Dipole Moment

Q: Arrange the following compounds in the correct order of dipole moment.

H 2 O > NH 3 > NF 3 > BeF 2 = CH 4 i.e., the dipole moment of the compounds is H 2 O = 1084D, NH 3 = 1.49D, NF 3 =0.24D, BeF 2 = CH 4 = 0

Q: Why BF3 dipole moment is zero?

Despite having three polar B—F bonds, BF 3 dipole moment is zero. Because BF 3 has sp2 hybridisation and a regular trigonal planal shape, this is the case. As a result, the individual dipole moments of polar bonds cancel out, resulting in a zero overall dipole moment.

Dipole Moment - Overview, Definition, Formula, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:30 PM IST

A dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating the polarity of the molecule. It arises when there is an uneven distribution of electron density, resulting in partial positive and negative charges at different ends of the molecule. The dipole moment is a vector quantity, having both magnitude and direction. The magnitude of the dipole moment is given by the product of the charge difference and the distance between the charges. It is expressed in Debye units (D).

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Dipole Moment
Some Solved Examples
Summary

Dipole Moment

When the covalent bond forms between two different atoms then because of the difference in electronegativity the electrons get shifted towards the more electronegative atom and thus form the polar covalent bond and this polar molecule is known as a dipole molecule. The more electronegative atom occupies a partial negative charge (δ-) and the other atom possesses a partial positive charge (δ+). This separation of charge gives rise to a bond dipole moment. The magnitude of a bond dipole moment is represented by the Greek letter mu (µ) and is given by the formula as shown below, where Q is the magnitude of the partial charges (determined by the electronegativity difference) and r is the distance between the charges: μ=Qr

Two images are shown and labeled, “a” and “b.” Image a shows a large sphere labeled, “C,” a left-facing arrow with a crossed end, and a smaller sphere labeled “H.” Image b shows a large sphere labeled, “B,” a right-facing arrow with a crossed end, and a smaller sphere labeled “F.”

(a) There is a small difference in electronegativity between C and H, represented as a short vector. (b) The electronegativity difference between B and F is much larger, so the vector representing the bond moment is much longer.

For diatomic molecules, there is only one bond, so its bond dipole moment determines the molecular polarity. Homonuclear diatomic molecules such as Br₂ and N₂ have no difference in electronegativity, so their dipole moment is zero. For heteronuclear molecules such as CO, there is a small dipole moment. For HF, there is a larger dipole moment because there is a larger difference in electronegativity.

Some Solved Examples

Example 1: The most polar compound among the following is :

Solution

Resultant dipole moment -

Let XY and XZ be two polar bonds inclined at an angle θ their dipole moments are μ1 and μ2

Resultant μR=μ12+μ22+2μ1μ2cos⁡θ

In the bond dipole vector of the C-F bond is not subtractive.

Example 2: The molecule which has zero dipole moment is :

1)CH₂Cl₂

2) BF₃

3)NF₃

4)ClO₂

Solution

The dipole moment of a compound having regular geometry and the same type of atom is zero.

BF₃ has a triangular planar structure hence its resultant dipole moment is zero.

Hence, the correct answer is Option (2)

Example 3: Which of the following isomers will have the highest dipole moment?

1) Ortho form

2)Meta form

3)Para form

4)All have equal dipole moment

Solution

Because the dipole moment is a vector quantity and the resultant dipole moment is highest when the angle between them is minimum.

Hence, the option number (1) is correct.

Example 4: H₂O has a net dipole moment, while BeF₂ has zero dipole moment, because:

1)H₂O molecule is linear while BeF₂ is bent.

2) The BeF₂ molecule is linear while H₂O is bent.

3)Fluorine is more electronegative than oxygen.

4)Be is more electronegative than oxygen.

Solution

As we have learned,

The structure of H₂O and BeF₂ are:

By seeing the bond angle we can say that BeF₂ molecule is linear while H₂O is bent. Moreover, a water molecule is sp³ hybridized and BeF₂ is sp hybridized.
Hence, option number (2) is correct.

Example 5: Which one of the following pairs of molecules will have permanent dipole moments for both members?

1) SiF₄ and NO₂
2) NO₂ and CO₂
3) NO₂ and O₃
4) SiF₄ and CO₂

Solution

Both NO₂ and O₃ are bent molecules with asymmetry. Hence both will exhibit permanent dipole moment.

Hence, the answer is the option(3).

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Summary

The dipole moment points from the positive to the negative charge and is quantified by the product of the charge difference and the distance between the charges, expressed in Debye units (D). The presence and magnitude of a dipole moment are determined by the electronegativity of atoms and the molecule's geometry. Polar molecules have significant dipole moments, while nonpolar molecules have zero dipole moments. Understanding dipole moments is essential for predicting molecular behavior in electric fields, interactions with other molecules, and solubility in solvents.

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Frequently Asked Questions (FAQs)

1. What is the best method for determining the greatest dipole moment?

A dipole moment occurs when the electronegativity of two atoms engaged in a bond is different. The bond's dipole moment and polarity increase as the electronegativity gap between the two atoms grows.

2. What is the dipole moment's symbol and dipole moment definition?

The dipole moment (µ) is the result of multiplying the magnitude of the charge Q by the distance r between the charges to get the net molecular polarity at each end of the molecular dipole. The partition of charges in a molecule is represented by dipolar moments. As a result, this article briefly discusses the definition and formula of dipole moments.

3. Arrange the following compounds in the correct order of dipole moment.

H₂O > NH₃ > NF₃ > BeF₂ = CH₄

i.e., the dipole moment of the compounds is H₂O = 1084D, NH₃ = 1.49D,

NF₃ =0.24D, BeF₂ = CH₄ = 0

4. What is permanent dipole moment?

Permanent Dipole Moments arise when the electronegativity of two atoms in a molecule differs significantly. The atom with the higher electronegativity will attract more electrons, resulting in a partial negative charge surrounding it and a partial positive charge around the atom with the lower electronegativity. Molecules possessing persistent dipole moments, as opposed to dipole moments generated by other molecules, are simply polar molecules. They're significant because a molecule's polarity influences many of its characteristics and interactions with other molecules.

5. Why BF3 dipole moment is zero?

Despite having three polar B—F bonds, BF₃dipole moment is zero. Because BF₃ has sp2 hybridisation and a regular trigonal planal shape, this is the case. As a result, the individual dipole moments of polar bonds cancel out, resulting in a zero overall dipole moment.

6. What is a dipole moment?

A dipole moment is a measure of the separation of positive and negative electrical charges in a molecule. It occurs when there is an uneven distribution of electrons, resulting in one end of the molecule being slightly more positive and the other slightly more negative.

7. How is dipole moment related to molecular polarity?

Dipole moment is directly related to molecular polarity. Molecules with a non-zero dipole moment are polar, while those with a dipole moment of zero are non-polar. The larger the dipole moment, the more polar the molecule.

8. What is the unit of dipole moment?

The SI unit of dipole moment is coulomb-meter (C⋅m). However, it is often expressed in debye (D), where 1 D = 3.336 × 10^-30 C⋅m.

9. Can a symmetrical molecule have a dipole moment?

Generally, symmetrical molecules do not have a dipole moment. However, there are exceptions, such as ozone (O3), which has a bent structure despite being composed of only one element.

10. How does electronegativity affect dipole moment?

Electronegativity differences between atoms in a molecule contribute to dipole moment. Larger electronegativity differences result in greater charge separation and, consequently, a larger dipole moment.

11. What is the formula for calculating dipole moment?

The dipole moment (μ) is calculated using the formula: μ = q × d, where q is the magnitude of the charge and d is the distance between the charges.

12. Why do some polar molecules have a net dipole moment of zero?

Some polar molecules, like carbon dioxide (CO2), have a net dipole moment of zero due to their linear symmetry. The individual bond dipoles cancel each other out, resulting in no overall dipole moment.

13. How does bond angle affect dipole moment?

Bond angle can significantly affect dipole moment. For example, in water (H2O), the bent structure (104.5°) contributes to its strong dipole moment, whereas the linear structure of carbon dioxide results in a zero net dipole moment.

14. Can temperature affect dipole moment?

Temperature can indirectly affect dipole moment by influencing molecular vibrations and rotations. However, the intrinsic dipole moment of a molecule remains constant with temperature changes.

15. What is the relationship between dipole moment and boiling point?

Molecules with higher dipole moments generally have higher boiling points. This is because stronger intermolecular forces (dipole-dipole interactions) require more energy to overcome, resulting in higher boiling points.

16. How does dipole moment influence solubility?

Molecules with similar dipole moments tend to be more soluble in each other. For example, polar molecules (with higher dipole moments) are more soluble in polar solvents, while non-polar molecules are more soluble in non-polar solvents.

17. Can a molecule with polar bonds be non-polar overall?

Yes, a molecule with polar bonds can be non-polar overall if the bond dipoles cancel each other out due to molecular geometry. An example is carbon tetrachloride (CCl4), which has polar C-Cl bonds but is non-polar due to its tetrahedral symmetry.

18. How does dipole moment affect intermolecular forces?

Dipole moment directly influences dipole-dipole interactions between molecules. Molecules with higher dipole moments experience stronger intermolecular attractions, affecting properties like boiling point, melting point, and solubility.

19. What is the difference between a permanent dipole and an induced dipole?

A permanent dipole exists in molecules with an inherent charge separation due to electronegativity differences. An induced dipole is temporary and occurs when an external electric field or a nearby polar molecule causes a momentary charge separation in a normally non-polar molecule.

20. How does molecular size affect dipole moment?

Molecular size can affect dipole moment in complex ways. Larger molecules may have more opportunities for charge separation, potentially leading to larger dipole moments. However, symmetry and bond cancellation effects in larger molecules can also result in smaller net dipole moments.

21. Can dipole moment be measured experimentally?

Yes, dipole moment can be measured experimentally using various techniques such as microwave spectroscopy, dielectric constant measurements, and laser-induced fluorescence.

22. Why do some molecules with polar bonds have no dipole moment?

Molecules with polar bonds may have no dipole moment if their molecular geometry results in a symmetrical distribution of charge. For example, BF3 has polar B-F bonds, but its trigonal planar structure results in a net dipole moment of zero.

23. How does hybridization affect dipole moment?

Hybridization can affect dipole moment by influencing molecular geometry and electron distribution. For instance, sp3 hybridization in methane (CH4) results in a tetrahedral structure with no dipole moment, while sp2 hybridization in formaldehyde (H2CO) contributes to its polar nature.

24. What is the relationship between dipole moment and dielectric constant?

Substances with higher dipole moments generally have higher dielectric constants. The dielectric constant is a measure of a material's ability to store electrical energy, which is influenced by the alignment of dipoles in an electric field.

25. How does dipole moment affect the behavior of molecules in an electric field?

Molecules with dipole moments tend to align themselves with an external electric field. This alignment can affect properties such as dielectric constant, refractive index, and the molecule's behavior in spectroscopic techniques.

26. Can a single atom have a dipole moment?

A single atom in its ground state cannot have a permanent dipole moment because it has a spherically symmetric electron distribution. However, atoms can have induced dipole moments in the presence of an external electric field.

27. How does dipole moment relate to molecular orbital theory?

In molecular orbital theory, dipole moment is related to the distribution of electron density in bonding and antibonding orbitals. Asymmetric electron distribution in these orbitals contributes to the overall dipole moment of the molecule.

28. What is the significance of dipole moment in drug design?

Dipole moment is crucial in drug design as it affects a molecule's solubility, membrane permeability, and binding to target proteins. Understanding and manipulating dipole moments can help in designing more effective and bioavailable drugs.

29. How does dipole moment influence hydrogen bonding?

Molecules with higher dipole moments are more likely to form strong hydrogen bonds. The partial charges created by dipole moments contribute to the electrostatic attraction in hydrogen bonding, affecting properties like boiling point and solubility.

30. Can dipole moment be used to predict a molecule's reactivity?

While dipole moment alone cannot predict reactivity, it can provide insights into a molecule's electron distribution and potential reaction sites. Molecules with higher dipole moments may be more reactive in certain types of reactions, particularly those involving polar or charged species.

31. How does dipole moment affect the vapor pressure of a liquid?

Liquids composed of molecules with higher dipole moments generally have lower vapor pressures. This is because the stronger intermolecular attractions (due to dipole-dipole interactions) require more energy to overcome, reducing the tendency of molecules to escape into the gas phase.

32. What is the relationship between dipole moment and polarizability?

While dipole moment and polarizability are related concepts, they are distinct. Dipole moment refers to the permanent charge separation in a molecule, while polarizability is the ease with which a molecule's electron distribution can be distorted by an external electric field. Molecules with high polarizability can often form strong induced dipoles.

33. How does the concept of dipole moment apply to ionic compounds?

Ionic compounds typically have very large dipole moments due to the complete transfer of electrons between atoms. However, in highly symmetrical ionic crystals (like NaCl), the overall dipole moment can be zero due to the cancellation of individual ion pair dipoles.

34. Can dipole moment change during a chemical reaction?

Yes, dipole moment can change during a chemical reaction as the electron distribution and molecular geometry are altered. This change in dipole moment can be used to monitor the progress of some reactions or to understand reaction mechanisms.

35. How does dipole moment affect the intensity of infrared (IR) absorption?

The intensity of IR absorption is directly related to the change in dipole moment during molecular vibrations. Vibrations that cause larger changes in dipole moment result in stronger IR absorption bands, making dipole moment crucial in IR spectroscopy.

36. What is the role of dipole moment in determining a molecule's melting point?

Molecules with higher dipole moments often have higher melting points due to stronger intermolecular forces. These forces require more energy to overcome, resulting in higher temperatures needed to transition from solid to liquid state.

37. How does dipole moment influence the miscibility of liquids?

Liquids with similar dipole moments are more likely to be miscible. This is why "like dissolves like" – polar liquids (high dipole moments) mix well with other polar liquids, while non-polar liquids (low or zero dipole moments) mix better with other non-polar liquids.

38. Can dipole moment be used to predict a molecule's shape?

While dipole moment alone cannot predict molecular shape, it can provide clues. A non-zero dipole moment in a molecule composed of the same atoms (like H2O) indicates a non-linear structure. However, a zero dipole moment doesn't necessarily mean a symmetrical shape (e.g., CO2 is linear but BF3 is trigonal planar).

39. How does dipole moment affect the behavior of molecules in a magnetic field?

Dipole moment itself doesn't directly affect a molecule's behavior in a magnetic field. However, molecules with permanent dipole moments often have unpaired electrons, which can make them paramagnetic and responsive to magnetic fields.

40. What is the significance of dipole moment in atmospheric chemistry?

Dipole moment is crucial in atmospheric chemistry, particularly in understanding the greenhouse effect. Molecules with strong dipole moments, like water vapor and carbon dioxide, are effective at absorbing infrared radiation, contributing significantly to the Earth's heat retention.

41. How does dipole moment relate to the concept of electronegativity?

Dipole moment is closely related to electronegativity. In a bond between atoms with different electronegativities, electrons are drawn towards the more electronegative atom, creating a dipole. The greater the electronegativity difference, the larger the bond dipole moment.

42. Can dipole moment be used to explain the trends in boiling points of the hydrogen halides (HF, HCl, HBr, HI)?

While dipole moment contributes to the trend, it doesn't fully explain it. HF has the highest dipole moment but not the highest boiling point in the series. This is because hydrogen bonding in HF plays a more significant role in determining its boiling point than just its dipole moment.

43. How does the concept of dipole moment apply to metallic bonding?

In metallic bonding, the concept of dipole moment is less applicable due to the delocalized nature of electrons. However, some surface phenomena in metals can be understood using concepts related to dipole moments, such as work function and surface dipole layers.

44. What is the relationship between dipole moment and surface tension?

Liquids with higher dipole moments generally have higher surface tensions. This is because the strong intermolecular attractions (resulting from dipole-dipole interactions) create a greater cohesive force between molecules at the surface.

45. How does dipole moment affect the rate of evaporation?

Molecules with higher dipole moments typically evaporate more slowly. The stronger intermolecular forces due to dipole-dipole interactions require more energy to overcome, reducing the rate at which molecules can escape from the liquid phase into the gas phase.

46. Can dipole moment explain why some gases deviate from ideal gas behavior?

Yes, dipole moment contributes to the deviation from ideal gas behavior. Gases composed of molecules with significant dipole moments experience stronger intermolecular attractions, leading to deviations from the ideal gas law, especially at high pressures or low temperatures.

47. How does dipole moment influence the critical temperature of a substance?

Substances with higher dipole moments generally have higher critical temperatures. The stronger intermolecular forces require more thermal energy to overcome, resulting in a higher temperature at which the liquid and gas phases become indistinguishable.

48. What is the significance of dipole moment in understanding enzyme-substrate interactions?

Dipole moment plays a crucial role in enzyme-substrate interactions by influencing the electrostatic complementarity between the enzyme's active site and the substrate. This affects the binding affinity and specificity of enzyme-substrate complexes.

49. How does dipole moment relate to the concept of polarization in chemistry?

Dipole moment is a measure of the degree of polarization in a molecule. Polarization refers to the separation of positive and negative charges, and the dipole moment quantifies this separation. Molecules with larger dipole moments are considered more polarized.

50. Can dipole moment help explain the differences in the physical properties of isomers?

Yes, dipole moment can help explain differences in physical properties of isomers. Structural isomers can have different dipole moments due to varying arrangements of atoms, leading to differences in properties like boiling point, solubility, and intermolecular interactions.

51. How does dipole moment affect the behavior of molecules in chromatography?

Dipole moment influences the interaction of molecules with the stationary and mobile phases in chromatography. Molecules with higher dipole moments may interact more strongly with polar stationary phases, affecting their retention times and separation.

52. What is the role of dipole moment in understanding the solvation of ions?

Dipole moment is crucial in ion solvation. Solvent molecules with higher dipole moments can more effectively orient themselves around ions, forming solvation shells. This affects properties like solubility, conductivity, and the stability of ionic compounds in solution.

53. How does dipole moment contribute to the phenomenon of dielectric heating (as in microwave ovens)?

Dipole moment is fundamental to dielectric heating. In a microwave field, molecules with permanent dipole moments (like water) rapidly align and realign with the oscillating electric field. This molecular motion generates heat, which is the basis for microwave cooking.

54. Can dipole moment explain why some molecules are more easily polarized than others?

While dipole moment and polarizability are related, they are distinct properties. Molecules with permanent dipole moments are not necessarily more easily polarized. Polarizability depends more on the looseness of electrons and molecular size. However, the presence of a dipole moment can influence how a molecule responds to external electric fields.

55. How does understanding dipole moment contribute to the design of new materials with specific properties?

Understanding dipole moment is crucial in materials science for designing materials with specific electrical, optical, and chemical properties. By manipulating molecular dipole moments, scientists can create materials with desired characteristics such as specific dielectric constants, refractive indices, or solubility profiles, which are important in applications ranging from electronics to drug delivery systems.