What are the postulates of valence bond theory?

CBSE Class 11
1

what are the postulates of valence bond theory?

2
  1. The atoms which unite to form a molecule do not lose their identity even after the formation of the molecule.
  2. The covalent bond is formed due to the interaction of only the valence electrons. The inner electrons do not participate in the bond formation.
  3. The formation of a covalent bond is due to overlap of atomic orbitals (abbreviated to AO’s ). If the two atoms, each having on unpaired electron, come together, the AO’s accommodating these unpaired electrons overlap (i.e, electron waves interact) and the spins of the two electrons get mutually neutralized, resulting in the formation of covalent bond which is localized between the two atoms. If the electrons present in the AO’s have parallel spins, no bond formation will occur, and no molecule will be formed.
  4. If the AO’s possess more than one unpaired electrons, more than one bond can be formed.
  5. Electrons already paired in the valence shell cannot take part in the bond formation. They can only take part in the bond formation if they can be unpaired with the use of lot energy.
  6. The stability of bond is accounted by the fact that the formation of bond is accompanied by release of energy.
  7. The strength of the covalent bond is related to the extent of overlapping of the atomic orbitals. The greater the overlapping, the stronger is the bond formed between two atoms.