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For other uses, see Valence.

In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties A chemical bond is the physical process responsible for the attractive interactions between Atoms and Molecules and which confers stability to diatomic and polyatomic History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Over the last century, the concept of valence evolved into a range of approaches for describing the chemical bond, including Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958) and all the advanced methods of quantum chemistry. Lewis structures, also called Lewis-dot diagrams are diagrams that show the bonding between Atoms of a In Chemistry, valence bond theory explains the nature of a Chemical bond in a Molecule in terms of atomic valencies. In Chemistry, a molecular orbital (or MO) is a region in which an Electron may be found in a Molecule. Valence shell electron pair repulsion (VSEPR theory (1957 is a model in Chemistry, which is used for predicting the shapes of individual Molecules based Quantum chemistry is a branch of Theoretical chemistry, which applies Quantum mechanics and Quantum field theory to address issues and problems in

Contents

History

The etymology of the word "valence" is from 1425, meaning "extract, preparation," from Latin valentia "strength, capacity," and the chemical meaning referring to the "combining power of an element" is recorded from 1884, from German Valenz. Etymology is the study of the History of Words &mdash when they entered a language from what source and how their form and meaning have changed over time [1]

In 1789, William Higgins published views on what he called combinations of "ultimate" particles, which foreshadowed the concept of valency bonds. William Higgins (1763-1825 an Irish chemist was one of the early proponents of Atomic theory, on whose works John Dalton is said to have based much of In Chemistry, valence bond theory explains the nature of a Chemical bond in a Molecule in terms of atomic valencies. [2] If, for example, according to Higgins, the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, then the strength of the force would be divided accordingly, and similarly for the other combinations of ultimate particles:

William Higgins' combinations of ultimate particles (1789)
William Higgins' combinations of ultimate particles (1789)

The exact inception, however, of the theory of chemical valencies can be traced to an 1852 paper by Edward Frankland, in which he combined the older theories of free radicals and “type theory” with thoughts on chemical affinity to show that certain elements have the tendency to combine with other elements to form compounds containing 3, i. William Higgins (1763-1825 an Irish chemist was one of the early proponents of Atomic theory, on whose works John Dalton is said to have based much of Sir Edward Frankland, KCB, FRS ( January 18, 1825 &ndash August 9, 1899) was a Chemist, one of the foremost In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell In Chemical physics and Physical chemistry, chemical affinity can be defined as electronic properties by which dissimilar Chemical species are capable of e. in the three atom groups (e. g. NO3, NH3, NI3, etc. ) or 5, i. e. in the five atom groups (e. g. NO5, NH4O, PO5, etc. ), equivalents of the attached elements. It is in this manner, according to Franklin, that their affinities are best satisfied. Following these examples and postulates, Franklin declares how obvious it is that:[3]

“ A tendency or law prevails (here), and that, no matter what the characters of the uniting atoms may be, the combining power of the attracting element, if I may be allowed the term, is always satisfied by the same number of these atoms. ”

This “combining power” was afterwards called quantivalence or valency (and valence by American chemists). [2]

Overview

The concept was developed in the middle of the nineteenth century in an attempt to rationalize the formulae of different chemical compounds. A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. In 1919, Irving Langmuir, borrowed the term to explain Gilbert N. Lewis's cubical atom model by stating that "the number of pairs of electrons which any given atom shares with the adjacent atoms is called the covalence of that atom. Irving Langmuir ( January 31, 1881 in Brooklyn New York – August 16, 1957 in Woods Hole Massachusetts) was an Gilbert Newton Lewis ( October 23, 1875 - March 23, 1946) was a famous American physical chemist known for the discovery The cubical atom was an early atomic model in which Electrons were positioned at the eight corners of a cube in a non-polar atom or molecule The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J " The prefix co-, e. g. co-author, means together, jointly, associated in action, partnered to a lesser degree, etc. ,; thus a co-valent bond, essentially, means that the atoms share valence. Hence, if an atom, for example, had a +1 valence, meaning it was missing an electron, and another a -1 valence, meaning it had an extra electron, then a bond between these two atoms would result because they would be complementing or sharing their out of balance valence tendencies. Subsequently, it is now more common to speak of covalent bonds rather than "valence", which has fallen out of use in higher level work with the advances in the theory of chemical bonding, but is still widely used in elementary studies where it provides a heuristic introduction to the subject.

"Number of bonds" definition

The number of bonds formed by a given element was originally thought to be a fixed chemical property and in fact, in many cases, this is a good approximation. For example, in many of their compounds, carbon forms four bonds, oxygen two and hydrogen one. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 However it soon became apparent that, for many elements, the valence could vary between different compounds. One of the first examples to be identified was phosphorus, which sometimes behaves as if it has a valence of three and sometimes as if it has a valence of five. Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 One method around this problem is to specify the valence for each individual compound: although it removes much of the generality of the concept, this approach has given rise to the idea of oxidation numbers (used in Stock nomenclature) and to lambda notation in the IUPAC nomenclature of inorganic chemistry. The oxidation number of a central atom in a coordination compound is the charge that it would have if all the Ligands were removed along with the Electron pairs Alfred Stock ( July 16 1876 – August 12 1946) was a German inorganic chemist. The IUPAC nomenclature of inorganic chemistry is a systematic method of naming Inorganic Chemical compounds as recommended by the International Union

IUPAC definition

The International Union of Pure and Applied Chemistry (IUPAC) has made several attempts to arrive at an unambiguous definition of valence. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization The current version, adopted in 1994,[4]:

The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and

This definition reimposes a unique valence for each element at the expense of neglecting, in many cases, a large part of its chemistry.

The mention of hydrogen and chlorine is for historic reasons, although both in practice mostly form compounds in which their atoms form a single bond. Exceptions in the case of hydrogen include the ion [HF2]− and the various boron hydrides such as diborane: these are examples of three-center two-electron bonds. Diborane is the Chemical compound with the formula B2H6 It is a colorless gas at room temperature with a repulsively sweet odor A three-center two-electron bond is an electron deficient Chemical bond where three atoms share two electrons Chlorine forms a number of fluorides—ClF, ClF3 and ClF5—and its valence according to the IUPAC definition is hence five. Fluoride is the reduced form of Fluorine. Both organic and Inorganic compounds containing the element fluorine are considered fluorides Chlorine monofluoride is a volatile Interhalogen compound with the Chemical formula ClF Chlorine trifluoride is the Chemical compound with the formula ClF3 Chlorine pentafluoride has formula ClF5 It was first synthesized in 1963 Fluorine is the element for which the largest number of atoms combine with atoms of other elements: it is univalent in all compounds except the ion [H2F]+. Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 In fact, the IUPAC definition can only be resolved by fixing the valences of hydrogen and fluorine as one, a convention which has been followed here.

Valences of the elements

Valences for the majority of elements are based on the highest known fluoride. [5]

Group → 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
↓ Period
1 1
H
2
He
2 3
Li		 4
Be
5
B		 6
C		 7
N		 8
O		 9
F		 10
Ne
3 11
Na		 12
Mg
13
Al		 14
Si		 15
P		 16
S		 17
Cl		 18
Ar
4 19
K		 20
Ca		 21
Sc		 22
Ti		 23
V		 24
Cr		 25
Mn		 26
Fe		 27
Co		 28
Ni		 29
Cu		 30
Zn		 31
Ga		 32
Ge		 33
As		 34
Se		 35
Br		 36
Kr
5 37
Rb		 38
Sr		 39
Y		 40
Zr		 41
Nb		 42
Mo		 43
Tc		 44
Ru		 45
Rh		 46
Pd		 47
Ag		 48
Cd		 49
In		 50
Sn		 51
Sb		 52
Te		 53
I		 54
Xe
6 55
Cs		 56
Ba		 *
 72
Hf		 73
Ta		 74
W		 75
Re		 76
Os		 77
Ir		 78
Pt		 79
Au		 80
Hg		 81
Tl		 82
Pb		 83
Bi		 84
Po		 85
At		 86
Rn
7 87
Fr		 88
Ra		 **
 104
Rf		 105
Db		 106
Sg		 107
Bh		 108
Hs		 109
Mt		 110
Ds		 111
Rg		 112
Uub		 113
Uut		 114
Uuq		 115
Uup		 116
Uuh		 117
Uus		 118
Uuo

* Lanthanides 57
La		 58
Ce		 59
Pr		 60
Nd		 61
Pm		 62
Sm		 63
Eu		 64
Gd		 65
Tb		 66
Dy		 67
Ho		 68
Er		 69
Tm		 70
Yb		 71
Lu
** Actinides 89
Ac		 90
Th		 91
Pa		 92
U		 93
Np		 94
Pu		 95
Am		 96
Cm		 97
Bk		 98
Cf		 99
Es		 100
Fm		 101
Md		 102
No		 103
Lr

Valences of chemical elements

     None      One      Two      Three      Four      Five      Six      Seven
Atomic number colors show state at standard temperature and pressure (0 °C and 1 atm)
Solids Liquids Gases Unknown
Borders show natural occurrence
Primordial From decay Synthetic Undiscovered

Other criticisms of the concept of valence

References

  1. ^ Valence - Online Etymology Dictionary.
  2. ^ a b Partington, J. R. (1989). A Short History of Chemistry. Dover Publications, Inc. ISBN 0-486-65977-1.  
  3. ^ Franklin, E. (1852). Phil. Trans. , vol. cxlii, 417.
  4. ^ Pure Appl. Chem. 66: 1175 (1994).
  5. ^ http://www.webelements.com/ (accessed 2006-02-20). Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1472 - Orkney and Shetland are left by Norway to Scotland, due to a Dowry payment
  6. ^ In the gas phase, LiF does indeed exist as discrete diatomic molecules as the valences would suggest: Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A. Frank Albert Cotton ( April 9 1930 – February 20 2007) was the W Sir Geoffrey Wilkinson ( 14 July 1921 &ndash 26 September, 1996) was an English Chemist. ; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn. ) New York:Wiley-Interscience. ISBN 0-471-19957-5.

External links

A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization Compendium of Chemical Terminology (ISBN 0-86542-684-8 is a book published by IUPAC containing internationally accepted definitions for terms in Chemistry.
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