Chapter 10 Study Guide

To augment VSEPR, and to explain some of the quantum mechanics involved in chemical bonds and typical chemical geometries, "Valence Bond (VB) Theory" is invoked, in which the overlap between atomic orbitals on different atoms is the source of the bonding energy. In order to reconcile VB theory with VSEPR-predicted structures, the hybridization of atomic orbitals to form "bonding sets" is presented. This is made possible by the linear nature of the Schrodinger equation. VB theory and hybridization combine to predict, among other things, the nature of covalent multiple bonds, which allow a much better understanding of isomerization in organic compounds.

Finally, "Molecular Orbital (MO) Theory" is another way to look at the quantum mechanics of molecules, in which the molecule is treated as a whole, using the same ideas as in hybridization theory.

Supplementary material: These are a few pages from a different textbook that do a better job of explaining how hybrid orbitals are constructed from atomic orbitals. page 1, page 2, page 3, and page 4.

These are necessary because the textbook sees fit to omit any discussion whatsoever of the signs of wavefunctions, understanding of which is necessary for discussion of how hybrid orbitals and molecular orbitals come about.

Suggested Problems

You should be able to:

1. Predict the geometries of small and large molecules
2. Identify isomers
3. Assign hybridization schemes based on geometries
4. Identify bond geometries (sigma, pi, etc.)
5. Assign bond dipoles and molecular dipoles
6. Discuss Valence Bond Theory
7. Discuss Molecular Orbital Theory
8. Identify bonding and antibonding orbitals
9. use a molecular orbital energy level diagram
10. Draw aromatic compounds

Important topics and concepts

1. VSEPR Theory
   1. The basic idea - electron groups repel each other
   2. The fundamental "base" geometries
   3. How "base" geometries give rise to other geometries through lone-pairs.
   4. Distortions from ideal VSEPR structures - why?
   5. Application to larger molecules. What information is not provided by VSEPR?
2. Valence Bond Theory
   1. Overlap as a source of bonding interaction
   2. Geometry problem - VSEPR and atomic orbitals have different shapes!
   3. Solution: Hybridization
      1. How to add and subtract orbitals
      2. sp hybrids
      3. sp² hybrids
      4. sp³ hybrids
      5. sp³d and sp³d² hybrids
   4. Multiple covalent bonding: geometry and naming
3. Geometric isomerism due to hindered rotation around double bonds
   • Difference between Geometric and structural isomerism
4. Molecular Orbital Theory
   1. Basic idea: wavefunctions that span the whole molecule
   2. Which orbitals "mix" and which don't.
   3. Bonding and antibonding MO's.
   4. "Filling Up" the molecular orbitals
   5. Predicting bond order and magnetic properties
5. Aromatics
   1. Special nature of Benzene: delocalized pi MOs.
   2. Substituent naming and isomers