Question

what is covalency ?explain the formation of covalent bond with the help of an example.

Answer 1

valence characterized by the sharing of electrons in a chemical compound; the number of pairs of electrons an atom can share. covalence. valence, valency - (chemistry) a property of atoms or radicals; their combining power given in terms of the number of hydrogen atoms (or the equivalent)

Answer 2

Covalency

The number of electrons shared by one atom of an element to achieve the nearest inert gas electron configuration is known as its covalency.

Formation of Covalent Bond

When both atoms in a reaction need to gain electrons to complete their octet, sharing of electron takes place.

A single atom of  HYDROGEN  has one electron, i.e. its ATOMIC NUMBER 1. It has its only electron in its first and only orbit. Now to be a stable molecule it needs to complete its duplet state. So a single hydrogen atom will remain unstable unit it attains one more electron. So we can say the valency of hydrogen is 1. The valency of an atom depends on its sharing capacity. So the hydrogen atom shares its single atom with another hydrogen atom. Now both hydrogen atoms have two (shared) electrons in its outer shell and it is a stable molecule H2. This bond formed by sharing electrons is nothing but a covalent bond.