Question

Which is the correct order of dipole moments of $B{F}_3,N{F}_3$ and $N{H}_3?$

• A. $N{H}_3>B{F}_3>N{F}_3$
• B. $B{F}_3>N{F}_3>N{H}_3$
• C. $N{H}_3>N{F}_3>B{F}_3$
• D. $N{F}_3>N{H}_3>B{F}_3$

Answer 1

Answer: (C)

$B{F}_3$ has zero dipole moment.



In $N{H}_3,N$ is more electronegative than $H$. So, nitrogen pulls the electron from H towards itself and the direction of moment is same due to $N-H$ bond as that of the lone pair of electrons on nitrogen.



In $N{F}_3,F$ is more electronegative than $N$. All $F$ atoms pull the electrons towards themselves and resultant dipole moment is opposite to the direction of that of the lone pair at $N$ atom. Hence, net dipole moment decreases.



Therefore, dipole moment of $N{H}_3$ is greater than $N{F}_3$. Hence, order of dipole moment is

$N{H}_3>N{F}_3>B{F}_3$