1. The Chemical Context of Life
Chemistry is extremely crucial to understanding modern biology
If you hated chemistry – that's alright (sort of), but these are the things you really need to remember

2. Elements Required by Life
About 25 of the 92 natural elements are essential
C,O,H,N make up 96% of living matter
P,S,Ca,K and a few others make up most of the remaining 4%
Trace elements are required only in minute quantities

3. Atomic Numbers and Weights
# of protons determines what element an atom is
An element can have different numbers of neutrons, creating different isotopes
An atom can gain or lose electrons, which changes the charge on the atom
(i.e. H+ has one fewer electron than H)
Cl- has 1 more electron than Cl
Ca2+ has 2 fewer electrons than Ca

5. Chemistry Terms
Chemical bond – the attraction of two atoms to each other, often by the sharing of electrons
Electronegativity – how badly an atom “wants” electrons
Fluorine is the most electronegative atom, the closer an atom is on the periodic table, the more electronegative (worry about F, O, N, Cl)
Charge – protons carry + charge, electrons carry – charge. If an atom has more protons than electrons, it will have a + charge

6. Chemical Bonding 3 main types of bonds: Covalent
Ionic: Attraction between + and - molecules
Weak: Two molecules adhere temporarily

7. Covalent Bonds
Two or more atoms share 2 electrons, tightly holding the two atoms together
This is the strongest form of chemical bonds
A double covalent bond is the sharing of 4 electrons
O=O

8. Most electronegative atoms – F, O, N, Cl
Polar Covalent Bonds
Sometimes one atom pulls “harder” than the other
This causes the electronegative atom to have more – charge, or what is called a partial – charge
Most electronegative atoms – F, O, N, Cl

9. Ionic Bonds
Attraction between a fully positively charged molecule and a fully negatively charged molecule
Often because one molecule “steals” an electron from the other

10. More About Ionic Bonds Called salts
The positively charged atom (or compound) is called a cation (cats are positive!)
The negatively charged atom is called the anion
Like a magnetic attraction
MUCH, MUCH weaker than covalent bonds, but stronger than most other weak bonds

11. Weak Bonds – The Hydrogen Bond
In polar atoms such as water, one atom has a partial + charge, the other has a partial -
The + charge on one molecule is attracted to the – charge on another molecule
This is a very weak attraction

12. Why Are H-Bonds So Important if They're Weak?
Millions of small, short term bonds
Temporary
Water’s properties

13. Chemical Reactions Involve breaking bonds and forming new ones
It always take a little bit of energy to break the initial bond in a reaction (Ea)

14. pH pH measures the amount of H+ (or H3O+) in a solution
pH = - log [H+]
The more acid there is, the lower the pH
The more basic the solution, the higher the pH
HCl → H+ + Cl- Or
HCl + H2O → H3O+ + Cl-
NaOH + H+ → Na+ + H2O
NH3+ H+ ↔ NH4+

15. pH Scale
Remember each pH unit represents a tenfold difference!

16. Internal pH of cells is tightly regulated
Buffers
Internal pH of cells is tightly regulated
Buffers help keep pH stable
If blood is too basic...
H2CO3 → H+ + HCO3-
If blood is too acidic...
H+ + HCO3- → H2CO3

17. Diffusion
Molecules are always moving around and bouncing off of each other
This causes them to spread apart

18. Diffusion Across a Membrane
Wherever it is more concentrated, more collisions will occur
Thus more molecules will get knocked across the membrane, if possible

19. Heat vs. Temperature
Kinetic energy is the energy of motion. Atoms and molecules are always moving, and thus always have kinetic energy. The faster the atom moves, the greater its kinetic energy
Heat is the total quantity of kinetic energy in matter
Temperature measures the average kinetic energy of a molecule
A calorie = the amount of heat energy it takes to raise 1g of water 1 degree celsius

20. Affects of High Temperature
More collisions= more diffusion
Easier to get bonds to break
Heat will cause most things to expand because the molecules move more and take up more space
Or in a confined space will increase the pressure as molecules collide more