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Polar Covalent Bond

January 28, 2013

Depending upon the relative electro negativities of the two atoms sharing electrons, partial transfer of electron density from one atom to the other takes place. When the electro negativities are not equal, electrons are not shared equally and due to these partial ionic charges develop. The greater the difference in electro negativity, the more ionic is the bond. Bonds which are partly ionic are termed as polar covalent bonds.

polar and non polar bonds

Non polar covalent bonds have equal sharing of the bond electrons and it plays its role when the electro negativities of the two atoms are equal.
Polar and Non Polar Covalent Bonds:

Non Polar Covalent Bond:

A bond which exists between two non metal atoms, have the same electro negativity and hence have equal sharing of the bonding of electron pair.

Example: In H-H molecule, each H atom has an electro negative value of 2.1, hence the covalent bond which exists between them is considered as non polar.

Polar Covalent Bond:

A bond which exists between two non metal atoms, have different electro negativity and hence have unequal sharing of the bonding of electron pair.

Example: In HCl, the electro negativity of the Cl atom is 3.0, and that of the H atom is 2.1

The bond is formed where the electron pair is displaced towards the more electronegative atom. This atom gets a partial-negative charge while the less electronegative atom acquires a partial-positive charge.

Inside a molecule, each polar bond exhibits a bond dipole.

A polar molecule necessarily contains polar bonds, but there are certain molecules with polar bonds and are non polar.

Polar Molecule

Molecules in which the bond dipoles are present do not cancel each other and hence results in a molecular dipole.

Examples

CO2 is a linear molecule having two bond dipoles which are equal and oppositely directed and hence the bond polarities cancel and the molecule is non polar.

HCN is a linear molecule having two bond dipoles which are in the same direction and not equal. Hence the bond polarities do not cancel each other, and the molecule becomes polar.

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