28.3.1—Terms: degenerate and non-degenerate d orbitals

Degenerate orbitals have the same energy. In an isolated transition-metal ion the five d orbitals are degenerate; surrounding ligands create an electric field that splits them into non-degenerate energy levels.

The splitting pattern depends on geometry: octahedral ligands approach along axes, while tetrahedral approaches lie between axes. The energy gap affects colour and magnetic behaviour.

In an octahedral complex, dxy, dxz and dyz form one set and dz², dx²−y² another, with different energies.

Degenerate does not mean identical shapes, and ligand-field splitting is not caused by changing the principal quantum number.