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# Nitrogen Trihalides

APCHEM-8LUBKE

The figure above represents any of the four trihalides of nitrogen, ${ NF }_{ 3 }$, ${ NCl }_{ 3 }$, ${ NBr }_{ 3 }$, and ${ NI }_{ 3 }$, where the X represents the halogen atoms. Here is some additional information regarding the elements involved.

N 3.0 70 pm
F 4.0 64 pm
Cl 3.0 99 pm
Br 2.8 114 pm
I 2.5 133 pm

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Which of the following is expected to be the LEAST polar molecule, and for what reason?

A

${ NI }_{ 3 }$

The bond polarities off-set the effect of the lone pair.

B

${ NBr }_{ 3 }$

The bonds 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

${ NCl }_{ 3 }$

Nitrogen and chlorine each have electronegativities of 3.0, so the bonds are nonpolar, which means the molecule will be nonpolar.

D

${ NF }_{ 3 }$

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.