2. Earth- the Water Planet About 71% of the Earth’s surface is covered in water Without water, life cannot exist Water has unique properties that enables the Earth to sustain life

3. Polar Molecule Chemical symbol : H2O Covalent bond: 2 atoms sharing electrons Oxygen holds on to electrons slightly more than the Hydrogen atoms creating a polar molecule

4. Water – A Polar Molecule Polarity of water molecule allows it to bond with adjacent water molecules Bond between molecules is called a hydrogen bond Hydrogen bonds are what give water some of it’s unique properties

5. Effects of Hydrogen Bonds 1. High Specific Heat Capacity Freezing point of water o° c Boiling point of water 100° c Hydrogen bonds hard to break so more energy is required to be absorbed/released in order to change phase Without this most or all water would be frozen in ice sheets or boiled away by the sun

6. Effects of Hydrogen Bonds 2. Cohesion/Adhesion H bonds attract water molecule to each other Cohesion: ability of water molecules to stick together Cohesion gives water a more uniform structure than most liquids Adhesion: ability of water to stick to other materials due to its polar nature

7. Effects of Hydrogen Bonds 3. Viscosity: tendency of a fluid to resist flow Most fluids change viscosity as they change temperature As water cools the viscosity rises more than in other liquids Ex) A 20 c drop in temperature increases viscosity of water by 60% Imp. because it affects the energy aquatic organisms must expend

8. Effects of Hydrogen Bonds 4. Surface Tension: water’s resistance to objects attempting to penetrate its surface Cohesive nature of water at its surface makes this possible Many small aquatic organisms rely on surface tension to rest (not float) on surface of the water Affects how quickly oceans take up atmospheric CO2 and release O2 into the atmosphere

9. Effects of Hydrogen Bonds 5. Ice Floats Most substances become dense and sink as they cool H bonds spread the molecules into a crystal structure that takes up more space than liquid water With more volume, ice is less dense than water so it floats By floating, ice forms a layer that insulates water below keeping water in liquid form

10. Fluid Properties: Density Density = specific weight/volume Density = specific weight/volume D = m/v (g/cm 3 ) D = m/v (g/cm 3 ) Density of water does not change much. Density of water does not change much. Very high levels of pressure are required to change the density of water. Very high levels of pressure are required to change the density of water.

11. Density and Temperature ????

12. Specific Gravity (SG) comparison of the specific weight of H 2 O to the same volume of water under different conditions (e.g., temperature). comparison of the specific weight of H 2 O to the same volume of water under different conditions (e.g., temperature). Often used to determine salinity via a hydrometer. Often used to determine salinity via a hydrometer. SG for water is usually 1.0 and, since it is dimensionless, has no units. SG for water is usually 1.0 and, since it is dimensionless, has no units.

13. Properties of Pure Water Latent heat of fusion: water requires a large loss of energy to pass from liquid to solid phase. Latent heat of fusion: water requires a large loss of energy to pass from liquid to solid phase. Reverse is true for latent heat of vaporization. Reverse is true for latent heat of vaporization. Meaning: large bodies of water resist changes in temperature, life processes remain constant. Meaning: large bodies of water resist changes in temperature, life processes remain constant. From Sumich, page 19

14. Physical Variables: Density Already mentioned as an aspect of fluids. Already mentioned as an aspect of fluids. Pure water is most dense at 4 o C. (1 g/cm 3 ) Pure water is most dense at 4 o C. (1 g/cm 3 ) Below this it becomes less dense and freezes at 0 o C. Below this it becomes less dense and freezes at 0 o C. Our purposes Density of freshwater 1 g/cm 3 Our purposes Density of freshwater 1 g/cm 3

15. Physical Variables: Density When you add impurities to water (e.g., salt), its density increases. When you add impurities to water (e.g., salt), its density increases. Density of saltwater (oceans) is 1.028 g/cm 3. Density of saltwater (oceans) is 1.028 g/cm 3. Thus, seawater freezes at a lower temp (-1.4 o C). Thus, seawater freezes at a lower temp (-1.4 o C). If seawater can freeze, why doesn’t it accumulate at the bottom of the ocean? If seawater can freeze, why doesn’t it accumulate at the bottom of the ocean?