1. Water’s Life support Properties
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2. Polar Covalent Bonds
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
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

3. Hydrogen Bonds
Hydrogen, within a polar covalent bond, is attracted to electronegative atoms in other molecules.
called a hydrogen bond

4. Cohesion
Hydrogen bonding causes molecules to stick together, a property called cohesion
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

5. Adhesion
Adhesion is the clinging of one substance to another unlike itself.
Caused by adhesion the water runs along the glass and does not fall straight.

7. Adhesion & Cohesion results in Capillary Action!
Capillary Action is
how plants obtain
water through
their root systems,
despite gravity!
Cohesion
Direction
of water
movement
Water-conducting
cells

8. Water’s hydrogen bonds moderate temperature
Has a greater ability to resist temperature change because of hydrogen bonds.
Heat is the energy associated with movement of atoms and molecules in matter
Temperature measures the intensity of heat

9. Difference between heat and temperature.
To raise the temperature, heat must break hydrogen bonds.
With so many hydrogen bonds between water molecules, it can absorb a great deal of heat, with only a slight temperature change.
Compare the water in a pool on a hot day, and a metal chair next to the pool!

10. Water’s heat capacity in nature
Large bodies of water can store huge amounts of heat from the sun, which can be later given off as it cools – heating the air.
Water resists temperature changes also stabilizes ocean temperatures (good for marine life).
70% of our bodies are made of water, which helps moderate our internal temperature

11. Ice
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

12. Ice
Water molecules
Are spaced out
Liquid water
Water molecules
are closer together

13. Ice in nature Prevents ponds & lakes from freezing solid.
Floating ice insulates the water below from the cold air above.
This floating ice acts as a
“blanket” allowing fish and other
aquatic forms of life to survive.

14. Ice in the Artic Provides a hunting ground for polar bears
Deflects heat from the Earth.