The achievements by Mendeleev were:

•Mendeleev kept some blank spaces in the periodic table for the elements that were yet to be discovered.

Eg:- Eka-aluminium, Eka-boron, Eka-silicon.

•He also predicted properties of some elements which were yet to be discovered.

Eg:- The properties of Eka-aluminium predicted by Mendeleev and those of element gallium were almost the same.

•When noble gases were discovered, they could be placed in a new group without disturbing the order.

The formula of the hydrides and oxides formed by an element were treated as one of the basic the properties of an element for its classification.