Question

What is the basis of Mendeleev’s periodic law?

Answer 1

Periodic table is the representation of chemical elements. So many scientists discovered periodic tables based on different periodic laws. Some of the scientists were Mendeleev, Mosley, Rutherford etc. But Mendeleev arranged the chemical elements based on the atomic masses of elements.

Complete answer:
Every chemical element has its atom, atom is a tiny particle. The chemical element has atomic number and atomic mass. Atomic mass can also be termed as molar mass. The atomic number of a chemical element can be given by the number of protons, the atomic mass can be given by the sum of the number of protons and number of neutrons.
The atomic mass is exactly double the atomic number for most of the chemical elements, but for some chemical elements it may be higher. For example, sodium is the element with atomic number $11$, but its atomic mass is $23$amu, which is higher than the double of that atomic number.
The Mendeleev periodic table is based on the periodic law, that elements are arranged in the order of increasing their atomic weights. He was not fully successful in constructing the periodic table.

Note:
Mendeleev left some gasp in the periodic table for some undiscoverable elements, and named those elements by preceding elements in that group by adding the prefix -eka. For example, he did not discover gallium at first and named the element as eka aluminum, used for the discovery of new elements.