# Experimental evidence for anomalous electronic configurations of chromium and copper

Chromium ($$\mathrm{3d^5\,4s^1}$$) and copper ($$\mathrm{3d^{10}\,4s^1}$$) are fairly well-known exceptions to the aufbau principle, often attributed to the stability of the half- or fully-filled 3d subshell (as discussed in this prior question).

However, what experimental evidence is there for this? Is there a spectroscopic method (for example) which can be used to probe electronic configurations?

• @ToddMinehardt, There is an article in the Journal of Chemical Education, The Full Story of the Electron Configurations of the Transition Elements, by W. H. Eugen Schwarz. He has theoretical explanations but no experimental discussion. I don't fully understand article either. It is based on "d-orbital" collapse! Nov 26, 2021 at 1:38
• Atomic spectroscopy (both emission and absorption) would give you this answer. Any method that involves spin-orbit coupling as well. I didn't pot this as a full answer because I am not sure Dec 3, 2021 at 0:12

I used XPS for my previous research with elemental analysis (i.e. ratio of elements and which oxidation state they are in). I am not an expert in this device but comparing metallic copper's 3d shell binding energy with a different element (let's say Zn) would show that their B.E.'s are pretty close. To the best of my knowledge, lower atomic numbered elements in the 3$$^{rd}$$ row would not show any 3d peak due to very low B.E. (this is the outermost shell).