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I am currently looking through a revision sheet, however it has caught me on a question 'Explain why a potassium atom can act as a reducing agent yet a potassium ion cannot'.

I have done brief searches, however none have given the answer I'm looking for. So please, why is this?

Also, if the explanation doesn't already include it; is this only the case with Potassium, and how is this to be determined? (How is it known whether it is referring to a cation or anion?)

Thanks,

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The ability of K to act as a reducing agent is mainly due to its electronic structure. $K = [Ar] 4s^1$ . In this case, such atom tends to donate his $4s^1$ electron (acting as a reducing agent). This is due to the gain in energy that produces to have its octet complete and stay in the cationic form $K^{+}=[Ar]$ which is quite more stable that the pure element one.

This is common to all elements in the first column of the periodic table, just because all of them have a quite similar electronic structure, just with more electrons on their inner orbitals.

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  • $\begingroup$ Ah, that explains it. Also, I'm quite a beginner at Chemistry, but is it completely impossible for K to be in an anionic form? $\endgroup$ – Revisor Sep 11 '14 at 9:56
  • $\begingroup$ It is not completely impossible but it is quite improvable and needs very strict and radical conditions. Such circunstances are far from the ones in nature. $\endgroup$ – Mael Sep 11 '14 at 9:59

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