Question

What are the demerits of Mendeleev's periodic table with respect to the arrangement of elements in ascending order? (Any three)

Answer 1

Demerits of Mendeleev's Periodic Table :
(a) Mendeleev arranged elements in the ascending order of their atomic masses. There was no fixed position for hydrogen in his periodic table, as it resembled alkali metals as well as halogens.
(b) Elements of higher atomic mass were placed before elements of lower atomic mass. Cobalt with atomic mass $58.93$ was placed before nickel with atomic mass $58.71$.
(c) Elements having different properties were placed in the same sub group like manganese $\left(Mn\right)$ was placed with halogens which had totally different properties