Question

Define the London force.

Answer 1

Hint: Think about all the types of intermolecular forces that are present and then narrow then down to the dispersion forces which is what London force is. Consider the presence of temporary dipoles.

Complete step by step solution:
The London force is a dispersion force that is the weakest of all intermolecular forces. It is a temporary attractive force that causes the electrons in two atoms or molecules to clump or align in such a way that they form temporary dipoles. This force is also sometimes called induced dipole-dipole interaction.
Due to a purely random incident, most of the electrons that are present in the atom or a molecule may be present at one side of the orbital at the same time. This can cause the electrons in the adjacent molecular or atomic orbital to move away, and this will create a partial positive charge in that location. This will cause more electrons from the previous atom or molecular orbital to gather there and cause a partial negative charge. Consequently, a partial positive and negative charge will develop at the ends of the molecular orbital and will thus cause an induced and temporary dipole moment. This dipole moment can be easily lost due to the revolution of electrons in their orbitals

Note: Please do not confuse the London Dispersion Forces with the regular dipole-dipole interactions. The regular interactions occur due to a difference in electronegativity of the atoms that are present in the molecules. Some atoms attract electrons towards themselves more strongly than other atoms. This will cause an increase in the electron density near that atom and will induce a dipole moment. This moment is not reversible as the London Dispersion Forces.