Rank the following intermolecular forces from strongest to weakest: hydrogen bonding, dipole-dipole, and London dispersion forces.

• A. London dispersion < dipole-dipole < hydrogen bonding
• B. Dipole-dipole < London dispersion < hydrogen bonding
• C. Hydrogen bonding > London dispersion > dipole-dipole
• D. Hydrogen bonding > dipole-dipole > London dispersion

Answer: (D)

The strongest among these intermolecular forces is hydrogen bonding. This interaction occurs when a hydrogen atom is covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine, and it is attracted to a lone pair on another electronegative atom in a neighboring molecule. The combination of a very positive hydrogen and a highly electronegative partner creates a strong, highly directional electrostatic attraction, often with partial covalent character, making it much stronger than ordinary attractions between molecules.

Dipole-dipole interactions arise from permanent dipoles in polar molecules. The partial positive end of one molecule is attracted to the partial negative end of another, which is weaker than a hydrogen bond because it lacks that specialized donor-acceptor pairing and highly localized charge found in hydrogen-bonded systems.

London dispersion forces come from fleeting, instantaneous dipoles caused by random electron movement. They are present in all molecules, including nonpolar ones, and grow with molecular size and surface area. However, they are generally weaker than both hydrogen bonding and typical dipole-dipole interactions for most common substances.

So the ranking from strongest to weakest is: hydrogen bonding > dipole-dipole > London dispersion.