Valence

Valence (cartoon) (labeled)
A chemical anthropomorphism cartoon depiction elements and marriage in terms of valence electrons. [3]
In chemistry, valence, valency, or “combining power”, refers to the ability of one type of atom to bond to another type of atom.

History
The main forerunner to the concept of the valence bond was the "hooked atoms" model of chemical attachment.

Irish chemist William Higgins’s 1789 theory of the division of forces between ultimate particles was said to foreshadow the valency bond.

English chemist Edward Frankland’s 1852 theory of “combining powers” is said to have launched the basic outline of valance theory. [1] The actual paragraph attributed to the inception of the “valence” theory of chemistry is found at the tail end of Frankland’s 1852 article “On a New Series of Organic Bodies Containing Metals” wherein he writes:

“When the formulae of inorganic chemical compounds are considered, even a superficial observer is struck with the general symmetry of their construction; the compounds of nitrogen, phosphorous, antimony, and arsenic especially exhibit the tendency of these elements to form compounds containing 3 or 5 equivalents of other elements, and it is in these proportions that their affinities are best satisfied; thus in ternal group we have NO3, NH3, NS3, PO3, PH3, PCl3, SbO3, SbH3, SbCl3, AsO3, AsH3, AsCl3, etc., and in the five-atom group NO5, Nh4O, NH4I, PO5, Ph4I, etc. Without offering any hypothesis regarding the cause of this symmetrical grouping of atoms, it is sufficiently evident from the examples just given that such a tendency or law prevails and that no matter what the character 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.”

Frankland's term “combining power” was soon afterwards called quantivalence or valency, by the English chemists, and later valence by American chemists.

In 1919, American chemist Irving Langmuir, borrowed the term valency to explain Gilbert Lewis's 1902 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"; and hence, thereafter, the concept of the “covalent bond” originated, meaning the sharing of two electrons. The prefix co- means "together", in the sense that a co-valent bond means that the atoms share valence.

In 1921, Julius Cohen, in his Organic Chemistry, stated that “degree of affinity” corresponded exactly to “valency”. [4]

References
1. Partington, J.R. (1989). A Short History of Chemistry. Dover.
2. (a) Frankland, Edward. (1852). “On a New Series of Organic Bodies Containing Metals”, Philosophical Transactions of the Royal Society of London, 142: 417-44.
(b) Palmer, William. (1944). Valency: Classical and Modern (Frankland and Kekule discover valency, pgs. 8-). Cambridge University Press.
3. Jarape. (year), “Valance Electrons”, JarpeScienceCartoons.Blogspot.com.
4. Cohen, Julius B. (1921). Organic Chemistry: for Advanced Students, Volume 1 (pg. 54). Arnold.

Further reading
● Lewis, Gilbert. (1923). Valence: and the Structure of Atoms and Molecule. The Chemical Catalog Company, Inc.
● Coulson, Charles A. (1952). Valence. Oxford at the Clarendon Press.
● Russell, Colin A. (1971). The History of Valency. Humanities Press.
● Russell, Colin. (2003). Edward Frankland: Chemistry, Controversy, and Conspiracy in Victorian England. Cambridge University Press.

External links
Valence (chemistry) – Wikipedia.

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