Question

How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Answer 1

Major difference between Mendeleev’s and the modern periodic table is that the Mendeleev periodic table was based on atomic masses whereas Modern periodic table depends on the atomic number.

Complete answer:
- Now, Mendeleev was the first scientist to arrange elements in a periodic table. Mendeleev’s periodic table was based on atomic masses. And that is what caused the main problem. The atomic mass of an element is the total of its neutron and proton. And then the isotopes of elements came into the picture. Many elements are known to have isotopes where the same elements have a different count of protons and therefore their atomic masses differ. This causes various anomalies in the Mendeleev’s periodic table.
- Since the modern periodic table was based on atomic numbers, it removes various anomalies that were contained in Mendeleev’s periodic table.
- The pair of cobalt and nickel were misplaced. Cobalt $Co$ have an atomic number twenty seven and nickel $Ni$ have an atomic number twenty eight and hence cobalt will be placed before nickel. But the atomic mass of cobalt is greater than nickel and therefore in Mendeleev’s periodic table cobalt was placed after nickel.
- The grouping of elements was not according to their chemical properties.
- If we considered Mendeleev’s periodic table, every isotope would be given different places because it has different atomic masses. But in the periodic table, the situation of isotopes did not create a problem.
- Hydrogen was not given a fixed place because it can donate one electron and become an alkali metal, or it can accept one electron and be in the group of halogens.

Note:
As in the modern periodic table, the elements are arranged in increasing atomic numbers. There is a possibility that every newly formed or discovered element can be placed in this elemental table and therefore this table is convenient and accurate.