UNIQUE PROPERTIES OF

WATERPages 24 - 26

POLAR MOLECULE A molecule with

opposite charges on different ends

A molecule with a charge distribution

ELECTRONEGATIVITY The tendency for an

atom to pull electrons toward itself

Oxygen is more electronegative than hydrogen, so the electrons spend more of their time closer to the oxygen atom giving it a slight negative charge and leaving the hydrogens with slight positive charges

COHESION Water attracted

to water Hydrogen

bonding between adjacent water molecules allows water molecules to bond with other water molecules

COHESION ALLOWS FOR TRANSPIRATION

COHESION ALLOWS FOR HIGH SURFACE TENSION

HIGH SPECIFIC HEAT It takes a great

deal of heat energy to change the temperature of water or to make water vaporize; therefore, large bodies of water can moderate temperature changes

EVAPORATIVE COOLING When sweat evaporates

from the skin, the water molecules that transition from liquid sweat to gaseous water vapor are the fastest moving molecules. As they shift phases it takes lots of energy and heat is given off. The water that remains is slower moving and much cooler. This results in lowering the body temperature.

FREEZING POINT As water freezes

each molecule forms stable hydrogen bonds with 4 other water molecules

The freezing point for water is 0°C

DENSITY Highly structured ice is less dense than

water and floats on top of water This allows life in bodies of water to

survive cold temps

SOLVENT OF LIFE Because of its

polar nature (+ and – charges) water can pull apart/ dissolve many other polar substances like sugar and ionic compounds like salt

ACIDIC AND BASIC CONDITIONS In solution some water

dissociates: H20 H+ + OH-

Chemical compounds that donate H+ to a solution is an acid

Chemical compounds that donate OH- is a base

pH scale describes how acidic or basic a solution is and ranges from 0 to 14 0 – most acidic (0 to 7) 7 – neutral (pure water) 14 – most basic (7 to 14) All living things

have an optimum pH level