Chemistry · Chemical Bonding · NEET
HF > H2O > NH3 > H2S. In Debye units: HF ≈ 1.91 D, H2O ≈ 1.85 D, NH3 ≈ 1.47 D, H2S ≈ 0.97 D. Two things set this order — the electronegativity difference between the atoms, and the molecule's shape. HF has the biggest electronegativity gap (F is the most electronegative atom), so it has the largest dipole.
Because fluorine is the most electronegative element. In HF the shared electron pair is pulled strongly toward F, creating a large charge separation. Also, HF has only one bond, so there is no cancelling of dipoles from other bonds. Big pull + no cancellation = highest dipole moment.
Sulfur is much less electronegative than oxygen, nitrogen or fluorine. So the S–H bonds are only weakly polar. On top of that, the H–S–H angle is small (about 92°), so the bond dipoles do not add up strongly. Weak bond polarity plus poor geometry gives H2S the smallest dipole (≈ 0.97 D).
HF is slightly higher (1.91 D) than H2O (1.85 D). Even though water has two O–H bonds, its bent shape at 104.5° means the two bond dipoles partly cancel. HF has just one very polar H–F bond with nothing to cancel it, so it edges ahead. Both are very close, so remember HF just above H2O.
This is a favourite NEET trap. In NH3 the lone-pair dipole points the same way as the sum of the N–H bond dipoles, so they add up (μ ≈ 1.47 D). In NF3 the N–F bond dipoles point toward F, which is opposite to the lone-pair dipole, so they partly cancel (μ ≈ 0.24 D). So NH3 > NF3 even though F is more electronegative than H.
Step 1: If the molecule is symmetric (like BF3, CO2, CH4, BeF2), its dipole is zero — put it last. Step 2: For the rest, larger electronegativity difference usually means larger dipole. Step 3: If shapes are similar, use electronegativity of the central/other atom. For hydrides: HF > H2O > NH3 > H2S follows falling electronegativity difference.
The correct order of dipole moments for molecules NH3, H2S, CH4 and HF, is:
Which of the following is the correct order of dipole moment?
Identify the correct order for dipole moment: H2O > NH3 > CHCl3.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
HF > H2O > NH3 > H2S. Remember it as electronegativity falling: F > O > N > S. The bigger the electronegativity gap with hydrogen, the bigger the dipole (with a small shape correction for HF vs H2O).
HF ≈ 1.91 D, H2O ≈ 1.85 D, NH3 ≈ 1.47 D, H2S ≈ 0.97 D. The Debye (D) is the unit used for dipole moment; 1 D = 3.336 × 10⁻³⁰ C·m.
Dipole moment is the vector sum of all bond dipoles. If the shape is symmetric (linear, trigonal planar, tetrahedral), the bond dipoles cancel and the net dipole is zero. If the shape is bent or pyramidal, they do not fully cancel, so there is a net dipole.
Yes. A lone pair has its own dipole. In NH3 and H2O it points in a direction that adds to the bond dipoles, raising the value. In NF3 it points opposite to the bond dipoles, lowering the value. This is why NH3 > NF3.
NTA asks 'correct order of dipole moment' almost every year (2019, 2023, 2024, 2025). One or two marks are nearly guaranteed if you know the hydride order plus the NH3 vs NF3 trap and which molecules are zero.
