Question

What is the valency of iron in ferrous sulphate?

Answer 1

In an atom, the outermost electron shell is known as valence shell and the number of electrons present in the valence shell are known as valence electrons. The valence of an element is defined as the combining capacity of an atom of element to form a chemical bond. For metals, it is equal to the number of valence electrons and for nonmetals, it is equal to the number of electrons required to complete the octet.

Complete answer:
Ferrous sulphate is a chemical compound which consists of iron in its $+ 2$ oxidation state and sulphate ions. Its chemical formula is $FeS{O_4}$. The electronic configuration of iron in ferrous sulphate is as follows:
Electronic configuration at ground state of iron: $[Ar]3{d^6}4{s^2}$
Electronic configuration of iron in its $+ 2$ i.e., after forming ferrous sulphate: $[Ar]3{d^6}4{s^0}$
As there were two electrons present in the valence shell of iron which combine with the electrons of sulphate ions to form ferrous sulphate. Hence, the valency of iron in ferrous sulphate is two.
As the half-filled and completely filled orbitals are more stable than partially filled orbitals, ferrous sulphate on heating converts into iron (III) compound i.e., it shows a valency of three in order to reach its stable half-filled d-orbital configuration.

Note:
It is important to note that the easiest way to calculate the valency of an element in an ionic compound is by oxidation number method. The oxidation state of an atom represents the number of electrons gained or lost by that atom while the forming of a chemical bond.