1. The Extraordinary Properties of Water

2. Water’s Unique Properties
Relatively High Boiling Point
Ability to Dissolve Other Substances
Cohesion and Adhesion
High Specific Heat
High Heat of Vaporization
Low Density of Ice

3. Structure of Water
A water molecule (H2O), is made up of three atoms --- one oxygen and two hydrogen. H O 1

4. Water is Polar
In each water molecule, the oxygen atom attracts more than its "fair share" of electrons because it is more electronegative than hydrogen
The oxygen end of the water molecule has a partially negative charge
The hydrogen end of the water molecule has a partially positive charge
Causes the water to be POLAR
However, Water is neutral (equal number of e- and p+) --- Zero Net Charge

5. Hydrogen Bonds Exist Between Water Molecules
Formed between a highly Electronegative atom of a polar molecule (Oxygen) and a Hydrogen
One hydrogen bond is weak, but many hydrogen bonds are strong

6. Interaction Between Water Molecules
Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of another water molecule to form a HYDROGEN BOND

7. Hydrogen Bonding Affects Boiling Point
Principle: The greater the forces of attraction the higher the boiling point or the greater the polarity the higher the boiling point.
In the case of water, hydrogen bonding exerts a very strong effect to keep the molecules in a liquid state until a fairly high temperature is reached.
If water behaved as a normal polar molecule it would boil at about -100 C based on its molecular weight.
Instead, water boils at +100 C, which is very abnormal. 
This animation shows how water molecules are able to break the forces of attraction i.e. the hydrogen bonds to each other and escape as the gas molecule.

8. Ionic solutes also dissolve in polar solvents
The polar nature of water and its hydrogen bonding makes it the universal solvent.
“Like Dissolves Like”
Water has the ability to dissolve other polar covalent substances, because of they also have partially positive and partially negative sides
Ionic solutes also dissolve in polar solvents
(ex: NaCl and H2O)

9. Ion-Dipole Forces
The force of attraction between an ion and a polar molecule (a dipole)
Example: NaCl breaks up because the ion dipole with water is stronger than the attraction of Na+ to Cl-
Diagram: Water will come into a molecule of NaCl and break off the individual ions by surrounding them based on the ion-dipole forces i.e.. Positive ends of water will attract to negatively charge chlorine and negatively charged ends of water will attract to the positively charged sodium

10. Adhesion and Cohesion: Make sure you know the difference
Cohesion: Water is attracted to water
Example: Water drops are composed of water molecules that like to stick together.
Adhesion: Water is attracted to other substances.
Example: Water drops stick to substances like pine needles or spider webs.

11. Cohesion is also caused by polarity and Hydrogen Bonding
Cohesion is the attraction between a polar water molecule to the oppositely charged part of neighboring water molecules.
Results in 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 1

12. Helps insects walk across water
Cohesion …
Helps insects walk across water

13. Cohesion causes water to exist in drops
The natural form of a water drop occurs in the state where the atoms in the molecule are using the least amount of energy.
For water, this state happens when a water molecule is surrounded on all sides by other water molecules, which creates a sphere or ball (perfectly round if it was in outer space).

14. Adhesion is also caused by polarity and Hydrogen Bonding
Adhesion is the attraction between two different substances.
Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton.
Adhesion results in capillary action
Capillary action-water molecules will “tow” each other along when in a thin glass tube.
Example: transpiration process which plants and trees remove water from the soil, and paper towels soak up water. 1

15. Adhesion Causes Capillary Action
Capillary action is important for moving water around.
It is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension.
Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules.
The height to which capillary action will take water in a uniform circular tube is limited by surface tension and, of course, gravity.

16. Adhesion Also Causes Water to …
Attach to a silken spider web
Form spheres & hold onto plant leaves

17. Adhesion and cohesion of water molecules aid in transporting water through plants
Water moves through the xylem tissue up to the tallest parts of the plant because of capillary action and transpiration. Capillary action is caused by the adhesion force attracting the water to the stem of the plant, and the cohesion force, which attracts the water
molecules to each other and causes the water to creep up the inside walls of the xylem cells. Finally, when water molecules escape through the stomata in a process called transpiration, the cohesion of water molecules pulls water molecules up to replace the departing molecule.

18. Check for Understanding
Explain what is happening in this picture using the forces of gravity, adhesion and cohesion.

19. Water’s high Specific Heat is also a result of polarity
Specific Heat - Amount of heat needed to raise or lower 1g of a substance 1° C.
Water has a very high specific heat because of the hydrogen bonding between water molecules
This means 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. 1

20. High Heat of Vaporization
Amount of energy to convert 1g or a substance from a liquid to a gas
In order for water to evaporate, hydrogen bonds must be broken.
Breaking bonds requires energy.
As water evaporates, it removes a lot of heat with it. (endothermic phase change)
Humans sweat, because as the sweat evaporates it removes heat from the body which maintains homeostasis within the body. 1

21. High Heat of Vaporization
It takes a large amount of energy to change the state of water. This benefits aquatic organisms, as bodies of water maintain fairly stable temperature conditions.
Water's heat of vaporization is 540 cal/g.
In order for water to evaporate, each gram must GAIN 540 calories (temperature doesn’t change oC).
As water evaporates, it removes a lot of heat with it (cooling effect). 1

22. Heat radiated from the sun warmed surface of the earth is
Water vapor in the Earth’s atmosphere forms a kind of global ‘‘blanket” which helps to keep the Earth warm.
Heat radiated from the sun warmed surface of
the earth is
absorbed and held
by the vapor. 1

23. Water is Less Dense as a Solid
Ice is less dense as a solid than as a liquid (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. 1

24. Water is Less Dense as a Solid
Which is ice and which is water? 1

25. Water is Less Dense as a Solid
Ice 1

26. Homeostasis
Ability to maintain a steady state despite changing conditions
Water is important to this process because:
a. Makes a good insulator
b. Resists temperature change
c. Universal solvent
d. Coolant
e. Ice protects against temperature extremes (insulates frozen lakes) 4