Question

1s² 2s² 2p⁶3s²3p⁶3d¹⁰4s¹ is the electronic configuration of Cu (Z = 29). Which rule is violated while writing this configuration? What might be the reason for writing this configuration?

Answer 1

1. The rule violated is Aufbau principle. The elements which have half filled or completely filled orbitals have greater stability. So copper can get stability by transferring one electron from 4s to 3d (their energies are close to each other).

2. So the electronic configuration of copper is 1s² 2s² 2p⁶3s²3p⁶3d¹⁰4s¹ not 1s² 2s² 2p 3s²3p⁶3d⁹ 4s²