Question

Account for the following:

Salts of Cupric (Cu²⁺) ion are coloured whereas salts of the Cuprous (Cu⁺) ion are colourless.

Answer 1

Salts of Cupric (Cu²⁺) ions are coloured, whereas salts of cuprous (Cu⁺) ions are colourless. This is due to the fact that the cupric ion has an incomplete d-orbital, whereas the cuprous ion has a complete one. Cuprous ions contain exactly half-filled d-orbitals, making d-d transitions impossible between them.