Periodicity i.e., repetition of similar properties is shown by the elements present in a group and separated by definite gaps of atomic number. For example,
(i) Elements in a group have same number of valence electrons and same valency.
(ii) Elements present in a group show similar chemical properties.
(iii) The atomic sizes of the elements in a group increase regularly.
(iii) The m.p. and b.p. of the elements in a group increase regularly.
