The dipole moments of NH3, H20, and NF3 (Figure 3-17) reveal the effect of
lone pairs, which can be dramatic. In ammonia, the averaged N - H bond polarities and
the lone pair all point in the same direction, resulting in a large dipole moment. Water
has an even larger dipole moment because the polarities of the 0 -H bonds and the
two lone pairs results in polarities all reinforcing each other. On the other hand, NF3 has
a very small dipole moment, the result of the polarity of the three N-F bonds opposing
polarity of the lone pair. The sum of the three N-F bond moments is larger than
the lone pair effect, and the lone pair is the positive end of the molecule. In cases such
as those of NF3 and SO2, the direction of the dipole is not easily predicted bccausc of
the opposing polarities. SO2 has a large dipole moment (1.63 D), with the polarity of
the lone pair prevailing over that of the S - 0 bonds.
The dipole moments of NH3, H20, and NF3 (Figure 3-17) reveal the effect oflone pairs, which can be dramatic. In ammonia, the averaged N - H bond polarities andthe lone pair all point in the same direction, resulting in a large dipole moment. Waterhas an even larger dipole moment because the polarities of the 0 -H bonds and thetwo lone pairs results in polarities all reinforcing each other. On the other hand, NF3 hasa very small dipole moment, the result of the polarity of the three N-F bonds opposingpolarity of the lone pair. The sum of the three N-F bond moments is larger thanthe lone pair effect, and the lone pair is the positive end of the molecule. In cases suchas those of NF3 and SO2, the direction of the dipole is not easily predicted bccausc ofthe opposing polarities. SO2 has a large dipole moment (1.63 D), with the polarity ofthe lone pair prevailing over that of the S - 0 bonds.
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