2 Exceptions to the Electron Configuration

[Victoria Luu - 1C]

Why does Cr and Cu have the exception applied to them?

[Andie Jian 1D]

Their p-orbitals of Cr and Cu only need one more electron to reach the much more stable state of all the p orbitals having 1 electron (5 in total), or 2 electrons in each orbital (10 in total). Therefore, in those cases, an electron will jump down from the higher energy s orbital to complete the orbitals in either of those ways.

[Matthew Mar 1J]

I think it's actually the d orbital that gets the electron, not the p orbital, since Cr: [Ar] 3d5 4s1
where putting the electron into the d orbital is actually more stable than putting it in to fill the s orbital like we'd expect ([Ar] 3d4 4s2).
The same goes with copper (Cu: [Ar] 3d10 4s1 rather than [Ar] 3d9 4s2).

[yea-lyn pak_1G]

The d orbital gets an extra electron, while the s orbital loses one, and this is so because it just makes the atom more stable.