## Molecular Orbital Theory

Experimentally, O_{2} is found to have two unpaired spins – VBT can not explain a simple molecule like O_{2} !

### Linear Combination of Atomic Orbitals

Assumptions:

1) Molecular Orbitals look like atomic orbitals, especially near the nucleus

2) Molecular Orbitals are constructed by interference patterns of atomic orbitals

3) The total number of molecular orbitals = the total number of atomic orbitals

4) Molecular wavefunctions are products of the molecular orbital functions

### Overlap of atomic orbitals

constructive interference gives bonding orbital, no nodes

destructive interference gives antibonding orbital one node, perpendicular to the internuclear axis

molecular orbitals are labeled by nodal properties:

0 nodes parallel to the internuclear axis: σ

1 node parallel to the internuclear axis: π

2 nodes parallel to the internuclear axis: δ

0 nodes perpendicular to the internuclear axis: bonding

1 node perpendicular to the internuclear axis: antibonding