Download THE CHEMICAL BASIS OF LIFE

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PART I THE CELL
2
THE
CHEMICAL BASIS
OF
LIFE
CHAPTER REVIEW
This chapter introduces you to chemistry, or specifically,
the study of the structure of atoms and how they react
with one another. Water is so important to living things
that the structure of H 2 O, in particular, is studied along
with the differences between acid and basic solutions.
CHAPTER KEY TERMS
After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms.
acid
hydrophobic
atom
ion
base
octet rule
buffer
pH scale
covalent bond
polar
electron
proton
hydrophilic
a. more H than OH _______________________
b. water loving _______________________
c. water hating _______________________
d. unit of an element _______________________
e. more OH than H _______________________
f. negatively charged subatomic particle _______________________
g. positively charged subatomic particle _______________________
h. negatively or positively charged atom _______________________
i. molecule that has a negative/positive region _______________________
j. maintains pH constant _______________________
k. atoms share pair of electrons _______________________
l. stable atoms have eight electrons in outer shell _______________________
m. numbers indicate acidity/basicity of solution _______________________
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S T U DY E X E R C I S E S
Study the text section by section as you answer the questions that follow.
2.1 THE NATURE
•
•
•
•
•
OF
MATTER (PP. 16–21)
Matter is composed of 92 naturally occurring elements, each composed of atoms.
Atoms have subatomic particles: neutrons, protons, and electrons.
Atoms of the same type that differ by the number of neutrons are called isotopes.
Atoms react with one another by giving up, gaining, and sharing electrons.
Bonding between atoms results in molecules with distinctive chemical properties and shapes.
1. Name the six elements commonly found in living things. ____________________________________________________
_____________________________________________________________________________________________________________
2. An element has nine protons and nine neutrons in each of its atoms. Its atomic number is a. _______________,
its atomic mass is
b. _________________,
and the number of electrons in this atom is
c. ________________.
3. In the periodic table of chemical elements, the horizontal rows are called a. _______________ and the vertical
columns are called b. _______________. The atoms in group 8 are called the c. _______________ because they
d. _______________ react
with other atoms.
4. Isotopes have the same atomic
a. _______________,
but they differ in the number of
b. _______________.
5. At least two forms of the oxygen atom exist in the environment: 168 O and 188 O.
a. Both atoms have eight electrons.
8
16 O
and
8
18 O
are _________________ of the element oxygen.
b. The numbers 16 and 18 represent _________________.
c. The atomic number of
d. The atomic number of
8
16 O
8
18 O
is _________________.
is _________________.
8
16 O is __________________.
of 188 O is __________________.
e. The number of protons in the atom of
f. The number of neutrons in the atom
g. How do 168 O and 188 O differ in number of subatomic particles? _________________.
6. Complete the following table with the correct numbers:
Isotope
Protons
Neutrons
Atomic Number
Atomic Mass
6
12 C
6
14 C
15
31 P
15
33 P
7. Indicate whether these statements are true (T) or false (F):
a.
A neutral atom has the same number of protons and electrons.
b.
The number of electrons in the outer shell determines the atom’s chemical properties.
c.
The electrons of an atom are located in energy levels (electron shells) at varying distances from the
nucleus.
d.
Electrons in the first shell possess more energy than do electrons in the second shell.
8. An atom of an element with an atomic number of 9 has a. ______________ electrons in its first shell
and
b. ______________
electrons in its second shell.
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9. An atom of the element neon (Ne) has eight electrons in its outer shell. An atom of the element sulfur (S) has
six electrons in its outer shell.
a. Which atom is reactive? ______________
b. Which atom is inert? ______________
c. Why is there a difference in the reactivity of these two elements? _____________________________________
_________________________________________________________________________________________________
10. The magnesium atom has an atomic number of 12 and an atomic weight of 24. Draw its simplified atomic
structure. Draw small circles to indicate the general distribution of electrons in concentric levels around the
nucleus. In the nucleus, indicate the number of protons and neutrons.
11. Calcium (Ca) has an atomic number of 20; chlorine (Cl) has an atomic number of 17.
a. The number of electrons in the outer shell of calcium is ______________.
b. The number of electrons in the outer shell of chlorine is ______________.
c. In a chemical reaction between these two atoms, ______________ calcium atom(s) will react with
______________ chlorine atom(s).
d. Which element will gain electrons in this reaction? ______________
e. What will its charge be after the reaction? ______________
f. Which element will lose electrons in this reaction? ______________
g. What will its charge be after the reaction? ______________
h. What type of bond forms between these two atoms? ______________
i. Write the formula for the compound produced through this chemical reaction. ______________
12. Water is a polar molecule.
a. Indicate on the following diagram which atoms are electronegative ( – ) and which are electropositive ( + ) in
relation to the others. Put – charges and + charges where appropriate.
b. Label a hydrogen bond.
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13. Place the appropriate letter next to each statement.
C—covalent bonding I—ionic bonding H—hydrogen bonding
a.
Electrons transfer between atoms.
b.
Atoms share electrons.
c.
This bond is present in Na Cl .
d.
This bond is present in the O 2 molecule.
e.
The hydrogen atom in one molecule is attracted to the oxygen atom of another molecule.
2.2 WATER’S IMPORTANCE TO LIFE (PP. 22–26)
• The existence of organisms is dependent on the chemical and physical properties of water.
• Organisms are sensitive to the hydrogen ion concentration [H ] of solutions, which can be indicated using the
pH scale.
14. In each of the pairs of statements that follow, place a check next to the one that correctly describes how
hydrogen bonding affects the properties of water. Hydrogen bonding causes water:
Pair 1
a.
to boil at a lower temperature than expected.
b.
to boil at a higher temperature than expected.
Pair 2
c.
d.
to be more dense as ice than as liquid water.
to be less dense as ice than as liquid water.
Pair 3
e.
f.
to absorb heat with a minimal change in temperature.
to absorb heat with a maximum change in temperature.
Pair 4
g.
to be cohesive—the water molecules cling to each other.
h.
molecules to shun one another.
15. Refer to the chemical properties of water when answering the following questions:
a. What makes water a good solvent? _______________________________________________________________
_______________________________________________________________________________________________
b. How does water moderate temperatures? __________________________________________________________
_______________________________________________________________________________________________
c. What allows ice to float on liquid water? __________________________________________________________
_______________________________________________________________________________________________
16. Place the appropriate letter next to each statement.
A—acid B—base
a.
They take up hydrogen ions in solution.
b.
HCl is an example.
c.
NaOH is an example.
d.
They release hydrogen ions in solution.
e.
They lower the pH.
f.
They raise the pH.
17. Complete the table for the following hydrogen ion concentrations [H + ]:
[H + ]
pH
Acid/Base/Neutral
1 10 –7
1 × 10 –3
1 × 10 –8
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18. Indicate whether these statements are true (T) or false (F):
a.
If the pH of blood changes from 7.4 to 7.6, it becomes more acidic.
b.
When an acid is added to a solution, the pH decreases.
c.
A basic pH indicates that OH – ions outnumber H + ions.
d.
An acidic pH indicates that H + ions outnumber OH – ions.
19. The following questions relate to buffers:
How do living things prevent drastic changes in pH?
a. __________________________________________________________________________________________________________
_______________________________________________________________________________________________
b. Complete the following reaction, showing how the carbonic acid buffer system deals with increasing
hydrogen ions in the blood:
H + + HCO 3 – → ______________
c. Complete the following reaction, showing how the carbonic acid buffer system deals with decreasing
hydrogen ions in the blood:
H 2 CO 3 → ______________
K E Y WO R D C RO S S WO R D
Review key terms by completing this crossword puzzle, using the following alphabetized list of terms:
1
2
5
3
4
6
7
acid
atom
base
buffer
compound
covalent bond
electron
hydrogen bond
ionic bond
isotope
molecule
8
9
10
Across
2 chemical bond in which the atoms share one pair of
electrons (two words)
7 atoms having the same atomic number but a different atomic weight due to the number of neutrons
8 molecule that contains atoms of more than one element
9 substance or group of substances that tend to resist
pH changes in a solution, thus stabilizing the solution’s relative acidity
10 weak bond that arises between a slightly positive hydrogen and a slightly negative oxygen, often on different molecules or separated by some distance (two
words)
12
Down
1 group of atoms bonded together
3 substance tends to raise the hydrogen ion concentration in a solution and to lower its pH numerically
4 negative subatomic particle, moving about in energy
levels around the nucleus of the atom
5 smallest particle of an element that displays its
properties
6 substance that tends to lower the hydrogen ion concentration in a solution and to raise its pH numerically
7 chemical bond in which ions attract one another by
opposite charges (two words)
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CHAPTER TEST
OBJECTIVE QUESTIONS
Do not refer to the text when taking this test.
1. An element has an atomic number of 11 and an
atomic weight of 23. The number of neutrons in
each atom is
a. 11.
b. 12.
c. 23.
d. 24.
2. The atom of an element has one proton and two
neutrons. Its atomic number is
a. 1.
b. 2.
c. 3.
d. 6.
3. The atom of an element has six protons and eight
neutrons. The number of electrons in this atom
if neutral is
a. 6.
b. 8.
c. 12.
d. 14.
4. The relationship between 126 C and 146 C is that they
are
a. molecules.
b. isomers.
c. isotopes.
d. polymers.
5. An atom has 11 protons and 12 neutrons. Its
atomic mass is
a. 1.
b. 11.
c. 12.
d. 23.
6. The energy possessed by electrons in the first
shell is ______________ than the energy possessed by electrons in the second shell.
a. greater
b. less
7. An element has an atomic number of 14. Its electron distribution over several energy shells is
a. 1–4–8.
b. 1–8–5.
c. 2–8–2.
d. 2–8–4.
8. An element has an atomic number of 13. The
number of electrons in each atom’s second shell
is
a. 1.
b. 2.
c. 4.
d. 8.
9. Select the reactive element by its atomic number.
a. 2
b. 10
c. 12
d. 18
10. Select the most stable element by its atomic
number.
a. 1
b. 8
c. 10
d. 16
11. When sodium interacts with chlorine, sodium
loses an electron while chlorine gains one. This
interaction forms
a. an ionic bond.
b. a condensation synthesis.
c. a condensation.
d. a covalent bond.
12. Select the incorrect association.
a. covalent bond—electrons transferred
b. hydrogen bond—between water molecules
c. ionic bond—charged particles formed
d. polar covalent bond—present in the water
molecule
13. Each is a property of water EXCEPT
a. easily changed from liquid to gas.
b. good solvent.
c. maximum density at 4°C.
d. molecules are cohesive.
14. Select the correct statement about acids.
a. They cannot be buffered in a solution.
b. They donate hydroxide ions in solution.
c. HCl is an example.
d. They tend to raise the pH.
15. Select the most basic pH of the given hydrogen
ion concentrations.
a. 1 × 10 –3
b. 1 × 10 –4
c. 1 × 10 –9
d. 1 × 10 –12
16. Select the incorrect statement about bases.
a. They can be buffered in solution.
b. They release hydroxide ions in solution.
c. NaOH is an example.
d. They tend to lower the pH.
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CRITICAL THINKING QUESTIONS
The introduction to this chapter is about radioactive atoms.
17. How do you know an isotope is radioactive? ________________________________________________________________
18. How do isotopes differ from one another? ___________________________________________________________________
19. Do isotopes have a different atomic number? ________________________________________________________________
20. Do isotopes have a different atomic mass? __________________________________________________________________
21. Do isotopes occupy a different position in the periodic table? ________________________________________________
22. What does the number of an atom (element) in the periodic table tell you? ___________________________________
Test Results: ______ number correct ÷ 22 = ______ × 100 = ______ %
EXPLORING
THE
INTERNET
ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials
ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological
concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter.
There is even an online tutorial service!
ANSWER KEY
CHAPTER KEY TERMS
a. acid b. hydrophilic c. hydrophobic d. atom e. base
f. electron g. proton h. ion i. polar j. buffer k. covalent
bond l. octet rule m. pH scale
7. a. T b. T c. T d. F 8. a. two b. seven 9. a.S
b. Ne c. S has six electrons in its outer shell, and if it reacts to gain two more it will have a stable outer configuration of eight; Ne already has a stable outer shell.
STUDY EXERCISES
1. carbon, hydrogen, nitrogen, oxygen, phosphorus,
sulfur 2. a. 9 b. 18 c. 9 3. a. periods b. groups
c. noble gases d. rarely 4. a. number b. neutrons
5. a. isotopes b. atomic mass c. 8 d. 8 e. 8 f. 10
g. 168 O has eight neutrons and 188 O has ten neutrons in the
nucleus.
6.
14
Protons
Neutrons
Atomic Number
Atomic Mass
6
6
6
12
6
8
6
14
15
16
15
31
15
18
15
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17.
10.
pH
12 P
12 N
Acid/Base/Neutral
7
neutral
3
acid
8
base
18. a. F b. T c. T d. T 19. a. The pH is stabilized
through the action of buffers, chemicals or combinations
of chemicals that take up excess H + or OH – to keep the
pH steady. b. H 2 CO 3 c. HCO 3 – + H +
KEYWORD CROSSWORD
11. a. two b. seven c. one, two d. Cl e. –1
f. Ca g. +2 h. ionic i. CaCl 2
12.
1
5
M
A
2
C
3
O
V
L
4
A
L
6
N
T
B
L
O
A
M
S
E
C
E
I
E
C
D
C
U
O
N
D
O
N
E
T
L
R
7
I
E
S
O
O
T
O
P
E
N
N
N
I
8
C
O
M
P
O
U
U
F
F
E
R
R
O
G
E
N
D
9
B
O
N
10
H
Y
D
B
D
CHAPTER TEST
13. a. I b. C c. I d. C e. H 14. b, d, e, g
15. a. The partial charges of the water molecule attract
and disperse charged particles in solution. b. It takes up
and releases large amounts of heat without much change
in temperature. c. Water is most dense at 4°C. It expands
as the temperature drops from this point; it is less dense
at 0°C, the temperature of ice. 16. a. B b. A
c. B d. A e. A f. B
1. b 2. a 3. a 4. c
10. c 11. a 12. a
17. gives off subatomic
trons 19. no 20. yes
5. d 6. b 7. d 8. d 9. c
13. a 14. c 15. d 16. d
particles 18. number of neu21. no 22. number of protons
15