Would you regard `Zn (Z=30) , Cd (Z=48) ` and `Hg (Z=80) as d- block elements ? Give reasons for your answer.

Explanation

The last `"electron"^(***)` in Zn ,Cd and Hg enters the 4s, 5s and 6s - orbitals respectively, Therefore on the basis of type of orbital filled , these three elements should be regarded as s-block elements .But the properties of these elements resemble more the d-block rather than s- block elements as listed below :
(i) Zn , Cd and Hg like other d- block elements form complexes but s-block elements usually do not.
(ii) Zn ,Cd and Hg like other d- block elements form many covalent compounds whereas s- block elements form only ionic compounds.
(iii) Like other d-block elements the first ionization energies of Zn, Cd and Hg are much higher than those of the s- block elements of th same period.
(iv) Like other d- block elements the atomic radii of Zn , Cd and Hg are much lower thant those of the s- block elements of the same period.
(v) Like other d- block elements the electrode potentials of Zn, Cd and Hg are much less negative than those of s- block elements of the same period.
from the above discussion , it is clear that the properties of Zn, Cd and Hg resemble more the d-block elements rather than the s-block element.
Therefore to make the periodic classification of elements more rational it is better to study them along with are d-block elements .