The two exceptions

[605720459 1I]

Can someone elaborate on why Cr and Cu are exceptions in the periodic electron configuration trend? Why is Cr 3d54s1 and Cu is 3d104s1, rather than having a full s orbital?

[Mikayla 2G]

There is stability in the symmetry of having all the d orbitals half full or fully full, and this stability leads to a lower energy when the d orbital is half full or fully full than the s-orbital being full, so electrons move to the d orbital because lower energy is preferable.

[Jessy Ji 2J]

Hi,

I think what the professor said in class was that it is because it is more stable for Cr to have an electron distribution with one unpaired electron in each of the d states. And the same thing with Cu.

[105743571]

It is more stable to fill the 3d orbital. When it does so, the 3d orbital will drop in energy level (below 4s1). This is why we write Cu as [Ar] 3d10 4s1 rather than [Ar] 4s1 3d10.

[Sarah Lesmeister 2F]

Half full d^5 and full d^10 subshells have lower energy, so it's more stable to fill those first.

[Aashna Bhandari 1L]

Hi! I believe these exceptions are due to the fact that it is more stable for the Cr and Cu atoms to exist with either a half or a full d orbital. I believe this is because that they are more stable when they are symmetric.

[arielle_cunanan3K]

Does that mean the elements in those two groups under Cr and Cu also follow this exception pattern for electron configuration?