In
many of these properties, the maxima occur at about the middle of each series which
indicates that one unpaired electron per d orbital is particularly a favourable configuration
for strong interatomic interaction Successive ionisation enthalpies do not increase as steeply as in the main group
elements with increasing atomic number Hence, the loss of variable number of electrons
from (n –1) d orbitals is not energetically unfavourable The involvement of (n–1) d electrons
in the behaviour of transition elements impart certain distinct characteristics to these
elements