(a) Polar molecules: H2O, NH3, CO, HCl
Non-polar molecules: H2, N2, CO2, and O2
(b) polar and non-polar molecules:
A molecule is said to be polar if the centres of positive and negative charges do not coincide. That is. they are separated h a very short distance (oF the order 10-10m) and hence they form an electric dipole. Such a molecule then possesses a permanent dipole moment. In the absence of an electric field, these dipole moments are directed in random directions.
Example H2O. HCl, NH3. CO etc.
A molecule is said to be non-polar if the centres of positive and negative charges coincide. So they cannot form an electric dipole and hence they have no permanent dipole moment. Example O2, N2, H2, CO2 etc.
In the presence of an electric field, the centres of gravity of positive and negative charges of a non-polar molecule get separated by a very short distance and form an electric dipole. Hence, the non-polar molecule gets a dipole moment b induction. The dipole moment so acquired is known as induced electric dipole moment. in the presence of an electric field, the dipoles get aligned parallel to the field and is said to be polarized and the phenomenon is known as electric polarization.
(c) A dielectric material, polar or non-polar, when placed in an electric field E0, the dipoles get aligned parallel to the field. The dielectric material set up a secondary electric field Ep of its own in a direction opposite to the applied field E0. This phenomenon is known as dielectric polarization. The net field strength gets reduced and is given as E = E0 – Ep.
