Question

Briefly explain the distribution of ‘d’ electrons in t_2g and e_g orbitals in octahedral complexes in a weak ligand field.

Answer 1

Under the influence of weak ligands the energy difference, Δ_o between t_2g and e_g sets is relatively small and hence all the five ‘d’ orbitals may be supposed to be degenerate.

The distribution of electrons in t_2g and e_g sets occurs according to Hund’s rule.

When the ligands are weak, the first three electrons numbered as 1,2,3 go to t_2g set those numbered 4, 5 go to e_g set, those numbered 6, 7, 8 go to t_2g set and the remaining two electrons numbered 9 and 10 will occupy e_g set. i.e., 

In complexes of weak ligands, Δ_o is less than P(P is called pairing energy which is the energy required to pair two electrons in the same orbital). Δ_o is the octahedral crystal field splitting energy, tends to force as many electrons into t_2g set while P tends to prevent the electrons to pair up in the t_2g level.