Copper exception

[705170809]

So I understand that the 4s^2 has a higher energy level than 3d^10 which is why it comes after 3d^10 say in element Bromine, however for Copper's electron configuration its exception makes it 3d^10 and 4s^1, but the 4s^1 is still after 3d^10, even though 4s^1 has a lower energy level than 3d^10, why is this?

[Dimitri Speron 1C]

This is because it is more stable for the entire 3d subshell to be filled than to have the 4s subshell with 2 and the 3d with 9. This is pretty much just how the math happens to work out and what is experimentally observed. A parallel to this is the electronic structure of Chromium, from the same subshell (3d) which has 3d5,4s1 instead of 3d4,4s2. Having this electron configuration is just more stable.

[AngelaZ 1J]

An electron configuration with a completely full or half full 3d subshell is more stable.

[Chem_Mod]

Put the above two together for the full answer.

[Manas Jinka]

An entire 3d subshell that is full is stable instead of having 2 electrons in the 4s and 9 electrons in the 3d orbital