Why do London forces occur?

Question

Nolan Allen · Accepted Answer

Random fluctuations in the electron cloud of one atom/molecule induce a spontaneous dipole in an adjacent molecule, leading to a temporary attractive force between the two induced dipoles.

London forces, which supply the intermolecular forces in non-polar substances, are ubiquitous in all substances and are also referred to as Van der Waals forces or instantaneous dipole-instantaneous dipole interactions. Because electrons are constantly moving, there may be a moment when a molecule has a temporary charge imbalance across it. Since electrons repel other electrons, this charge imbalance (known as a 'dipole') can induce another dipole in a neighbouring molecule. The #delta-# end of one will be attracted to the #delta+# end of the other (here #delta# just means the charge is very small), causing a temporary attraction. London forces are very weak because they only last for a very brief period of time, but due to the incredibly large number of electrons in a substance they have a significant effect. They are stronger if there are more electrons present (for example Iodine, #I_2#, has stronger intermolecular forces than #Br_2#, which has stronger forces than #Cl_2#). They are weaker than interactions between permanent dipoles and induced or permanent dipoles, and a lot weaker than hydrogen bonds.

Paisley Boney · Answer

undefined London dispersion forces occur due to temporary fluctuations in electron distribution within atoms or molecules, creating temporary dipoles. These temporary dipoles induce similar dipoles in neighboring atoms or molecules, leading to weak attractions between them. These forces arise from the movement of electrons within atoms or molecules and are present in all molecules, regardless of polarity.