Download Water for Life - Sonoma Valley High School

Water: a special molecule
• Water is the most
common molecule on
Earth & in living
organisms.
• Chemistry of living
organisms takes place
in water.
Structure of The Water Molecule
• H20 is polar: it has a
negative end and a
positive end.
– Oxygen is negative
– Hydrogen is positive
– Polarity makes water
a good solvent.
– Most things dissolve in
water: sugars, salts, etc.
– Water is called the
universal solvent
Hydrogen Bonds
• Water molecules
are attracted to
each other.
• (-) Oxygen is
attracted to the
(+) Hydrogen of
another water
molecule
• The attraction is
called a Hydrogen
bond.
Hydrogen bonds are very weak
Cohesion
• Cohesion: Molecules of
the same type are
attracted to each
other.
– Surface tension is a
result of cohesion.
Think: This water strider is more dense
than the water. Why doesn't it sink?
Adhesion
 Adhesion: Molecules of
different types are
attracted to each
other.
 Plants move water up
stems in part due to
adhesion.
Water adhering to the sides of a test tube
causes the meniscus
Capillary action
 Capillary action is the combination of cohesion and
adhesion.
 This is the reason water can move up a paper towel against
the force of gravity.
High heat capacity of water
• Heat capacity is the amount
of energy it take to raise the
temperature of a substance
1°C.
• Water must gain or lose a lot
of energy for temperature to
change.
• Result: a stable aquatic
environment & the internal
environment of cells.
Review
 Give an example, not used in this PowerPoint, of each of
the special properties of water.