Dipole Moment — Polarity, zero dipole
Chemical Bonding
15
JEE Qs
8%
Hard
75
min
Always determine the correct molecular geometry first using VSEPR theory and then perform vector addition of individual bond dipoles and lone pair contributions to find the net dipole moment.
🧮 Key Formulas
✅ Key Points for JEE
- 1Dipole moment is a vector quantity, directed from the positive pole to the negative pole (or less electronegative to more electronegative atom).
- 2For polyatomic molecules, the net dipole moment is the vector sum of all individual bond dipoles and lone pair contributions.
- 3Highly symmetrical molecules (e.g., CO2, CCl4, BF3, XeF4) often have zero net dipole moment even if individual bonds are polar, due to perfect vector cancellation.
- 4Lone pairs contribute significantly to the overall dipole moment, and their spatial orientation (determined by VSEPR) is crucial for predicting the net dipole moment (e.g., NH3 vs NF3).
- 5Cis-trans isomers often exhibit different dipole moments; trans isomers of identical substituents tend to have zero dipole moment due to cancellation, while cis isomers usually have a net dipole moment.
⚠️ Common Mistakes
- ✕Confusing bond polarity with molecular polarity: a molecule can have polar bonds but be nonpolar overall due to symmetrical geometry.
- ✕Incorrectly determining molecular geometry using VSEPR theory, leading to wrong vector addition/cancellation.
- ✕Ignoring the contribution of lone pairs to the overall dipole moment, especially when comparing similar molecules (e.g., H2O vs CO2, NH3 vs NF3).
📝 Practice Questions
See allQ75.Total number of non bonded electrons present in NO2− ion based on Lewis theory is 2025 (29 Jan Shift 2) JEE Main Previous Year Paper
Q71.The number of molecules/ions that show linear geometry among the following is ________ SO2, BeCl2, CO2, N−3 , NO2, F2O, XeF2, NO+2 , I−3 , O3
Q69.Arrange the following compounds in increasing order of their dipole moment : HBr, H2 S, NF3 and CHCl3 (1) H2 S < HBr < NF3 < CHCl3 (2) NF3 < HBr < H2 S < CHCl3 (3) HBr < H2 S < NF3 < CHCl3 (4) CHCl3 < NF3 < HBr < H2 S
Q64.Which of the following statement is true with respect to H2O, NH3 and CH4 ? A. The central atoms of all the molecules are sp3 hybridized. B. The H −O −H, H −N −H and H −C −H angles in the above molecules are 104.5∘, 107.5∘ and 109.5∘ , respectively. C. The increasing order of dipole moment is CH4 < NH3 < H2O. D. Both H2O and NH3 are Lewis acids and CH4 is a Lewis base. E. A solution of NH3 in H2O is basic. In this solution NH3 and H2O act as Lowry-Bronsted acid and base respectively. Choose the correct answer from the options given below: (1) A, B and C Only (2) A, D and E Only (3) C, D and E Only (4) A, B, C and E Only
Q70.Which of the following linear combination of atomic orbitals will lead to formation of molecular orbitals in homonuclear diatomic molecules [internuclear axis in z -direction] ? A. 2pz and 2px B. 2 s and 2px C. 3 dxy 2025 (24 Jan Shift 1) JEE Main Previous Year Paper and 3 dx2−y2 D. 2 s and 2pz E. 2pz and 3dx2 −y2 Choose the correct answer from the options given below: (1) A and B Only (2) D Only (3) E Only (4) C and D Only
Q53.Given below are two statements : Statement (I): Experimentally determined oxygen-oxygen bond lengths in the O3 are found to be same and the bond length is greater than that of a O = O (double bond) but less than 2025 (24 Jan Shift 2) JEE Main Previous Year Paper that of a single (O −O) bond. Statement (II) : The strong lone pair-lone pair repulsion between oxygen atoms is solely responsible for the fact that the bond length in ozone is smaller than that of a double bond (O = O) but more than that of a single bond (O −O). In the light of the above statements, choose the correct answer from the options given below : (1) Both Statement I and Statement II are false (2) Statement I is false but Statement II is true (3) Statement I is true but Statement II is false (4) Both Statement I and Statement II are true
NCERT Chapters
- Class 11 Chemistry Ch 4: Chemical Bonding and Molecular Structure