Ever come to work
• And get the feeling it’s not
going to be such a good day?
The Key To Life On
(or one of them, anyway)
Why Water Is Your Friend
• Water has several
properties which make
• Capillary action
• Surface tension
• Fluid nature
– Temperature buffer
– Solvent ability
Atomic Structure Determines
• Oxygen’s 8 protons attract shared electrons more
than hydrogen’s one proton.
• This leads to unequal sharing, which results in
polar covalent bonds and a polar molecule
• The positive and negative areas of different water
molecules attract each other and form weak bonds
called hydrogen bonds
Polarity leads to cohesion
• Hydrogen bonding causes
cohesion (water sticking
to water) and adhesion
(water sticking to other
• This gives water important
properties, among them is
• Land plants could not
circulate water without it.
• Because of cohesion, water molecules resist
movement, and therefore temperature change,
better than most molecules.
• Since all organisms are composed of a large % of
water, this helps keep their temperature moderate.
• This is crucial because the chemistry of life can
only happen in a narrow temperature range. Too
cold = reactions happen too slowly. Too hot =
Temperature and evolution
• Water’s temperature
buffering effect causes
the oceans to be a
stable environment -
very important for the
early evolution of life
when conditions on
land were severe and
Ice and Life
• Ice is less dense than liquid water; it floats.
• If it sank, lakes and oceans would freeze solid, and
early life, existing totally within them, would have
Ice vs. Frozen Benzene
• Because of its polarity, water’s charged areas can
pull apart ionic or polar compounds and surround
them in a hydration shell - this is what is meant by
• This is crucial to life because the chemistry of life
must occur in solution.
• When you get dehydrated, your chemistry is
disrupted, sometimes to a fatal extent.
A water-soluble protein
• Water’s solvent ability and ability to flow
make it a good transport substance for
nutrients, wastes, etc. in a cell, an organism
(eg - blood) and an ecosystem (rivers, etc.)
• All of water’s crucial properties can be
traced back to the atomic structure of
oxygen and hydrogen, an example of the
theme of Structure is Related to Function.
Let’s review with this clip
H has 1 p+
Great Solvent H- bonding
The rxns of li fe need to occur in solution
Transport Medium Capillary action
(H20 to plant roots )
High specific heat
Great temp. buffer
Rxns of life must occur in a range of moderate temp.
Water, pH and Life
• Another aspect of
water crucial to the
therefore the existence
of life is the pH of
solutions in and
around organisms and
Hydronium and Hydroxide ions
• Polarity leads to water molecules periodically
pulling each other apart (dissociation).
• Hydronium (H3O+) and hydroxide (OH-) ions are
Acids and Bases
• If a substance such as HCl is dissolved, it
adds H+ ions to the solution, which will
bond to water molecules to make more
hydronium ions. This is an acid.
• A base, like NaOH, dissolves to form
something (like OH-) that pulls H+ ions off
of hydroniums, thus decreasing their
amount in the solution.
Importance of pH to Life
• Once again, it all boils down to chemistry.
Too high or too low pH can disrupt the
chemistry of life.
• Other pH related effects include the damage
acid rain can do to life and in-animate
structures. Chemicals such as nitrates and
sulfates in pollution react with water in the
atmosphere to form nitric & sulfuric acid.
So drink up and stay healthy
• Let’s see how you notes on water stack up
to these, which are found in the General
folder in the handouts folder and are titled
Good Notes Example.