Iron

Abstract

Iron is the fourth most abundant element in the earth’s crust; in the elemental form it occurs only rarely but in the combined state it is universally common. Iron has a very ancient history; it was probably first used by man nearly 6000 years ago (iron from meteorites), iron production beginning around 1200 B.C. Iron is the first member of the group VIII triad, lying above ruthenium and osmium. Unlike all the elements we have so far considered, iron does not show the maximum oxidation state corresponding to the removal of all (eight) of its valence electrons. The maximum oxidation state shown is +6 but states above +3 are all relatively unimportant; notice that with iron it is the +3 state that has the completely half-filled (3d⁵) shell. As with manganese, however, the predominance of the +2 oxidation state continues to assert itself, and in the elements to follow, that is Co, Ni, and Cu, compounds in this state assume even greater preponderance.