Which of the following substances would you expect to have a...

Which of the following substances would you expect to have a nonzero dipole moment? Explain, and show the direction of each. $\begin{array}{llll}{\text { (a) } \mathrm{NF}_{3}} & {\text { (b) } \mathrm{CH}_{3} \mathrm{NH}_{2}} & {\text { (c) } \mathrm{XeF}_{2}} & {\text { (d) } \mathrm{PCl}_{5}}\end{array}$

Which of the following substances would you expect to have a nonzero dipole moment? Explain, and show the direction of each.
$\begin{array}{llll}{\text { (a) } \mathrm{NF}_{3}} & {\text { (b) } \mathrm{CH}_{3} \mathrm{NH}_{2}} & {\text { (c) } \mathrm{XeF}_{2}} & {\text { (d) } \mathrm{PCl}_{5}}\end{array}$

Key Concepts

Vector Addition of Bond Dipoles

The overall dipole moment of a molecule is determined by the vector sum of its individual bond dipoles. Each bond’s polarity contributes a vector quantity to the molecule’s total dipole, and the geometric orientation of these vectors dictates whether they add constructively to produce a net dipole or cancel each other out to yield a nonpolar molecule.

Symmetry and Dipole Cancellation

Symmetry plays a central role in determining if a molecule has a net dipole moment. Even if a molecule has polar bonds, a symmetrical arrangement can result in their dipole vectors canceling out, yielding a nonpolar molecule. This concept is critical when evaluating molecules with multiple bonds to predict overall polarity.

Electronegativity Differences

This concept involves the relative ability of atoms to attract electrons in a bond. Variations in electronegativity between bonded atoms result in polar bonds, which are a necessary component of a molecule's overall dipole moment. The differences determine the direction and magnitude of individual bond dipoles.

Molecular Geometry

The three-dimensional arrangement of atoms within a molecule, or its molecular geometry, is crucial in determining whether the polar bond dipoles add up to a net dipole moment. Specific geometries, such as bent or trigonal pyramidal shapes, typically lead to a nonzero dipole moment, while linear or symmetrical arrangements can cancel out the individual bond dipoles.

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