# Unusual oxidation states of alkali metals

When going through list of oxidation states on Wikipedia I encounterd there that sodium, potassium, rubidium and caesium exhibit oxidation states of -1, but not lithium, even though its electronegativity is more than that of the others. How's that possible? Can some one provide an example.

• I believe the only reason for Li(-1) never being observed is that nobody cares. It should be, just as the rest of alkali metals. – Ivan Neretin Feb 21 at 13:00
• – Mithoron Feb 21 at 16:24
• – Mithoron Feb 21 at 16:32
• chemistry.stackexchange.com/a/34111/68148 can helium anion be prepared – Harsh jain Feb 21 at 17:18

You are talking about alkalides, salts where the anion is an alkali metal. There is a very brief overview on Wikipedia which also provides a couple of examples, including $$\ce{[Na(\text{cryptand[2.2.2]})]+Na-}$$. A good university level inorganic text book such as Greenwood and Earnshaw or Housecroft and Sharpe will provide more detail.
If you are interested in unusual oxidation states of alkali metals you might also like to know that in electrochemical experiments there is some evidence for $$\ce{Cs^3+}$$, which is isoelectronic with $$\ce{Xe^2+}$$. Again I think Greenwood and Earnshaw discusses this, but I don't have it to hand at the moment to confirm.
• $\ce{Cs^{3+}}$? Wow! Do you have some refs? – Oscar Lanzi Feb 22 at 1:31