Question

Write two limitations of Mendeleev’s Periodic table.

Answer 1

Hint: The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements, which are arranged according to their atomic number, electron configuration, and regular occurring chemical properties. The structure of the table shows several periodic trends. Mendeleev used an idea of arranging the elements in the periodic table according to their increasing atomic masses and not atomic numbers.

Complete step by step answer:

According to Mendeleev's theory, the physical and chemical properties of the elements are the periodic function of their atomic masses. The trends occur at a regular interval of the occurrence of the atomic masses of the elements. Due to this, Mendeleev faced a great problem in placing the hydrogen in the periodic table. Indeed, the increasing order of atomic masses was also a problem as some elements whose atomic number is greater than the other but the atomic mass being less than the other created a great ambiguity.
The limitations of Mendeleev’s periodic table are:
(i) Elements that show large variations in their physical and chemical properties were added to the same group of the periodic table.
(ii) Mendeleev could not fit hydrogen at a particular place in the periodic table.

Note:
Sometimes this method of arranging the elements meant there were gaps in his horizontal rows or 'periods'. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered. He was also able to work out the atomic mass of the missing elements, and so predict their properties. And later, when the elements were discovered, Mendeleev was right. The properties of the elements matched with the properties as predicted by Mendeleev earlier.