1. Acids and Bases; Electrophiles and Nucleophiles 2-2 Acid and base strengths are measured by equilibrium constants. Brønsted-Lowry acid: a proton donor. Brønsted-Lowry base: a proton acceptor. In water:

2. Water itself is both an acid and a base: The pH of a solution is defined: In pure water, the pH is 7. In acidic solutions the pH is less than 7 and in basic solutions the pH is above 7. The behavior of a general acid, HA, in water can be described: The pK A is the pH at which the acid is 50% dissociated. If the pK A is less than 1, the acid is termed strong; if greater than 4, weak.

4. We can estimate relative acid and base strengths. The relative strength of a weak acid, HA, increases with: Increasing electronegativity of A (CH 4 < NH 3 < H 2 O < HF) Increasing size of A (HF < HCl < HBr < HI) Resonance in A -

5. Lewis acids and bases interact by sharing an electron pair. Lewis Acid: A species containing an atom that is at least two electrons short of a closed outer shell. Lewis Base: A species containing at least one lone pair of electrons.

6. A Lewis base shares its lone pair with a Lewis acid to form a new covalent bond:

7. The dissociation of a Brønsted acid is the reverse of the association of a Lewis acid and a Lewis base: Note that the curved arrow points to the departing anion.

8. Electrophiles and nucleophiles also interact through movement of an electron pair. Many processes in organic chemistry exhibit characteristics of acid-base reactions. The carbon atom in chloromethane is termed electrophillic. The oxygen in the hydroxide is termed nucleophillic. The reaction of chloromethane and hydroxide ion is an example of a nucleophillic substitution reaction.

9. The terms Lewis acid and nucleophile are synonymous. Nucleophilic substitution is a general reaction of the class of compounds called haloalkanes. Additional examples include: The C-X bond in these examples constitutes the functional group, or center of chemical reactivity for the haloalkane class of organic compounds.