Account for the following: Cu+2 salts are coloured, while Zn+2 salts are white. - Chemistry

Account for the following:

Cu⁺² salts are coloured, while Zn⁺² salts are white.

Zn²⁺ salts are white while Cu²⁺ salts are coloured. Why ?

Solution 1

Zn²⁺ salts have a completely filled set of d-orbitals (3d¹⁰), while Cu²⁺ has an incompletely filled set of d-orbitals (3d⁹), and therefore, d–d transition is possible in Cu²⁺, leading to blue colour.

Solution 2

Element/Ion	Electronic Configuration
Zn	3d¹⁰ 4s²
Zn²⁺	3d¹⁰
Cu	3d¹⁰ 4s¹
Cu²⁺	3d⁹

The colours of salts of transition metals are due to the d-d transition that depend on the presence of incompletely filled d-orbitals. Zn²⁺ has completely filled d-orbitals (3d¹⁰), while Cu²⁺ has incompletely filled d-orbitals (3d⁹); therefore, d-d transition is possible in Cu²⁺, which imparts colour to copper(II) salts.