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On this table I realized that elemental potassium could adopt oxidation states of -1, 0, and +1.

http://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements

Does this mean that elemental potassium can function as both an oxidizer and a reducer? I understand that oxidizers are reduced (gain electrons), and that reducers are oxidized (lose electrons). How can potassium anion be formed? The potassium anion must be extremely unstable due to potassium's extremely low electronegativity, correct?

Also in what compound does potassium actually have a negative oxidation state?

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    $\begingroup$ nature.com/nature/journal/v317/n6034/abs/317242a0.html This abstract seems to suggest the ion is made in a solution of liquid crown ether. I'm assuming the affinity of the crown ether for K+ is so strong that a potassium atom can take an electron from another potassium atom. $\endgroup$ – Brinn Belyea Aug 12 '14 at 3:40
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    $\begingroup$ Which table are you referring to? @brinnb This might be a similar approach like solvated electrons from sodium or potassium $\ce{Na/K (s) + (n + m) NH3 (l) ->[][-78~^\circ\mathrm{C}] [Na(NH3)_{n}]+/[K(NH3)_{n}]+ + [e- . (NH3)_{m}]}$. $\endgroup$ – Martin - マーチン Aug 12 '14 at 4:33
  • $\begingroup$ Martin, thank you, and I have included the link to the table on the OP. $\endgroup$ – Dissenter Aug 12 '14 at 4:34
  • $\begingroup$ Take a look here $\endgroup$ – Freddy Aug 12 '14 at 5:09
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    $\begingroup$ @Dissenter Ya this book help to prepare for JEE but just for class 11 when you don't know to much stuff. I don't think anyone can realize about it unless he/she have read it in some books or using stack exchange ;) $\endgroup$ – Freddy Aug 12 '14 at 5:22
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Compounds having potassium anions are referred to as potassides and are rare, usually involving K- within a cyrpt such as:

enter image description here

Crystalline Salts of Na- and K- (Alkalides) that Are Stable at Room Temperature J. Am. Chem. Soc. vol. 121, pages 10666-10667 describes preparation of K+(aza222)K- , where "aza222" is the compound in the above figure, but with the 6 H's replaced with methyl groups. The compound is formed by dissolving potassium metal in methyl amine solution of the methylated aza222.

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