Lecture #27
  CURMUDGEON GENERAL'S WARNING. These "slides" represent highlights from lecture and are neither complete nor meant to replace lecture. It is advised not to use these as a reliable means to replace missed lecture material. Do so at risk to healthy academic performance in 09-105.

Exam III Review

Review for Exam III
Topics outlined
Topics outlined (continued)
Problem 14.62
(Part c)
Reviewing heteronuclear diatomic molecules and the atomic orbitals from which molecular orbitals are constructed, we examined the HCl molecule as shown.
If we add an electron to ozone to produce the ozonide ion, what happens to the total bond order? Bond length? Bond strength?
Here is an underlying feature of a large collection of molecules of extreme importance. There is a ring of delocalized electrons, shown as the red alternating (conjugated) single bond double bond sequence.
A very simple model conceptually identical to that for the particle-in-a-box can be applied to electrons delocalized about a ring. The formula for the allowed energy levels is reminiscent of the one we had for chains of delocalized electrons and the calculations of transition energies follow exactly the same line of reasoning. The ring structure shown absorbs light of approximately 600 nm wavelength.
Constructing molecular orbitals starts with a look at the alignment of the valence atomic orbitals.
For homework 6, you described the bonding in butane, butene, and butyne using molecular orbitals (that were localized molecular orbitals). Now describe what's going on with the thiocyanate ion.
Another particle-in-a-box example.