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Three of the bond energies of $\ce{O2,\ O2^{-},\ O2^{2-},\ O2^+}$ have the values approximately $200, 490$ and $625\ \mathrm{kJ\ mol^{-1}}$. The value for one of the species is uncertain and, therefore, not given. Write the bond energies of each compound.

My Attempt

I know that higher the bond order of a compound, higher its bond energy. So the bond order of $\ce{O2,\ O2^{-},\ O2^{2-},\ O2^+}$ are $2,\ 1.5,\ 1,\ 2.5$ respectively.

However I am not sure which one's bond energy is not known. I am thinking that it might be $\ce{O2^{+}}$ since it is unstable, however it is just a total guess.

Is there some way to logically deduce which one it is, or is this one of these things that we are just suppose to know?

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    $\begingroup$ That would be quite strange; why the one with the strongest bond of all would be unstable? Indeed, there are compounds with $\ce{O2+}$, like $\ce{O2+[PtF6]-}$. Also, there surely are compounds with $\ce{O2-}$ and $\ce{O2^2-}$, and I feel some $\ce{O2}$ around as I write this. They are all stable and pretty well known. $\endgroup$ – Ivan Neretin Jun 22 '16 at 21:38
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    $\begingroup$ a) small dianions tend to eject an electron in vacuum b) bond energy is well defined (and easily measured) for free molecule/ion in vacuum $\endgroup$ – permeakra Jun 22 '16 at 21:54
  • $\begingroup$ There's no reason to speculate on reasons why they didn't put that specific one. It's just homework and you're supposed to find correlation between bond order and energy. $\endgroup$ – Mithoron Jun 22 '16 at 22:48

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