valence

/vay"leuhns/, n.

1. Chem.

a. the quality that determines the number of atoms or groups with which any single atom or group will unite chemically.

b. the relative combining capacity of an atom or group compared with that of the standard hydrogen atom. The chloride ion, Cl-, with a valence of one, has the capacity to unite with one atom of hydrogen or its equivalent, as in HCl or NaCl.

2. Immunol. the number of determinants per molecule of antigen.

3. the capacity of one person or thing to react with or affect another in some special way, as by attraction or the facilitation of a function or activity.

Also, valency.

[1865-70; < L valentia strength, worth, equiv. to valent- (s. of valens), prp. to be strong + -ia n. suffix; see -ENCE]

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Number of bonds (see bonding) an atom can form.

Hydrogen (H) always has valence 1, so other elements' valences equal the number of hydrogen atoms they combine with. Thus, oxygen (O) has valence 2, as in water (H₂O); nitrogen (N) has valence 3, as in ammonia (NH₃); and chlorine (Cl) has valence 1, as in hydrochloric acid (HCl). The valence depends on the number of unpaired electrons in the outermost (and, in transition elements, the next) shell of the atom's structure. The sharing of the unpaired (valence) electrons in a bond mimics the stable configuration of the noble gases, whose outer shells are full. Elements that can achieve stable configurations by various combinations have more than one valence.

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▪ France

      town, capital of Drôme département, Rhône-Alpes région, southeastern France. Valence lies on the left bank of the Rhône River and is connected by road to Lyon and Grenoble.

      Built on a succession of terraces bordering the Rhône, the town is dominated by the ancient Cathedral of Saint-Apollinaire, which was consecrated by Pope Urban II in 1095 and completed early in the 12th century. Damage done to the cathedral during the Wars of Religion (1569–98) was repaired in the 17th century. The Champ de Mars, a vast esplanade south of the cathedral, offers a fine view of the Rhône River valley. Valence probably became a bishopric in the 4th century and was ruled by its bishops until Louis XI in 1450 persuaded them to give up their temporal power in exchange for royal protection and a university (suppressed after the French Revolution).

      Valence is an important administrative and service centre, as well as a commercial centre for the fruit and vegetable products of the Rhône River valley. The town's industries include metallurgy and the manufacture of electrical equipment, electronics, textiles, and jewelry. Its industry has merged with that of Lyon and Grenoble. Valence has an industrial port on the Rhône. Pop. (1999) 64,260; (2005 est.) 64,900.

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