Question

Give a reason for the following:

Mendeleev's contributions to the periodic table laid the foundation for the Modern Periodic Table.

Answer 1

Mendeleev found that there was a close relation between atomic weights and properties of elements. He also found that when elements are arranged in increasing order of their atomic weights, the properties repeat at regular intervals.
He even left some gaps for the elements not know at that time whose properties resembled the neighbouring elements. Predicted properties of eKa Aluminium (before discovery) are exactly the same as actual properties of gallium element (after discovery).
Moreover, he arranged all the 63 elements known at that time. Still, there were many drawbacks in this periodic table, but Mendeleeff laid the foundation of modern periodic table.