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My textbook says that NH3 has more dipole moment than NF3 despite F being more electronegative than H, because the dipole moment due to the lone pair on N points in the same direction as the ones due to the H atoms, but not the F atoms. But this is the only time it talks about a dipole moment being caused by a lone pair. In multiple examples and questions involving calculating dipoles with H20, HF, etc (that contain lone pairs), they are just ignored. It's the same with other websites.
Are lone pairs negligible when calculating dipoles if they are on O, F, etc atoms?

Hayden Soares
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    I think you are missing the very point of it, and the lone pairs are not the issue. Think of a molecule where N is connected to N, that is, N2. N is more electronegative than H and less so than F, so the dipole moment should be somewhere between those of NH3 and NF3, shouldn't it? Is it? – Ivan Neretin Dec 23 '20 at 13:07
  • Otherwise stated when you think of the actual electronegativity of a fragment the distribution of electrons, either in the other bonds or in lone pairs is important, too. Also the electrical dipole moment is a vector. It can be that it sums to zero. So it is not you neglect lone pairs, just the effect is cancelled by some other(s). – Alchimista Dec 24 '20 at 11:45

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