Putting Electrons in the MH3 System

• Rule 5: Molecules with similar structures will
have qualitatively similar MO’s, with the major
difference being the number of valence ē
occupying the common MO system.
• The group orbital configuration developed
for CH3 applies any other MH3, where M = a
main group element.

• Deposit 6, 7 or 8 ē depending on M. 3 H
atoms contribute 3 ē and:
• B contributes 3
• C contributes 4
• N contributes 5
• Even ! systems (M = B or N):
• 6 ! of BH3 occupy MO’s A-C of either planar
or pyramidal form.
• 8 ! of NH3 occupy MO’s A-D of either planar or pyramidal form. D’/D are occupied and influence structure.
Substantial stabilization of D’ in pyramidal form.
• Follow Rule 6: Total energy is the sum of the molecular orbital energies of individual valence ē.