Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

4. Cobalt - nickel

Explanaion:

Introduction to Mendeleev's Periodic table:

The pair of the element in the periodic table where the element occurring before has more atomic mass than the later occurring one. It is also considered to be a drawback of Mendeleev’s periodic table.

Reasons of anomalous:

The size of an atom is less

Electronegativity is very high as a result ionization enthalpy increases.

The charge to radius ratio is large.

The below image shows the anomalous pairs of elements in Mendeleev's periodic table;