Lewis theory of valence

W. M. Latimer and W. H. Rodebush, J. Am. Chem. Soc. 42 (1920), 1419. This paper is often cited as the discovery of H-bonding (but see Jeffrey, note 5). Its title, Polarity and ionization from the standpoint of the Lewis theory of valence, reflects the strong influence of G. N. Lewis on all aspects of the early development of H-bond theory. 

Most chemists still tend to think about the structure and reactivity of atomic and molecular species in qualitative terms that are related to electron pairs and to unpaired electrons. Concepts utilizing these terms such as, for example, the Lewis theory of valence, have had and still have a considerable impact on many areas of chemistry. They are particularly useful when it is necessary to highlight the qualitative similarities between the structure and reactivity of molecules containing identical functional groups, or within a homologous series. Many organic chemistry textbooks continue to use full and half-arrows to indicate the supposed movement of electron pairs or single electrons in the description of reaction mechanisms. Such concepts are closely related to classical valence-bond (VB) theory which, however, is unable to compete with advanced molecular orbital (MO) approaches in the accurate calculation of the quantitative features of the potential surface associated with a chemical reaction. 

Latimer WM, Rodebush WH (1920) Polarity and ionization from the standpoint of the Lewis theory of valence. J Am Chem Soc 42 1419-1433... 

Obviously the Lewis theory of valence is unable to provide any satisfactory explanation of the stability and the physical origin of the chemical bond. Moreover, Lewis did not really understand the mechanism of the pairing of electrons. However, as shown below, quantum mechanics confirms very nicely most of the intuitive ideas of Lewis and consequently the essential features of its chemical formulas. 

The first quantitative theory of chemical bonding was developed for the hydrogen molecule by Heitler and London in 1927, and was based on the Lewis theory of valence in which two atoms shared electrons in such a way that each achieved a noble gas structure. The theory was later extended to other, more complex molecules, and became known as valence bond theory. In this approach, the overlap of atomic orbitals on neighbouring atoms is considered to lead to the formation of localized bonds, each of which can accommodate two electrons with paired spins. The theory has been responsible for introducing such important concepts as hybridization and resonance into the theory of the chemical bond, but applications of the theory have been limited by difficulties in generating computer programs that can deal efficiently with anything other than the simplest of molecules. 

It is also noteworthy that Alfred Stock, who is universally acclaimed as the discoverer of the boron hydrides (1912). " was also the first to propose the use of the term "ligand (in a lecture in Berlin on 27 November 1916). Both events essentially predate the formulation by G. N. Lewis of the electronic theory of valency (1916). It is therefore felicitous that, albeit some 20 years after Stock s death in 1946, two such apparently disparate aspects of his work should be connected in the emerging concept of boranes as ligands . 

The apparent inertness of the noble gases gave them a key position in the electronic theories of valency as developed by G. N. Lewis (1916) and W. Kossel (1916) and the attainment of a stable octet was regarded as a prime criterion for bond formation between atoms (p. 21). Their monatomic, non-polar nature makes them the most nearly perfect gases known, and has led to continuous interest in their physical properties. 

Why do we want to model molecules and chemical reactions Chemists are interested in the distribution of electrons around the nuclei, and how these electrons rearrange in a chemical reaction this is what chemistry is all about. Thomson tried to develop an electronic theory of valence in 1897. He was quickly followed by Lewis, Langmuir and Kossel, but their models all suffered from the same defect in that they tried to treat the electrons as classical point electric charges at rest. 

It was G. N. Lewis who extended the definitions of acids and bases still further, the underlying concept being derived from the electronic theory of valence. It provided a much broader definition of acids and bases than that provided by the Lowry-Bronsted concept, as it furnished explanations not in terms of ionic reactions but in terms of bond formation. According to this theory, an acid is any species that is capable of accepting a pair of electrons to establish a coordinate bond, whilst a base is any species capable of donating a pair of electrons to form such a coordinate bond. A Lewis acid is an electron pair acceptor, while a Lewis base is an electron pair donor. These definitions of acids and bases fit the Lowry-Bronsted and Arrhenius theories, and cover many other substances which could not be classified as acids or bases in terms of proton transfer. 

G. N. Lewis, J. Am. Chem. Soc. 38 (1916), 762 G. N. Lewis, Valence and the Structure of Atoms and Molecules (New York, The Chemical Catalog Co., 1923). As observed by Pauling (in note 51, p. 5), this remarkable work forms the basis of the modern electronic theory of valence. ... 

Noyes himself had been a student of Ostwald. Lewis had spent the academic year 190001 at the institutes of Ostwald and Nernst. Colloquium topics at MIT in the period from roughly 1905 to 1910 included both chemical and physical topics Alfred Werner s coordination theory of valence, tautomerism, and the absolute size of atoms. 

Irving Langmuir, "The Structure of Molecules," BAAS Rep. Edinburgh. 1921 (1922) 468469. G. N. Lewis. "The Atom and the Molecule," 762785 Irving Langmuir, "The Structure of Atoms and the Octet Theory of Valence." Proc. NAS 5 (1919) 252259, and JACS "The Arrangement of Electrons in Atoms and Molecules,"... 

For general accounts see W. H. Brock, The Fontana History of Chemistry (London Fontana Press, 1992), 508-569, and references therein M.J. Nye, From Chemical Philosophy to Theoretical Chemistry. Dynamics of Matter and Dynamics of Disciplines (Berkeley University of California Press, 1993), 139-223 R. E. Kohler, The Lewis-Lang-muir theory of valence and the chemical... 

G. N. Lewis s first sketch of the octet theory of valence electrons. 

This method, Huckel s 1st method or the H(eitler) L(ondon) S(later) P(auling) method or the Valence bond (V.B.) method, fits directly on to the electron pair theory of valency of Lewis, Langmuir, Ingold and others. Each configuration can be described by bond lines, each of which signifies an electron pair between the various atoms. It can be proved that these lines never intersect in the canonical structures configurations, in which this is the case, can be regarded as combinations of the former. 

The unique character of hydrogen, and its relation to the other univalent elements as interpreted by the aid of Lewis s dectronic theory of valency, have been the subject of an interesting communication by Lowry.6... 

Lewis published these ideas in his 1923 book Valence and the Structure of Atoms and Molecules, and they were widely taken up and developed in the U.S.A. and Europe, for example, by N. V. Sidgwick at Oxford, whose Electronic Theory of Valency appeared in 1927. The Nobel Prize in Chemistry was left unfilled in 1919, 1924 and 1933 for lack of candidates of suitable stature, and Lewis would have been an appropriate candidate for any of these years. In fact, he was nominated for a Nobel Prize by the inorganic chemist and historian of chemistry, J. R. Partington (1886-1965) at the University of London. For the first half-century after the award of the first Nobel Prize in Chemistry to van t Hoff in 1901, the chemistry prize went to those who had discovered or characterised new chemical elements, new physico-chemical principles, new chemical reactions, or had elucidated the structure and accomplished the synthesis of natural products. The first award for research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances went in 1954 to Linus Pauling at Caltech. 

The Lewis (1916) theory of valence may be considered as the first serious attempt to account for both polar and nonpolar bonds and, consequently, to describe the electronic structure of any chemical species. This theory is based on the famous octet rule, which may be stated as every atom tends to acquire eight electrons in its outer shell, those being normally arranged in pairs at the four corners of a tetrahedron. Moreover, assuming the interpenetrability of atomic shells, Lewis shows that, in a nonpolar compound, each atom can satisfy the octet rule by sharing one or more electron pairs with the neighboring atom(s). This pairing of elec-... 

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