Question

Why is the Ti⁴⁺ ion colourless?

Answer 1

1. Ti⁴⁺ has an electronic configuration of 3d⁰ (no electrons in the d-orbitals).
2. Colour in transition metal ions is due to d-d electronic transitions, where electrons jump between split d-orbitals by absorbing visible light.
3. Since Ti⁴⁺ has no d-electrons, no d-d transitions can occur to absorb visible light.
4. As no visible light is absorbed, the ion transmits all wavelengths and appears colourless.

Thus, Ti⁴⁺ with completely empty d-orbitals is colourless.