Electron Configuration and Unfilled Orbitals

[Jessica Chen 1F]

Given that an Au atom (gold) has an electron configuration of [Xe] 5d9, 6s2, does that mean the 6s subshell would start to be filled before the 5d subshell was completely filled? Is that possible and why?

[Brian Chhoy 4I]

Yes the 6s orbital would begin to fill before the 5d orbital because it has a lower energy than that of the 5d orbital. Keep in mind that lower energy orbitals always fill up before higher orbitals. If you need more clarification: https://www.chemguide.co.uk/atoms/prope ... oblem.html

[MadisonB]

Another explanation for this is that the most balanced state might not be the one that goes in order with the set rules. Lower energy fills before higher energy, and the most balanced state is strived for as well.