Question

Give a reason for the following:

Cu⁺² salts are paramagnetic, while Cu⁺ salts are diamagnetic.

Cu(II) is paramagnetic but Cu(I) is diamagnetic. Give reason (At. no. of Cu = 29).

Answer 1

The electronic configurations of Cu²⁺ and Cu⁺ are [Ar] 3d⁹ 4s⁰ and [Ar] 3d¹⁰ 4s⁰, respectively. Cu²⁺ has one unpaired electron, making it paramagnetic, whereas Cu⁺ has no unpaired electrons, making it diamagnetic.

Answer 2

1. Atomic number of Cu = 29, electronic configuration is [Ar] 3d¹⁰ 4s¹.
2. Cu(I) ion has oxidation state +1, so it loses one 4s electron. Its configuration becomes 3d¹⁰ (fully filled d-orbitals).
3. Since all electrons in Cu(I) are paired in the 3d¹⁰ configuration, the Cu(I) ion is diamagnetic (no unpaired electrons).
4. Cu(II) ion has oxidation state +2, so it loses one 4s electron and one 3d electron. Configuration becomes 3d⁹.
5. With one unpaired electron in the 3d⁹ configuration, the Cu(II) ion is paramagnetic (has unpaired electrons).

Therefore, Cu(II) ion is paramagnetic due to the presence of one unpaired electron, while Cu(I) is diamagnetic because all electrons are paired.