2) indicate a decreasing tendency to form divalent
cations across the series This general trend towards less negative E
o
values is related to the increase in the sum of the first and second
ionisation enthalpies It is interesting to note that the E
o values for Mn,
Ni and Zn are more negative than expected from the general trend Whereas the stabilities of half-filled d subshell (d
5) in Mn
2+ and completely
filled d subshell (d
10) in zinc are related to their E 
e values; for nickel, Eo
value is related to the highest negative enthalpy of hydration