Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at "Periodic Law" ?

Explanation

(i) When Mendeleev started his work, 63 elements were known. He studied the compounds of these elements with oxygen and hydrogen. He selected hydrogen and oxygen as they are very reactive and formed compounds with most elements. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification.
(ii) Elements with similar properties were arranged in a group.
(iii) Mendeleev observed that elements were automatically arranged in the order of increasing atomic masses.