Cohesion may be based on the forces of intermolecular interaction, including hydrogen bonds, and/or chemical bonds. They determine the physical and physico-chemical properties of a substance, such as its state of aggregation, volatility, solubility, mechanical properties, etc. The intensity of intermolecular and interatomic interactions (and, consequently, of the forces of cohesion) diminishes sharply with distance. Cohesion is stronger in solids and liquids, i.e. in condensed states, where the distances between molecules, atoms, or ions are small (in the order of a few angstroms). In gases, the average distance between molecules is large compared with their sizes; therefore, cohesion in them is insignificant. The cohesion energy density is a measure of the intensity of intermolecular interactions. It is equivalent to the work required to separate mutually attracting molecules to an infinitely large distance from each other, which, in practice, corresponds to evaporation or sublimation of the substance.