Question

What were the two criteria used by Mendeleev in creating his periodic table?

Answer 1

Hint: In the periodic table created but the Mendeleev , the elements were arranged according to the increasing order of the number of protons and neutrons present in the nucleus and on the basis of atomic radii, ionization energy, electron affinity, electron configuration etc. Now answer the statement.

Complete step by step answer:
Dmitri Mendeleev was a Russian scientist and proposed the periodic law to construct his periodic table of elements. At that time, the structure of atoms was unknown and he considered that the properties of the elements were in some way related to their atomic masses. He reversed the order of some pairs of elements and asserted that their atomic masses were incorrect to place certain elements into the correct group from the point of view of their chemical properties. So, the two criteria used by the Mendeleev in creating his periodic table are as follows;
1. In his periodic table, he arranged the elements in horizontal rows and vertical columns according to the atomic masses i.e. in the increasing order of their atomic masses.
2. He placed the elements according to their similar properties i.e. the physical and chemical in such a way that the elements with similar properties occupy the same vertical column or group.

Note: Mendeleev left some gaps in the periodic table for the elements unknown at that and predicted their properties from the trends that he observed among the properties of related elements. For example, both gallium and germanium were unknown at his time and he left the gap under aluminum and silicon and called these elements as eka-aluminum and eka-silicon and his predictions were proved to be correct when these elements were discovered later on.