Oxidation states of first transition series

One of the notable features of transition elements is the great variety of oxidation states they show in their compounds. Table 8.3 lists the common oxidation states of the first row transition elements.

Table 8.3: Oxidation states of first transition series elements

From Table 8.3 it is clear that as the number of unpaired electrons in 3d orbitals increases, the number of oxidation states shown by the element also increases. Scandium has only one unpaired electron: it shows three oxidation states, while manganese with 5 unpaired d electrons shows six different oxidation states. The elements which give the greatest number of oxidation states occur in or near the middle of the series — manganese, for example, shows oxidation states from +2 to +7.

Loss of 4s and 3d electrons progressively leads to formation of ions. The transition elements display a variety of oxidation states in their compounds. Loss of one 4s electron leads to the formation of an $\mathrm{M^+}$ ion; loss of two 4s electrons gives an $\mathrm{M^{2+}}$ ion, while loss of unpaired 3d and 4s electrons gives $\mathrm{M^{3+}}$, $\mathrm{M^{4+}}$ ions, and so on. Some examples are as shown in Table 8.4.

Table 8.4: Electronic configuration of various ions of 3d elements (species below are the metal atom M and its ions; the book prints charges with circled ⊕ signs — rendered here as clean superscripts)