A
consequence of this factor is reflected in the electronic configurations
of Cr and Cu in the 3d series For example, consider the case of Cr,
which has 3d
5 4s
1 configuration instead of 3d
44s
2; the energy gap
between the two sets (3d and 4s) of orbitals is small enough to prevent
electron entering the 3d orbitals Similarly in case of Cu, the
configuration is 3d
104s
1 and not 3d
94s
2 The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 4