Water : A Molecule Essential for Life

Thoughts to Ponder…… Why cant we survive more than a week without water? How do insects walk on water? How does water rise up 300 feet from the roots of a redwood tree? Why does water take so long to boil? Why do oil and water not mix?

Life is dependent on Water Source: Why?

Water has unique properties that arise from its structure

Water is a Polar Molecule

Hydrogen Bond Formation

Strength in Numbers! Source: bonddiagram.gif. Water molecules, with the hydrogen bonds represented by the dotted lines

Properties of Water due to Hydrogen Bonding Cohesion / Surface Tension Adhesion High heat capacity Solvent of polar and ionic compounds; creates a hydrophobic effect on nonpolar substances Density of ice less than liquid water

Water molecules stick together Creates surface tension

Water molecules are attracted to different molecules Capillarity – a special case that results from the relative attraction of the molecules for each other and the solid surface its in contact with

A great deal of E is needed to break hydrogen bonds Temperature changes are minimized

Specific Heat Specific heat – amount of heat needed to change the temperature of 1g. of a substance 1degree Celsius. High specific heat allows water to act as a heat sink. Water will retain its temperature after absorbing large amounts of heat, and retain its temperature after losing equally large amounts of heat.

Water dissolves polar and ionic substances due to its ability to form hydrogen bonds

Water cannot dissolve nonpolar substances. Hydrophobic effect- results when water molecules interact with each other and exclude nonpolar substances Causes molecules like DNA to fold into their specific shapes

Ice is less dense then water - it floats Ponds, lakes, streams, ocean surfaces freeze from the top down. Aquatic organisms receive insulating protection

Large amounts of heat E are needed to disrupt hydrogen bonds. Heat helps water to begin evaporating. Sweat evaporates using the heat from your body…cools your body down!

Now that you know the properties of water, what other ways can you think that it supports life?

Imagine how life on Earth would change if hydrogen bonding between water molecules no longer could form