Electric Dipole, Polar & Non-Polar Molecules

Electric Dipole:

An electric dipole is formed when two equal & opposite charges are separated by some distance.

Electric Dipole Moment (p):

It is defined as the product of magnitude of either charge & distance of separation between both the charges.

p=q x 2l.

The direction of dipole moment is from negative to positive charge.

The unit of dipole moment is coulombmeter or Cm.

The dimensional formula of dipole moment is [LTA].

Polar & Non-Polar Molecules:

All matter consists of atoms & molecules. The molecules can behave as electric dipoles. There are two types of molecules polar & non-polar.

Polar Molecule:

If the centre of mass of positive & negative charge doesn't coincide with each other, then the molecule is said to be polar molecule.
A substance consisting of polar molecules is known as polar substance.
Such type of molecule has permanent dipole moment(p).
Examples- water, HCl, Ammonoa (NH3), alcohol etc.

Non-Polar Molecule:

If the centre of mass of positive & negative charge coincide with each other, then the molecule is said to be non-polar molecule.
A substance consisting of non-polar molecules is known as polar substance.
A non-polar molecule has symmetrical shape.
Examples- methane, benzene, nitrogen molecule, oxygen molecule etc.
A non-polar substance has zero dipole moment. But when some electric field is applied, the non-polar molecule is stretched & becomes a polar molecule. Then some dipole moment is developed called as induced dipole moment.
Induced electric dipole moment disappears when the external field is removed & hence the substance becomes a non-polar one having zero dipole moment.

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