Textbook 2A.5 part a

[Ariana 1D]

For the ground state electron configuration for Cu+, would the answer be [Ar] 4s1 3d9 or [Ar] 3d10? I'm just not sure that after we pull that electron from the 4s orbital, if the lone electron is going to gravitate to the 3d orbital since it's a higher energy orbital or remain in the 4s orbital.

[Star_Garcia_3B]

The correct ground state electron configuration for Cu+ is [Ar] 3d¹⁰. The removal of an electron occurs from the outermost shell first, and in this case, it's from the 4s orbital. The electron configuration [Ar] 3d¹⁰ represents a stable, fully-filled 3d subshell.