Example 4.3

Example . . Which of the d series of the transition metals exhibits the largest number of oxidation states and why? Table . contains the thermochemical parameters related to the transformation of the solid metal atoms to M + ions in solution and their standard electrode potentials. The observed values of E V and those calculated using the data of Table . are compared in Fig. . . The unique behaviour of Cu, having a positive E V , accounts for its inability to liberate H from acids. Only oxidising acids (nitric and hot concentrated sulphuric) react with Cu, the acids being reduced. The high energy to transform Cu(s) to Cu + (aq) is not balanced by its hydration enthalpy. The general trend towards less negative E V values across the . . Trends in the + /M Standard Electrode Potentials . The E o (M + /M) value for copper is positive (+ .34V). What is possible reason for this? (Hint: consider its high D a H o and low D hyd H o ) Why is Cr + reducing and Mn + oxidising when both have d configuration? + is reducing as its configuration changes from d to d , the latter having a half-filled t 2g level (see Unit ). On the other hand, the change from Mn + to Mn + results in the half-filled ( d ) configuration which has extra stability.