Water’s unique properties allow life to exist on Earth.
A. Life depends on hydrogenbonds 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.
2. Hydrogen bonds are responsible for fiveimportant properties of water. a. Cohesion b. Adhesion c. High specific heat d. High heat of vaporization e. Less dense as a solid
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
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 athin glass tube
c. High Specific Heat – amount of heat neededto raise or lower 1g of a substance 1°C. - ex. Hot sand vs. cold water -water resists temperature change bothfor heating and cooling - water can absorb or release large amounts of heat energy with little change inactual temperature
d. High Heat of Vaporization – Amount of energy requiredto 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 withit
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 wherebymolecules are set at fixed distances
4. Water is important for homeostasis (ability to maintain asteady state despite changing conditions) a. makes a good insulator b. resists temperature change c. coolant d. ice protects against extremes (insulates frozen lakes)