Intermolekulare

Intermolecular forces are the forces of attraction or repulsion that act between molecules. They are distinct from intramolecular forces that hold the atoms within a molecule together. Intermolecular forces influence phase behavior, solubility, viscosity, boiling and melting points, and other bulk properties.

The main categories include London dispersion (van der Waals) forces, dipole-dipole interactions, hydrogen bonds, and ion-dipole interactions, plus other electrostatic interactions between charged species and polar molecules. London dispersion arise from temporary fluctuations in electron density and exist in all molecules; they become stronger with molecular size and surface area. Dipole-dipole interactions occur between molecules with permanent dipoles. Hydrogen bonds are a strong subset of dipole-dipole interactions, typically involving hydrogen attached to nitrogen, oxygen, or fluorine, and an electronegative partner on another molecule.

Ion-dipole interactions describe the attraction between ions and polar molecules, important in solutions. While individually weaker than covalent bonds, these intermolecular forces collectively shape the properties of liquids, solids, and biological systems. Their strength depends on distance and orientation and generally falls in the range of a few to several tens of kilojoules per mole.

Intermolecular forces help explain why water has a relatively high boiling point for its size, why noble gases condense only at low temperatures, how proteins fold, and how solvents mix. They are studied through calorimetry, spectroscopy, and computational methods in chemistry and biophysics.