intermoleculars

Intermolecular forces are the noncovalent forces that mediate interactions between molecules. They influence a substance’s phase behavior, solubility, boiling and melting points, viscosity, surface tension, and many other properties. These forces are distinct from intramolecular bonds, such as covalent bonds, which hold atoms together within a molecule.

The main types of intermolecular forces are London dispersion forces, dipole-dipole interactions, hydrogen bonding, ion-dipole interactions, and ion-induced dipole or dipole-induced dipole interactions. London dispersion forces arise from fluctuations in electron distribution that create temporary dipoles and are present in all molecules, becoming stronger with molecular size and polarizability. Dipole-dipole interactions occur between polar molecules with permanent dipoles. Hydrogen bonds are a relatively strong, directional subset of dipole-dipole interactions involving hydrogen bonded to fluorine, oxygen, or nitrogen. Ion-dipole forces occur when ions interact with polar molecules, while induced dipole interactions involve an ion or molecule inducing a dipole in a neighboring species. Additional specific interactions, such as π–π stacking, also contribute in certain systems.

Strengths vary widely, from weak dispersion in small nonpolar molecules to stronger hydrogen bonds (roughly a few to several tens of kilojoules per mole). These forces are weaker than covalent bonds but sufficient to govern phenomena like boiling points, crystallization, and macromolecular folding.

In practice, intermolecular forces explain why water has a high boiling point for its size, why hydrocarbons stratify by polarity, and how proteins adopt stable three-dimensional structures. They are central to chemistry, physics, and biology, affecting solubility, phase diagrams, and material properties.