Question

Why is the Sc³⁺ ion colourless?

Answer 1

1. The Sc³⁺ ion has the electronic configuration 3d⁰; it has no electrons in its d-orbitals.
2. Colour in transition metal ions arises from d-d transitions, where electrons jump between d-orbitals, absorbing visible light.
3. Since Sc³⁺ has empty d-orbitals, there are no electrons to promote, so no d-d transitions occur.
4. As a result, Sc³⁺ does not absorb visible light and appears colourless.
5. Similarly, ions with completely filled d-orbitals are also colourless because no vacant d-orbitals are available for electron promotion.