What is the ground-state electron configuration of a neutral Copper (Cu) atom (Z = 29)?
[Ar] 4s² 3d⁹
[Ar] 3d¹⁰ 4s¹
[Ar] 3d⁹ 4s²
[Ar] 4s¹ 4p⁶
📝 Detailed explanation
Copper is an exception to the Aufbau principle. To achieve the stability of a completely filled d-subshell, an electron from the 4s orbital is promoted to the 3d orbital, resulting in the [Ar] 3d¹⁰ 4s¹ configuration.
