Question

Zn\(^{2+}\) salts are white while Cu\(^{2+}\) salts are blue in colour. Why?

Hint:

Transition metal colour is due to d-d transitions; fully filled orbitals prevent absorption of visible light.

Answer 1

Step 1: Electronic Configurations: - Zn\(^{2+}\) = \(3d^{10}\) (fully filled, no d-d transitions)
- Cu\(^{2+}\) = \(3d^9\) (one unpaired electron, d-d transitions possible) 

Step 2: Reason for Colour: - Zn\(^{2+}\) has no unpaired d-electrons → No d-d transitions → Appears white.
- Cu\(^{2+}\) has d-d transitions absorbing red-orange light, reflecting blue.