This sequence depicts various iron compounds in different oxidation states and forms:

FeO - Iron oxide (II), also known as ferrous oxide or wüstite.Fe - Elemental iron.FeCl2 - Iron (II) chloride, a compound of iron and chlorine.Fe(OH)2 - Iron (II) hydroxide, also known as ferrous hydroxide.FeO - Iron (II) oxide, another occurrence of ferrous oxide.Fe2O3 - Iron (III) oxide, also known as ferric oxide or hematite.FeCO3 - Iron (II) carbonate, a compound of iron, carbon, and oxygen.Fe(OH)3 - Iron (III) hydroxide, also known as ferric hydroxide.Fe2O3 - Iron (III) oxide, another occurrence of ferric oxide or hematite.