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

  • 1
    $\begingroup$ My guess is that it was observed in spectra of the of transition metal ions. $\endgroup$
    – 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.

If your question means

How are the bonding energies measured for the elements in columns 6 and 11 in various electron configurations?

Then ESCA would be one technique.

  • 4
    $\begingroup$ 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'.' $\endgroup$
    – bon
    Oct 31 '15 at 23:28
  • $\begingroup$ It isn't an abnormality of only columns 6 and 11, the fact that different stoichiometries exists shows that an element can have more than one electron configuration. If no "abnormalities" existed, then the Lewis dot would work for everything. $\endgroup$
    – MaxW
    Oct 31 '15 at 23:48
  • 1
    $\begingroup$ Could you please explain what these "different electronic configurations" are, and how they lead to "different stoichiometries" observed in the chromium chlorides? $\endgroup$
    – orthocresol
    Nov 1 '15 at 0:11
  • $\begingroup$ Max, I hope to get more answers. Thank you for yours. With ESCA I'm not fully satisfied because this is a technique introduced long after the knowledge about the aperiodical filling of the electron shells. $\endgroup$ Nov 1 '15 at 6:34

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