Nitrogen trifluoride dipole moment

H2O2 (hydrogen peroxide) chirality, 80 symmetry elements, 82 NF3 (nitrogen trifluoride) dipole moment, 98, 99 NFl3 (ammonia)... 

Nitrogen trifluoride is very stable at ambient temperatures. It is much less reactive than other nitrogen trihahdes. The molecule has a very low dipole moment and the lone pair of electrons on the nitrogen atom does not usually form complexes. 

Problem 2.33 Nitrogen trifluoride (NF,) and ammonia (NH,) have an electron pair at the fourth corner of a tetrahedron and have similar electronegativity differences between the elements (1.0 for N and F and 0.9 for N and H). Explain the larger dipole moment of ammonia (I.46D) as compared with that of NF, (0.24 D). ... 

The dipole moment of nitrogen trifluoride (0.234 D) is much smaller than that of ammonia (1.42 D), though the structures are very similar. One explanation of this apparent anomaly is that in the trifluoride the moment associated with the positive nitrogen atom and its lone pair of electrons is opposite in direction to the moment along the same axis associated with the three N-F bonds. In ammonia the polarities are reversed and the moments due to the N-H bonds and to the electron pair on nitrogen operate in the same direction (154). 

Now, what kind of dipole moment would we expect for nitrogen trifluoride, NF3, which, like ammonia, is pyramidal Fluorine is the most electronegative element of all and should certainly pull electrons strongly from nitrogen the N—F bonds should be highly polar, and their vector sum should be large—far larger than for ammonia with its modestly polar N—H bonds. 

What are the facts Nitrogen trifluoride has a dipole moment of only 0.24 d. It is not larger than the moment for ammonia, but rather is much smaller. 

Problem 1.7 In Sec. 1.12 we rejected two conceivable electronic configurations for ammonia, (a) If nitrogen were 5/ 2-hybridized, what dipole moment would you expect for ammonia What is the dipole moment of ammonia (b) If nitrogen used p orbitals for bonding, how would you expect the dipole moments of ammonia and nitrogen trifluoride to compare How do they compare ... 

You can see this effect of lone pairs on the dipole moment of nitrogen trifluoride, NF3. Judging by the electronegativity difference, you would expect each N—F bond to be quite polar. Yet the dipole moment of nitrogen trifluoride is only 0.2 D. (By contrast, ammonia has a dipole moment of 1.47 D.) The explanation for the small dipole moment in NF3 appears in Figure 10.19. The lone pair on nitrogen has a dipole-moment contribution that is directed outward from the nucleus, because the electrons are offset from the nuclear center. This dipole-moment contribution thus opposes the N—F bond moments. ... 

Explain why nitrogen trifluoride has a small dipole moment even though it has polar bonds in a trigonal pyramidal arrangement. 

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