(a) State Mendeleev's periodic law.
(b) Describe about the merits of Mendeleev's periodic table.

Explanation

(a) Mendeleev.s periodic law:
Mendeleev.s periodic law states that the physical and chemical properties of elements are a periodic function of their atomic weights.
(b) Merits of Mendeleev.s periodic table:
(i) The comparative studies of elements were made easier.
(ii) The table shows the relationship in properties of elements in a group.
(iii) The table helped to correct the atomic masses of some elements later on. At the time on Mendeleev, the atomic weight of Au and Pt were known as 196.2 and 196.7 respectively. However, Mendeleev placed Au (196.2) after Pt (196.7) saying that atomic weight of A is incorrect, which was later on found to be 197.
(iv) At the time of Mendeleev, about 70 elements were known and thus blank spaces we for unknown elements which helped further discoveries.
Both Gallium (Ga) in III group and Germanium (Ge) in IV group. were unknown at that time by Mendeleev predicted their existence and properties. He referred the predicted elements as eka-aluminium and eka-silicon. After discovery of the actual elements, their properties were found to match closely to those predicted by Mendeleev.