Question

List two observations which posed a challenge to Mendeleev’s Periodic Law.

Answer 1

Following are the two observations which posed a challenge to Mendeleev’s Periodic Law.
(i) Increasing order of atomic weights could not be maintained while matching chemical properties. Chemical properties do not depend upon atomic mass.
(ii) Isotopes have different atomic mass but same chemical properties. Deciding the position of isotopes was difficult in order of atomic masses.