Question

Give examples of two pairs of elements where reversal of atomic mass can be observed in the Mendeleev's table and why he did this type of reversal?​

Answer 1

Explanation:

Anomalous pairs are those pairs of elements in which the increasing order of atomic masses was not obeyed. Mendeleev placed these elements according to a similarity in properties and not in the increasing order of their atomic mass.

(A) Ar ( at mass = 39.9) is placed before K (at mass = 39.1)

(B) Co (at mass = 58.9) is placed before Ni (at mass = 58.6)

(C) Te (at mass = 127.6 ) is placed before I (at mass = 126.9).

(D) Al and Si is not anomalous pair of elements in the Mendeleev's periodic table. Al (at mass = 27.0) is placed before Si (at mass = 28.4)