A covalent bond is a chemical bond involving the sharing of electron pairs between atoms. These electron pairs are termed bonding pairs and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding.

For example

(i) Dihydrogen, H - H

Each hydrogen atom contributes one electron. The two electrons are paired and occupy the space around both the nuclei. So these two electrons, which tie the two atoms of hydrogen are shared by both.

(ii) Dichlorine. Cl - Cl

(iii) Methane, CH4; here C has 4 electrons in valence shell. One electron

from each hydrogen combines with valance electrons of carbon

forming four pairs

H: C : H

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H---C---H

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H : C : H.