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Valence (city, France)

Valence (väläNs´), city (1990 pop. 65,026), capital of Drôme dept., SE France, in Dauphiné, on the Rhône River. Its many manufactures include metallurgical products, textiles, leather goods, and jewelry. It is also a processing and trade center for a fertile farm area. An old Roman town, it was taken by the Visigoths (413) and the Arabs (c.730), then changed hands many times. Although nominally under the control of various European powers, it was actually ruled by its own bishops from 1150 until the 15th cent., when its citizens put themselves under the protection of the dauphin. Its Romanesque cathedral (11th cent.; partially restored) is a tourist attraction. Its university was founded in 1452.

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valence (in chemistry)

valence, combining capacity of an atom expressed as the number of single bonds the atom can form or the number of electrons an element gives up or accepts when reacting to form a compound. Atoms are called monovalent, divalent, trivalent, or tetravalent, according to whether they form one, two, three, or four bonds (see chemical bond).

The Relationship of Electrons and Valence

For purposes of describing chemical behavior, an atom can be considered as a positively charged nucleus surrounded by negatively charged electrons orbiting in concentric spherical shells. The number of positive charges in the nucleus determines how many electrons normally surround the nucleus; as atomic number increases, the electron shells are filled, starting with those nearest the nucleus.

The valence of an atom is determined by the number of electrons in the outermost, or valence, shell. The atom exists in its most stable configuration when its outermost shell is completely filled; in combining with other atoms, it thus tends to gain or lose valence electrons in order to attain a stable configuration. If the valence shell of the atom is nearly complete, as in chlorine and other nonmetals, the atom will tend to accept electrons to complete it; if the valence shell has few electrons, as in potassium and other metals, the atom will tend to lose these electrons, so that the next shell below the valence shell becomes a completed outermost shell.

The valence of many elements is determined from their ability to combine with hydrogen or to replace it in compounds. For example, one oxygen atom combines with two hydrogen atoms to form water and the valence of oxygen is thus determined to be 2. Similarly, chlorine accepts one electron in combining with a single atom of hydrogen to form hydrogen chloride, HCl, and chlorine's valence is 1. Zinc does not combine with hydrogen but does replace it in compounds; in a typical replacement reaction, one zinc atom replaces two hydrogen atoms, as in the equation Zn+H2SO4→ZnSO4+H2, so that zinc has a valence of 2.

Valence Number

Atoms are assigned numbers, called valence numbers, oxidation numbers, or oxidation states, which range in value from -4 through 0 to +7 and describe the combining behavior of the atoms in chemical reactions, particularly oxidation-reduction reactions (see oxidation and reduction). Metals, which commonly donate electrons and form compounds in which they exist in the positive, or cationic, state, are assigned positive oxidation numbers (see cation). For a metal such as zinc, which donates two electrons to achieve a stable electron configuration, the oxidation number is +2. Nonmetals, which commonly accept electrons and in compounds exist in the negative, or anionic, state, are assigned negative oxidation numbers (see anion). The oxidation number is -1 for chlorine and the other halogens, which accept one electron to complete their valence shell.

Some elements, like the transition metals, have electron configurations in which electrons from their inner shells can also be used as valence electrons; these elements can have several different oxidation states. For example, iron can have a valence of +2 or +3, and chromium can have a valence of +2, +3, or +6. Iron in the +3 oxidation state, Fe+3, acts as an oxidizing agent, accepting one electron to attain the Fe+2 state, while ferrous iron, Fe+2, by donating an electron in going to the +3 state, acts as a reducing agent.

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valence

va·lence / ˈvāləns/ • n. Chem. the combining power of an element, esp. as measured by the number of hydrogen atoms it can displace or combine with: carbon always has a valence of 4. ∎  [as adj.] relating to or denoting electrons involved in or available for chemical bond formation: molecules with unpaired valence electrons. ∎  Linguistics the number of grammatical elements with which a particular word, esp. a verb, combines in a sentence.

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valence

valence (valency) Measure of the ‘combining power’ of a particular element, equal to the number of single chemical bonds one atom can form, or the number of electrons it gives up or accepts when forming a compound. Hydrogen has a valency of 1, carbon 4, and sulphur 2, as seen in compounds such as methane (CH4), carbon disulphide (CS2), and hydrogen sulphide (H2S). See also atomic number; covalent bond; ionic bond

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valence

valenceabeyance, conveyance, purveyance •creance • ambience •irradiance, radiance •expedience, obedience •audience •dalliance, mésalliance •salience •consilience, resilience •emollience • ebullience •convenience, lenience, provenience •impercipience, incipience, percipience •variance • experience •luxuriance, prurience •nescience • omniscience •insouciance • deviance •subservience • transience •alliance, appliance, compliance, defiance, misalliance, neuroscience, reliance, science •allowance •annoyance, clairvoyance, flamboyance •fluence, pursuance •perpetuance • affluence • effluence •mellifluence • confluence •congruence • issuance • continuance •disturbance •attendance, dependence, interdependence, resplendence, superintendence, tendance, transcendence •cadence •antecedence, credence, impedance •riddance • diffidence • confidence •accidence • precedence • dissidence •coincidence, incidence •evidence •improvidence, providence •residence •abidance, guidance, misguidance, subsidence •correspondence, despondence •accordance, concordance, discordance •avoidance, voidance •imprudence, jurisprudence, prudence •impudence • abundance • elegance •arrogance • extravagance •allegiance • indigence •counter-intelligence, intelligence •negligence • diligence • intransigence •exigence •divulgence, effulgence, indulgence, refulgence •convergence, divergence, emergence, insurgence, resurgence, submergence •significance •balance, counterbalance, imbalance, outbalance, valance •parlance • repellence • semblance •bivalence, covalence, surveillance, valence •sibilance • jubilance • vigilance •pestilence • silence • condolence •virulence • ambulance • crapulence •flatulence • feculence • petulance •opulence • fraudulence • corpulence •succulence, truculence •turbulence • violence • redolence •indolence • somnolence • excellence •insolence • nonchalance •benevolence, malevolence •ambivalence, equivalence •Clemence • vehemence •conformance, outperformance, performance •adamance • penance • ordinance •eminence • imminence •dominance, prominence •abstinence • maintenance •continence • countenance •sustenance •appurtenance, impertinence, pertinence •provenance • ordnance • repugnance •ordonnance • immanence •impermanence, permanence •assonance • dissonance • consonance •governance • resonance • threepence •halfpence • sixpence •comeuppance, tuppence, twopence •clarence, transparence •aberrance, deterrence, inherence, Terence •remembrance • entrance •Behrens, forbearance •fragrance • hindrance • recalcitrance •abhorrence, Florence, Lawrence, Lorentz •monstrance •concurrence, co-occurrence, occurrence, recurrence •encumbrance •adherence, appearance, clearance, coherence, interference, perseverance •assurance, durance, endurance, insurance •exuberance, protuberance •preponderance • transference •deference, preference, reference •difference • inference • conference •sufferance • circumference •belligerence • tolerance • ignorance •temperance • utterance • furtherance •irreverence, reverence, severance •deliverance • renascence • absence •acquiescence, adolescence, arborescence, coalescence, convalescence, deliquescence, effervescence, essence, evanescence, excrescence, florescence, fluorescence, incandescence, iridescence, juvenescence, luminescence, obsolescence, opalescence, phosphorescence, pubescence, putrescence, quiescence, quintessence, tumescence •obeisance, Renaissance •puissance •impuissance, reminiscence •beneficence, maleficence •magnificence, munificence •reconnaissance • concupiscence •reticence •licence, license •nonsense •nuisance, translucence •innocence • conversance • sentience •impatience, patience •conscience •repentance, sentence •acceptance • acquaintance •acquittance, admittance, intermittence, pittance, quittance, remittance •assistance, coexistence, consistence, distance, existence, insistence, outdistance, persistence, resistance, subsistence •instance • exorbitance •concomitance •impenitence, penitence •appetence •competence, omnicompetence •inheritance • capacitance • hesitance •Constance • importance • potence •conductance, inductance, reluctance •substance • circumstance •omnipotence • impotence •inadvertence • grievance •irrelevance, relevance •connivance, contrivance •observance • sequence • consequence •subsequence • eloquence •grandiloquence, magniloquence •brilliance • poignance •omnipresence, pleasance, presence •complaisance • malfeasance •incognizance, recognizance •usance • recusance

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Valence

VALENCE

VALENCE , chief town of the department of Dôme, s.e. France, part of the ancient province of Dauphiné. The establishment of the Jewish community in Valence does not go back earlier than 1323; however, the decision of the council held in the town in 1248 that prohibited all relations between Christians and Jews may lead to the assumption that isolated Jews were living there at the time. This decision appears to have been decreed in the wake of the accusation of ritual murder of *Valreas in 1247 as a result of which the high constable of Valence had all the Jews on his lands imprisoned and their possessions confiscated. In 1441, when the community numbered 18 families, the bishop recalled the obligation of the Jews to wear the distinctive sign so that "guests be not regarded as citizens." In 1463, 14 Jews of Valence were ordered to pay a severe fine to the dauphin "for having practiced excessive usury and having spoken evilly of His Majesty…." In 1476 the same dauphin granted the Jews of Valence a new letter of protection; however, at the close of the century this community disappeared, as did the other communities of Dauphiné. At the beginning of World War ii, there were about 50 Jewish families in Valence, half of whom were refugees from *Alsace. In the early 1970s, there were about 800 Jews in Valence, mainly of North African origin.

bibliography:

Gross, Gal Jud, 204; A. Prudhomme, in: rej, 9 (1884), 235–41; S. Grayzel, The Church and the Jews (19602), 234f.; P. de Torey, Catalogue des Acres du Dauphin Louis ii (1899), passim; Z. Szajkowski, Analytical Franco-Jewish Gazetteer (1966), 186.

[Bernhard Blumenkranz]

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Valence

Valence

Valence, in chemistry, refers to a number assigned to elements that reflects their ability, or capacity, to react (combine) with other elements. It also refers to the type of reactions the element will undergo. Thus, the value of valence is associated with the number of electrons, if any, that an element loses or accepts from another atom during a chemical reaction. The term valence, also referred to as valency or valence number, is derived from the Latin word for strength and can reflect an elements strength or affinity for certain types of reactions. The concept was formulated in the nineteenth century as a way to organize formulas of the various chemical compounds.

Oftentimes, Greek prefixes are used to describe an atoms or a materials valency. For example, uni/mono stands for 1, while bi/di stands for 2, tri for 3, and tetra for 4. For instance, a unimetal will have a valence of 1.

The electrons in an atom are located at different energy levels. The electrons in the highest energy level are called valence electrons. In accord with the octet ruleand to become more energetically stable atoms gain, lose, or share valence electrons in an effort to obtain a noble gas configuration in their outer shell. The configuration of electrons in an atoms outer shell determines its ability and affinity to enter into chemical reactions.

The valence number of an element can be determined by using a few simple rules relating to an elements location on the periodic table. In ionic compounds (formed between charged atoms or groups of atoms called ions) the valence of an atom is the number of electrons that atom will gain or lose to obtain a full outer shell. In group one of the periodic table, elements are assigned a valence number of 1. A valence number of 1 means that an element will generally react to lose one electron to obtain a full outer shell. Group two elements are assigned a valence number of 2. A valence number of 2 means that a group two element will generally react to lose two electrons to obtain a full outer shell. Group 17 elements are assigned a valence number of negative one (-1). A valence number of -1 means that a group two element will generally react to gain one electron to obtain a noble gas electron configuration. Reflecting an inability to react with other elements, Nobel gases, already maintaining a stable arrangement of electrons, are assigned a valence of zero (O).

The term valence can also refer to the charge or oxidation number on an atom. In magnesium atoms (Mg+ 2), for instance, the valence is +2. An atom or ion with a charge of +2 is said to be divalent.

In covalent compounds the valence of an atom may be less obvious. In this case, it is the number of bonds formed, that is, whether the bonds are single, double, or triple bonds. A carbon atom with two single bonds and one double bond carries a valence of four (4). In water (H2O), the valence of oxygen is 2 and the valence of hydrogen is 1. In both cases the valence number gives an indication of the number of bonds each atom forms.

Valence bond theory is similar to molecular orbital theory in that it is concerned with the formation of covalent bonds. Valence bond theory describes bonds in term of interactions between outer orbitals and hybridized orbitals to explain the formation of compounds.

Valence Shell Electron Pair Repulsion (VSEPR) theory is one of the favored models to explain covalent bonds. This theory states that molecules will be shaped to minimize the repulsion that takes place between valence electrons. Because they are all negatively charged, valence shell electrons repel one another. VSEPR theory states that the atoms of a molecule will arrange themselves and assume a shape around a central atom to minimize repulsion between valence electrons.

See also Atomic models; Atomic number; Atomic theory; Chemical bond; Chemistry.

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Valence

Valence

Valence refers to a number assigned to elements that reflects their ability to react with other elements and the type of reactions the element will undergo. The term valence is derived from the Latin word for strength and can reflect an element's strength or affinity for certain types of reactions.

The electrons in an atom are located at different energy levels. The electrons in the highest energy level are called valence electrons. In accord with the octet rule— and to become more energetically stable—atoms gain, lose, or share valence electrons in an effort to obtain a noble gas configuration in their outer shell. The configuration of electrons in an atom's outer shell determines its ability and affinity to enter into chemical reactions .

The valence number of an element can be determined by using a few simple rules relating to an ele ment's location on the periodic table . In ionic compounds (formed between charged atoms or groups of atoms called ions) the valence of an atom is the number of electrons that atom will gain or lose to obtain a full outer shell. In group one of the periodic table, elements are assigned a valence number of 1. A valence number of 1 means that an element will generally react to lose one electron to obtain a full outer shell. Group two elements are assigned a valence number of 2. A valence number of 2 means that a group two element will generally react to lose two electrons to obtain a full outer shell. Group 17 elements are assigned a valence number of negative one (-1). A valence number of -1 means that a group two element will generally react to gain one electron to obtain a noble gas electron configuration. Reflecting an inability to react with other elements, Nobel gases, already maintaining a stable arrangement of electrons, are assigned a valence of zero (O).

The term valence can also refer to the charge or oxidation number on an atom. In magnesium atoms (Mg+2) the valence is +2. An atom or ion with a charge of +2 is said to be divalent.

In covalent compounds the valence of an atom may be less obvious. In this case it is the number of bonds formed, that is, whether the bonds are single, double, or triple bonds. A carbon atom with two single bonds and one double bond carries a valence of four (4). In water (H2O), the valence of oxygen is 2 and the valence of hydrogen is 1. In both cases the valence number gives an indication of the number of bonds each atom forms.

Valence bond theory is similar to molecular orbital theory in that it is concerned with the formation of covalent bonds. Valence bond theory describes bonds in term of interactions between outer orbitals and hybridized orbitals to explain the formation of compounds.

Valence Shell Electron Pair Repulsion (VSEPR) theory is one of the favored models to explain covalent bonds. This theory states that molecules will be shaped so as to minimize the repulsion that takes place between valence electrons. Because they are all negatively charged, valence shell electrons repel one another. VSEPR theory states that the atoms of a molecule will arrange themselves and assume a shape around a central atom so as to minimize repulsion between valence electrons.

See also Atomic models; Atomic number; Atomic theory; Chemical bond; Chemistry.

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"Valence." The Gale Encyclopedia of Science. . Encyclopedia.com. (October 17, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/valence

"Valence." The Gale Encyclopedia of Science. . Retrieved October 17, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/valence

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Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

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http://apastyle.apa.org/

Notes:
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