Question

How does crystal field theory explain the colour and magnetism of complexes?

Answer 1

The Crystal field theory considers ionic bond arising purely from electrostatic interaction between metal atom (positively charged) and ligands ( negatively charged). The transition metal ion is considered to be positive charge equal to its oxidation state. The central metal atom is surrounded by negatively charged ligands. The ligands were considered as point charges.

The energy of d orbitals remains degenerate (same energy) in the free transition metal ion . When ligand approach the metal ion, there arises attraction between the nucleus of the metal ion and the ligands. In the same time, there will be repulsion between the electrons present in the metal atom and the negative ends of the ligands. Due to this repulsion, the energy of the metal ion will no longer be degenerate. Consequently, the degeneracy is split.