Which is the correct ground-state electron configuration for copper?

Which is the correct ground-state electron configuration for copper?

• A. [Ar] 4s2 3d9
• B. [Ar] 4s2 3d5
• C. [Ar] 4s2 3d10
• D. [Ar] 4s1 3d10

Answer: (D)

The important idea is that transition metals favor configurations that maximize stability of the d subshell. For copper, the most stable arrangement is to have a full 3d subshell (10 electrons) with the remaining electron occupying the 4s orbital. That gives a ground-state configuration of [Ar] 3d10 4s1, which is often written as [Ar] 4s1 3d10. This tiny shift of one electron from 4s into 3d lowers the overall energy because a full d10 subshell provides extra stabilization through electron–electron interactions and exchange energy. The alternative picture, with 4s2 3d9, leaves the d subshell not fully filled and misses out on that extra stabilization, making it higher in energy overall. The key takeaway is that the most stable copper ground state has a filled 3d subshell and only one electron in 4s, hence the configuration with 3d10 and 4s1. Writing it as [Ar] 4s1 3d10 emphasizes the same occupancy, since the order of the subshells in the notation doesn’t change the actual electrons present.

The important idea is that transition metals favor configurations that maximize stability of the d subshell. For copper, the most stable arrangement is to have a full 3d subshell (10 electrons) with the remaining electron occupying the 4s orbital. That gives a ground-state configuration of [Ar] 3d10 4s1, which is often written as [Ar] 4s1 3d10. This tiny shift of one electron from 4s into 3d lowers the overall energy because a full d10 subshell provides extra stabilization through electron–electron interactions and exchange energy.

The alternative picture, with 4s2 3d9, leaves the d subshell not fully filled and misses out on that extra stabilization, making it higher in energy overall. The key takeaway is that the most stable copper ground state has a filled 3d subshell and only one electron in 4s, hence the configuration with 3d10 and 4s1. Writing it as [Ar] 4s1 3d10 emphasizes the same occupancy, since the order of the subshells in the notation doesn’t change the actual electrons present.