Question

Give reasons for the following:

Most of the compounds formed by transition elements are coloured.

Answer 1

1. Transition metal atoms/ions have one or more unpaired electrons in their (n − 1)d orbitals.
2. When visible light falls on these compounds, electrons are excited from lower energy d-orbitals to higher energy d-orbitals (d-d transitions).
3. The d-orbitals split into two sets (t_2g and e_g) due to the influence of surrounding ligands (crystal field splitting).
4. The energy difference between these split orbitals corresponds to visible light energy, so specific wavelengths are absorbed.
5. The absorbed light’s complementary color is transmitted or reflected, giving the compound its characteristic color.
6. Compounds with completely filled or empty d-orbitals are colorless due to the lack of d-d transitions.