Chemistry · Chemical Bonding · NEET
The SHAPE is the same, but the DIRECTION of the bond dipoles is flipped. A bond dipole always points from the less electronegative atom toward the more electronegative atom. In N-H, nitrogen (EN 3.0) is more electronegative than hydrogen (EN 2.1), so each bond dipole points from H toward N (toward the top, toward the lone pair). In N-F, fluorine (EN 4.0) is more electronegative than nitrogen, so each bond dipole points from N toward F (away from the top, away from the lone pair). This one flip changes everything.
The lone pair on nitrogen is a concentrated region of negative charge sticking out on one side of the molecule (the top of the pyramid). This makes that side more negative, so it acts like a small dipole pointing away from the nitrogen, out toward the lone pair. This is often called the orbital dipole. It exists in BOTH NH3 and NF3 and points in the same direction in both (toward the lone pair, at the apex).
They ADD. In NH3 the three N-H bond dipoles each point up toward the nitrogen and lone pair. The lone-pair dipole also points up. Because both point the same way, they REINFORCE each other and the total dipole moment is large (1.47 D, about 4.90 x 10^-30 C m in NCERT).
They partly CANCEL. In NF3 the three N-F bond dipoles point down toward the fluorine atoms (away from the lone pair). The lone-pair dipole still points up. Because they point in OPPOSITE directions, they oppose each other. The net dipole is small (0.24 D, about 0.8 x 10^-30 C m in NCERT). This is why NF3 has a much lower dipole moment even though N-F is a very polar bond.
This is the exact trap NTA sets. A single N-F bond is indeed MORE polar than a single N-H bond. But dipole moment is a VECTOR sum of the whole molecule, not one bond. In NF3 those strong N-F dipoles point away from the lone pair and are opposed by the lone-pair dipole, so the total shrinks. In NH3 the weaker bond dipoles point WITH the lone pair, so the total is larger. Direction beats bond strength here.
NH3 = 1.47 D (4.90 x 10^-30 C m) and NF3 = 0.24 D (0.8 x 10^-30 C m), from NCERT. You do not need to memorize exact numbers for NEET; just remember NH3 > NF3 and the reason (add vs oppose).
Identify the correct answer.
Which of the following is the correct order of dipole moment?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
NH3 has the higher dipole moment (1.47 D) compared to NF3 (0.24 D), even though both are pyramidal with a lone pair on nitrogen.
In NF3 the three N-F bond dipoles point down toward fluorine while the lone-pair dipole points up. They are in opposite directions and partly cancel, so the net dipole moment is very small.
A bond dipole points toward the more electronegative atom. In N-H, N is more electronegative, so the dipole points toward N (up, toward the lone pair). In N-F, F is more electronegative, so the dipole points toward F (down, away from the lone pair).
Yes. The lone pair on nitrogen is concentrated negative charge on one side, creating its own dipole (orbital dipole) pointing toward the lone pair. It adds to the bond dipoles in NH3 and opposes them in NF3.
Yes, it is a repeat favourite. NEET 2024 and NEET 2019 Odisha both tested NH3 vs NF3 dipole moment directly, and it also appears inside dipole-moment order questions.
