Example 4.4

Example . Fig. . : Observed and calculated values for the standard electrode potentials (M + ® M°) of the elements Ti to Zn series is related to the general increase in the sum of the first and second ionisation enthalpies. It is interesting to note that the value of E V for Mn, Ni and Zn are more negative than expected from the trend. Element (M) DDDDD a H o (M) DDDDD i H o DDDDD H o DDDDD hyd H o (M + ) E o /V Ti - - . - - . - - . - - . - - . Co - - . Ni - - . Cu - . Zn - - . Table . : Thermochemical data (kJ mol - ) for the first row Transition Elements and the Standard Electrode Potentials for the Reduction of M II to M. The stability of the half-filled d sub-shell in Mn + and the completely filled d configuration in Zn + are related to their E o values, whereas E o for Ni is related to the highest negative D hyd H o . An examination of the E o (M + /M + ) values (Table . ) shows the varying trends. The low value for Sc reflects the stability of Sc + which has a noble gas configuration. The highest value for Zn is due to the removal of an electron from the stable d configuration of Zn + . The comparatively high value for Mn shows that Mn + ( d ) is particularly stable, whereas comparatively low value for Fe shows the extra stability of Fe + ( d ). The comparatively low value for V is related to the stability of V + (half-filled t 2g level, Unit ). Table . shows the stable halides of the d series of transition metals. The highest oxidation numbers are achieved in TiX (tetrahalides), VF