During my chemistry lessons and self studies, I have come upon many instances where I observed that during calculations of spin only magnetic moment of transition elements only the d orbital electrons are to be counted. To gain a deeper insight into these instances of "calculations", I would like to expand my question as follow around the same point (i.e. spin only magnetic moment):

  1. Is spin only magnetic moment calculated only for ions? If not, what would be it for $\ce{Cr^0}$: I mean would the $\mathrm{4s^1}$ electron be taken into consideration? If yes, then why?
  2. Are there some other instances apart from $\ce{Cr^0}$ which supports your views?

1 Answer 1

  • Any unpaired electron is taken into consideration while trying to quantify spin only magnetic moment.

  • valence electrons can be unpaired (not always), and inner shell electrons are paired so the latter don’t contribute (since they are fully filled). That’s why usually only the outer shell electrons are considered.

  • and no it’s not calculated for ions only. You can use it for individual atoms too!

  • In your example $\ce{Cr^0}$, you can certainly consider that one unpaired electron in the s orbital,

    • so giving a total of 6 unpaired electron it’s magnetic moment would be $\sqrt{48}$

By using the spin-only formula $M =\sqrt{n(n+2)}$ where $n$ is the number of unpaired electron and $M$ has the units of magnetic moment.

Caution this formula is applicable for d block elements only.

  • Another example would be niobium, molybdenum it also has one unpaired electron in the 5s orbital and certainly we consider that electron while quantifying spin only magnetic moment.

Furthermore, the spin only magnetic moment of molybdenum is very close to that of chromium.

I am telling very close but not same because theoretically calculated magnetic moment don’t usually coincide with experimentally calculated they differ ever so slightly

Sources -

  • NCERT Chemistry for class 12 (pg no 221)

  • Descriptive Inorganic Chemistry by James E. House and Kathleen E. House by Elsevier. 2nd edition (pg no 329)

  • Shriver and Atkins Inorganic Chemistry, 5th edition (pg no 478)

  • 2
    $\begingroup$ :The answer is consistent with many questions which I saw over the net, but I want some more 'trusted' sources and references. $\endgroup$
    – glucose
    Commented Apr 17, 2019 at 11:17
  • 3
    $\begingroup$ NCERT is oversimplified in several parts, don't trust it blindly. You'll end up regretting it later. $\endgroup$ Commented Apr 17, 2019 at 13:35
  • 5
    $\begingroup$ I have said previously many times, i am still saying now. don't ever trust NCERT textbook. They are full of notorious errors. I am saying this from my experience as it was my high school textbook and I regret studying from it. $\endgroup$ Commented Apr 17, 2019 at 14:18
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    $\begingroup$ @Chemist Trusted sources include published articles, papers, books (from a good publisher!). Nothing opinion based here. $\endgroup$ Commented Apr 17, 2019 at 14:25
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    $\begingroup$ @Chemist : No. I do not feel the answer to be incorrect but I find it somewhat incomplete without reliable references and sources. $\endgroup$
    – glucose
    Commented Apr 17, 2019 at 14:42

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