FIRST YEAR

Module-III 

Need for approximation methods in multi-electron systems. Born-Oppenheimer

approximation. Variation theorem (elementary idea only).

Quantum mechanical concept of bonding – (mixing of wave functions of different atoms).

Valence bond theory of H2 molecule (derivation not required). Molecular orbital theory of H2+

ion H2 molecule - linear combination of atomic orbitals (LCAO) and coefficients in the linear

combination (derivation not required). Potential energy diagram of H2 molecule formation –

equilibrium geometry. Bonding and antibonding molecular orbitals, bond order. MO diagrams

of homonuclear and heteronuclear diatomic molecules – He2, Li2, Be2, B2, C2, N2, O2, F2, CO

and NO. Comparison of VB and MO theories.