Question

The figure above represents any of the four trihalides of nitrogenf, $N{F}_3,NC{l}_3,NB{r}_3$, and $N{I}_3$, where the X represents the halogen atoms. Here is some additional information regarding the elements involved.

Element	Electronegativity	Atomic Radius
$N$	$3.0$	$70pm$
$F$	$4.0$	$64pm$
$Cl$	$3.0$	$99pm$
$Br$	$2.8$	$114pm$
$I$	$2.5$	$133pm$

Of the four nitrogen trihalides, only one is not a molecular dipole. Which one is the nonpolar molecule, and why is it nonpolar?

• A. $N{I}_3$. The bond polarities off-set the effect of the lone pair.
• B. $NB{r}_3$. The bond are virtually nonpolar, and the size of the bromine atoms causes the bond angles to be larger than the normal ${109.5}^{\circ }$ for tetrahedral orbital geometry.
• C. $NC{l}_3$. Nitrogen and chlorine each have electronegativities of $3.0$, so the bonds are nonpolar, which means the molecule will be nonpolar.
• D. $N{F}_3$. The electron density in the three N-F bonds is drawn toward the base of the trigonal pyramidal structure, while the lone pair places electron density at the top of the pyramid. The effects off-set.

Answer 1

Answer: (D)

$N{F}_3$. The electron density in the three N-F bonds is drawn toward the base of the trigonal pyramidal structure, while the lone pair places electron density at the top of the pyramid. The effects off-set.

In ${NF}_3$, As $F$ has more electron negativity it falls down where as the lone pair above it will pull up which will totally balance. Hence ${NF}_3$ is a non polar molecule.