What is the basic difference in the approach between the Mendeleev’s Periodic Law and the ModernPeriodic Law?

The basic difference in the approach between Mendeleev’s Periodic Law and the Modern Periodic Law lies in the basis of classification of elements.

1. Mendeleev’s Periodic Law: Mendeleev classified elements based on their atomic masses. He arranged elements in the increasing order of their atomic masses in a periodic table. This was the basis of Mendeleev’s Periodic Law which states that "The properties of elements are a periodic function of their atomic masses".

2. Modern Periodic Law: The Modern Periodic Law, on the other hand, is based on atomic numbers of elements, not their atomic masses. According to the Modern Periodic Law, "The properties of elements are a periodic function of their atomic numbers". This means that elements are arranged in the increasing order of their atomic numbers in the modern periodic table.

In summary, the key difference between the two lies in the fact that Mendeleev used atomic masses as the basis for his classification, while the Modern Periodic Law uses atomic numbers.