How did atomic number prove a better basis for the classification of elements?

By choosing atomic number as the basis of classification the anomalies in the original Mendeleev’s periodic table was rectified as discussed below:

1. Inversion in Mendeleev’s table: The anomaly of having the element of higher atomic mass before the element with lower atomic mass is now removed because the element having higher atomic mass had lower atomic number in such cases.

2. Position of isotopes: The isotopes of an element have different atomic masses but same atomic number. Hence according to atomic number as the basis of classification they are allotted the same place in the periodic table.