f-block elements – Inner transition elements
In the inner transition elements there are two series of elements.
1) Lanthanoids ( previously called lanthanides)
2) Actinoids ( previously called actinides)
Lanthanoid series consists of fourteen elements from Cerium (58Ce) to Lutetium (71Lu) following Lanthanum (57La).These elements are characterised by the preferential filling of 4f orbitals, Similarly actinoids consists of 14 elements from Thorium (90Th) to Lawrencium (103Lr) following Actinium (89Ac).These elements are characterised by the preferential filling of 5f orbital.