Water : A Molecule Essential for Life

Thoughts to Ponder……

• Why can’t 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: http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-earth.html

Why?

Water has unique properties that arise from

its structure

http://www.lenntech.com/images/Water%20molecule.jpg

Water is a Polar Molecule

http://rst.gsfc.nasa.gov/Sect20/water_molecules_con_c_la_784.jpg

Hydrogen Bond Formation

http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html

Strength in Numbers!

Source: www.personal.psu.edu/.../ 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

Cohesion

• 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 it’s in contact with

Adhesion

•A great deal of E is

needed to break

hydrogen bonds

•Temperature changes

are minimized

HIGH HEAT CAPACITY

http://i.telegraph.co.uk/multimedia/archive/01549/perspiration_1549996c.jpg

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

Universal SolventThe “Great Dissolver”

• 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

Hydrophobic effect on Nonpolar

substances

• Ice is less dense then water - it floats

• Ponds, lakes, streams, ocean surfaces freeze from the top down.

• Aquatic organisms receive insulating protection

DENSITY

• 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!

Vaporization

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