Download (a) Atoms - Warren County Schools

Name the levels of life from the
smallest to the largest!!!
Learning check
List levels of life.
Name 3 subatomic particles, charges, how to
calculate and location
What is in the element box?
Important elements in organisms
Why do we use Bohr models and Lewis Dot
structure?
Can you draw an atom using Bohr’s model?
Define an isotope and how are they used?
Describe how the periodic table is organized.
Learning Check
•
•
•
•
•
•
•
•
Periods vs. Groups
Counting atoms in compounds
How compounds are formed
Parts of an equation
Explain why atoms bond
Ions – positive and negative
Describe functions of ions in organisms
Draw compounds bonding – ionic and
covalent
Levels of the Organization of
Life
•
•
•
•
•
•
•
•
Subatomic particle
Atom
Molecule(compound)
Organelle
Cell
Tissue
Organ
Organ system
organism
populations
community
ecosystem(biome)
biosphere
What is this a picture of ? Name
3 facts about this object!
ELEMENTS, ATOMS,
AND MOLECULES
Copyright © 2009 Pearson Education, Inc.
How are atoms studied?
• Atoms are the building blocks of matter
• Atoms are too small in size to study
easily
• Size of Earth : soda can = soda can : atom
Democritus
• Not until around 460 B.C., did a Greek
philosopher, Democritus, develop the idea
of atoms. He asked this question: If you
break a piece of matter in half, and then
break it in half again, how many breaks will
you have to make before you can break it no
further? Democritus thought that it ended at
some point, a smallest possible bit of
matter. He called these basic matter
particles, atoms.
Democritus
• He said in the world this was “atoms and
void”. No space between the atoms.
ATOMS
Atoms: smallest unit of matter that still retains
the properties of an element.
.
2.4 Atoms consist of protons, neutrons, and
electrons
• An atom is the smallest unit of matter that still
retains the properties of a element
– Atoms are made of over a hundred subatomic
particles, but only three are important for biological
compounds
– Proton—has a single positive electrical charge (nucleus)
– Electron—has a single negative electrical charge (shells)
– Neutron—is electrically neutral (nucleus)
Copyright © 2009 Pearson Education, Inc.
Electron
cloud
Nucleus
2
Protons
2
Neutrons
2
Electrons
2e–
Mass
number = 4
Protons
Protons are located in the nucleus of the atom.
They are positively charged.
Neutrons
Neutrons are located in the nucleus.
They have NO charge!
Electrons
Electrons are located in the shells around
the atom.
They are negatively charged.
Electron shells
a) Atomic number = number of Electrons
b) Electrons vary in the amount of energy
they possess, and they occur at certain
energy levels or electron shells.
c) Electron shells determine how an atom
behaves when it encounters other atoms
Parts of an Atom
Protons and neutrons make up the nucleus and
has the most mass. Electrons do not weigh as
much. SO the atomic mass is only the
Protons + the Neutrons
How Do You Think These
Pictures are Related?
What do you think is in this
picture?
Atoms make up substances called
elements which are the building
blocks of matter.
There are 110 elements
2.1 Living organisms are composed of about 25
chemical elements
• Living organisms are composed of matter,
which is anything that occupies space and has
mass (weight)
– Matter is composed of chemical elements
– Element—a substance that cannot be broken down to
other substances
– There are 92 elements in nature—only a few exist in a
pure state
– Life requires 25 essential elements; some are called
trace elements
Copyright © 2009 Pearson Education, Inc.
1. ELEMENTS ARE PURE SUBSTANCES MADE OF
ONLY 1 KIND OF ATOM AND ARE THE BUILDING
BLOCKS OF MATTER.
2. ELEMENTS CANNOT BE BROKEN DOWN INTO A
SIMPLER SUBSTANCE
3. ELEMENTS HAVE THEIR OWN UNIQUE SET OF
PROPERTIES THAT NO OTHER ELEMENT HAS.
• ELEMENTS ARE MADE OF ONLY 1 KIND OF
ATOM
• SOME COMMON ELEMENTS
– HYDROGEN (H), HELIUM (He), OXYGEN (0),
– Notice that the first letter is capital and the next letter
is lower case.
Why Are Elements Different?
• Elements differ in their number of protons,
neutrons, and electrons. This is why their
atomic numbers and masses are different.
• Helium has two protons, two neutrons, and two
electrons
• Carbon has six protons, six neutrons, and six
electrons
Copyright © 2009 Pearson Education, Inc.
Why Do Some Elements Have Different
Symbols?
They are older elements that were name
in a different language like Latin.
Copper – cuprum
Iron – Ferrous
Gold - aurum
Silver - argentum
Elements in Organisms
• 4 elements that make up 96% of human
body: Carbon(C), Hydrogen(H),
Oxygen(O), Nitrogen(N)
2.2 CONNECTION: Trace elements are common
additives to food and water
• Some trace elements are required to prevent
disease
– Without iron, your body cannot transport oxygen
– An iodine deficiency prevents production of thyroid
hormones, resulting in goiter
Copyright © 2009 Pearson Education, Inc.
2.2 CONNECTION: Trace elements are common
additives to food and water
• Several chemicals are added to food for a variety
of reasons
– Help preserve it
– Make it more nutritious
– Make it look better
• Check out the “Nutrition Facts” label on foods
and drinks you purchase
Copyright © 2009 Pearson Education, Inc.
Where Do you Find a
Information on All Elements?
Element Info in Each Box
Atomic weight
Atomic Number
Symbol
Name
Information from the periodic table
Atomic Number- Number of Protons
in an atom
Silver = 47 protons
Atomic Weight - total number of particles in an
atom's nucleus
Atomic Weight is not very helpful – you need to
find the atomic mass
To find the Atomic Mass:
Round the atomic weight
Krypton's mass
number is 84 since
its atomic weight,
83.80, rounds up to
84.
Mass Number = (Number of Protons) + (Number of Neutrons)
84 = 36 + 48
2.4 Atoms consist of protons, neutrons, and
electrons
• Neutrons and protons are packed in the atom’s
nucleus
– The negative charge of electrons and the positive
charge of protons keep electrons near the nucleus
– The number of protons is the atom’s atomic number
– Carbon with 6 protons has an atomic number of 6
– The mass number is the sum of the protons and neutrons
in the nucleus (carbon-12 is written 12C)
Copyright © 2009 Pearson Education, Inc.
VALENCE ELECTRONS
• Number of electrons in the outermost.
Determines how the element will bond.
GROUPS: determined by valence
electrons.
Group 1 – one valence electron
Group 2 – 2 valence electrons
Now let’s learn how to draw an
element
• Two models we will use:
1.Bohr’s model
2.Lewis Dot Structure
How do you calculate Valance Electrons?
You determine the number of electrons.
Then place the electrons in electron shells.
Bohr’s Model: This is a model used to place
electrons in their shells.
Bohr Diagrams
1) Find your element on the periodic table.
2) Determine the number of electrons – it is
the same as the atomic number.
3) This is how many electrons you will draw.
4) The number of shells are determined by
the period.
Bohr Diagrams
C
1) Draw a nucleus with the element
symbol inside. Place Protons and
neutrons in the nucleus.
2) The electrons will go in the orbits
around the nucleus. Fill order of
shells, 2,8,8,18.
3) Place an X over the atom. This splits
the atom into quarters. Since
electrons are negative and repel each
other place electrons into different
quarters. Clockwise!
4) Place all electrons until gone!
Hydrogen
Helium
First
shell
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Sodium
Magnesium
Aluminum
Silicon
Phosphorus
Sulfur
Chlorine
Argon
Second
shell
Third
shell
2.6 Electron arrangement determines the chemical
properties of an atom
• An atom may have one, two, or three electron
shells
– The number of electrons in the outermost shell
determines the chemical properties of the atom
– The first shell is full with two electrons, whereas the
second and third will hold up to eight electrons
Copyright © 2009 Pearson Education, Inc.
Bohr Diagrams
1) Add the electrons.
2) Phosphorous has 15
electrons.
3) The first shell can
only hold 2 electrons.
Lewis Dot Structure
Copy the instructions from the sheet I gave you!!!!!!!
This is an easier way to draw
Electrons in shells!!!!
This is how you will draw
atoms bonding!!!!
Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell
electrons
1
2
13
14
15
16
17
H
18
He:

Li Be


B 


C


Na Mg


Al

N



O




 Si 
P
 S





: F  :Ne :




:Cl  :Ar :


Isotopes
 Atoms with the same number of protons, but
different numbers of neutrons.
 Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl
37Cl
17
17
chlorine - 35
chlorine - 37
2.5 CONNECTION: Radioactive isotopes can help
or harm us
• Living cells cannot distinguish between isotopes
of the same element
– Therefore, when radioactive compounds are used in
metabolic processes, they act as tracers
– Radioactivity can be detected by instruments
• With instruments, the fate of radioactive tracers
can be monitored in living organisms
Copyright © 2009 Pearson Education, Inc.
Isotopes
of an element have
different mass numbers
because
they have
different numbers of neutrons,
but they have
the same atomic number.
2.5 CONNECTION: Radioactive isotopes can help
or harm us
• Radioactive tracers are frequently used in
medical diagnosis
• Sophisticated imaging instruments are used to
detect them
– An imaging instrument that uses positron-emission
tomography (PET) detects the location of injected
radioactive materials
– PET is useful for diagnosing heart disorders and
cancer and in brain research
Copyright © 2009 Pearson Education, Inc.
2.5 CONNECTION: Radioactive isotopes can help
or harm us
• In addition to benefits, there are also dangers
associated with using radioactive substances
– Uncontrolled exposure can cause damage to some
molecules in a living cell, especially DNA
– Chemical bonds are broken by the emitted energy,
which causes abnormal bonds to form
Copyright © 2009 Pearson Education, Inc.
Learning Check AT 2
Naturally occurring carbon consists of three isotopes,
12C, 13C, and 14C. State the number of protons,
neutrons, and electrons in each of these carbon atoms.
12C
6
13C
14C
6
6
#P _______
_______
_______
#N _______
_______
_______
#E _______
_______
_______
• http://www.idph.state.ia.us/eh/common/pdf/
radiological_health/radioisotopes.pdf
ISOTOPIC NOTATION
isotopes are atoms with the same number of
protons but different number of neutrons
A
Z
X
A = mass number
(the total number of protons + neutrons)
Z = atomic number
(the total number of protons)
X = element symbol
PRACTICE PROBLEMS
15N
7
# protons = ____
8
7
# neutrons= ____
#electrons = ___
35P
15
# p = ____
20
# n= ____
15
#e- = ___
33
# n= ____
27
#e- = ___
62Cu2+
29
# p = ____
76Se3-
# p = 34
____
42
# n= ____
37
#e- = ___
Ways the Periodic Table is Organized
1. ELEMENTS ARE ORGANIZED IN THE
PERIODIC TABLE ACCORDING TO
ATOMIC NUMBER
2. ELEMENTS ARE ORGANIZED IN THE
PERIODIC TABLE OF ELEMENTS
ACCORDING TO THEIR SIMILAR
CHARACTERISTICS
• 3 major groups: metals, nonmetals and metalloids
Arrangement of the Periodic table
3. Periods – Rows are called periods. The
Elements in these rows have the same number
of electron shells.
4. Groups – Columns are called groups. These
elements have the same properties because of
the number of valence electrons.
Bohr Diagrams
• Find out which period
(row) your element is in.
• Elements in the 1st
period have one energy
level.
• Elements in the 2nd
period have two energy
levels, and so on.
www.chem4kids.com
Groups
When a column
goes from top to
bottom, it's
called a group.
Groups are often called
families because these
elements seem to be
related.
**Elements in the same group show
similarities in their chemical and
physical properties.
Valence Electrons
The number of valence electrons determines how
an atom will bond.
The behavior of an atom is determined by its
electrons.
Shell
Maximum Number
Numb
of Electrons in the Shell
er
1
2
3
4
5
2x1=2
2x4=8
2 x 9 = 18
2 x 16 = 32
2 x 25 = 50
2.3 Elements can combine to form compounds
• Compound—a substance consisting of two or
more different elements combined in a fixed
ratio
– There are many compounds that consist of only two
elements
– Table salt (sodium chloride or NaCl) is an example
– Sodium is a metal, and chloride is a poisonous gas
– However, when chemically combined, an edible
compound emerges
Copyright © 2009 Pearson Education, Inc.
• MOLECULES ARE 2 OR MORE ATOMS
ATTACHED TOGETHER
– THEY CAN BE THE SAME KIND
(ELEMENTS)
– THEY CAN BE DIFFERENT KINDS
Just one molecule of a COMPOUND!!
Examples: H2O, NaCl, H2, O2, N2 .
How Compounds Form
• FOR A COMPOUND TO FORM, A
CHEMICAL CHANGE MUST TAKE
PLACE (A REACTION)
• THE ELEMENTS THAT COMBINE MAKE
A NEW SUBSTANCE WITH NEW
PHYSICAL PROPERTIES
• COMPOUNDS CANNOT BE BROKEN
DOWN PHYSICALLY. REQUIRES A
CHEMICAL CHANGE
• MORE COMMON THAN ELEMENTS
Common Compounds for Life
•
•
•
•
CO2
H2O
C6H12O6
NaCl
• COMPOUNDS ARE MADE OF 2 OR
MORE DIFFERENT KINDS OF
ELEMENTS.
• COMPOUNDS ARE IDENTIFIED BY A
CHEMICAL FORMULA
NaCl
+
=
TABLE
SALT
Why Do Elements Bond to Form
Compounds?
Elements bond to fill their outer
shell and become stable!!!
THEY WANT TO BE HAPPY
+
Sodium
Chlorine
Sodium Chloride
Sodium
Chlorine
Sodium Chloride
The elements lose their properties
in a compound!
How to Count Atoms
Chemical Formula
Definition – Short way to write a compound
using symbols.
Subscript – Small number that is written
below the element.
Coefficient – The large number in front of the
symbols.
Subscripts
• A subscript refers to the number found on the lower
right side of an element or attached to a compound.
• These numbers tell you how many atoms of which
elements the equation is made up of.
• In this equation it explains that, on the product side,
there are 2 hydrogen atoms as well as 2 oxygen
atoms.
• A subscript can never be changed to balance an
equation.
Ba(OH)2 –
1) In this compound there are three
.different elements (Ba), Oxygen (O) and
Hydrogen (H).
2) In this compound the subscript 2 goes
with the O and H
3) Since Ba is not in the parentheses and it does
not have a subscript there is one Ba.
4. Oxygen is in the parentheses and the
two elements in the paraentheses so
there parentheses are Oxygen (O) and
Hydrogen (H) is 2. Same for Hydrogen.
Coefficients
• In other words a coefficient is used to display 2 or
more of the entire unit it appears in front of. The
coefficient used in this example shows that, in the left
reactant, there are 4 hydrogen, and in the product,
there are 4 hydrogen and 2 oxygen.
• The coefficient does not effect the oxygen in the
reactant because it is not a compound with hydrogen
but is separated by the plus sign.
Chemical Changes Through Chemical
Reactions
A chemical reaction – Process in which the
physical and chemical properties of the original
substance change as new substances with
different properties are formed
http://www.eepybird.com/dc
m1.html
CHEMICAL REACTIONS
!
Reactants: Zn + I2
Product: Zn I2
What is a Chemical Equation?
• A chemical equation is described as a symbolic
representation of a chemical reaction.
• The reactants of the reaction are found on the
left and the products on the right, separated
by an equal sign or directional arrows
What Makes up a Chemical
Equation?
• There are several parts that make up a chemical
equation, other then the 3 previously listed
(reactants,
• products,
• and the yield symbol).
Introduction
– Chemical reactions occur when bonds
between the outermost parts of atoms are
formed or broken
– Chemical reactions involve changes in
matter, the making of new materials with
new properties, and energy changes.
– Symbols represent elements, formulas
describe compounds, chemical equations
describe a chemical reaction
• The charcoal used in a grill is basically carbon. The
carbon reacts with oxygen to yield carbon dioxide. The
chemical equation for this reaction, C + O2  CO2,
contains the same information as the English
sentence but has quantitative meaning as well.
• Show video of gummi bear and zinc and H
gas!!!!
Equation for gummi bear
2KClO3 -- 2KCl + O2 melting
C6H12O6 +6O2 ----- 6CO2 + 6H2O
The energy released is coming from the bonds
in the sugar!! This is where we get our
energy!!!
Why do elements bond?
• Elements bond to fill their outer shells.
This make the element stable. TO BE
HAPPY!
• Elements will either gain, lose or share
electrons to fill their outer shell.
2.7 Ionic bonds are attractions between ions of
opposite charge
• An ion is an atom or molecule with an electrical
charge resulting from gain or loss of electrons
– When an electron is lost, a positive charge results;
when one is gained, a negative charge results
• Two ions with opposite charges attract each
other
– When the attraction holds the ions together, it is
called an ionic bond
Animation: Ionic Bonds
Copyright © 2009 Pearson Education, Inc.
An ion is an atom, or group of atoms, that has a net positive or
negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
Cl-
17 protons
18 electrons
2.5
Formation of Ions from Metals
 Ionic compounds result when metals react with
nonmetals
 Metals lose electrons to match the number of valence
electrons of their nearest noble gas
 Positive ions form when the number of electrons are
less than the number of protons
•
Group 1 metals 
ion 1+
Group 2 metals 
ion 2+
Group 13 metals  ion 3+
Formation of Sodium Ion
Sodium atom
Na 
2-8-1
11 p+
11 e0
– e
Sodium ion

Na +
2-8 ( = Ne)
11 p+
10 e1+
2.5
Ions Function
• There are nine types of most
essential ions of our body which
plays a role in supporting and
sustaining health and life.
• Out of nine, five are positively
charged ions and four are
negatively charged ions.
Ion (Electrolytes) Function
• The positively charged ions are
called cations ; these are Na+ , K+ ,
Ca++ , Mg++, and H+ .
• The negatively charged ions are
called anions ; these are Cl- , HCO3, PO43- , and OH- .
Electrolytes Functions
• The Sodium (Na+), Chloride (Cl-),
Potassium (K+) and Bicarbonate
(HCO3-) are called principle
electrolytes and are present in the
blood and various body fluids.
• Potassium (K+) is essential for
heart function.
• Our kidneys play a vital role in
maintaining the electrolyte balance.
They filter out excess!! Over work
them!!!
• The osmosis regulates the movement
of water in cells. Theconcentration of
electrolytes or ions to a moves water
from higher concentration of
electrolytes or ions to areas or lower
concentration.
• Using ion channels, cells continually
adjust their inside and outside electrical
charges. Normal levels of calcium ions,
for example, are 20,000 times higher
outside the cell than inside. Heart cells,
using special voltage-sensitive calcium
channels, can quickly upset this ratio,
generating the spike of energy needed
for a heartbeat. Through the controlled
movement of ions across its membrane,
the cell returns to its resting state and
then recharges its battery to begin the
next cycle.
• http://www.medicinenet.com/electrolytes/ar
ticle.htm
Three types of Chemical Bonds
•
Chemically combining of two or more
atoms
1. Covalent Bonds
2. Ionic Bonds
3. Hydrogen bonds
These are not all the bonds but all we are going to
cover.
Ionic Bonds
Ionic Bond – valence electrons are
TRANSFERRED from one ion to
another!!!,
K
F
Drawing an Ionic Compound
1. Draw the Lewis Dot structure for
the atoms.
2. Show the electron(s) transfering
from one atom to another.
Ionic bonding
Ionic bonding involves 3 steps (3
energies)
1) loss of an electron(s) by one
element,
2) gain of electron(s) by a second
element,
3) attraction between positive and
negative
Ionic Bonds: One Big Greedy Thief Dog!
1). Ionic bond – electron from Na is transferred
to Cl, this causes a charge imbalance in each
atom. The Na becomes (Na+) and the Cl
becomes (Cl-), charged particles or ions.
Covalent Bonds
• One or more
pairs of
electrons are
shared by two
atoms
2.8 Covalent bonds join atoms into molecules
through electron sharing
• A covalent bond results when atoms share
outer-shell electrons
– A molecule is formed when atoms are held together
by covalent bonds
Animation: Covalent Bonds
Copyright © 2009 Pearson Education, Inc.
Covalent Bond
• Between nonmetallic elements of similar
electronegativity.
• Formed by sharing electron pairs
• Stable non-ionizing particles, they are not
conductors at any state
• Examples; O2, CO2, C2H6, H2O, SiC
NONPOLAR
COVALENT BONDS
when electrons are
shared equally
H2 or Cl2
2. Covalent bonds-
Two atoms share one or more pairs of outer-shell
electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
POLAR COVALENT
BONDS
when electrons are
shared but shared
unequally
H2O
Polar Covalent Bonds: Unevenly
matched, but willing to share.
- water is a polar molecule because oxygen is more
electronegative than hydrogen, and therefore electrons
are pulled closer to oxygen.
Octet Rule = atoms tend to gain, lose or share electrons so
as to have 8 electrons
C would like to Gain 4 electrons
N would like to Gain 3 electrons
O would like to Gain 2 electrons
Transfer of
electron
Na
Sodium atom
Cl
Chlorine atom
Transfer of
electron
Na
Sodium atom
Cl
Chlorine atom
+
–
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
2.9 Unequal electron sharing creates polar
molecules
• Atoms in a covalently bonded molecule
continually compete for shared electrons
– The attraction (pull) for shared electrons is called
electronegativity
– More electronegative atoms pull harder
Copyright © 2009 Pearson Education, Inc.
2.9 Unequal electron sharing creates polar
molecules
• In molecules of only one element, the
pull toward each atom is equal,
because each atom has the same
electronegativity
Copyright © 2009 Pearson Education, Inc.
2.9 Unequal electron sharing creates polar
molecules
• Water has atoms with different
electronegativities
– Oxygen attracts the shared electrons more strongly
than hydrogen
– So, the shared electrons spend more time near
oxygen
– The result is a polar covalent bond
Copyright © 2009 Pearson Education, Inc.
2.9 Unequal electron sharing creates polar
molecules
• In H2O the oxygen atom has a slight negative
charge and the hydrogens have a slight positive
charge
– Molecules with this unequal distribution of charges
are called polar molecules
Copyright © 2009 Pearson Education, Inc.
(–)
(–)
O
H
(+)
H
(+)
2.10 Hydrogen bonds are weak bonds important in
the chemistry of life
• Some chemical bonds are weaker than covalent
bonds
• Hydrogen, as part of a polar covalent bond, will
share attractions with other electronegative atoms
– Examples are oxygen and nitrogen
• Water molecules are electrically attracted to
oppositely charged regions on neighboring
molecules
– Because the positively
charged
region is always a
Animation:
Water Structure
hydrogen atom, the bond is called a hydrogen bond
Copyright © 2009 Pearson Education, Inc.
Hydrogen bond
WATER’S LIFE-SUPPORTING
PROPERTIES
Copyright © 2009 Pearson Education, Inc.
2.11 Hydrogen bonds make liquid water cohesive
• Hydrogen bonding causes molecules to stick
together, a property called cohesion
– Cohesion is much stronger for water than other
liquids
– This is useful in plants that depend upon cohesion to
help transport water and nutrients up the plant
Copyright © 2009 Pearson Education, Inc.
2.11 Hydrogen bonds make liquid water cohesive
• Cohesion is related to surface tension—a
measure of how difficult it is to break the surface
of a liquid
– Hydrogen bonds are responsible for surface tension
Animation: Water Transport
Copyright © 2009 Pearson Education, Inc.
Adhesion
Water-conducting
cells
Direction
of water
movement
Cohesion
150 µm
2.12 Water’s hydrogen bonds moderate
temperature
• Because of hydrogen bonding, water has a
greater ability to resist temperature change than
other liquids
– Heat is the energy associated with movement of
atoms and molecules in matter
– Temperature measures the intensity of heat
• Heat must be absorbed to break hydrogen bonds;
heat is released when hydrogen bonds form
Copyright © 2009 Pearson Education, Inc.
2.13 Ice is less dense than liquid water
• Water can exist as a gas, liquid, and solid
– Water is less dense as a solid, a property due to
hydrogen bonding
Copyright © 2009 Pearson Education, Inc.
2.13 Ice is less dense than liquid water
• When water freezes, each molecule forms a
stable hydrogen bond with four neighbors
– A three-dimensional crystal results
– There is space between the water molecules
• Ice is less dense than water, so it floats
Copyright © 2009 Pearson Education, Inc.
Hydrogen bond
Ice
Hydrogen bonds
are stable
Liquid water
Hydrogen bonds
constantly break and re-form
2.14 Water is the solvent of life
• A solution is a liquid consisting of a uniform
mixture of two or more substances
– The dissolving agent is the solvent
– The substance that is dissolved is the solute
Copyright © 2009 Pearson Education, Inc.
2.14 Water is the solvent of life
• Water is a versatile solvent that is fundamental
to life processes
– Its versatility results from its polarity
– Table salt is an example of a solute that will go into
solution in water
– Sodium and chloride ions and water are attracted to each
other because of their charges
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Ion in
solution
Salt
crystal
2.15 The chemistry of life is sensitive to acidic and
basic conditions
• A few water molecules can break apart into ions
– Some are hydrogen ions (H+)
– Some are hydroxide ions (OH–)
– Both are extremely reactive
– A balance between the two is critical for chemical
processes to occur in a living organism
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2.15 The chemistry of life is sensitive to acidic and
basic conditions
• Chemicals other than water can contribute H+ to
a solution
– They are called acids
– An example is hydrochloric acid (HCl)
– This is the acid in your stomach that aids in digestion
• An acidic solution has a higher concentration of
H+ than OH–
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2.15 The chemistry of life is sensitive to acidic and
basic conditions
• Some chemicals accept hydrogen ions and
remove them from solution
– These chemicals are called bases
– For example, sodium hydroxide (NaOH) provides
OH– that combines with H+ to produce H2O (water)
– This reduces the H+ concentration
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2.15 The chemistry of life is sensitive to acidic and
basic conditions
• A pH scale (pH = potential of hydrogen) is used
to describe whether a solution is acidic or basic
– pH ranges from 0 (most acidic) to 14 (most basic)
– A solution that is neither acidic or basic is neutral
(pH = 7)
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pH scale
0
1
Acidic solution
Increasingly ACIDIC
(Higher concentration of H+)
Battery acid
2
Lemon juice, gastric juice
3
Grapefruit juice, soft drink,
vinegar, beer
4
Tomato juice
5
Rain water
6
Human urine
Saliva
NEUTRAL
[H+]=OH–]
7
Pure water
Human blood,
tears
8
Seawater
Increasingly BASIC
(Lower concentration of H+)
Neutral solution
9
10
Milk of magnesia
11
Household ammonia
12
Household bleach
13
Oven cleaner
Basic solution
14
Acidic solution
Neutral solution
Basic solution
2.16 CONNECTION: Acid precipitation and
ocean acidification threaten the environment
• When we burn fossil fuels (gasoline and heating
oil), air-polluting compounds and CO2 are
released into the atmosphere
– Sulfur and nitrous oxides react with water in the air
to form acids
– These fall to Earth as acid precipitation, which is rain,
snow, or fog with a pH lower than 5.6
– Additional CO2 in the atmosphere contributes to the
“greenhouse” effect and alters ocean chemistry
Copyright © 2009 Pearson Education, Inc.
2.17 EVOLUTION CONNECTION: The search
for extraterrestrial life centers on the search
for water
• An important question is, has life evolved
elsewhere?
– Water is necessary for life as we know it
• The National Aeronautics and Space
Administration (NASA) has evidence that water
was once abundant on Mars
– Scientists have proposed that reservoirs of water
beneath the surface of Mars could harbor microbial
life
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August 1999
September 2005
New deposit
CHEMICAL REACTIONS
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2.18 Chemical reactions make and break bonds,
changing the composition of matter
• You learned that the structure of atoms and
molecules determines the way they behave
– Remember that atoms combine to form molecules
– Hydrogen and oxygen can react to form water
2H2 + O2
2H2O
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2.18 Chemical reactions make and break bonds,
changing the composition of matter
• The formation of water from hydrogen and
oxygen is an example of a chemical reaction
• The reactants (H2 and O2) are converted to H2O,
the product
– Organisms do not make water, but they do carry out
a large number of chemical reactions that rearrange
matter
– Photosynthesis is an example where plants drive a
sequence of chemical reactions that produce glucose
Copyright © 2009 Pearson Education, Inc.
2 H2
O2
2 H2 O
Atoms
have positively
charged
have neutral
have negatively
charged
(b)
(a)
number present
equals
(c)
number may
differ in
atomic number of
each element
number in outer
shell determines
formation of
(d)
Chemical
Bonds
electron transfer
between atoms
creates
ions
electron sharing
between atoms
creates
(e)
unequal
sharing creates
attraction between
ions creates
equal
sharing creates
nonpolar
covalent bonds
(g)
(f)
can lead to
example is
water
has important
qualities due
to polarity and
(h)
Atoms
have positively
charged
(a)
have neutral
atomic number of
each element
(c)
(b)
number may
differ in
number present
equals
(d)
have negatively
charged
number in outer
shell determines
formation of
Chemical
Bonds
electron transfer
between atoms
creates
ions
electron sharing
between atoms
creates
(e)
unequal
sharing creates
attraction between
ions creates
equal
sharing creates
nonpolar
covalent bonds
(g)
(f)
can lead to
example is
water
has important
qualities due
to polarity and
(h)
Fluorine atom
Potassium atom
You should now be able to
1. Describe the importance of chemical elements to living
organisms
2. Explain the formation of compounds
3. Describe the structure of an atom
4. Distinguish between ionic, hydrogen, and covalent bonds
5. List and define the life-supporting properties of water
6. Explain the pH scale and the formation of acid and base
solutions
7. Define a chemical reaction and explain how it changes the
composition of matter
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