Question

The maximum covalency is equal to the number of :

(A)- paired p-electrons

(B)- unpaired s-electrons

(C)- the number of unpaired s and p electrons

(D)- s-and p-electrons in the valence shell

Answer 1

Hint: Covalency is the number of electrons contributed by an atom of the element for sharing of electrons with other atoms, that is mutually shared for covalent bonding.

$$\text{Covalency}=8–[\text{Number of the group to which the element belongs}]$$

Complete step by step answer:

-The maximum number of covalent bonds which an atom of that element can form with neighbouring 

atoms are known as its maximum covalency.

-An element can show a maximum covalency which is equal to its group number. For example, the Chlorine element shows the maximum valency of seven which is its group number.

-For elements not having d-orbital, which is the first element of each group, the maximum covalency is equal to the total number of unpaired electrons in s-and p-orbitals in their valence shell. The maximum covalency of the first elements of each group is 4, because of the following reasons-

(i) small atomic size

(ii) no vacant d-orbitals

(iii) highly electronegative nature

-The valence characterized by the sharing of electrons in a chemical compound is what we call covalency. For example, Be contains two valence electrons, hence its maximum covalency is 2.

So, the correct answer is “Option C”.

Note: The elements having d-orbital like P, S, Cl, Br, I can show variable valency by increasing the number of unpaired electrons under excited conditions. The electrons in such elements on absorbing energy get excited from paired orbitals to vacant d-orbitals of the same shell. The elements, H, N, O, and F since do not have d-orbitals in their valence shell hence on excitation cannot show variable valency. This is the reason why $NC{l}_3$ exists but not $NC{l}_5$.