8.3.8 Chemical Reactivity and EƟ Values

The metals of the first series with the exception of copper are relatively more reactive and are oxidised by 1M H+, though the actual rate at which these metals react with oxidising agents like hydrogen ion (H+) is sometimes slow. For example, titanium and vanadium, in practice, are passive to dilute non oxidising acids at room temperature. The EƟ values for M2+/M (Table 8.2) indicate a decreasing tendency to form divalent cations across the series. This general trend towards less negative EƟ values is related to the increase in the sum of the first and second ionisation enthalpies. It is interesting to note that the EƟ values for Mn, Ni and Zn are more negative than expected from the general trend. Whereas the stabilities of half-filled d subshell (d5) in Mn2+ and completely filled d subshell (d10) in zinc are related to their E e values; for nickel, EƟ value is related to the highest negative enthalpy of hydration.