. Write important limitation of Mendeleev's Periodic Table
(i) Position of hydrogen
It is still not certain whether to place
hydrogen in group I A or VII A.
(ii) Anomalous pairs of elements
Ar (40) and K (39); Co (58.9) and Ni
(58.6); Te (127.6) and I (126.9) the
arrangement was not justified. In this
case, the periodic law is violated.
(iii) Position of isotopes three isotopes
of hydrogen with atomic mass 1, 2,
and 3. According to Mendeleev’s
periodic table these should be placed
at three separate places.