1. Water Necessary for Life

2. Structure of Water H 2 0 Covalent Bonds –Electrons are shared Oxygen is more electronegative than other molecules –Means it pulls on the “shared” electrons more Since electrons are negative, then there is a slight negative charge on Oxygen side of molecule Leaves a slight positive charge on Hydrogen side of molecule H + O -

3. Polarity Polar molecules have a slightly positive side and a slightly negative side –they act like magnets –Water is a polar molecule So are proteins and carbs –Earth also has “poles”, due to magnetic charges

4. Polarity (cont) Polar molecules are hydrophillic –‘water – loving’ –Attracted to other water molecules and other polar molecules –Opposite – hydrophobic –Nonpolar molecules are ‘water-fearing’, like oil

5. Hydrogen Bonds The attraction between the negative side of one polar molecule and the positive side of another polar molecule –Allows polar molecules to be attracted like magnets –weak bond – easily broken

6. Water Drop on Leaf Notice how the drop forms as the molecules all stick together

7. Adhesion and Cohesion Notice how the water drop is attracted to the branch The branch is made of polar molecules adhesion – sticking to other polar molecules cohesion – sticking to other water molecules

8. Surface Tension Creates a thin “film” or surface on top of the water Caused by Adhesion and Cohesion –Allows for water strider to sit on top of water despite the fact that it is heavier and more dense than water

9. Universal Solvent Positive and negative poles are attracted to charges in salts and other polar molecules, causing them to dissolve easily

10. Density Water is more dense than ice so ice floats – allows lakes to freeze from top down, which is good for the fish.

11. Capillary Action Water will “climb” up very thin tubes –Allows for water to travel up the stems of plants

12. Life exists because of water remember, we are over 70% water, the Earth is over 70% water