which results in the formation of stable d configuration. The trend in the third ionisation enthalpies is not complicated by the s orbital factor and shows the greater difficulty of removing an electron from the d (Mn + ) and d (Zn + ) ions. In general, the third ionisation enthalpies are quite high. Also the high values for third ionisation enthalpies of copper, nickel and zinc indicate why it is difficult to obtain oxidation state greater than two for these elements.
Although ionisation enthalpies give some guidance concerning the relative stabilities of oxidation states, this problem is very complex and not amenable to ready generalisation. One of the notable features of a transition elements is the great variety of oxidation states these may show in their compounds. Table . lists the common oxidation states of the first row transition elements.
Sc Ti Co Ni Cu Zn + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Table . : Oxidation States of the first row Transition Metal (the most common ones are in bold types) . . Oxidation States The elements which give the greatest number of oxidation states occur in or near the middle of the series.
Manganese, for example, exhibits all the oxidation states from + to + . The lesser number of oxidation states at the extreme ends stems from either too few electrons to lose or share (Sc, Ti) or too many d electrons (hence fewer orbitals available in which to share electrons with others) for higher valence (Cu, Zn). Thus, early in the series scandium(II) is virtually unknown and titanium (IV) is more stable than Ti(III) or Ti(II). At the other end, the only oxidation state of zinc is + (no d electrons are involved).
The maximum oxidation states of reasonable stability correspond in value to the sum of the s and d electrons upto manganese (Ti IV O , V V O + , V1 O