What are polar molecules and non polar molecules?

Answer:

Polar molecules: Molecules in which the centre of mass of the positive charges (nuclei) does not coincide with the centre of mass of the negative charges (electrons), even in the absence of an external electric field. Such molecules have a permanent electric dipole moment. Examples: \(\text{H}_2\text{O}\), HCl, \(\text{NH}_3\), CO.

Non-polar molecules: Molecules in which the centres of positive and negative charges coincide, so they have no permanent dipole moment. They acquire an induced dipole moment only when placed in an external electric field. Examples: \(\text{H}_2\), \(\text{O}_2\), \(\text{N}_2\), \(\text{CO}_2\), \(\text{CH}_4\).