1. Notes 4 - The Chemistry of Life

2. Central Questions What are the characteristics of water important to life? What are acids and bases? What is the pH scale? (include which end is acidic and basic)

3. Bond Types Covalent bond—share electrons, strongest Ionic bonds—electrons are gained or lost; break down in water (salt) Hydrogen bonds—attraction between partial positive and partial negative charges; common in water

4. Importance of Water Water is essential for all life on Earth Water makes up about 2/3 of a cell’s mass (weight) Water is polar, meaning is has a slight charge at each end of the molecule

5. Characteristics of Water Water is the ‘universal solvent’ and is the solvent for virtually all processes in a cell. Water has a high heat absorption capacity—it can absorb large changes in temperature (helps keep temperature constant) Water absorbs a lot of heat while evaporating (sweat cools you)

6. Characteristics of Water (cont’d) Solid water is less dense than liquid, so ice floats (lakes and oceans don’t freeze solid and fishies live!) Water is liquid at room temperature Water is cohesive and adhesive (sticks together)

7. Acids and Bases Acids—split to release hydrogen ions (H+) when dissolved in water Bases—split to release hydroxide ions (OH-) when dissolved in water + + Acid Base H+ OH- Leftover

8. pH Scale The pH scale is a measurement of the concentration of hydrogen ions (H+) in a solution AcidicNeutral Basic 0 --------------------------- 7 ------------------------ 14 Lots of H+WaterLittle H+

9. Central Questions What are the characteristics of water important to life? What are acids and bases? What is the pH scale? (include which end is acidic and basic)