Electronic Configuration of D-Block Elements:
In the transition elements, d-orbitals of penultimate shell are successively filled. The first transition series involves the filling of 3d orbitals. It starts from scandium (Z = 21) and goes up to zinc (Z = 30).
The second transition series involves the filling of 4d-orbitals and includes 10 elements from yttrium (Z = 39) to cadmium (Z = 48).
The third transition series involves filling of 5d-orbitals. The first element of this series is lanthanum (Z = 57). It is followed by fourteen elements called lanthanides which involve the filling of 4f-orbitals. The next nine elements from hafnium (Z = 72) to mercury (Z = 80) belong to third transition series.
The general electronic configuration of transition elements is (n-1)d1-10 ns1-2.