Van der Waals forces are discovered by a physicist named Johannes Diderik van der Waals. They are also known as Van der Waals interactions and depend on the distance between the atoms or molecules. Greater distance decreases the interaction between atoms or molecules and vice versa.
Van der Waals interactions are different from chemical bonding. In chemical bonding, atoms are bonded with the help of an ionic or covalent bond whereas Van der Waals interactions are the attraction between the molecules or atoms and are very weak forces.
When mutual repulsion occurs between the atoms due to their electronic clouds at a specific distance called Van der Waals contact distance. Van der Waals interaction is the sum of forces, such as forces between the instantaneously induced dipoles, forces between permanent dipoles and induced dipoles, and forces between permanent molecular dipoles.
Characteristics of Van der Waals interactions
These are the characteristics of Van der Waals’s interactions:
- Van der Waals interactions are very weak than covalent and ionic bonds.
- They have no directional properties.
- Van der Waals forces work at very short ranges.
- These forces are additive and unsaturated.
- They are temperature independent.
Van der Waals interactions are anisotropic which means they rely on the relative orientation of the molecules. Regardless of orientation, the induction and dispersion interactions are always attractive whereas the electrostatic interaction changes sign as the molecules rotate. According to the molecules’ mutual orientation, the electrostatic force can be either attractive or repulsive.
Due to the molecules’ thermal rotation, both the attractive and repulsive components of the electrostatic force can be explored. Molecules in thermal motion allow the electrostatic force to be significantly averaged out. This effect is also described as generally overcome or disrupted by random thermal movements near room temperature. This refers to the electrostatic component of the van der Waals force.
Types of Van der Waals interactions
These are the three types of forces under Van der Waals interactions:
- Debye forces
- Keesom interactions
- London dispersion forces
Debye forces are the type of Van der Waals interaction discovered by chemist Peter Debye.
These forces are arises by the interaction between atoms or molecules and permanent dipoles. This results in the formation of induced dipoles in the atoms or molecules.
For instance, in a molecule, the induced dipole is formed due to a repulsive force between the electrons and a permanent dipole of other molecules. They are not dependent on the temperature.
Keesom interaction is an electrostatic type of Van der Waals interaction named after physicist Willem Hendrik Keesom. These forces always originate from permanent dipole interactions.
These forces are arises by the following interactions:
- In ionic molecules, keesom interaction arises by the interaction of positive and negative charges.
- In polar molecules, these forces are formed by the interaction between dipoles.
- These forces are also formed by the interaction between permanent multipoles.
London dispersion forces
London dispersion forces are Van der Waals interactions discovered by physicist Fritz London. These forces are formed by the interaction between instantaneous multipoles of a molecule and other atoms or molecules called dispersion forces, London forces, or instantaneous dipole-induced dipole forces.
Dispersion forces are directly proportional to the polarizability of a molecule. This means greater forces lead to an increase in the polarizability of the molecule. Polarizability also depends on the total number of electrons and their spreading area.
Factors affecting Van der Waals interactions
These are the factors that affect the van der Waals interactions:
Number of electrons
The strength of van der Waals interaction is directly proportional to the number of electrons involves in the atom or molecule. A greater number of electrons increases the strength of van der Waals forces or interaction. This is due to the larger number of electrons involves in the formation of dipoles. In this way, more dipoles mean more strength of van der Waals interaction.
Shape of molecules
Open chain molecules have stronger van der Waals forces or interaction whereas branched chain molecules have lower or weaker van der Waals interaction. For example, the boiling point of butane (open chain) is -5.0 oC and the boiling point of isobutane (closed or branched chain) is -11.7 oC.
Application of Van der Waals interactions
These are the application of Van der Waals interactions:
- Van der Waals interaction help to stabilize the structure of the protein.
- These forces are responsible for the stability and adhesion of colloids.
- The stability of the polymer chain is due to van der Waals interaction.
- In liquid and solid states, inert gases show cohesion properties due to van der Waals interaction.
- They are used in physical adsorption to adsorb the molecules on the adsorbent.
Van der Waals interaction in organisms
Van der Waals interactions are present in many organisms that help them to climb on trees or hard surfaces.
Few reptiles have the ability to climb on surfaces to find food, etc. For example, geckos can climb on a hard surface. This is due to van der Waals interaction between the gecko’s toes and the hard surface.
Geckos can climb on smooth surfaces like glass, Teflon, polydimethylsiloxane, etc, Later studies revealed that the adhesion of geckos on these surfaces is due to the electrostatic interaction, not the van der Waals interaction.
Arthropods have the same mechanism for climbing on surfaces. For example, the climbing spider on the web and hard surfaces.
What is an example of a van der Waals interaction?
Microfiber cloth uses van der Waals interaction to remove the dirt from the surfaces. In this way, this cloth does not affect the surface of the substance. Secondly, spiders and other arthropods use the van der Waals interaction for climbing.
Is the van der Waals force a polar interaction or a non-polar interaction?
These forces occur in polar molecules like water, etc.
What forces makeup van der Waals forces?
London dispersion forces, debye force, and keesom interaction make up the van der Waals forces.
What are the uses of van der Waals interaction?
Van der waals interaction uses in:
- Protein structure
- Polymer chain