What is the basic difference in approach between Mendeleev Periodic Law and the Modem Periodic Law

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#1

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.”