1 . d -Block elements : The elements lying in the middle of periodic table belonging to groups 3 to 12 are known as d – block elements . Their
general electronic configuration is ( n – 1 ) d 1-10 ns 1-2 where ( n – 1 ) stands for penultimate ( last but one ) shell .
2 . Transition element : A transition element is defined as the one which has incompletely filled d orbitals in its ground state or in any one of its oxidation states .
3 . Zinc , cadmium , mercury are not regarded as transition metals due to completely filled d – orbital .
4 . f-Block elements : The elements constituting the f -block are those in which the 4 f and 5 f orbitals are progressively filled in the latter two long periods .
5 . Lanthanoids : The 14 elements immediately following lanthanum , i . e ., Cerium ( 58 ) to Lutetium ( 71 ) are called lanthanoids . They belong to first inner transition series . Lanthanum ( 57 ) has similar properties . Therefore , it is studied along with lanthanoids .
6 . Actinoids : The 14 elements immediately following actinium ( 89 ), with atomic numbers 90 ( Thorium ) to 103 ( Lawrencium ) are called actinoids . They belong to second inner transition series . Actinium ( 89 ) has similar properties . Therefore , it is studied along with actinoids .