Van der Waals forces, also known as the van der Waals interactions, are the weak interactions existing at a molecular or atomic level. These are the short term attractive forces that exist between uncharged molecules of substances. The bonds formed due to the Van Der Waals interaction are the secondary bonds, while ionic and covalent bonds act as primary bonds. Van der Waals force is named after a Dutch scientist Johannes Diderik van der Waals. He discovered these forces in 1873 while working on the characteristics of real gases. He observed that the electrons distributed unevenly throughout an atom or molecule tend to move continuously and form a temporary dipole. The temporary dipole formed in an atom forms another temporary dipole in the neighbouring atom, and the process goes on and on. The domino effect existing between the temporary dipoles establishes a force of attraction known as the van der Waals force. The force of attraction exists between atoms or molecules of a substance or two different substances, thereby helping two objects stick to each other. The strength of van der Waals force typically lies between 0.4 kJ/mole and 4 kJ/mole and they tend to act over a distance less than or equal to 0.4 nm.
Characteristics of van der Waals Force
1. Van der Waals forces are additive in nature and are made up of several individual interactions.
2. These forces are weaker than the covalent, ionic, and hydrogen bonding.
3. The interaction between molecules increases when the distance between the molecules is less or when they are placed close to each other. This means that van der Waals forces work well in a short-range.
4. Van der Waals forces are not directional in nature.
5. These forces do not depend on temperature, except the dipole-dipole interaction.
6. Van der Waals forces do not get saturated.
7. The solids that are held together with the help of van der Waals forces have a low boiling point, while the solids held together by covalent, ionic, or metallic bonds tend to have a high boiling point.
Examples of van der Waals Force
1. Gecko Lizards
Geckos lizards make use of van der Waals forces to climb flat surfaces such as walls and roofs. This is a result of the force of attraction between the footpads of the lizard and the surface. A similar type of attraction helps some of the animals walk on the surface of the water.
2. Polymer Formation
A polymer chain is formed by attaching a number of basic building units of the polymer known as ‘mer’ together with the help of a covalent bond. Van der Waals forces play a prominent role in polymer formation. The polymer molecules are held together primarily by covalent or ionic bonds. The van der Waals force helps in establishing a secondary bond between the polymer molecules. For instance, polyethene has a polymer chain that consists of repeating monomers of two covalently bonded carbon atoms that contains two hydrogen atoms each. The polymer chains of polyethene are held together with the help of van der Waals forces.
3. Nano Technology
Van Der Waals forces are highly applicable in nanotechnology as they are effective at the nano range of distance. These forces are highly used in nanotechnology, surface and colloidal science, and various other related fields to bind two objects together at a nanoscale. This is because the van der Waals forces tend to work effectively when the distance between the molecules is significantly less, which, in the case of nanomaterials, is a few tenths of nanometres.
4. Protein Structure
The structure of protein molecules is quite complex in nature. Van der walls forces are the weak forces that are responsible to establish a force of attraction between the protein molecules and other molecules of the solution or the surfaces. These forces typically act between the hydrophobic side chains and help to maintain the quarternary structure of the protein molecule. In simpler words, Van Der Waals force is accountable to provide stabilization to the tertiary structure of the protein molecules.
5. Graphite
Graphite is the allotropic form of carbon. The structure of graphite consists of a number of graphene sheets that are laid parallel to each other. Each sheet of graphene contains carbon atoms arranged in a honeycomb pattern. These sheets are bonded to each other weakly with the help of van der Waals forces.
6. DNA
Deoxyribonucleic acid or DNA is a molecule that contains all the genetic information of a living being. Almost every cell of an organism contains a two-stranded DNA molecule. The double helix structure of DNA consists of a number of rungs. Van der Waals forces acting between the base pairs of neighbouring rungs help to hold the bases at an optimal angle. This helps to compactly pack the structure of the DNA molecule and provides the necessary steadiness.
7. Water Droplets
Van der Wall forces play a prime role in water droplet formation. Two water molecules present close to each other containing opposite charges get attracted to each other and establish a temporary weak interaction. These forces also exist between the molecules of a number of other liquids. The magnitude of van der Walls force existing between the iodine molecules is one of the strongest out of all the liquids. This is because the number of electrons possessed by an iodine molecule is quite high.
