- Water is a bent molecule that is polar. The polar nature of water is due to the high electro negativity of the oxygen pulling the electrons away from the hydrogens.

-oxygen has a slight negative charge
-hydrogen has a slight positive charge

-Because of the polar ends found in water, an attraction known as a Hydrogen Bond is formed between water molecules.


Properties of water:

a) Good Solvent:
- Water dissolves more different substances than
any other solvent known (universal solvent). - Because water is polar, it attracts other ionic substances or polar substances, causing them
to stay in solution.
- Small non polar molecules dissolve somewhat in water. (ex: CO2, 02)
- Large non polar molecules do not dissolve in water. (ex: oils and fats)


b) High Specific Heat Capacities :
- Since water molecules are held together by strong electrical attractions (Hydrogen Bonds), there is less movement between molecules as the temperature increases.
- Therefore, water is able to absorb a lot of heat energy without much increase in temperature or increase in motion of molecules and water remains liquid over a wide range of temperatures. (0°C - 100°C)
- This property is particularly important in maintaining stable body temperatures in organisms.


c) Low Density as a Solid:
- Below 3.8°C, water crystallizes where each water molecule is "bonded" to 4 other water molecules.
-This ordered bonding puts more space between molecules, thus ice has a lower density than liquid water and thus floats on liquid water.
- Water is the only substance that expands when it becomes a solid.
- Ice is a good insulator, thus although lakes, rivers and ponds freeze over, the livingorganisms below the ice are protected.

d) High Surface Tension:
- Water exhibits both cohesion and adhesion.
- Cohesion is the tendency of like molecules to cling together whereas adhesion is the tendency of unlike molecules to cling together. Together these properties are called capillarity and allows water molecules to stick together so surface acts as a membrane.

e) Capillary Action:
-Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water.
-The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw.
-Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water


BLACKBOARD QUESTIONS?

1. Covalent and ionic bonds differ. Describe two of these things differences.
2. Is water a polar molecule? Explain in detail.
3. Hydrogen bonds form between water molecules. Why is it that hydrogen bonds do not form between methane (CH4) molecules? Use diagrams to prove your answer!