The elements having less than 8 electrons in their outermost shell always have a tendency to attain an octet in order to attain a noble gas configuration by gaining or losing electron forming ionic compounds. In case of carbon with atomic number 6 there are four electrons in its outermost shell due to which it is termed as tetravalent.

It gains or loses four electrons to attain the nearest noble gas configuration.

Carbon has two possibilities to attain noble gas configuration.

(i) One of the possibilities is to attain four electrons and form C^4– anion. But it will be difficult for the nucleus to hold four more electrons firmly.

(ii) Another possibility is to lose four electrons forming C⁴⁺ cation. But this will also be difficult due to the requirement of large energy to lose four electrons from the outermost shell. As a result the atom will contain six protons and two electrons.

Therefore carbon shares its valence electrons present in its outermost shell with the electrons in the outermost shell of the combining atoms of other elements.

Due to this sharing of four electrons of carbon with the electrons of other combining atoms, carbon is said to form covalent bonds.

The covalent bond can be further divided into non-polar and polar covalent bonds.

Bond formed as a result of sharing of equal number of electrons between the atoms of a compound is called nonpolar covalent bond.

For example, the bond between two chlorine atoms is a non-polar covalent bond due to the formation of bond by sharing equal number of electrons. The nonpolar covalent bonds requires large amount of energy to break due to its high strength.

Bond formed as a result of sharing of unequal number of electrons between the atoms of a compound is called polar covalent bond.

For example, the bond between oxygen and hydrogen in water molecule is polar covalent bond due to unequal sharing of electrons. Electrons are more inclined towards oxygen atom thereby acquires a partial negative charge.