quality:corruption
Yb(II) vs. Yb(III)

Although usually trivalent, ytterbium readily forms divalent compounds. This behavior is unusual for lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has a valence electron configuration of 4 f because the fully filled f -shell gives more stability. The yellow-green ytterbium(II) ion is a very strong reducing agent and decomposes water, releasing hydrogen gas, and thus only the colorless ytterbium(III) ion occurs in aqueous solution. Samarium and thulium also behave this way in the +2 state, but europium (II) is stable in aqueous solution. Ytterbium metal behaves similarly to europium metal and the alkaline earth metals, dissolving in ammonia to form blue electride salts.