What is the basic difference in approach

What is the basic difference in approach between the Mendeleev’s periodic law and the modern periodic law?

Mendeleev’s periodic law It states that the properties of the elements are a periodic function of their atomic weights. Modem periodic law It states that the properties of the elements are a periodic function of their atomic numbers, thus, change in the base of classification of elements from atomic weight to atomic number is the basic difference between Mendeleev s periodic law and the modern periodic law.