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Halogens like $\ce{Cl,Br,I}$ generally show oxidation states between $-1$ and $+7$. However, is it possible that they can show an oxidation state beyond $-1$ (e.g. $-3$)?

I was thinking of some compound in which chlorine is bonded with a less electronegative element and forms more than one bond with such element(s).

Is it theoretically possible?

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    $\begingroup$ Cl, Br & I typically have oxidation state of -1, expect with compounds containing more electronegative atom than these (N, O & F). $\endgroup$
    – Khan
    Sep 16, 2016 at 10:51
  • $\begingroup$ 'Typically' they show -1, but can they show beyond that? That is my question $\endgroup$
    – Amritansh Singhal
    Sep 16, 2016 at 10:54
  • $\begingroup$ would you like to tell, what is meant by beyond? be precise, just write it instead of letting people to guess $\endgroup$
    – Khan
    Sep 16, 2016 at 10:57
  • $\begingroup$ I'm sorry if you didn't understand what I meant by beyond. I meant can they show something like -3,-5 or -7 $\endgroup$
    – Amritansh Singhal
    Sep 16, 2016 at 10:59
  • $\begingroup$ I don't think so,,, $\endgroup$
    – Khan
    Sep 16, 2016 at 11:02

1 Answer 1

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Yes, they can show oxidation states lower than -1. For example in hyperlithiated compounds, like $\ce{Li3Cl}$, the chlorine would formally have an oxidation state of -3.

However, a word of caution, oxidation states are a tricky thing. They are determined by adopting the hypothetical view that the compound you are looking at consists only of single-atomic ions, e.g. in the case of $\ce{Li3Cl}$ of 3 $\ce{Li+}$ and $\ce{Cl^{3-}}$. The hypothetical charges of these "ions" are then your oxidation states. Clearly, this view has nothing to do with the real bonding situation in the compound and oxidation numbers correlate very poorly with the real electron distribution. It is simply a useful little device for keeping track of redox reactions. So, the -3 oxidation state of chlorine in $\ce{Li3Cl}$ does not mean that chlorine has a 10-electron valence shell. The real bonding situation will be somewhat more complicated.

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    $\begingroup$ I wager it's more like Li has 1/3 there. $\endgroup$
    – Mithoron
    Feb 27, 2020 at 2:00
  • $\begingroup$ I agree. We may have structures in which the lithium does not transfer its electrons fully to the halogen. Moreover, the proposed compounds seem to be only computational results, not experimentally realized. $\endgroup$
    – Oscar Lanzi
    Apr 14, 2022 at 1:56

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