1. The Properties of Water

2. 1. Polar: electrons shared unequally a. unequal charge attracts other H 2 O molecules & ions b. H 2 0 bonds easily w/ other H 2 O molecules c. H bonds hold H 2 O molecules to each other Go to Section: Water is a Polar Molecule Slide # 2

3. Water is Cohesive Slide # 3 2. Cohesion: tendency of molecules to stick to each other a.Water molecules are attracted to other water molecules b. Positive charge on H + attracts negative charge on O –

4. Go to Section: Water has Surface Tension Slide # 4 3. Surface tension: attraction of water molecules to one another cause them to stick together and are drawn inward toward each other. a. Surface tension allows a water strider to rest on the surface of water without breaking water’s surface

5. 4. Adhesion: tendency of molecules to stick to other surfaces a. Adhesion allows water to stick to surface of cells b. Allows water to be pulled from roots to leaves Go to Section: Water is Adhesive Slide # 5

6. Water has Capillary Action 5. Capillary Action a. Cohesion and adhesion work together in capillary tubes in plant stems b. Water creeps up thin tubes of plants c. Capillary action allows plants to draw up water from roots to stems, like water being drawn up through a straw Slide # 6

7. Water Resists Temperature Changes 1. It takes more heat to increase the temperature of water (than other substances) 2. Water must lose a lot of heat when it cools a. Coastal areas are usually cooler in the summer and warmer in the winter than places farther inland 3. Large bodies of water provide a “heat sink” near coastal areas Slide # 7

8. 5. Expansion of Water a. Water that freezes in the cracks of rocks often break the rocks apart contributing to soil formation. b. Ice is less dense than water; ice floats c. Ice on lakes, ponds, rivers, etc. forms from the top down Go to Section: Water Expands When it Freezes Slide # 8 d. Allows underwater life to survive even if surface is frozen over

9. 1. Ionic Bonding: bond created when oppositely charged atoms attract each other. 2. Ion: a + or - charged atom created when an atom loses or gains electrons. Slide # 9 Types of Chemical Bonds: Ionic Bonds Sodium Atom Chlorine Atom 11 p+ 17 p+ 11 e־ 17 e־ 0 charge Sodium Ion Chlorine Ion 11 p+ 17 p+ 10 e־ 18 e־ +1 charge-1 charge

10. 1. Covalent Bond – bond created when 2 or more atoms share a pair of electrons. a. Why is covalent bonding important to biology? b. Chemical bonds store and transfer energy in the environment and within organisms. Slide # 10 Types of Chemical Bonds: Covalent Bonds

11. Types of Chemical Bonds: Polar Covalent Slide # 11 Oxygen has greater mass than hydrogen & exerts a greater pull on the shared electrons The electrons that are shared between hydrogen and oxygen are shared unequally, thus creating a polar molecule.

12. 1.Hydrogen Bond – weak bond between a positive hydrogen ion/atom and a negative area on another compound. 2.Importance of hydrogen bonding a. Gives water unique properties. b. Holds the 2 halves of DNA together. Types of Chemical Bonds: Hydrogen Bonds Slide # 12 Hydrogen bonds

13. Solutions 1. Solution: a liquid that has a substance dissolved in it. 2. Solute: substance that is dissolved EXAMPLE: Salt 3. Solvent: substance doing the dissolving EXAMPLE: Water 4. WATER is the Universal Solvent Slide # 13

14. Water is the Universal Solvent 1. Water can form solutions with everything EXCEPT fats oils, and waxes 2. Water is the solvent in MOST solutions 3. Our nutrients and wastes are dissolved in water so it can be transported in and out of our cells. Water is the solvent in our blood Slide # 14

15. UNIQUE PROPERTIES OF WATER: 1. Water can break apart (disassociate) to form hydrogen ions (H + ) & hydroxide ions (OH¯). 2. H + & OH¯ ions are the most reactive ions in nature. Slide # 15

16. 1. pH scale: measurement system; tells how much H + ions are in a solution 2. pH scale ranges from 0 – 14 3. Each step (number) on the pH scale is a factor of 10 a. EX: A solution w/ a pH of 5 has 10 times as many H + ions as a solution w/ a pH of 6 Go to Section: Acids and Base How much more acidic is a solution w/ a pH of 6 than a solution w/ a pH of 8? 100 Slide # 16

17. 1. Acid: releases H + ions into a solution a. pH below 7 H+ > OH - 2. Base: releases OH – ions into a solution a. pH above 7 H+ < OH - 3. Buffer: weak acid or weak base that can react w/ strong acids or strong bases to prevent sharp, sudden changes in pH Go to Section: Acids, Bases and Buffers Lemons are acidic Bleach is a strong base Slide # 17

18. pH Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A. Acid B. Neutral C. Base Stronger Weaker Weaker Stronger Slide # 18 H + > OH ─ H + = OH ─ H + OH ─

19. Hydrogen Ions verses Hydroxide Ions Slide # 19

20. Pure water Human blood Oven cleaner Bleach Ammonia solution Soap Sea water Milk Normal rainfall Acid rain Tomato juice Lemon juice Stomach acid Neutral Increasingly Basic Increasingly Acidic Go to Section: pH Scale Slide # 15

21. Properties of Water Cornell Notes 1. How is water a “polar” molecule? (Hint: Draw a molecule of water & label the charges). 2. What are hydrogen bonds and where do they form? (Hint: Draw a diagram to help you explain this answer!) 3. What is the difference between cohesion and adhesion with respect to water?

22. Properties of Water Cornell Notes 5. What does the phrase “universal solvent” mean with respect to water? 4. What are the properties of water and how are the properties of water important to living organisms? 6. What is the pH scale and how can it be used to interpret the relative strengths of acids, bases, and neutral solutions?