association complex

In chemistry, a complex is a substance, either an ion or a neutral molecule, formed by the union of simpler substances. These are held together by chemical forces dependent on atomic structures, not just physical ones. The formation of complexes significantly impacts solution behavior.1

Chemical association refers to the aggregation of atoms or molecules into larger units. These units are held together by forces weaker than chemical bonds. The resulting aggregate is known as an association complex. Because the forces are weak, an equilibrium often exists between the association complex and its simpler molecules. This equilibrium is governed by the law of mass action.2

Forces driving association include:
* Hydrogen bonds: A hydrogen atom bonded to an electronegative atom forms a bridge to another electronegative atom in a different molecule.2
* Dipolar attraction: Molecules are held together by the attraction between positive and negative charges within them, especially if the molecule is polar.2
* London forces: At low temperatures, these weak forces between atoms can also cause molecular association.2

Water is a prime example of an associated compound, with its molecules held together by hydrogen bonds in both ice and liquid states.2