The modern periodic table solved many defects of the Mendeleev’s periodic table.
A few exemplification of them are:
1. The wrong position of some elements like argon and potassium, cobalt and nickel due to atomic weights, has been solved by arranging the elements in the order of increasing atomic number without changing their own places.
2. The isotopes of the same element have the same atomic numbers. Therefore, they find the same position in the modern periodic table.
3. It separates metals from non-metals.
4. The representative and transition elements have been separated in the modern periodic table.
There are more still.
