Intermolecular Forces

What Are Intermolecular Forces?

Intermolecular forces are the forces of attraction or repulsion between molecules. They are weaker than the bonds within molecules (intramolecular forces) but are crucial for determining the physical properties of substances, such as boiling and melting points.

The main types of intermolecular forces include:

• Dipole-Dipole Forces
• Induced Dipole-Dipole (London Dispersion) Forces
• Hydrogen Bonding

Dipole-Dipole Forces

These forces occur between polar molecules, where there is a permanent dipole moment. The positive end of one molecule is attracted to the negative end of another.

For example, in hydrogen chloride (HCl), the positive hydrogen is attracted to the negative chlorine of another molecule.

Induced Dipole-Dipole (London Dispersion) Forces

These forces are present in all molecules, whether polar or nonpolar. They arise due to temporary dipoles formed when electron clouds fluctuate, inducing a dipole in a neighboring molecule.

The strength of London dispersion forces increases with the size of the electron cloud (molecular size).

Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction. It occurs when hydrogen is bonded to a highly electronegative atom (like nitrogen, oxygen, or fluorine), and this hydrogen is attracted to a lone pair of electrons on another electronegative atom.

For example, in water (H₂O), the hydrogen atoms form hydrogen bonds with the oxygen atoms of neighboring water molecules.