2. A. Life depends on hydrogen
bonds in water.
1. Water is a polar molecule.
a. Polar molecules have slightly charged regions.
_
O
H H
+ +
b. Nonpolar molecules do not have charged
regions.
c. Hydrogen bonds form between slightly positive
hydrogen atoms and slightly negative oxygen
atoms.
4. 2. Hydrogen bonds are responsible for five
important properties of water.
a. Cohesion
b. Adhesion
c. High specific heat
d. High heat of vaporization
e. Less dense as a solid
5. 3. Properties of water
a. Cohesion – Attraction between particles of the
same substance (why water is attracted to itself)
- results in high surface tension (a measure of the
strength of water’s surface)
- produces a surface film on water that allows
insects to walk on the surface of water
6. b. Adhesion – attraction between two different substances
- water will make hydrogen bonds with other
surfaces such as glass, soil, and plant tissues
- capillary action – water molecules will climb up a
thin glass tube
7. c. High Specific Heat – amount of heat needed
to raise or lower 1g of a substance 1°C.
- ex. Hot sand vs. cold water
-water resists temperature change both
for heating and cooling
- water can absorb or release large
amounts of heat energy with little change in
actual temperature
9. d. High Heat of Vaporization – Amount of energy required
to convert 1g of a substance from a liquid to a gas
- In order for water to evaporate, hydrogen bonds
must be broken.
- As water evaporates, it removes a lot of heat with
it
10. e. Water is less dense as a solid – ice floats
- liquid water has hydrogen bonds that are
constantly being broken and reformed
- frozen water forms a crystal-like lattice whereby
molecules are set at fixed distances
11. 4. Water is important for homeostasis (ability to maintain a
steady state despite changing conditions)
a. makes a good insulator
b. resists temperature change
c. coolant
d. ice protects against extremes (insulates
frozen lakes)