Editing Linus Pauling (section)

===Nature of the chemical bond===
[[File:Linus Pauling 1955a.jpg|thumb|Linus Pauling with an inset of his Nobel Prize in 1955]]

In the late 1920s, Pauling began publishing papers on the nature of the [[chemical bond]]. Between 1937 and 1938, he took a position as George Fischer Baker Non-Resident Lecturer in Chemistry at [[Cornell University]]. While at Cornell, he delivered a series of nineteen lectures<ref>{{Cite web |title=Outline of the George Fischer Baker Lectureship, Cornell University |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/1937s.3-outline-01-large.html |url-status=live |archive-url=https://web.archive.org/web/20211112063624/http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/1937s.3-outline-01-large.html |archive-date=November 12, 2021 |access-date=April 13, 2022 |website=[[Oregon State University]] |language=en}}</ref> and completed the bulk of his famous textbook ''The Nature of the Chemical Bond''.<ref name="The George Fischer Baker Lectureship and the Beginnings of the Manuscript">{{Cite web |date=July 30, 2014 |title=The George Fischer Baker Lectureship and the Beginnings of the Manuscript |url=https://paulingblog.wordpress.com/2014/07/30/the-george-fischer-baker-lectureship-and-the-beginnings-of-the-manuscript/ |url-status=live |archive-url=https://web.archive.org/web/20220307085556/https://paulingblog.wordpress.com/2014/07/30/the-george-fischer-baker-lectureship-and-the-beginnings-of-the-manuscript/ |archive-date=March 7, 2022 |access-date=June 3, 2015 |website=The Pauling Blog |publisher=[[Oregon State University]] |language=en}}</ref><ref name="Pauling1960" />{{rp|Preface}} It is based primarily on his work in this area that he received the [[Nobel Prize in Chemistry]] in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances".<ref name="Nobel" /> Pauling's book has been considered "chemistry's most influential book of this century and its effective bible".<ref name="Genes2001">{{Cite book |last=Watson |first=James D. |url=https://archive.org/details/passionfordnagen0000wats |title=A passion for DNA: genes, genomes, and society |date=2001 |publisher=[[Oxford University Press]] |isbn=978-0-19-860428-0 |edition=2003 |location=[[Oxford]] |ol=7401431M |author-link=James Watson |via=[[Internet Archive]]}}</ref> In the 30 years after its first edition was published in 1939, the book was cited more than 16,000 times. Even today, many modern scientific papers and articles in important journals cite this work, more than seventy years after the first publication.<ref name="Google">{{Cite web |title=The nature of the chemical bond (citations and estimated counts) |url=https://scholar.google.com/citations?view_op=view_citation&hl=en&user=b0B12YAAAAAJ&citation_for_view=b0B12YAAAAAJ:j5aT6aphRxQC |access-date=May 27, 2015 |website=Google Scholar}}</ref>

Part of Pauling's work on the nature of the chemical bond led to his introduction of the concept of [[orbital hybridization]].<ref>{{Cite web |last=Pauling |first=Linus |year=1928 |title=London's paper. General ideas on bonds |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/sci3.001.21.html |access-date=June 2, 2015 |publisher=Oregon State University Libraries Special Collections}}</ref> While it is normal to think of the electrons in an atom as being described by [[atomic orbital|orbital]]s of types such as ''s'' and ''p'', it turns out that in describing the bonding in molecules, it is better to construct functions that partake of some of the properties of each. Thus the one 2s and three 2p orbitals in a carbon atom can be (mathematically) 'mixed' or combined to make four equivalent orbitals (called sp<sup>3</sup> hybrid orbitals), which would be the appropriate orbitals to describe carbon compounds such as [[methane]], or the 2s orbital may be combined with two of the 2p orbitals to make three equivalent orbitals (called sp{{sup|2}} hybrid orbitals), with the remaining 2p orbital unhybridized, which would be the appropriate orbitals to describe certain [[alkene|unsaturated]] carbon compounds such as [[ethylene]].{{r|Pauling1960|pages=111–120}} Other hybridization schemes are also found in other types of molecules.
Another area which he explored was the relationship between [[ionic bond]]ing, where electrons are transferred between atoms, and [[covalent bond]]ing, where electrons are shared between atoms on an equal basis. Pauling showed that these were merely extremes, and that for most actual cases of bonding, the [[Introduction to quantum mechanics|quantum-mechanical]] [[wave function]] for a polar molecule AB is a [[linear combination|combination]] of wave functions for covalent and ionic molecules.{{r|Pauling1960|page=66}} Here Pauling's ''[[electronegativity]]'' concept is particularly useful; the electronegativity difference between a pair of atoms will be the surest predictor of the degree of ionicity of the bond.<ref>{{Cite web |last=Pauling |first=Linus |date=1930s |title=Notes and Calculations re: Electronegativity and the Electronegativity Scale |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/sci5.001.14.html |access-date=February 29, 2008 |publisher=Oregon State University Libraries Special Collections}}</ref>

The third of the topics that Pauling attacked under the overall heading of "the nature of the chemical bond" was the accounting of the structure of [[aromatic hydrocarbon]]s, particularly the prototype, [[benzene]].<ref>{{Cite web |last=Pauling |first=Linus |date=January 6, 1934 |title=Benzene |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/sci2.004.6.html |access-date=February 29, 2008 |publisher=Oregon State University Libraries Special Collections}}</ref> The best description of benzene had been made by the German chemist [[Friedrich August Kekulé von Stradonitz|Friedrich Kekulé]]. He had treated it as a rapid interconversion between two structures, each with alternating single and [[double bond]]s, but with the double bonds of one structure in the locations where the single bonds were in the other. Pauling showed that a proper description based on quantum mechanics was an intermediate structure which was a blend of each. The structure was a superposition of structures rather than a rapid interconversion between them. The name "[[resonance (chemistry)|resonance]]" was later applied to this phenomenon.<ref>{{Cite web |last=Pauling |first=Linus |date=July 29, 1946 |title=Resonance |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/notes/1946a.3.html |access-date=February 29, 2008 |publisher=Oregon State University Libraries Special Collections}}</ref> In a sense, this phenomenon resembles those of hybridization and also polar bonding, both described above, because all three phenomena involve combining more than one electronic structure to achieve an intermediate result.{{citation needed|date=August 2023}}