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.