1. Chemistry Review & Water
Chapters 2 & 3

2. YOU MUST KNOW The 3 subatomic particles and their significance
The types of chemical bonds and how they form
The importance of hydrogen bonding to the properties of water
Four unique properties of water and how each contributes to life on Earth
How to interpret the pH scale
How changes in pH can alter biological systems
The importance of buffers in biological systems

3. Bonding Review Covalent Bonds Atoms share electrons
Can have single, double, triple bonds
Relatively strong bonds
Many different types for specific kinds of molecules (ex. peptide, glycosidic, phosphodiester)
Can be polar or non-polar (are electrons shared equally?)

4. Van de Waals Interactions
Ionic Bonds
Atoms gain/lose electrons, resulting in charges which attract them to each other
Van de Waals Interactions
Weak connections, break and reform, as a result of asymmetrical distribution of electrons (aka intermolecular forces)

5. WATER Polarity: Uneven distribution of charges around a molecule
Hydrogen side of water molecule being slightly positive while oxygen side is slightly negative
Attraction between positive side of one water molecule and negative side of next = Hydrogen bond

6. 1. Cohesion Water molecules are attracted to other water molecules
Water forms into droplets (which join together when close)
Water has strong surface tension (remember penny lab?)
Water can move as a column in plants (1:55)

7. Adhesion
Attraction between water molecules and other types of molecules
Also at play in movement of water in vascular plants (capillary action)
Once adhesion moves water up the vascular tissue, adhesion keeps it from dropping back down

8. Less dense in solid form
High Specific Heat
The amount of heat required to raise or lower the temperature of a substance by 1 degree C
Makes temperature of Earth stable (ocean temps stable)
Helps plants and animals maintain temperatures
Evaporative cooling
Less dense in solid form
Ice floats – insulates large bodies of water to keep them from freezing entirely (life can survive the winter)

9. 4. Solvent Capable of dissolving an abundance of other molecules
Makes it extremely valuable in transporting molecules in your body
Water being transported by cohesion and adhesion in plants is carrying dissolved substances everywhere it goes
Blood is composed mainly of water – carries dissolved substances around your body (glucose, ions, amino acids)
Also makes it an excellent
medium for metabolic reactions
*Remember
Solvent = substance doing the dissolving
Solute = substance that gets dissolved
Together they make a solution

10. Hydrophilic molecules – molecules that dissolve in water
Generally polar (polar solvent-water-dissolves polar solutes)
Ex. glucose and other carbohydrates, ions such as sodium (Na+, Ca++, Cl-)
Hydrophobic molecules – don’t dissolve in water
Generally non-polar (charges evenly distributed around molecule, atoms share electrons equally)
Ex. Lipids, methane

11. pH Buffers Weak acids/bases that minimize changes in pH
Ex. Carbonic acid (H2CO3) – in living systems
Moderates pH changes in blood plasma

12. Molarity (M)
Number of moles (6.022 x1023 molecules) per liter of solution
How we quantify the concentration of a solution
Sample Problem:
How many grams of sucrose (C12H22O11) would you add to 0.75L of water to make a 0.6M aqueous solution?

13. Step 1: Determine the molecular mass of sucrose.
C12H22O11 - (12 molecules of carbon x 12) + (22 molecules of hydrogen x 1) + (11 molecules of oxygen x 16) = (144) + (22) + (176) = 342g/mol
Step 2: Solve for number of moles in the solution
Molarity (M) = m (moles)/V (volume in liters)
0.6M = m/0.75L m = 0.45 moles
Step 3: Determine g in 0.45 moles
342 g/mol = X/0.45 mol X = 154g