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 '16 at 10:51
  • $\begingroup$ 'Typically' they show -1, but can they show beyond that? That is my question $\endgroup$ – Amritansh Singhal Sep 16 '16 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 '16 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 '16 at 10:59
  • $\begingroup$ I don't think so,,, $\endgroup$ – Khan Sep 16 '16 at 11:02

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 at 2:00

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