Question

Question 3.3 What is the basic difference in approach between the Mendeleev’s Periodic Law and the Modern Periodic Law?

Class XI Classification of Elements and Periodicity in Properties Page 92

Answer 1

Mendeleev's periodic table : it is based on atomic weight . I mean , physical and chemical properties of elements are periodic function of their atomic weight .

but
Morden periodic table : it is based on atomic number . I mean , physical and chemical properties of elements are periodic function of their atomic number .

Thus, we see that the basic classification change from atomic weight to atomic number is the basic difference in approach between Mendeleev's periodic table and Morden periodic table.

Answer 2

Mendeleev's Periodic law is based upon atomic weights of elements, whereas Modem Periodic Law is based upon atomic number of elements. Mendeleev stated : "The properties of the elements are a periodic function of their atomic weights."
Modern Periodic Law states : "The physical and chemical properties of the elements are periodic functions of their atomic numbers."