CBSE Class 10 Answered

Modern periodic table was arranged on the basis of atomic numbers.Modern periodic law stated that the physical and chemical properties are the periodic functions of their atomic numbers.

Mendeleev's periodic table was arranged on the basis of atomic masses. Mendeleev's periodic law stated that the physical and chemical properties are the periodic functions of their atomic masses.

So, the first disadvantage that isotopes of the same elements occupy different positions was removed as the isotopes will have different atomic masses but same atomic numbers. So, the isotopes of the same element in the modern periodic table occupied one position only.

The position of hydrogen in the modern periodic table was a speical place above the periodic table since in some properties it resembled alkali metals, in some others it resembled halogens and some other properties were unique.