Question

Using electronegativity values, determine bond polarities and the net dipoles in a molecule of PCl3 and indicate if the molecule will be polar.

Answer 1

Solution:

PCl₃ is polar molecule due to its trigonal pyramidal geometry. Out of 5 valence electrons, only three electrons of phosphorus are used for bonding with chlorine, while the other two are unshared (lone pair). Hence, its hybridization is sp3. Due to presence of lone pair on phosphorous atom, the three chlorine atoms are thus not in the same plane as the phosphorus atom. Electronegativity is the tendency of a bonded atom to attract electrons to itself. The difference in electronegativity (ΔE_N) between bonded atoms can indicate whether the bond is nonpolar, polar covalent, or ionic. According to Pauling, when:

a) ΔE_N < 0.4 is considered to be nonpolar.

b) ΔE_N = 0.5 to 1.7 are considered polar covalent.

c) ΔE_N > 1.7 is considered ionic.

The electronegativity of P is 2.19 and the electronegativity of Cl is 3.16, hence the difference between electronegativity (ΔE_N) of Cl and P will be (3.16-2.19)= 0.97

Hence, PCl₃ is considered to be polar covalent molecule.