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Featured Golden Rules of Chemistry: 5. Delocalization of charge over a larger area is stabilizing. 8. Reactions will occur if the products are more stable than the reactants (motive) and the energy barrier is low enough (opportunity).

1. Acid strength is described by the quantities Ka and pKa. The stronger the acid, the lower pKa.

2. In an acid-base reaction, equilibrium favors formation of the weaker acid-weaker base (side with higher acid pKa value).

3. For acids that deprotonate to give an anion conjugate base, the stronger acid will produce the more stable anion conjugate base. In other words, when analyzing relative acid strength, compare the relative stabilities of the anion conjugate bases.

4. Use five rules when determining relative stabilities of anions (i.e. when you are predicting relative acid strength) These five rules are actually application of the following two principles: 1) negative charge is neutralized by nuclear positive charge and 2) delocalizing negative charge over a larger area is stabilizing.

a) Across a row of the Periodic Table, negative charge on a more electronegative atom is more stable. (Principle 1)

b) Down a column of the Periodic Table, larger anions are more stable than smaller ones. (This is more confusing than you think, so make sure you understand it). (Principle 2 dominates here)

c) Hybridization: The more S orbital character of the hybridization on the atom that has the negative charge, the more stable the anion (stability of anions is in the order sp>sp2>sp3) Principle 1)

d) Charges distributed over more atoms are better. (Nature hates isolated charges, so spreading a charge around by resonance is very stabilizing) (Pinciple 2)

e) Inductive Effect: Electronegative atoms such as F on atoms adjacent to the atom(s) with the negative charge will pull some of the charge away, thus spreading it out and leading to stabilization. (Principle 1 and 2)

5. To say it in a new way, in an acid-base reaction, equilibrium favors the side opposite that with the stronger acid, meaning the side with the more stable anion is favored.

7. In buffered aqueous solution, an acid will be present predominantly in its deprotonated state if the pH of the solution is a larger value than the pKa of the acid. If you are interested in this derivation click here

HOMEWORK:

Read: Sections 4.1-4.7 in the eBook.

There is no daily quiz or homework because of the exam.