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Chapter 22: Problem 70

The structures of the \(\mathrm{NH}_{3}\) and \(\mathrm{NF}_{3}\) molecules are similar, yet the dipole moment for the \(\mathrm{NH}_{3}\) molecule is rather large (1.47 debye) and that of the NF \(_{3}\) molecule is rather small (0.24 debye). Provide an explanation for this difference in the dipole moments.

Short Answer

Expert verified
The difference in the dipole moments of \(\mathrm{NH}_{3}\) and \(\mathrm{NF}_{3}\) can be explained by the directions of their bond dipoles. In \(\mathrm{NH}_{3}\), all bond dipoles add up, creating a large overall dipole moment. In contrast, the bond dipoles in \(\mathrm{NF}_{3}\) partially cancel each other out due to the molecule's geometry, resulting in a smaller overall dipole moment.

Step by step solution

01

Identify Structures and Dipole Moments

The \(\mathrm{NH}_{3}\) and \(\mathrm{NF}_{3}\) molecules have trigonal pyramidal structures. In \(\mathrm{NH}_{3}\), hydrogen is electron-poor and nitrogen is electron-rich, creating a dipole moment directed from hydrogen to nitrogen. In \(\mathrm{NF}_{3}\), fluorine is more electronegative than nitrogen, creating individual bond dipole moments directed from nitrogen to fluorine.
02

Explain NH3 Dipole Moment

In \(\mathrm{NH}_{3}\), the individual bond dipole moments all point to the nitrogen atom. Because of the symmetric, pyramidal shape of the molecule, these bond dipoles do not cancel out, resulting in a large overall molecular dipole moment (1.47 debye).
03

Explain NF3 Dipole Moment

In \(\mathrm{NF}_{3}\), although each N-F bond has a strong dipole moment, the geometry of the molecule causes these dipoles to be oriented in such a way that they partially cancel each other out. The resulting overall dipole moment is smaller (0.24 debye).

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Most popular questions from this chapter

Without doing detailed calculations, explain in which of the following materials you would expect to find the greatest mass percent of hydrogen: seawater, the atmosphere, natural gas \(\left(\mathrm{CH}_{4}\right),\) ammonia.

All the group 15 elements form trifluorides, but nitrogen is the only group 15 element that does not form a pentafluoride. (a) Suggest a reason why nitrogen does not form a pentafluoride. (b) The observed bond angle in \(\mathrm{NF}_{3}\) is approximately \(102.5^{\circ} \mathrm{C} .\) Use VSEPR theory to rationalize the structure of the \(\mathrm{NF}_{3}\) molecule.

Polonium is the only element known to crystallize in the simple cubic form. In this structure, the interatomic distance between a Po atom and each of its six nearest neighbors is \(335 \mathrm{pm}\). Use this description of the crystal structure to estimate the density of polonium.

The structure of \(\mathrm{N}\left(\mathrm{SiH}_{3}\right)_{3}\) involves a planar arrangement of \(\mathrm{N}\) and \(\mathrm{Si}\) atoms, whereas that of the related compound \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\) has a pyramidal arrangement of N and \(\mathrm{C}\) atoms. Propose bonding schemes for these molecules that are consistent with this observation.

Use VSEPR theory to predict the probable geometric structures of the molecules (a) \(\mathrm{O}_{2} \mathrm{XeF}_{2} ;\) (b) \(\mathrm{O}_{3} \mathrm{XeF}_{2}\) (c) OXeF \(_{4}\).
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