Chemical Bonding and Molecular Structure Part - 15 | Class 11th

Ø  Energies of various Molecular Orbitals:

The various M.Os are filled in the increasing order of their energies (Aufbau Principle). The increasing order of energy is:

σ1s < σ*1s < σ2s < σ*2s < (π2p_x = π2p_y) <σ2pz < (π*2p_x= π*2p_y) < σ*2p_z

For O₂, F₂ and Ne₂, the order is:

σ1s < σ*1s < σ2s < σ*2s < σ2p_z < (π2p_x = π2p_y) < (π*2p_x= π*2p_y) < σ*2p_z

                  Molecular Orbital Diagram for N₂                        Molecular Orbital Diagram for O₂

Ø  Bond Order: It is defined as the half of the difference between the number of bonding electrons (N_b) and the number of anti-bonding electrons (N_a).

       i.e. Bond order (B.O) = ½ [N_b –N_a]

A molecule is stable only if the bond order is positive. (i.e. N_b >N_a). a negative bond order (i.e. N_b < N_a or N_b = N_a) means an unstable molecule.

For a single bond, B.O = 1, for a double bond B.O = 2 and so on. Bond order gives an approximate measure of the bond length. In general, as the bond order increases, bond length decreases and bond enthalpy increases.