Normally the 3d orbitals of transition element ions all have the same energy. But when ligands come along and bond to the ions, some of the orbitals are given more energy than others. This splits the 3d orbitals into two different energy levels.
Electrons tend to occupy the lower orbitals (the ground state). To jump to higher energy levels (excited states) they need energy equal to the energy gap, ΔE. They get this energy from visible light.
The energy absorbed when electrons jump can be worked out using this formula:
ΔE=hv where v = frequency of light absorbed (hertz/Hz) and h= Planck's constant (6.63x10^-34)
The amount of energy needed to make electrons jump depends upon the central metal ion and it's oxidation state, the ligands and the coordination number, as these affect the size of the energy gap.
The colours of compounds are the compliment of those that are absorbed. When visible light hits a transition metal ion, some frequencies are absorbed when electrons jump to higher orbitals. The frequencies absorbed depend on…