Question

Why does copper show abnormal electronic configuration?

Answer 1

Copper has atomic number 29. 

Its expected and actual electronic configurations are:

₂₉Cu (Expected): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s²

(Actual): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

Explanation:

i. The energy difference between the 3d and 4s orbitals is very low. 

ii. The d-orbital being degenerate, acquires more stability when it is half-filled (3d⁵) or completely filled (3d¹⁰). 

iii. Due to the inter-electronic repulsion, one electron from the 4s orbital is transferred to the 3d orbital in Cu so that Cu has completely filled 3d¹⁰ orbital, thus acquiring more stability.