1. Last hour:
Shortcomings of MO theory:
Overestimates ionic character of bonding
Underestimates electron correlation
Valence Bond Theory: construct molecular function by exchange of electron pairs  more correlation “built in”, but overestimates correlation
Better still mixed approaches
Polyatomic molecules: Hybridization
sp hybrid orbitals (from 2s and 2p):
Hybrid orbitals are directional
Use Walsh diagrams to determine bond angles, e.g., for triatomic molecules

2. sp2 hybrid orbital in BH3
from McQuarrie & Simon “Physical Chemistry”

3. General shape of sp2 hybrid orbitals
from McQuarrie & Simon “Physical Chemistry”

4.  bond in ethene
from McQuarrie & Simon “Physical Chemistry”

5.  bond in ethene

6.  system in butadiene

7. from Demtröder “Molecular Physics”

8. sp3 hybrid orbitals in CH4

9. from McQuarrie & Simon “Physical Chemistry”

10. Learning Goals for Chapter 24 – Electronic States of Polyatomic Molecules
After this chapter, the related homework problems, and reading the relevant parts of the textbook, you should be able to:
explain hybrid orbitals;
use Walsh diagrams to determine molecular geometry and electron configurations for small molecules;