Van Der Waals Forces: Definition, Formula, Examples, Questions

Edited By Shivani Poonia | Updated on Jul 02, 2025 07:57 PM IST

The forces that hold atoms together within a molecule are strong covalent or ionic bonds, the Van der Waals forces are relatively weak, consisting of transitory dipoles induced by the movement of electrons. These forces hold the key to physical material properties, the structure of biological macromolecules, and interactions between different substances.

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Understanding Van der Waals Forces
Van der Waal Forces
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Some Solved Examples
Summary

Van Der Waals Forces: Definition, Formula, Examples, Questions

Understanding Van der Waals Forces

Van der Waals forces are intermolecular forces that are weak and result from the interactions between uncharged atoms or molecules. They depend on the distance of the molecules from one another and are generally divided into three types: London dispersion forces, dipole-dipole interaction, and dipole-induced dipole interaction.

Van der Waal Forces

Van der Waal's force of attraction is the force of attraction between the molecules. This force is weaker compared to bonds like covalent and ionic bonds.

Van der Waal forces can be divided into various categories as follows:

Ion-dipole interaction: This type of interaction exists between an ion and a polar molecule like HF, HCl, H₂O, etc. The ion can be like Na⁺. This type of interaction is responsible for the dissolution of ions in solution.
Dipole-Dipole interaction: This type of interaction exists between two or more polar molecules. These dipoles can be H-Cl and H-Cl, NH₃ and NF₃, etc. Hydrogen bonding is a special type of dipole-dipole interaction.
Ion-induced dipole interaction: This type of interaction exists between the ion and non-polar molecule. The charge on the ion distorts the electron cloud of the non-polar molecule and thus induces a dipole in the non-polar molecule. Then the ion and the induced dipole attract each other.
Dipole-induced dipole interaction: This kind of interaction exists between a polar and a non-polar molecule. For example, CCl₄ in H₂O. One of the dipole molecules distorts the electron cloud in the non-polar molecule and thus creates the dipole in the non-polar as well.
Instantaneous dipole-dipole interaction: This type of interaction exists between two non-polar molecules. This force is also known as the London forces. At any instant, electrons in one non-polar molecule come closer to each other and then this molecule becomes a dipole for instance. This instantaneous dipole distorts the electron cloud in another non-polar molecule and thus both behave like polar molecules. For example CCl₄ and CCl₄.

The strength of these forces follows the given order:

Ion-Dipole > Dipole-Dipole > Ion-Induced Dipole > Dipole-Induced Dipole > London Forces

Some Solved Examples

Example 1

Question: The strength of the hydrogen bond is intermediate between which of the following?

1) Van der Waals and covalent
2) Ionic and covalent
3) Ionic and metallic
4) Metallic and covalent

Solution: The strength of hydrogen bonds is indeed intermediate between Van der Waals forces and strong covalent bonds. Therefore, the correct answer is option (1).

Example 2

Question: HF has the highest boiling point among hydrogen halides because it has:

1) Strongest Van der Waals interaction
2) Lowest ionic character
3) Strongest hydrogen bonding
4) Lowest dissociation enthalpy

Solution: HF exhibits the strongest hydrogen bonding among hydrogen halides, which significantly raises its boiling point compared to others. Thus, the correct answer is option (3).

Example 3

Question: The interaction energy of London forces between two particles is proportional to r^x , where r is the distance between the particles. What is the value of x?

1) 6
2) -6
3) 3
4) -3

Solution: The interaction energy of London forces is proportional to 1r6, indicating that x = -6. Therefore, the correct answer is option (2).

Example 4

Question: Which of the following interactions is the strongest?

1) London dispersion forces
2) Dipole-dipole interactions
3) Hydrogen bonds
4) Ion-dipole interactions

Solution: Ion-dipole interactions are the strongest among the listed types of interactions. Hence, the correct answer is option (4).

Example 5

Question: In which of the following scenarios would you expect dipole-induced dipole interactions to occur?

1) Between two polar molecules
2) Between a polar molecule and a nonpolar molecule
3) Between two nonpolar molecules
4) Between two ionic compounds

Solution: Dipole-induced dipole interactions occur between a polar molecule and a nonpolar molecule. Therefore, the correct answer is option (2).

Summary

The most frequently overlooked bonds in chemistry are the van der Waals forces. They form the basis for an understanding of molecular interactions and the behavior of matter. These are weak intermolecular forces due to the interactions between uncharged molecules: London dispersion forces, dipole-dipole interactions, and dipole-induced dipole forces.

Frequently Asked Questions (FAQs)

1. What are Van der Waals forces?

Van der Waals forces are weak intermolecular attractions between molecules or atoms. They are caused by temporary fluctuations in the electron distribution around molecules, creating momentary dipoles that can attract each other.

2. How do Van der Waals forces differ from covalent or ionic bonds?

Van der Waals forces are much weaker than covalent or ionic bonds. They occur between molecules rather than within them, and don't involve the sharing or transfer of electrons. Instead, they result from temporary electron fluctuations and dipole interactions.

3. Why are Van der Waals forces important in chemistry?

Van der Waals forces play a crucial role in determining the physical properties of substances, such as boiling points, melting points, and solubility. They are also responsible for the condensation of gases and the cohesion of liquids.

4. What are the three types of Van der Waals forces?

The three types of Van der Waals forces are: 1) Dipole-dipole interactions, 2) Dipole-induced dipole interactions, and 3) London dispersion forces (also called instantaneous dipole-induced dipole interactions).

5. Why are Van der Waals forces considered "weak" interactions?

Van der Waals forces are considered weak because they involve much less energy than covalent or ionic bonds. They typically range from 0.4 to 4 kJ/mol, compared to hundreds of kJ/mol for covalent bonds.

6. What is the general formula for Van der Waals forces?

The general formula for Van der Waals forces is F = -C/r^6, where F is the force, C is a constant that depends on the properties of the molecules involved, and r is the distance between the molecules.

7. How do Van der Waals forces change with distance between molecules?

Van der Waals forces decrease rapidly as the distance between molecules increases. They are inversely proportional to the sixth power of the distance (1/r^6), meaning they become very weak at larger distances.

8. How do London dispersion forces arise?

London dispersion forces arise from temporary fluctuations in electron distribution around atoms or molecules. These fluctuations create momentary dipoles, which can induce dipoles in neighboring molecules, leading to a weak attraction.

9. How do Van der Waals forces affect the boiling points of substances?

Stronger Van der Waals forces between molecules lead to higher boiling points. This is because more energy is required to overcome these intermolecular attractions and separate the molecules into the gas phase.

10. How do Van der Waals forces contribute to surface tension?

Van der Waals forces contribute to surface tension by creating cohesive forces between molecules at the surface of a liquid. These forces pull surface molecules inward, creating a "skin-like" effect and minimizing the surface area.

11. Why do larger molecules generally have stronger Van der Waals forces?

Larger molecules have more electrons and a greater surface area for interaction, which increases the probability of temporary dipole formation and interaction. This leads to stronger overall Van der Waals forces between larger molecules.

12. How do Van der Waals forces affect the solubility of substances?

Van der Waals forces influence solubility by determining how well molecules of a substance interact with solvent molecules. Substances with similar Van der Waals forces tend to be more soluble in each other, following the "like dissolves like" principle.

13. What is the difference between dipole-dipole interactions and London dispersion forces?

Dipole-dipole interactions occur between molecules with permanent dipoles, while London dispersion forces occur between all molecules due to temporary electron fluctuations. Dipole-dipole interactions are generally stronger than London dispersion forces.

14. How do Van der Waals forces explain the behavior of noble gases?

Noble gases, despite being monatomic and non-polar, can be liquefied and solidified due to Van der Waals forces, specifically London dispersion forces. These weak attractions become significant at very low temperatures or high pressures.

15. What is the relationship between molecular mass and the strength of Van der Waals forces?

Generally, as molecular mass increases, the strength of Van der Waals forces also increases. This is because larger molecules have more electrons, leading to stronger London dispersion forces.

16. How do Van der Waals forces affect the viscosity of liquids?

Stronger Van der Waals forces between molecules in a liquid lead to higher viscosity. This is because the intermolecular attractions make it more difficult for molecules to flow past each other.

17. Why are Van der Waals forces important in biological systems?

Van der Waals forces play crucial roles in biological systems by contributing to protein folding, DNA base pairing, and membrane formation. They help stabilize molecular structures and facilitate recognition between biomolecules.

18. How do Van der Waals forces differ from hydrogen bonding?

Van der Waals forces are weaker and less specific than hydrogen bonds. Hydrogen bonds occur between a hydrogen atom bonded to a highly electronegative atom and another electronegative atom, while Van der Waals forces can occur between any molecules or atoms.

19. What is the Lennard-Jones potential, and how does it relate to Van der Waals forces?

The Lennard-Jones potential is a mathematical model that describes the interaction energy between two neutral atoms or molecules as a function of their distance. It includes both the attractive Van der Waals forces and the repulsive forces that occur at very short distances.

20. How do Van der Waals forces contribute to the gecko's ability to climb walls?

Geckos can climb walls due to millions of tiny hairs on their feet that maximize surface area contact. This large surface area allows for numerous weak Van der Waals interactions, which collectively create a strong adhesive force.

21. What is the difference between physisorption and chemisorption, and how do Van der Waals forces relate to this?

Physisorption involves weak Van der Waals forces between an adsorbate and a surface, while chemisorption involves the formation of chemical bonds. Physisorption is reversible and doesn't change the chemical nature of the adsorbate, unlike chemisorption.

22. How do Van der Waals forces affect the melting points of substances?

Stronger Van der Waals forces between molecules lead to higher melting points. More energy is required to overcome these intermolecular attractions and separate the molecules from their ordered solid state into a liquid.

23. How do Van der Waals forces contribute to the properties of polymers?

Van der Waals forces play a crucial role in determining the properties of polymers. They contribute to the cohesion between polymer chains, affecting characteristics such as elasticity, strength, and melting point.

24. What is the Hamaker constant, and how does it relate to Van der Waals forces?

The Hamaker constant is a measure of the strength of Van der Waals interactions between macroscopic bodies. It depends on the properties of the materials involved and is used to calculate the Van der Waals force between particles or surfaces in various media.

25. How do Van der Waals forces affect the behavior of gases at high pressures?

At high pressures, gases deviate from ideal gas behavior partly due to Van der Waals forces. These intermolecular attractions cause gas molecules to occupy less volume than predicted by the ideal gas law, leading to phenomena like gas liquefaction.

26. What is the role of Van der Waals forces in crystal formation?

Van der Waals forces can contribute to crystal formation, especially in molecular crystals. They help determine the packing arrangement of molecules in the crystal lattice and influence properties such as crystal shape, hardness, and solubility.

27. How do Van der Waals forces affect the mixing of liquids?

Van der Waals forces influence the miscibility of liquids. Liquids with similar Van der Waals forces tend to mix well, while those with very different forces may separate into layers. This principle is often summarized as "like dissolves like."

28. What is the difference between Keesom forces and Debye forces in Van der Waals interactions?

Keesom forces are dipole-dipole interactions between molecules with permanent dipoles, while Debye forces are dipole-induced dipole interactions between a polar molecule and a non-polar molecule. Both are types of Van der Waals forces, but Keesom forces are generally stronger.

29. What is the significance of the Van der Waals equation of state?

The Van der Waals equation of state is an improvement on the ideal gas law that accounts for the volume of gas molecules and the attractive forces between them (Van der Waals forces). It provides a more accurate description of real gas behavior, especially at high pressures or low temperatures.

30. How do Van der Waals forces contribute to the phenomenon of capillary action?

Van der Waals forces contribute to capillary action by creating adhesive forces between liquid molecules and the walls of a narrow tube. These forces, combined with the cohesive forces within the liquid, cause the liquid to rise against gravity in the tube.

31. What is the relationship between Van der Waals forces and the critical point of a substance?

The critical point of a substance is the temperature and pressure at which the liquid and gas phases become indistinguishable. Van der Waals forces play a crucial role in determining this point, as they are the intermolecular forces that must be overcome for the phase transition to occur.

32. What is the role of Van der Waals forces in supramolecular chemistry?

In supramolecular chemistry, Van der Waals forces are crucial for the self-assembly of molecular structures. They contribute to the formation of host-guest complexes, molecular recognition processes, and the creation of complex molecular architectures.

33. How do Van der Waals forces affect the properties of nanoparticles?

Van der Waals forces significantly influence nanoparticle properties due to their high surface area-to-volume ratio. These forces can cause nanoparticle aggregation, affect their interactions with surrounding media, and influence their optical and electronic properties.

34. What is the role of Van der Waals forces in the formation of clathrate compounds?

Van der Waals forces play a crucial role in the formation of clathrate compounds, where small molecules are trapped within cavities of a crystal lattice. These forces help stabilize the guest molecules within the host structure without forming chemical bonds.

35. How do Van der Waals forces contribute to the phenomenon of adsorption?

Van der Waals forces are a primary mechanism for physical adsorption (physisorption) of molecules onto surfaces. They allow molecules to adhere to surfaces without forming chemical bonds, influencing processes like gas storage, purification, and catalysis.

36. How do Van der Waals forces affect the behavior of liquid crystals?

Van der Waals forces play a crucial role in liquid crystal behavior by influencing molecular alignment and ordering. They contribute to the anisotropic properties of liquid crystals and affect their response to external fields, which is important for display technologies.

37. What is the significance of Van der Waals forces in colloidal systems?

In colloidal systems, Van der Waals forces are a primary factor in determining stability and aggregation behavior. They contribute to the attractive forces between colloidal particles and play a role in phenomena like flocculation and coagulation.

38. How do Van der Waals forces contribute to the properties of aerogels?

Van der Waals forces are important in the structure and properties of aerogels. They help maintain the delicate network structure of these ultra-low density materials and contribute to their unique thermal and acoustic insulation properties.

39. What is the role of Van der Waals forces in the self-assembly of monolayers?

Van der Waals forces play a crucial role in the self-assembly of monolayers, such as self-assembled monolayers (SAMs) on surfaces. They contribute to the ordering and packing of molecules on the surface and influence the stability and properties of the resulting monolayer.

40. What is the significance of Van der Waals forces in the field of tribology?

In tribology, the study of friction, wear, and lubrication, Van der Waals forces play a significant role. They contribute to adhesion between surfaces, affect the behavior of lubricants, and influence phenomena like atomic-scale friction and wear mechanisms in nanoscale systems.

41. What role do Van der Waals forces play in the states of matter?

Van der Waals forces help determine whether a substance exists as a solid, liquid, or gas at room temperature. Stronger forces tend to keep molecules closer together, favoring solid or liquid states, while weaker forces allow for easier separation into the gas state.

42. Why are Van der Waals forces important in nanotechnology?

In nanotechnology, Van der Waals forces become increasingly significant due to the high surface area-to-volume ratio of nanomaterials. These forces can affect the behavior and properties of nanomaterials, influencing their assembly, adhesion, and interactions with other materials.

43. How do Van der Waals forces affect the compressibility of substances?

Van der Waals forces influence compressibility by determining how closely molecules can be pushed together. Substances with stronger Van der Waals forces are generally less compressible because their molecules are already held more tightly together.

44. How do Van der Waals forces affect the volatility of liquids?

Liquids with stronger Van der Waals forces between molecules tend to be less volatile. This is because more energy is required to overcome these intermolecular attractions and allow molecules to escape into the gas phase.

45. How do Van der Waals forces contribute to the properties of thin films?

Van der Waals forces play a significant role in thin film properties by influencing adhesion to substrates, cohesion within the film, and interactions between layers in multilayer films. They can affect film stability, wetting behavior, and other surface phenomena.

46. What is the difference between short-range and long-range Van der Waals forces?

Short-range Van der Waals forces operate at distances of a few nanometers or less and decrease rapidly with distance. Long-range Van der Waals forces can act over larger distances (up to 100 nm) and are important in colloidal systems and between macroscopic bodies.

47. How do Van der Waals forces affect the behavior of surfactants?

Van der Waals forces influence the behavior of surfactants by contributing to their amphiphilic nature. They play a role in micelle formation, surface tension reduction, and the ability of surfactants to solubilize non-polar substances in water.

48. What is the significance of Van der Waals forces in molecular recognition processes?

Van der Waals forces are crucial in molecular recognition processes, such as enzyme-substrate interactions or drug-receptor binding. They contribute to the specificity and strength of these interactions, often working in concert with other non-covalent forces.

49. What is the relationship between Van der Waals forces and the cohesive energy density of a substance?

The cohesive energy density of a substance is largely determined by Van der Waals forces between its molecules. Stronger Van der Waals forces lead to higher cohesive energy density, which in turn affects properties like surface tension, viscosity, and solubility parameters.

50. How do Van der Waals forces affect the behavior of quantum dots?

Van der Waals forces influence the behavior of quantum dots by affecting their surface properties, aggregation tendencies, and interactions with surrounding media. These forces can impact the optical and electronic properties of quantum dots, which are crucial for their applications.