Question

What type of transitions impart colour to the transition metal ions?

Answer 1

1. The colour of transition metal ions is mainly due to d-d transitions between the split d-orbitals in their compounds or hydrated ions.
2. In the presence of ligands, the five degenerate d-orbitals split into two groups: (t_2g) and (e_g).
3. When visible light falls on these ions, electrons in lower-energy d-orbitals get excited to higher-energy d-orbitals (d-d transitions), absorbing specific wavelengths.
4. The absorbed wavelength corresponds to the energy difference between the split d-orbitals, and the transmitted light shows the complementary colour.
5. Transition metal ions with completely filled or empty d-orbitals do not show colour, as d-d transitions are not possible in these cases.