PCl3, or phosphorus trichloride, is a polar molecule. This polarity arises from the molecular geometry and the difference in electronegativity between phosphorus and chlorine.
To break it down, phosphorus has an electronegativity of approximately 2.19, while chlorine’s electronegativity is about 3.16. This difference means that chlorine atoms attract the bonding electrons more strongly than the phosphorus atom does. As a result, the P-Cl bonds have a dipole moment, with a partial negative charge (δ-) near the chlorine atoms and a partial positive charge (δ+) near the phosphorus atom.
Furthermore, PCl3 has a trigonal pyramidal shape due to the presence of a lone pair of electrons on the phosphorus atom. This shape prevents the dipole moments of the P-Cl bonds from canceling out, leading to an overall dipole moment for the molecule. Consequently, the asymmetrical nature of the molecule confirms that PCl3 is polar.