In other words, we can say that the third ionisation enthalpy of Fe is
lower than that of Mn The lowest common oxidation state of these metals is +2 To
form the M
2+ ions from the gaseous atoms, the sum of the first and
second ionisation enthalpy is required in addition to the enthalpy of
atomisation The dominant term is the second ionisation enthalpy
which shows unusually high values for Cr and Cu where M
+ ions
have the d
5 and d
10 configurations respectively