Covalent Bond

Like Kossel, Lewis also assumed that atoms attain noble gas electronic configuration in the process of bond formation. However, the way the noble gas electronic configuration is achieved, is different. Lewis proposed that this is achieved by sharing of a pair of electrons between the two atoms. Both the atoms contribute an electron each to this pair. For example, two hydrogen atoms form a molecule by sharing a pair of electrons.

This shared pair of electrons contributes towards the stability of both the atoms and is said to be responsible for bonding between the two atoms. Such a bond is called covalent bond and the compounds so obtained are called covalent compounds.

Octet Rule

In the process of bond formation, the elements of second period acquire eight electrons in their valence shell. This is called Octet rule.

In case of H₂ and Cl₂ the atoms are linked by a single line while in case of O₂ the atoms are linked by two lines. These lines represent bonds. When two atoms are bound by sharing a single pair of electron, they are said to be joined by a single bond. When two pairs of electrons are shared (as in case of O₂), the two atoms are said to be bound by a double bond. In nitrogen (N₂) the two atoms are joined by a triple bond as they share three pairs of electrons.

Properties of Covalent Compounds

• The covalent compounds have low melting and boiling points due to weak forces of interaction between the molecules.
• The covalent compounds are poor conductors of electricity as these lack ionic species.
• The covalent compounds are generally insoluble in water and dissolve in non-polar solvents like benzene, carbon tetrachloride, etc.