Iron(II)
In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+.
The adjective ferrous or the prefix ferro- is often used to specify such compounds — as in "ferrous chloride" for iron(II) chloride, FeCl2. The adjective "ferric" is used instead for iron(III) salts, containing the cation or Fe3+. The word ferrous is derived from the Latin word ferrum for iron.
Iron(II) atoms may also occur as coordination complexes, such as the polymer iron(II) oxalate dihydrate, [Fe(C2O4)(H2O)2]n or [Fe2+][C2O2−4][H2O]2n; and organometallic compounds, such as the neutral molecule ferrocene, Fe(C2H5)2 or [Fe2+][C5H−5]2. Ferrous ion Fe+2 and its salts are short lived and more prone for the air oxidation and immediately turned to the Ferric Fe+3 which in turn more stable. Hence in the Qualitative analysis of the salts Ferrous ion solution is not preferable to store rather we can prepare insitu.
Iron is almost always encountered in the oxidation states 0 (as in the metal), +2, or +3. Solid iron(II) salts are relatively stable in air, but in the presence of air and water they tend to oxidize to iron(III) salts that include hydroxide (HO−) or oxide (O2−) anions.