How are polar and nonpolar molecules differentiated on the basis of symmetry and intermolecular forces? What are the conditions under which they are called symmetrical?
Polar molecules are those that have charge centers (both positive and negative) separated by a certain distance. This is due to the presence of strong and weak electronegative atoms in the molecule, which causes the localization of electrons near the more electronegative atom (or atoms). This is what results in charge center separation. Due to this unequal sharing of electrons, polar molecules are non-symmetrical. In comparison, non-polar molecules have a uniform distribution of electrons about all atoms, failure of which will cause charge center generation and polarity of the molecule. This results in symmetry of the molecule about its center. The main intermolecular forces responsible for interactions between non-polar molecules are London dispersion forces. In comparison, polar molecules use dipole-dipole interactions for interacting with other polar molecules.
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