Why most of the compounds of transition elements are coloured ?Explain in detail .?
Transition metal ions are coloured because their d orbitals become split in terms of energy when the ion gains ligand groups. I think two are higher level energy orbitals and three are lower energy orbitals. When the ion gains energy (as it might do from light or heat or even sound), electrons from the lower energy orbitals jump to the higher energy orbitals. When they return to lower energies, the energy is given off as electromagnetic wavelengths. This doesn’t have to happen solely with d orbitals but only with d orbitals can you get a small enough gap between the orbitals to produce a visible spectrum.