The basic difference in approach between Mendeleev's periodic law and modern periodic law is the change on the basis of classification of elements from

The basic difference in approach between Mendeleev's periodic law and Modern periodic. law is as follows : The Mendeleev's periodic law is based on atomic weight while modern periodic law is based on atomic number. i.e. according to Mendeleev's periodic law. If the element are arranged in order of increasing atomic weights their properties vary in definite manner from member to member of the series, but return more or less nearly to same value at certain fixed points in the series, while according to modern periodic law. Physical and chemical properties of the elements are periodic function of their atomic numbers.