1. Why are we spending so much money going to Mars? Gusev Crater on Mars (taken by the Mars Exploration Rover Spirit on Jan. 10, 2004

2. Solid Liquid Gas The Amazing Water Molecule Water covers 75% of the Earth’s Surface and makes up 45%-95% of living organisms

3. Water is polar. Hydrogen bonds form between water molecules. -- ++ ++ ++ -- H H O Water is both cohesive (sticks to itself) and adhesive (sticks to other types of molecules)

4. Figure 3.3 Walking on water

5. In ice, water molecules form a crystal lattice. In liquid water, no lattice forms, so liquid water is denser than ice.

6. As a result, ice floats.

7. Figure 3.5 The structure of ice (Layer 2)

8. Ice floats and frozen benzene sinks

9. Liquid Gas Molecules have thermal energy n Thermal energy = the kinetic energy of molecular motion Temperature = a measure of how much thermal energy the average molecule of an object possesses Heat = the total amount of thermal energy that an object has: can be transferred from warmer to cooler objects

10. Heat vs. Temperature The Pacific Ocean has a low temperature, but a lot of heat

11. Ice watersteam Water has high specific heat = the amount of energy required to raise the temperature of 1 gram of substance 1° Celsius

12. Areas near large bodies of water have a fairly stable temperature

13. Evaporative cooling Water has a high Heat of Vaporization: the amount of heat that must be transferred to a liquid to change it from liquid to gas

14. Water as a solvent Since water is polar, the positive and negative ends of a water molecule will be attracted to charged ions or other polar molecules Solvent Solute Solution

15. Like dissolves Like Hydrophilic: ionic or polar substances that have an affinity for water Hydrophobic: non-ionic or nonpolar substances that do not have an affinity for water

16. Chemical reaction: hydrogen bond shift OR

17. Acids, Bases, and the pH scale n Acids = substances that release H+ ions (increasing H + concentration) HCl  H + + Cl - n Bases = substances that release OH - ions or accept H + ions (decreasing H + concentration) NaOH  Na + + OH - NH 3 + H +  NH 4

18. Figure 3.9 The pH of some aqueous solutions pH = -log[H + ] Example: Water [H + ] = 10 -7 M So the pH is -log(10 -7 ) = -(-7) = 7

19. Buffers are substances that help maintain a constant pH in a solution Example: Carbonic acid