Question

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

Answer 1

Mendeleev's periodic law:-

1. Dmitri Ivanovich Mendeleev was a Russian chemist and was perhaps the most important contributor to the early development of a periodic table of elements where elements were arranged on the basis of their fundamental property, the atomic mass, and also on the basis of similarity of the chemical properties.
2. There were just 63 elements that were known at his time.
3. He studied the compounds of these elements with oxygen and hydrogen as these are very reactive and formed compounds with most elements.
4. 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.
5. Elements with similar properties were arranged in a group.
6. Mendeleev observed that elements were automatically arranged in the order of increasing atomic masses at regular intervals.
7. On basis of this, Mendeleev gave a periodic law, that states "the properties of elements are a periodic function of their atomic masses".

Properties of Mendeleev's periodic table:-

1. This table contains 8 vertical columns, called the groups, and 7 horizontal rows, called the periods.
2. In order to group the elements which have similar properties together, at some places, he placed an element with a slightly greater atomic mass before an element with a slightly lower atomic mass.
3. He even predicted the existence of those elements which were yet to be discovered for example Eka-boron, eka-aluminum, and eka-silicon, which were named Scandium, Gallium and Germanium, respectively after their discoveries.