There are two types of covalent bonds on the basis of electronegativity of bonding atoms.
- Polar covalent bond
- Non polar covalent bond
Polar covalent bond
It is a covalent bond in which bonded atoms have dissimilar electronegativity. During the formation of a covalent bond, sharing of electrons take place.
Since the more electronegative atom attracts the shared electrons more strongly, the electron density gets shifted toward a more electronegative atom.
Hence it acquires partial negative charge and another atom acquires partial positive charge.
Example : Hydrochloric acid (HCl)
Electronegativity of hydrogen atom is 2.20 and chlorine atom is 3.16 (very large). The difference between the electronegativities of hydrogen and chlorine is very large.
Chlorine attracts shared pair of electron towards itself hence acquires partial negative charge as shown in the above figure.
The electron density is away from the hydrogen atom hence it acquires a partial positive charge.
Polar bonds are partially ionic in character and stronger due to electrostatic attraction between two poles.
|Percentage ionic character||Nature of bond|
|0.1 – 0.8||0.5 – 15||Covalent|
|0.9 – 1.8||19 – 47||Polar covalent|
|1.9||50||Equally ionic and covalent|
|2 – 3.2||55 – 93||Ionic|
Non-polar covalent bond
Consider two atoms which are similar or identical having similar electronegativity take part in covalent bonding. The electron pair forming the bond is shared equally between two atoms so the formed bond is non-polar. hence the distribution of electron density over both atoms is equal.
Example – Chlorine molecule
Electronegativity of chlorine atom is 3.16. During the formation of covalent bond, each electron is shared by both chlorine atom.
This is shown in the given figure. There is increase in electron density between two atoms.
Due to same electronegativity both atoms pull the electron density towards each other.
Since the value of electronegativity is same for both atoms, electron density is equally shared ( pulled ) by the both atoms. Hence no atom gains partial positive or partial negative charge.
How to identify polar and non polar Bond
- The nature of polar and non-polar bond can be determined by knowing the value of electronegativities of bonding atom. (But this is not a reliable way because of molecules like carbon dioxide even having electronegativity difference are non-polar). This is due to their symmetrical shape.
- The polar nature of the bond is also determined by
dipolemoment. The dipole moment is the product of net positive or negative charge and distancebetween the two charged ends. If the value of dipole moment is zero then the molecule is non polar otherwise it is polar.
Data taken from John Emsley, The Elements, 3rd edition. Oxford: Clarendon Press, 1998.