# How it was observed, that elements in columns 6 and 11 assume abnormal electron configuration?

Reading this question about why do elements in columns 6 and 11 assume abnormal electron configurations I wondering, how this was observed.

• My guess is that it was observed in spectra of the of transition metal ions. – Wildcat Oct 31 '15 at 10:16

How it was observed, that elements in columns 6 and 11 assume abnormal electron configuration?

I assume you to mean

How it was first observed, that elements in columns 6 and 11 assume abnormal electron configurations?

Chemists (starting with alchemists) have were doing stoichiometric reactions for a very long time.

The point is that if there was only a single "normal electron configuration" for chromium, then there would only be one chromium chloride. However chemists have synthesized three.

• Chromium(II) chloride, also known as chromous chloride.
• Chromium(III) chloride, also known as chromic chloride or chromium trichloride
• Chromium(IV) chloride

Thus the fact that there must be "abnormal" electron configurations was first discovered by stoichiometry, not spectroscopy.

Other columns in the periodic chart do have elements with multiple electron configurations. So such an "abnormality" isn't unique.

• I don't see how 'abnomal configurations' follow from different chlorides. Iron has two chlorides ($\ce{FeCl2}$ and $\ce{FeCl3}$) but it does not have the same 'abnormal configurations'.' – bon Oct 31 '15 at 23:28