London Dispersion Forces | Chemistry

A neutral atom has electrons equally distributed and constantly revolving around the nucleus. However, there are moments when electrons are unevenly distributed, distorting the atom. One side becomes electron-rich (partially negative), and the other becomes electron-deficient (partially positive), creating a temporary dipole. This dipole instantly forms and vanishes as electrons redistribute.

When a neutral atom approaches a temporary dipole, the temporary dipole's positive side attracts the neutral atom's electrons. This pulls and distorts the neutral atom's electron cloud, making it polarized and creating an induced dipole. The side closer to the temporary dipole's positive end becomes partially negative, and the opposite side becomes partially positive.

London Dispersion Forces (LDF), also known as Van der Waals forces, are the attractive forces between a temporary dipole and an induced dipole. These are weak and temporary intermolecular forces between particles. LDFs are present in all substances, both polar and non-polar, but are dominant in non-polar molecules.

London Dispersion Forces exist in all substances, including polar molecules like hydrogen fluoride and non-polar molecules like carbon dioxide. They are the dominant intermolecular forces in all non-polar molecules, such as fluorine gas, chlorine gas, bromine, and iodine.

The strength of London Dispersion Forces depends on the number of electrons. More electrons lead to stronger LDFs, and fewer electrons result in weaker LDFs. For example, in Group 7, as you move down the group, the number of electrons increases, leading to stronger LDFs and higher boiling points.