Question

Define valency of an element. Give the relation between the valency of an element and the num­ber of valence electrons in its atoms.

Answer 1

Valency of an atom:

1. The outermost electron shell of an atom is called the valence shell or valence orbit, and the electrons present in the outermost shell of an atom are called valence electrons.
2. Stability in an atom is achieved by donating, accepting, or sharing some or all valence electrons.
3. So, the number of electrons that an atom needs to accept, donate or share to achieve a stable octet electronic configuration ($8$ electrons) is called its valency.
4. Alternatively, the combining capacity of the atom of an element with the atoms of other elements to acquire eight electrons (or two electrons in Helium) in its outermost shell is known as its valency.

Relation between the valency of an element and the num­ber of valence electrons in an atom:

1. The valency of an element is determined by the number of valence electrons present in the atom.
2. If the number of valence electrons isknown, then the electrons lost or gained are calculated or shared by an atom of the element to achieve the nearest noble gas electronic configuration.
3. Thus, the valency of an element is either equal to the number of valence electrons in its atom or equal to the number of electrons lost or gained by an atom to complete eight electrons in the valence shell.