Aufbau principle does not give the correct arrangement of filling up of atomic orbitals in

Options

(a) Cu and Zn
(b) Co and Zn
(c) Mn and Cr
(d) Cu and Cr

Correct Answer:

Cu and Cr

Explanation:

The electronic configuration of chromimum and copper are different than that we expected. According to Aufbau’s principle the electronic configurations of copper and chromium are : Cr = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴. Cu = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁹. However, the actual configurations are, Cr = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵. Cu = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰. this is due to the fact that half filled and completely filled electronic configurations have lower energy. Thus to become more stable one of the 4s electrons goes into the nearby 3d-orbitals so that 3d-orbitals get half-filled in Cr and completely filled in Cu.