The Chemistry of
Life
Properties of Water
The Water Molecule
• Neutral Charge
– All Molecules Are Neutral
The Water Molecule
• Polarity
– A water molecule is polar because
there is an uneven distribution of
electrons between the oxygen and
hydrogen atoms.
(+)
(—)
Hydrogen Bonds
• Polar water molecules act like magnets
and attract each other
• Hydrogen Bonds
– The attraction of the Hydrogen end
(+) of one molecule for the Oxygen
end (-) of another water molecule.
– They are the strongest bonds that
can form between molecules
Hydrogen Bonds
Cohesion
• The attraction
between molecules
of the same
substance (e.g.
water).
• Allows some insects
and spiders to walk
on water.
Adhesion
• Attraction between molecules of
different substances
• Responsible for Capillary forces in
plants
Solutions & Suspensions
• Water is usually part of a
mixture.
• There are two types of mixtures:
– Solutions
– Suspensions
Solution
• Ionic compounds disperse as ions in
water
• Evenly distributed
• SOLUTE
– Substance that is being dissolved
• SOLVENT
– Substance into which the solute
dissolves
Solution
Suspensions
• Substances that
don’t dissolve but
separate into tiny
pieces.
• Water keeps the
pieces suspended
so they don’t
settle out.
Acids, Bases & pH
• 1 water molecule in 550 million
naturally dissociates into a Hydrogen
Ion and a Hydroxide Ion
H2O 
H+
Hydrogen Ion
Acid
+ OH
-
Hydroxide Ion
Base
The pH Scale
•
•
•
•
•
•
Indicates the concentration of H+ ions
Ranges from 0 – 14
pH of 7 is neutral
pH 0 – 6.99 is acid … H+
pH 7.01 – 14 is basic… OHEach pH unit represents a factor of
10 change in concentration
Acids
• Strong
Acid = pH
1-3
H+ ions
Bases
• Strong
Base = pH
11 – 14
OH-ions
Buffers
• Weak acids or bases that react
with strong acids or bases to
prevent sharp, sudden changes in
pH.
Weak Acid
Weak Base