Valence Bond theory (VBT)

VBT

Definition :

It explaind that " half filled atomic orbital combine to form new bigger orbitals".

Given by heitler and London(1927)
"Two orbital form covalent Bond by overlapping"
Most important conditions are:
  • The two orbitals which overlap should be Valence orbital
  • Are half filled Retain it's properties
  • For proper alignment, Half filled orbitals should be close to on another.
Assumption:
  1. covalent Bond formation in hydrogen molecule:
  2. It has one partially filled 1st atomic orbital.
  3. By linear combination of atomic orbital wave function,the wave function of molecules are obtained.
  4. This actually obtain by using resonance.
  5. Bond energy is formed by paring of electrons.
  6. In between two nuclei ,electron pair is present.
  7. The orbitals which overlap must have symmetry and energy.the more storger the overlap the more stronger will be Bond between orbitals.
  8. Heitler and London explain that the electrons should be same and their wave function should express their similarity.
  9. The Pauli's exculsion principle should explain in electron pairing and their spin qauntum value number for both electrons should be different.

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