Question

What are the limitations of Mendeleev periodic table:

Answer 1

Hint: Dmitry Mendeleev was a Russian chemist and proposed the first periodic table to the world. He proposed that the most fundamental property was the mass of the atom and positioned them in its increasing order in horizontal row till he came up against an element which had properties related close to the first element. This was the main cause of the limitations to the periodic table.

Complete Solution :
Mendeleev’s periodic law is grounded on “the chemical and physical properties of elements are a periodic function of their atomic masses”
The limitations or defects in Mendeleev’s periodic classification are mentioned below-
Despite being a historic achievement Mendeleev’s periodic table had some defects in it. The following were the main defects in it:
1. Position of hydrogen
Hydrogen resembles alkali metals as well as halogens. Therefore, it could neither be placed with alkali metals nor with halogens.
2. Position of isotopes
Each of the isotopes of the same elements should have been given a different position in the periodic table. Rather they are chemically similar, they had to be given the same position.
3. Anomalous pairs of elements
An element of higher atomic mass has been placed before an element of lower atomic mass at some places in the periodic table. For example, Argon (39.91) is positioned before (39.1)

Note: Mendeleev’s periodic table had some blank spaces in it. These unoccupied spaces were for elements that were yet to be found out. It was a very successful attempt. He put forward the existence of an unspecified element that he called eka-aluminium. The element gallium came across us four years later and its properties complimented very closely with the speculated properties of eka-aluminium.