What is the actual configuration of copper (Z = 29)? Explain about its stability.

Explanation

Copper (Z = 29)
Expected configuration : `1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(9)4s^(2)`
Actual configuration : `1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(1)`
The reason is that fully filled orbitals have been found to have extra stability.
Copper has the electronic configuration `[Ar]3d^(10)4s^(1)` and not `[Ar]3d^(9)4s^(2)` due the symmetrical distribution and exchange energies of d electrons.
Symmetry leads to stability. The full filled configuration have symmetrical distribution of electrons and hence they are more stable than unsymmetrical configuration.