-218 is 3.0 min. If you start
with 2 0 .0 g, how long will it be before only 1 .0 g
remains?
58. An unknown radioisotope exhibits 8540 decays per
second. After 350.0 min, the number of decays has
decreased to 1250 per second. What is the half-life?
SECTION 3__________
M astering Concepts
59. Define transmutation. Are all nuclear reactions also
transmutation reactions? Explain.
60. Relate binding energy per nucleon to mass number.
61. Referring to Figure 7, would you expect 2oCa to be
radioactive? Explain.
62. W hat is a chain reaction? Give an example of a nuclear
chain reaction.
63. Explain the purpose of control rods in a nuclear reactor.
64. Why is the fuel of a nuclear reactor enriched?
M astering Problems
69. Smoke Detectors Americium-241, a radioisotope used
in smoke detectors, is produced by bombarding plutonium-238 with neutrons to produce plutonium-240, which
is bombarded with neutrons to produce plutonium-241.
The plutonium-241 decays to americium-241. Write the
balanced nuclear equations for each reaction.
70. Exit Signs Exit signs are coated with a paint containing
phosphors. These phosphors are activated by the
radioisotope tritium ( ^H), produced by bombarding
lithium- 6 with neutrons to produce lithium-7. The
lithium-7 then undergoes alpha decay to produce the
tritium. Write balanced nuclear equations for both steps.
71. Control Rods Bombarding uranium-235 with neutrons
produces samarium-149, which is used in nuclear
reactor control rods. What other element is produced?
72. The Sun }H + jH —> ^He + y is one of the fusion
reactions in the Sun. The mass of }H is 1.007825 amu,
the mass of [H is 2.014102 amu, and the mass of ^He is
3.016029 amu.
a. What is the mass defect of ^He?
b. What energy is released by the process?
SECTION 4____________
M astering Concepts
73. What property of isotopes allows radiotracers to be
useful in studying chemical reactions?
74. Which unit of radiation dose, rem or rad, is most useful
for describing the effect of radiation on living tissue?
75. PET Scans In PET scans, the radiotracer emits
positrons, which travel a few millimeters before
interacting with electrons. How can the original
radiotracer be detected?
Intensity v.
Distance From
the Source
■ F ig u re 32
65. Describe what is meant by the terms critical mass,
subcritical mass, and supercritical mass. Which is
shown in Figure 32? How can you tell?
66
. Explain how it is possible that fission (the splitting of
nuclei) and fusion (the combining of nuclei) both
release tremendous amounts of energy.
67. Describe the current limitations of fusion as a power
source.
68
. Why does nuclear fusion require so much heat? How is
heat contained within a tokamak reactor?
Distance from
the source
■ Figure 33
76. Figure 33 shows a simplified graph of radiation intensity
versus distance from the source. Explain this graph and
what it implies about a method of reducing the effects of
radiation exposure.
C h a p te r 24 • Assessment
895
M a s te rin g P roblem s
87. Sheet Metal A company plans to monitor the thickness
of sheet metal during production. What would you
recommend the company do to determine a safe
distance for workers from the gamma source?
Decay Series
Source
......................................... ?
«*g
**~ »■
■ F igure 34
7 7 . Figure 34 shows the position of two workers near a
radioactive gamma source. The worker at Position A
is 2.5 m from the source and receives an exposure of
0.98 mrem/s*m2. The worker at Position B receives
an exposure of 0.50 mrem/s-m2. What is the distance
of the worker at Position B from the source?
7 8 . A worker stands near a machine that uses a cobalt-60
gamma source to sterilize medical equipment. The
workers dose 2.0 m from the source is 0.85 mrem/s-m2.
What is the workers dose at a distance of 3.5 m?
7 9 . Safe Exposure The intensity of a radioactive source is
1.15 mrem/s*m 2 at a distance of 0.50 m. What is the
minimum distance a person could be from the source to
have a maximum exposure of 0.65 mrem/s*m2?
Mass number
■ Figure 35
88
. Figure 35 shows part of the decay series of a radio­
isotope. For each segment on the graph, tell whether
alpha decay or beta decay occurs, and identify the
change in atomic number and mass number.
89. Make and Use Graphs Thorium-231 decays to lead207 by emitting the following particles in successive
steps: (3, a , a , (3, a , a , a , (3, |3, a . Plot each step of the
decay series on a graph of mass number versus atomic
number. Label each plotted point with the symbol of the
radioisotope.
90. Apply Chemical treatment is often used to destroy
80. Technetium-104 has a half-life of 18.0 min. How much of
a 165.0 g sample remains after 90.0 minutes have passed?
81. A bromine-80 nucleus can decay by gamma emission,
positron emission, or electron capture. What is the
product nucleus in each case?
82. The half-life of plutonium-239 is 24,000 y. How much
nuclear waste generated today will remain in 1 0 0 0 years?
83. Red Blood Cells A medical researcher is using a
chromium-51 source to study red blood cells. The
gamma-emission intensity at a distance of 1.0 m is
0.75 mrem/s*m2. At what distance would the intensity
drop to 0.15 mrem/s-m2?
84. The binding energy per nucleon reaches a maximum
around what mass number? Explain how this number is
related to the fission and fusion processes.
85. You have an alpha source, a beta source, and a gamma
source. Design a plan to use a Geiger counter, paper, and
foil to determine the identity of each source.
86
896
. What is the half-life of radon-222 if a sample initially
contains 150 mg and only 18.7 mg after 11.4 days?
C h a p te r 24 • Nuclear Chemistry
harmful chemicals. For example, bases neutralize acids.
Why can’t chemical treatment be applied to destroy the
fission products produced in a nuclear reactor?
91. Compare A biological concern about working around
some radioactive materials is the radioactive dust a
person might inhale. Compare the effect of alpha
radiation outside the body and inside the body.
92. Interpret Small radioactive sources are often used for
laboratory experiments. The radioactive substance is
enclosed in a metal container with a small window. A
gamma source might be covered with a stainless steel
window. What would you expect the window of an alpha
source to be like? Why?
93. Analyze Some radioisotopes used for medical imaging
have half-lives as short as several hours. Why is a short
half-life beneficial? Why is it a problem?
94. Infer The production of electricity at nuclear fission
reactor facilities is controversial. Think about the
benefits and dangers of this technology. Explain your
opinion about whether nuclear reactors should be
used.
CHALLENGE PRORI FM
95.
W R IT IN G
Use the information in Table 8 to calculate the
mass defect and binding energy of deuterium ( jH),
a hydrogen isotope involved in fusion reactions in
the Sun.
T a b le 8 Mass of Particles
Particle
Mass (amu)
Hydrogen
1.007941
Deuterium
2.014102
Neutron
1.008665
a. Find the mass of the nucleons.
b. Find the mass defect by subtracting the mass
of the nucleons from the mass of the deuterium.
c. Find the binding energy using the conversion
1 amu = 931.49 MeV.
CUMULATIVE REVIEW
9 6 . Identify each property as chemical or physical.
a. The element mercury has a high density.
b. Solid carbon dioxide sublimes at room temperature.
c. Zinc oxidizes when exposed to air.
d. Sucrose is a white crystalline solid.
9 7 . Why does the second period of the periodic table
contain eight elements?
9 8 . Draw each molecule and show the locations of hydrogen
bonds between the molecules.
a. two water molecules
b. two ammonia molecules
c. one water molecule and one ammonia molecule
9 9 . W hat process takes place in each situation?
a. a solid air-freshener cube getting smaller and
smaller
b. dewdrops forming on leaves in the morning
steam rising from a hot spring
d. a crust of ice forming on top of a pond
c.
1 0 0 . If the volume of a sample of chlorine gas is 4.5 L at
0.65 atm and 321 K, what volume will the gas occupy
at STP?
1 0 1 . The temperature of 756 g of water in a calorimeter
increases from 23.2°C to 37.6°C. How much heat was
given off by the reaction in the calorimeter?
1 0 2 . Explain what a buffer is and why buffers are found in
body fluids.
1 0 3 . Explain how the structure of benzene can be used to
explain its unusually high stability compared to other
unsaturated cyclic hydrocarbons.
► C h e m is tr y
104. Marie Curie and Irene Curie Joliot Research and
report on the lives of Marie Curie and her daughter,
Irene Curie Joliot. What kind of scientific training did
each receive? What was it like to be a female chemist
in their time? What discoveries did each make?
105. Nuclear Waste Evaluate environmental issues
associated with nuclear wastes. Research the Yucca
Mountain nuclear waste disposal plan, the Hanford
nuclear site, or a local nuclear facility. Prepare a
poster or multimedia presentation on your findings.
106. Radioactive Sources Students in your school
might not realize how beneficial radioactive sources
can be. Create a poster showing some common,
beneficial uses of radioactive sources. Be sure to
point out safeguards that are taken to ensure the
sources are safe.
DBQ Document-Based Questions
Half-Lives The National Institute o f Standards and
Technology (NIST) maintains a database o f radionuclide
half-lives. In 1992, researchers at NIST measured the
half-lives shown in Table 9.
Data obtainedfrom: Unterweger, M.P., Hoppes, D.D., andSchima, F.J. 1992.
Newand revisedhalf-lifemeasurements results, Nud. Instrum. Meth. Phys. Res,
A312:349-352.
T a b le 9 Half-Lives
Radionuclide
Half-life
Fluorine-18
1.82951 h
Molybdenum-99
| Samarium-153
65.9239 h
46.2853 h
107. Fluorine-18 is used in medical imaging. If a lab has
a sample containing 15 g of fluorine-18, how much
fluorine-18 will remain in the sample after 8 .0 h?
108. Technetium-99 can be used for diagnostic tests of the
heart and lungs. Because of technetium-99’s very
short half-life, medical facilities produce it from
molybdenum-99. If the facility has a 25-g sample of
molybdenum-99, how much will it have one week
(168 h) later?
109. Samarium-153 is used in the production of a drug
to treat pain from bone tumors. Radiation released
by the samarium hinders the tumor growth, thereby
reducing pain. How much of a 1.0 g sample of
samarium-153 is left after 4 days (96 h)?
C h a p te r 24 • Assessment
897
MULTIPLE CHOICE
1. Geologists use the decay of p otassium -40 in volcanic
4.
W h ich statem ent is N O T true of alpha particles?
rocks to determ ine their ages. Potassium -40 has a
A . They carry a charge o f 2 + .
half-life o f 1.26 x 1 0 9 years, so it can be used to date
B. They are represented by the symbol jHe.
very old rocks. If a sample o f rock 3.15 x 1 0 8 years
C. They are m ore penetrating than (1 particles.
old contains 2.73 X IO* 7 g o f potassium -40 today,
D. They have the sam e com position as helium
nuclei.
how m uch potassium -40 was originally present in
the rock?
A . 1.71 X IO" 8 g
C . 3.25 X 10 7 g
B . 2.30 X 1 0 _ 7 g
D. 4 .3 7 X 1 0~ 6 g
Use the graph below to answ er questions 5 a n d 6.
130
to generate neutrons by bom barding stable beryllium
induced transm utation?
sB + n
C. ^Be
•^ B + ? H f n
D. iB e +
it
N.
100
</i
¥/X\
c yu
WM
Bandof stability
o
/
*
4-*
i r s
3 80
AH'
Oi
C
m
<4_ /O
o
/■ } r , x v
—
Q) 60 n/p atio = 1.28 y
_Q
¥
E SO
/iH
3
2 40
JT
/ :r /
30
j/ ji f
20
is the balanced nuclear equation describing this
B. *Be +
refjresents a table atorr
110
atoms. A neutron is released in the reaction. W hich
^B + n
■
120 _ Each point or the nranh
atom s with deuterons ( jH ), the nuclei o f deuterium
A. 4 Be +
The Band o f S tability
062P
h
1
1\28
ruv
140
2 . In the early 1930s, van de G raaf generators were used
's + n
10
0
Use the fig u re below to answ er question 3.
n/pratio = 1.0
1
0
10
1
1
2030 40 50 60 70 80 90
Num ber o f protons
5. W h y will calciu m -35 undergo positron emission?
A . It lies above the line of stability.
V
B. It lies below the line of stability.
c
C . It has a high n eutron-to-proton ratio.
D. It has an overabundance o f neutrons.
6
. Based on its position relative to the band o f stability,
which process will jJjZn undergo?
A+B
J
A. beta decay
B. electron capture
C . nuclear fusion
Reaction coordinate
D. positron emission nuclear fusion
7. A solution of 0 .600 M HC1 is used to titrate 15.00 m L
3. W hich is N O T a correct description o f this reaction?
o f KOH solution. The end point o f the titration is
A . This is a synthesis reaction.
reached after the addition of 27.13 m L o f HC1.
B . This reaction releases energy.
W hat is the concentration o f the KOH solution?
C. This reaction is endotherm ic.
A . 9.00 M
C. 0.332M
D. This reaction will occu r spontaneously.
B. 1.09M
D. 0.0163M
898
C h a p te r 24 • Nuclear Chemistry
SHORTANSWFR
.CHEMISTRY
Use the fig u r e below to an sw er questions 8 to 10.
Use the fig u re below to answ er Q uestions 14 a n d 15.
e~ flow
Zinc
Copper
t
8
1 4 . D uring which segments are particles changing
. Identify the an od e and cath od e o f this apparatus.
states o f m atter?
A. AB, CD, E F
B. AB, EF
C. BC , CD, DE
9 . W rite the oxidation half-reaction.
1 0 . Explain the function o f the salt bridge in this
D. BC , EF
E . BC , DE
apparatus.
1 5 . D uring which segm ents are particles losing
1 1 . Predict the p rodu cts o f this reaction.
kinetic energy?
A l ( N 0 3 ) 3 (aq) + C a S 0 4 ( a q ) - >
A. BC , D E
B. AB, D E
C. AB, CD, E F
EXTENDED RESPONSE
D. BC, D E, EF
E. AB, CD, DE
1 6 . In the first steps o f its radioactive decay series,
Use the fig u re below to an sw er Q uestions 12 a n d 13.
th o riu m -232 decays to rad iu m -228, which then
decays to actin iu m -228. W h at are the balanced
+
+
+
HF
nuclear equations describing these first two decay
H20
steps?
h 3o +
1 2 . Identify the acid and the base for the forward
reaction. Explain how you can tell.
1 3 . Explain how you can identify the conjugate acid
and conjugate base for the forward reaction.
A. 232Th
90 i n
2 2 8 n
B. l o T h
2 2 8
C. 2 9oTh
2 2 8
90 i n
D. 232Th
22=Ra
+ 2t 1
t ie , 228
88 Ra
88
.
88
88 Ra
88 Ra
90 i n
E. 232Th
W h a t are they?
,
2 2 8
2 2 8 p
+ e > 88 Ka '
+ ^He
2 2 8
88 Ra
+ e+, 2ggRa -
88 Ra,
«Ra ■
89
Ac ■
22 8
89
2 2 8
89
Ac + e
Ac + e
- e'
2 g8A c
228
Ac
8 9 -
+ e-
N E E D E X T R A H ELP?
I f Y o u M is s e d
Q u e s tio n . . .
R e v ie w S e c t io n . . .
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2 4 .2
2 4 .3
1 5 .5
2 4 .1
2 4 .2
2 4 .2
1 8 .4
2 0 .1
2 0 .1
2 0 .1
9 .2
1 8 .1
1 8 .1
1 2 .4
1 2 .4
2 4 .2
C h a p te r 24 • Assessment
899