Question

Boron trifluoride ($B{F}_3$) is a nonpolar molecule, whereas ammonia ($N{H}_3$) is a polar molecule. The difference in polarities is related to the fact that :

• A. $B{F}_3$ has no hydrogen bonding and $N{H}_3$ does
• B. $B{F}_3$ is a triangular planar and $N{H}_3$ is pyramidal
• C. $B{F}_3$ is a Lewis base and $N{H}_3$ is a lewis acid
• D. the B-F bond is less polar than the N-H bond
• E. boron is more electronegative than nitrogen

Answer 1

The correct option is B $B{F}_3$ is a triangular planar and $N{H}_3$ is pyramidal

Though the $B-F$ bond in $B{F}_3$ is polar, but they arrange themselves in trigonal planar geometry and hence cancel out each other due to symmetry.Therefore, there is no net dipole moment.

Whereas in $N{H}_3$, the shape of molecule is trigonal pyramidal with no symmetry, hence there is a net dipole moment.