Outline # 2 Chemical Basis of Life 

Water
-- water had several unique properties due to its polarity
A. Water is a Polar Molecule
1. happens in covalently bonded molecules
2. oxygen has a slightly negative charge and hydrogen has a slightly
positive end
3. the electrons are unevenly shared; greater pull towards oxygen that
creates charged ends
4. uneven sharing creates a polar molecule
5. this makes water very effective at dissolving ionic & other polar
substances
B. Hydrogen Bonding
1. holds water molecules together
2. positive region of one water molecule is attracted to negative end of another
3. because the atoms have not transferred an e-, hydrogen bond is weaker than ionic bond
--it is strong enough to make water cling to itself
4. Hydrogen bonding accounts for water’s life supporting properties
C. Cohesion & Adhesion
1. cohesion: attractive force between same/similar substances
2. creates a sort of “skin” when something is slightly overfilled
3. surface tension: a property of liquids such that their surfaces behave
like a thin, elastic film
water has high surface tension and beads up easily
alcohol has low surface tension and does not bead up easily
4. adhesion: attractive force between unlike substances
5. combo of cohesion & adhesion allows water to move upwards inside
narrow cavities, going against gravity
-- called “capillarity” or capillary action
-- this is how water moves upward to the tops of trees
D. Temperature Moderation
-- aka Heat capacity
1. water is like a heat sponge
2. water must gain/lose lots of energy (heat) before it changes phase
3. heat works to break hydrogen bonds between the water molecules
4. after bonds have been broken, then temp increases & phase changes
5. water can absorb lots of heat energy from an organism so that it does
not overheat b/c it has so many H+ bonds.
E. Low Density of Ice
1. ice is less dense than water
2. molecules of ice are less densely packed than liquid water
3. ponds and lakes freeze from top to bottom
F. Water is the “Universal Solvent”

1. Water is consider to be the “universal solvent”.
2. More substances will dissolve in water than any other liquid.
3. This includes other polar substances (such as sugar) and ionic compounds (such as salt).