Van der Waals force: weak intermolecular attractions and their roles
Van der Waals forces are weak, short-range noncovalent interactions between atoms and molecules — including dispersion, dipole and induced-dipole effects — important in chemistry, biology and materials.
Overview
The term van der Waals force denotes a family of relatively weak, noncovalent attractions that act between neutral atoms, molecules and ions. In chemistry these forces are classed among intermolecular forces and are distinct from the strong bonds that hold atoms together inside a molecule. They operate between separate molecules or particles and are typically short-range, becoming much weaker as separation increases. Van der Waals is often used loosely to mean all noncovalent interactions of this kind, though it specifically refers to the weak physical forces described below.
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Types and characteristics
Van der Waals interactions arise from electrical effects associated with electrons and charge distributions. The principal categories are:
- London dispersion forces — instantaneous fluctuations in the positions of electrons produce temporary dipoles that induce complementary dipoles in neighbors. These dispersion forces are present between all atoms and molecules and depend on the polarizability of the partners.
- Dipole–dipole interactions — permanent molecular dipoles align so that partial positive and negative regions attract. Such partial charges are often denoted δ+ and δ−.
- Dipole–induced dipole forces — a permanent dipole in one species can distort the electron cloud of another, inducing an attractive interaction.
Many van der Waals potentials fall off rapidly with distance; at long range the energy of dispersion and orientation-averaged dipolar interactions commonly follows an inverse power law. These effects are nonbonding: weaker than covalent or ionic bonds and generally weaker than hydrogen bonds, but they add up and can determine structural stability.
Origin and historical background
The forces are named after the Johannes Diderik van der Waals, a Dutch physicist who investigated real gases and developed concepts about molecular attraction and finite molecular size. His work laid conceptual foundations for understanding how attractive forces between particles affect macroscopic properties such as pressure and phase behavior. Today the quantum-mechanical origin of dispersion interactions is understood in terms of correlated electron fluctuations and polarizability.
Where they matter: examples and applications
Although individually small, van der Waals forces are crucial across many fields. In supramolecular chemistry they govern how components self-assemble; in biological macromolecules they help proteins fold and membranes form; in polymer science they influence material toughness, glass transition and adhesion. Nanomaterials and layered solids rely on these forces for stacking and exfoliation, a subject of interest in nanotechnology and condensed matter physics. van der Waals interactions also affect solubility and miscibility of organic compounds, altering how substances dissolve in solvents.
Important distinctions and practical notes
Van der Waals forces are not a single mechanism but a set of related phenomena that share an electrostatic origin and short range. They can be modulated by molecular size, shape, and electronic structure; larger, more polarizable atoms produce stronger dispersion. Experimental probes such as atomic force microscopy and spectroscopy can measure their effects at surfaces and between molecules. In many practical systems the combined van der Waals energy can rival or exceed other noncovalent contributions, so accounting for them is essential in modeling, material design and understanding molecular recognition.
For further reading on basic definitions and how these forces are treated in different disciplines, see introductory texts and reviews in physical chemistry and materials science, which discuss both the classical viewpoints and the modern quantum description of van der Waals interactions.
Additional references: nationality and biography context, atomic orbitals, ionic interactions.
Illustrative effect of van der Waals forces
In addition to mainly electrostatic forces, geckos also use Van der Waals forces to adhere to surfaces without glue or suction cups. The undersides of their feet are full of the finest hairs. Each hair can only transmit a small force, but due to the high number, the sum of the forces is still sufficient for the animal to walk upside down on ceilings. This is also possible on smooth surfaces such as glass. The sum of the contact forces of a gecko is about 40 N.
Cause
The London dispersion interaction also occurs between non-polar small particles (noble gas atoms, molecules), if these are polarizable, and leads to a weak attraction of these small particles.
Electrons in a microparticle (atom) can only move within certain limits, which leads to a constantly changing charge distribution in the microparticle. As soon as the center of positive charges is spatially separated from the center of negative charges, one can speak of a dipole, because here there are two (di-, from the Greek δίς "twice") electric poles. However, single nonpolar molecules can only be called temporary dipoles, because their polarity depends on the electron distribution, and this is constantly changing. (In polar molecules, on the other hand, the dipole property is permanent because of the electronegativities of the atoms and the structure of space, so they are called permanent dipoles or dipoles in the strict sense).
If two non-polar molecules come close to each other long enough (i.e. at low relative velocity), they enter into an electrostatic interaction with each other.
If, for example, particle A shows a pronounced negatively charged side to neighbour B, then the electrons of neighbour B (from the facing side) are repelled. Thus the dipoles align with each other. Such a shift of charge due to an electric field is called an influence. This means that the negative pole of a temporary dipole influences a positive pole vis à vis the neighbouring molecule. Thus, particle B becomes an "influenced" dipole. In technical literature, this is called "induced dipole" (lat. inducere: to introduce).
Van der Waals forces occur between the original, temporary dipole and the induced dipole. From now on, the dipoles influence each other, their electron displacement synchronizes.
If two atoms or molecules come close enough to each other, one of the following situations can occur.
- Two temporary dipoles meet: the particles attract each other.
- A temporary dipole meets a particle without a dipole moment: The dipole induces a rectified dipole moment in the non-dipole, which again creates an attractive force between the two particles.
Van der Waals binding energy: 0.5-5 kJ/mol (corresponds to 5-50 meV/molecule)
Quantum mechanical consideration
In the above description, however, electrons are treated as classical particles and the insights of quantum mechanics are not taken into account. In the quantum mechanical model of the atom, the electron is 
described by a stationary wave function ψ whose magnitude square always remains the same at a given point in the atom. This initially suggests the idea that the electron behaves like a classical extended charge distribution, with a charge density given by the product of the electron charge and the magnitude square of the wave function:
Accordingly, the charge distribution would be invariant, and the spontaneous emergence of temporary dipoles consequently impossible. Since 
is typically axisymmetric around the atomic nucleus, the dipole moment, for example of a noble gas atom, would always be zero.
Taking a closer look at the quantum mechanical charge density operator
where 
is the location operator of the electron, however, this turns out to be a fallacy. An electron does not behave like an extended charge distribution, but like a point charge whose location is indeterminate, since the presence of the other atom/molecule leads to constant "location measurements". For the expectation value of the charge density indeed results
however, it is not an eigenvalue of the charge density operator. The charge density has a certain fuzziness, which just leads to the fact that with a certain probability the center of gravity of the electronic charge distribution does not lie in the atomic nucleus and thus a dipole moment arises. In this way, in the picture of quantum mechanics, the Van der Waals forces can be understood.
Questions and answers
Q: What is the van der Waals force?
A: The van der Waals force is a type of intermolecular force that attracts molecules together. It is the weakest type of intermolecular force.
Q: Who was Johannes Diderik van der Waals?
A: Johannes Diderik van der Waals was a Dutch scientist who lived from 1837 to 1923, and the van der Waals force was named after him.
Q: What are partial charges?
A: Partial charges are slight differences in charge between one end of a molecule or ion and another, created when electrons shift their orbits as a response to each other. They are described by using the variables δ- or δ+.
Q: How does Van der Walls Force compare to other forces?
A: Van der Walls Force is weaker than covalent bonds and usually weaker than hydrogen bonds, but still plays an important role in many areas such as chemistry, enzymes, polymer science, nanotechnology, surface science, and condensed matter physics.
Q: What properties do Van der Walls Forces define for organic compounds?
A: Van Der Walls Forces define many properties of organic compounds including their ability to dissolve.
Q: What does "supramolecular" mean?
A: Supramolecular refers to interactions between molecules on a larger scale than just individual atoms or molecules interacting with each other.
Related articles
Author
AlegsaOnline.com Van der Waals force: weak intermolecular attractions and their roles Leandro Alegsa
URL: https://en.alegsaonline.com/art/104141
Sources
- chemguide.co.uk : "intermolecular bonding - van der Waals forces"
- chem.libretexts.org : "Van der Waals Forces"