Van der Waals Forces – Definition, Types, Examples

Van der Waals forces are weak intermolecular forces that attract nearby atoms and molecules. Unlike covalent, ionic, and metallic bonds, these interactions arise from temporary or permanent differences in the distribution of electrical charge. Although individual van der Waals interactions are weak, they play a major role in determining the physical properties of substances and are essential in chemistry, biology, materials science, and nanotechnology.

Molecules inherently possess energy and their electrons are constantly in motion. As electrons move, temporary concentrations of negative charge develop in one region or another, creating corresponding positive regions elsewhere. These temporary or permanent charge imbalances produce attractive and repulsive forces between neighboring atoms and molecules.

Van der Waals forces are the sum of the attractive and repulsive electrical forces between atoms and molecules that are not associated with covalent or ionic bonding. Depending on the definition used, the term may include London dispersion forces, Debye forces, Keesom forces, and sometimes hydrogen bonding.

Key Takeaways: Van der Waals Forces

• Van der Waals forces are weak, distance-dependent intermolecular forces between atoms and molecules.
• They arise from temporary or permanent differences in electrical charge distribution.
• The term commonly includes London dispersion forces, Debye forces, and Keesom forces.
• Some scientists also include hydrogen bonding, while others classify it separately.
• Van der Waals forces are much weaker than ionic, covalent, and metallic bonds.
• Although weak individually, they strongly influence boiling points, melting points, viscosity, solubility, biological structures, and surface adhesion.
• All atoms and molecules experience van der Waals forces.

How Van der Waals Forces Work

Van der Waals forces arise from uneven distributions of electrons within atoms and molecules. Because electrons are constantly moving, temporary regions of positive and negative charge develop. These charge imbalances create weak electrostatic attractions between neighboring particles.

In nonpolar molecules, the attractions result from temporary dipoles that form when electrons become unevenly distributed. In polar molecules, permanent dipoles contribute additional attractions. Although each interaction is weak, the combined effect of countless van der Waals interactions can significantly influence the behavior of matter.

Properties of Van der Waals Forces

Van der Waals forces display several important characteristics:

• The forces are additive.
• They are weaker than ionic, covalent, and metallic bonds.
• They are generally non-directional, particularly London dispersion forces.
• They act only over very short distances.
• Attraction increases as molecules approach one another.
• Strong repulsion occurs when electron clouds begin to overlap.
• They occur between all atoms and molecules.

Components of Van der Waals Forces

Van der Waals forces are among the weakest intermolecular forces. Their strength typically ranges from less than 1 kJ/mol to several kilojoules per mole and acts over distances of less than approximately 0.6 nm. When the distance becomes very small, repulsion dominates as electron clouds overlap.

Several interactions contribute to van der Waals forces:

Pauli Repulsion

A negative component prevents molecules from collapsing into one another. This repulsion results from the Pauli exclusion principle, which prevents electrons from occupying the same quantum state.

Keesom Force

An attractive or repulsive electrostatic interaction occurs between permanent dipoles. This interaction is called the Keesom force, named after Dutch physicist Willem Hendrik Keesom.

Debye Force

An attractive interaction occurs when a permanent dipole induces a dipole in a neighboring molecule. This interaction is called the Debye force, named after Peter J. W. Debye.

London Dispersion Force

The London dispersion force is the attraction between atoms and molecules caused by instantaneous fluctuations in electron distribution. Even nonpolar molecules experience London dispersion forces. The force is named after physicist Fritz London.

Types of Van der Waals Forces at a Glance

*Some scientists classify hydrogen bonding separately rather than as a van der Waals force.

Strength and Range of Van der Waals Forces

Van der Waals forces are relatively weak compared with chemical bonds. However, they become significant when large numbers of molecules interact.

Several factors increase van der Waals force strength:

• Larger electron clouds
• Greater molecular mass
• Increased polarizability
• Larger surface area
• Closer molecular contact

For example, iodine (I₂) is a solid at room temperature while chlorine (Cl₂) is a gas because iodine’s larger electron cloud produces stronger dispersion forces.

The forces act only over short distances and decrease rapidly as particles move apart.

Why Van der Waals Forces Are Important

Van der Waals forces influence many physical properties of matter, including:

• Boiling point
• Melting point
• Viscosity
• Solubility
• Surface tension
• Crystal structure
• Molecular recognition
• Protein folding
• DNA stability
• Surface adhesion

Without van der Waals forces, many gases would not condense into liquids, biological molecules would not maintain their structures, and numerous materials would behave very differently.

Real-World Examples of Van der Waals Forces

Van der Waals forces affect many familiar phenomena:

Condensation of Noble Gases

Noble gases such as argon, krypton, and xenon are nonpolar atoms. The only attractive forces between them are London dispersion forces. These interactions allow them to condense into liquids at sufficiently low temperatures.

Plastic Wrap Adhesion

Part of the clinginess of plastic wrap results from van der Waals attractions between the plastic and nearby surfaces.

Protein Folding

Van der Waals interactions help stabilize the three-dimensional structures of proteins.

DNA Base Stacking

The stacked nitrogenous bases within DNA are partially stabilized by van der Waals attractions.

Cell Membranes

Van der Waals interactions between hydrocarbon chains help maintain the structure and integrity of biological membranes.

Van der Waals Forces, Geckos, and Arthropods

Geckos, insects, and some spiders possess millions of microscopic hairs called setae on their foot pads. These structures maximize contact with surfaces and allow van der Waals interactions to develop between the animal and the surface.

Geckos can climb smooth surfaces such as glass and may even hang from a single toe. Although electrostatic forces and surface lipids may contribute to adhesion, experiments indicate van der Waals forces are the primary mechanism responsible for their remarkable climbing ability.

Gecko feet are sticky primarily because millions of tiny contact points generate van der Waals attractions between the setae and the climbing surface.

Biomimetic Adhesives and the Real-Life Spiderman

Scientists have developed synthetic adhesives inspired by gecko feet. One example is Geckskin, a material based on the structure of gecko setae.

In 2014, DARPA tested a gecko-inspired climbing system that allowed a 100-kg researcher carrying an additional 20 kg of equipment to climb an 8-meter glass wall using specialized paddles. Researchers continue exploring gecko-inspired materials for applications in robotics, manufacturing, medicine, and military equipment.

Van der Waals Forces vs Chemical Bonds

While both involve electrical attraction and repulsion, van der Waals forces differ from chemical bonds:

Van der Waals Forces and Phase Changes

Van der Waals forces play an important role in phase changes because they help hold molecules together in liquids and solids. During melting, molecules gain enough energy to partially overcome intermolecular attractions. During boiling, molecules gain enough energy to completely overcome the attractive forces holding them together in the liquid phase.

In general, substances with stronger van der Waals forces have:

• Higher melting points
• Higher boiling points
• Lower vapor pressures
• Greater viscosities

For example, methane (CH₄) and octane (C₈H₁₈) are both nonpolar molecules whose intermolecular attractions are dominated by London dispersion forces. Octane contains more electrons and has a larger surface area, so it experiences stronger dispersion forces and has a much higher boiling point than methane.

The energy required for a phase change often reflects the strength of the intermolecular forces between particles. Stronger van der Waals attractions require more energy to overcome.

Van der Waals Forces and Periodic Trends

The strength of van der Waals forces generally increases as atoms and molecules become larger and contain more electrons. Larger electron clouds are more easily distorted, producing stronger temporary dipoles and stronger London dispersion forces.

This trend is particularly evident among the noble gases:

As atomic size and electron count increase from helium to xenon, London dispersion forces become stronger. As a result, the boiling points increase steadily.

A similar trend occurs among the halogens:

The increasing strength of London dispersion forces explains why fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature.

These trends demonstrate how even weak intermolecular forces can strongly influence the physical properties of matter when many molecules interact together.

Study Tip

A useful rule of thumb is:

Larger atoms and molecules usually have stronger London dispersion forces, which often means higher melting points and boiling points.

This relationship helps explain many periodic trends and physical property differences among chemically similar substances.

Common Misconceptions

Van der Waals Forces Occur Only in Nonpolar Molecules

False. All atoms and molecules experience London dispersion forces.

Van der Waals Forces Are Chemical Bonds

False. They are intermolecular attractions rather than true chemical bonds.

Van der Waals Forces Are Too Weak to Matter

False. They influence boiling points, melting points, biological structures, adhesion, and many other important phenomena.

Geckos Stick to Walls Using Suction

False. Their adhesion primarily results from van der Waals interactions between microscopic foot hairs and the surface.

Frequently Asked Questions

What are van der Waals forces in simple terms?

Van der Waals forces are weak attractions between atoms and molecules caused by temporary or permanent differences in electrical charge.

Are van der Waals forces stronger than hydrogen bonds?

No. Hydrogen bonds are generally stronger than ordinary van der Waals interactions.

Do nonpolar molecules have van der Waals forces?

Yes. Even completely nonpolar molecules experience London dispersion forces.

Why do larger molecules often have higher boiling points?

Larger molecules have more electrons and are more easily polarized, resulting in stronger dispersion forces that require more energy to overcome.

Are van der Waals forces important in biology?

Yes. They help stabilize proteins, DNA, cell membranes, and many other biological structures.

Are van der Waals forces always attractive?

No. The overall interaction includes both attractive and repulsive components. Repulsion dominates when atoms approach too closely.

References and Further Reading

• Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J. (2002). “Evidence for van der Waals adhesion in gecko setae”. Proceedings of the National Academy of Sciences. 99 (19): 12252–6. doi:10.1073/pnas.192252799
• Dzyaloshinskii, I. D.; Lifshitz, E. M.; Pitaevskii, L. P. (1961). “General theory of van der Waals’ forces”. Soviet Physics Uspekhi. 4 (2): 153. doi:10.1070/PU1961v004n02ABEH003330
• Israelachvili, J. (1985–2004). Intermolecular and Surface Forces. Academic Press. ISBN 978-0-12-375181-2.
• Parsegian, V. A. (2006). van der Waals Forces: A Handbook for Biologists, Chemists, Engineers, and Physicists. Cambridge University Press. ISBN 978-0-521-83906-8.
• Wolff, J. O.; Gorb, S. N. (18 May 2011). “The influence of humidity on the attachment ability of the spider Philodromus dispar (Araneae, Philodromidae)”. Proceedings of the Royal Society B: Biological Sciences. 279 (1726): 139–143. doi:10.1098/rspb.2011.0505