1. Atomic weight = Equivalent weight x Valency
2. By using the formula, the atomic weight of Beryllium was calculated as 13.5 (Equivalent weight of Be = 4.5, valency = 3)
3. With this atomic weight the element should be placed in wrong group.
4. So Mendeleeff predicted its valency is only 2. From that he calculated the atomic weight of Beryllium as 9.
5. Now it fitted into correct group.
6. Similarly, Mendeleeff corrected atomic weights of Indium and Gold.
