What is London force?

London dispersion forces, also called van der Waals forces, are weak intermolecular forces that arise from the temporary fluctuations in the electron distributions of atoms or molecules. These forces are generally much weaker than covalent bonds, ionic bonds, or hydrogen bonds, but they can be significant for large molecules or molecules with low polarity.

London dispersion forces are caused by the instantaneous dipole moments that occur when the electrons in an atom or molecule move. These dipole moments can induce dipole moments in neighboring atoms or molecules, creating an attractive force between them. The strength of the London dispersion force depends on the polarizability of the atoms or molecules involved. Polarizability is a measure of how easily the electron distribution of an atom or molecule can be distorted.

London dispersion forces are always present between atoms or molecules, but they are only significant for large molecules or molecules with low polarity. This is because the strength of the London dispersion force increases with the number of electrons in the molecule and decreases with the polarity of the molecule. For example, the London dispersion force is stronger for hexane (C6H14) than for water (H2O) because hexane is a larger molecule with a lower polarity.

London dispersion forces are responsible for the attractive forces between noble gas atoms, which are otherwise nonpolar. They are also responsible for the boiling points of molecular compounds. The boiling point of a compound increases with the strength of the London dispersion forces between the molecules.