London force

London forces, also known as dispersion forces or London dispersion forces, are a type of van der Waals force that are considered the weakest of the intermolecular forces. They are named after the German-American physicist Fritz London who first proposed their existence in 1930. London forces are a quantum mechanical phenomenon that arise due to the instantaneous polarization of electron density within molecules or atoms. This temporary polarization leads to the creation of temporary dipoles that induce similar dipoles in neighboring particles, resulting in an attractive force between them.

Overview

London forces are present in all molecular interactions, but they are particularly significant in nonpolar molecules and noble gas atoms because these entities lack stronger intermolecular forces such as hydrogen bonding or dipole-dipole interactions. Despite being the weakest of the van der Waals forces, London dispersion forces play a crucial role in the physical properties of substances, including their boiling and melting points, viscosity, and solubility.

Mechanism

The mechanism of London forces involves the momentary fluctuation of electron density within an atom or molecule, which creates a temporary dipole. This dipole, in turn, induces a dipole in a neighboring atom or molecule. The induced dipole then attracts the original dipole, leading to an attractive force between the two particles. The strength of London forces is influenced by the polarizability of the molecule, which is the ease with which its electron cloud can be distorted. Larger and more polarizable molecules will have stronger London dispersion forces.

Significance

London forces are significant in explaining why nonpolar substances like noble gases and hydrocarbons have measurable boiling points and can exist in liquid or solid states under certain conditions. Without London dispersion forces, these substances would not be able to condense from gases to liquids or solids at low temperatures.

Applications

Understanding London forces is essential in various scientific fields, including chemistry, physics, and materials science. They are considered in the design of pharmaceuticals, in the study of polymer materials, and in the development of new materials with specific physical properties.

See also

• Intermolecular force
• Van der Waals force
• Hydrogen bond
• Dipole-dipole interaction