Textbook Question 5A

[Kailyn_Kaiser_2G]

The question is asking to write the ground state electron configuration for Cu+. The answer is [Ar] 3d10. I know 4s2 fills up first, but 3d10 is written first. Why is 3d10 the answer if 4s2 is full? I know adding the electron would make 3d10 a full shell, so does the 4s2 shell just not fill up?

[aditipatel2K]

Hi! The electron configuration for Cu is [Ar]4s^1 3d^10 rather than [Ar]4s^2 3d^9 because [Ar]4s^1 3d^10 is more stable since the whole d orbital is full. Thus for Cu+ it is [Ar]3d^10 because you need to remove from 4s before 3d. I hope this helps!