Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at ''periodic law'' ?

Explanation

(i) The process adopted by Mendeleev for the classification of elements is as follows :
(ii) Mendeleev determined the relation between atomic masses of elements and their properties. He examined that physical and chemical properties of elements are periodic function of their atomic masses. He arranged all known 63 elements according to their atomic masses.
(iii) He examined the compounds formed by elements hydrogen and oxygen. He used these elements because they are very reactive and form different compounds with other elements like hydride and oxides.
(iv) The chemical properties of hydrides and oxides were used to determine the chemical properties of different elements and that again was used for their classification. He recorded properties of all 63 elements and paired the elements which exhibit same chemical properties.
(v) He arranged elements on the basis of their similarities in chemical properties and found that most of the elements were arranged in order of their increasing atomic masses.
(vi) In this arrangement, he also observed the periodic recurrence of elements with similar physical and chemical properties. He formulated the periodic law which states that the properties of elements are the periodic function of their atomic masses.