chemical association


chemical association

      the aggregation of atoms (atom) or molecules (molecule) into larger units held together by forces weaker than chemical bonds that bind atoms in molecules. The term is usually restricted to the formation of aggregates of like molecules or atoms. polymerization also denotes the formation of larger units by the union of like small units but usually with chemical bonds between the smaller units.

      The molecular aggregate formed by association is commonly known as an association complex. Because of the weakness of the forces holding the small units together, an equilibrium is often observed between an association complex and the corresponding simple molecules. The equilibrium mixture behaves chemically much as would the small molecules by themselves, because the removal of some by chemical reaction shifts the equilibrium in such a way as to disassociate more of the aggregate in accordance with the law of mass action.

      The forces tending to make like molecules associate are of three kinds. Most important is the hydrogen bond (or bridge), in which a hydrogen atom bonded to an electronegative atom forms a bridge to another electronegative atom. If these two electronegative atoms are in different molecules, the formation of the bridge unites the two. Molecules may also be held together, if the temperature is not too high, by dipolar attraction, resulting from the separation of positive and negative charges in each molecule. The molecule as a whole may be polar, one part having an excess of positive charge and another an excess of negative charge, or it may contain polar groups. At sufficiently low temperatures the relatively weak London forces (i.e., forces acting between any two atoms brought close together) may also be strong enough to produce molecular association.

       water is one of the most highly associated compounds. An ice crystal is a giant network of water molecules held together by hydrogen bonds. In liquid water the molecules are connected to one another in much the same manner as in ice, but less regularly, and the hydrogen bonds are constantly broken and formed.

* * *


Universalium. 2010.

Look at other dictionaries:

  • chemical association — cheminė asociacija statusas T sritis fizika atitikmenys: angl. chemical association vok. chemische Assoziation, f rus. химическая ассоциация, f pranc. association chimique, f …   Fizikos terminų žodynas

  • association chimique — cheminė asociacija statusas T sritis fizika atitikmenys: angl. chemical association vok. chemische Assoziation, f rus. химическая ассоциация, f pranc. association chimique, f …   Fizikos terminų žodynas

  • Chemical Industries Association — Abbreviation CIA Legal status Not for profit organisation Purpose/focus Chemical engineering and pharmaceutical companies in the UK Location Kings Buildings, Smith Square, London, SW1P 3JJ …   Wikipedia

  • Chemical Society of Japan — Formation 1878 Type Learned society Headquarters Tokyo Location Japan …   Wikipedia

  • Chemical Weapons Convention — Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction Drafted September 3, 1992[1] Signed January 13, 1993[1] Location Paris and New York[ …   Wikipedia

  • Chemical castration — is the administration of medication designed to reduce libido and sexual activity, usually in the hope of preventing rapists, child molesters and other sex offenders from repeating their crimes. Unlike surgical castration, where the testicles or… …   Wikipedia

  • Chemical Science (journal) — Chemical Science   Abbreviated title (ISO) Ch …   Wikipedia

  • Chemical Wedding (film) — Chemical Wedding Theatrical poster Directed by Julian Doyle Produced by David …   Wikipedia

  • Chemical Society of Japan — Sociedad Química de Japón Logotipo de la CSJ Acrónimo CSJ Tipo Sociedad científica …   Wikipedia Español

  • Chemical lace — (sometimes referred to as Schiffli Lace) is a form of machine made lace. This method of lace making is done by embroidering a pattern on a sacrificial fabric that has been chemically treated so as to disintegrate after the pattern has been… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.