Describe the modern periodic law for the classification of elements. In the modern periodic table how many (a) groups and (b) periods are there?

Modern periodic law says that elements' Chemical and physical properties are periodic functions of their atomic number. The elements are arranged in the increasing order of the atomic numbers in this modern periodic table; thus, the element occurs at regular intervals with similar chemical and physical properties. 

(a) There are 18 groups in the modern periodic table. 

(b) There are 7 periods in the modern periodic table.