Acid-base chemistry Lewis theory

Lewis made additional valuable contributions to the theory of colored substances, radiation, relativity, the separation of isotopes, heavy water, photochemistry, phosphorescence, and fluorescence. As a major in the U.S. Army Chemical Warfare Service during World War I, he worked on defense systems against poison gases. From 1922 to 1935 he was nominated numerous times for the Nobel Prize in chemistry. Lewis s death, while measuring the dielectric constant of hydrogen cyanide on March 23, 1946, precluded his receiving the prize, which is not awarded posthumously, see also Acid-Base Chemistry Lewis Structures. 

Up to this point, we have dealt with the subject of acid-base chemistry in terms of proton transfer. If we seek to learn what it is that makes NH3 a base that can accept a proton, we find that it is because there is an unshared pair of electrons on the nitrogen atom where the proton can attach. Conversely, it is the fact that the hydrogen ion seeks a center of negative charge that makes it leave an acid such as HC1 and attach to the ammonia molecule. In other words, it is the presence of an unshared pair of electrons on the base that results in proton transfer. Sometimes known as the electronic theory of acids and bases, this shows that the essential characteristics of acids and bases do not always depend on the transfer of a proton. This approach to acid-base chemistry was first developed by G. N. Lewis in the 1920s. 

Luder, W. F., and Zuffanti, S. (1946). The Electronic Theory of Acids and Bases. Wiley, New York. A small book that is a classic in Lewis acid-base chemistry. Also available as a reprint volume from Dover. 

Refs. [i] Finston H, Rychtman AC (1982) A new view of current acid-base theories. Wiley, New York [ii] Hand CW, BlewittHL (1986) Acid-base chemistry. Macmillan, New York [iii] )ensen WB (1980) The Lewis acid-base concepts. Wiley, New York [iv] Tanabe K (1989) New solid acids and bases. Elsevier, Amsterdam... 

In this chapter, we explain how the scientific understanding of acids and bases has changed through time. We start by explaining how to measure their strengths using the pH scale. We also explain the multiple theories of acid-base chemistry, from Lavoisier s first attempt to classify these materials, to the modern understanding of Lewis acids and bases. 

The Lewis theory, by virtue of its broader definition of acids, allows acid—base theory to include all of the Bronsted-Lowry reactions and, as we shall see, a great many others. Most of the reactions we shall study in organic chemistry involve Lewis acid—base interactions, and a sound understanding of Lewis acid—base chemistry will help greatly. 

A very useful book discussing many aspects of acid-base chemistry in term of Ihe Lewis dehnilion is Jensen, W. B. The Lewis Acid-Base Ciwcepts An Overview Wiley New York, 1980. Usanovich. M. Zhur. Obschei Khim. 1939.9.182. Finsion, H. L. Rychtiiian, A. C- A New View of Current Acid-Base Theories Wiley New York. 1982. 

Two acid-base theories are used in organic chemistry today the Br0nsted theory and the Lewis theory. These theories are quite compatible and are used for different purposes. ... 

As we have seen, the Lewis theory of acid-base interactions based on electron pair donation and acceptance applies to many types of species. As a result, the electronic theory of acids and bases pervades the whole of chemistry. Because the formation of metal complexes represents one type of Lewis acid-base interaction, it was in that area that evidence of the principle that species of similar electronic character interact best was first noted. As early as the 1950s, Ahrland, Chatt, and Davies had classified metals as belonging to class A if they formed more stable complexes with the first element in the periodic group or to class B if they formed more stable complexes with the heavier elements in that group. This means that metals are classified as A or B based on the electronic character of the donor atom they prefer to bond to. The donor strength of the ligands is determined by the stability of the complexes they form with metals. This behavior is summarized in the following table. 

Considerable progress in the development of theoretical and synthetic coordination and organometallic chemistry was made with the use of electron ideas. Lewis elaborated in 1923 the classic electron theory of acids and bases [30], and used it to explain the coordination ideas of Werner [31] (in Ref. 32, this achievement is ascribed to Sidgwick). A Lewis acid (A) is a acceptor of the electron pair and a Lewis base (B) is its donor [33], In other words, A is a species that can form a new covalent bond by accepting a pair of electrons and B is a species that can form a new covalent bond by donating a pair of electrons. The fundamental Lewis acid-base theory is described by a direct equlibrium [Scheme (1.1)], leading to the formation of the adduct (acid-base complex) ... 

Electron donation-acceptance reactions, which are considered to be Lewis acid-base interactions, also include the formation of coordination compounds, complex formation through hydrogen bonding, charge transfer complex formation, and so on. It should be apparent that the Lewis theory of acids and bases encompasses a great deal of both inorganic and organic chemistry. 

The chemistry of coordination compounds is a broad area of inorganic chemistry that has as its central theme the formation of coordinate bonds. A coordinate bond is one in which both of the electrons used to form the bond come from one of the atoms, rather than each atom contributing an electron to the bonding pair, particularly between metal atoms or ions and electron pair donors. Electron pair donation and acceptance result in the formation of a coordinate bond according to the Lewis acid-base theory (see Chapter 5). However, compounds such as H3N BC13 will not be considered as coordination compounds, even though a coordinate bond is present. The term molecular compound or adduct is appropriately used to describe these complexes that are formed by interaction of molecular Lewis acids and bases. The generally accepted use of the term coordination compound or coordination complex refers to the assembly that results when a metal ion or atom accepts pairs of electrons from a certain number of molecules or ions. Such assemblies commonly involve a transition metal, but there is no reason to restrict the term in that way because nontransition metals (Al3+, Be2+, etc.) also form coordination compounds. 

Lewis s research was wide-ranging and outstanding. He published important papers on chemical bonds, acid-base theory, and thermodynamics. He also developed firm ideas about howto build a chemistry department. His philosophy of education was something less than egalitarian. Writing in the Journal of Chemical Education, the distinguished chemist Gerald Branch spelled out Lewis s ideas "[F]or a chemist to be useful to... 

The designation of electron-pair donors and acceptors as Lewis bases and Lewis acids is firmly and fittingly ingrained in the language of chemistry. G. N. Lewis laid the foundation for this important theory approximately 80 years ago and Lewis acids have since become increasingly important because of their central role in synthetic organic chemistry. This is clearly illustrated by an ever-increasing number of publications and books. 

R, Robinson, Outline of an Electrochemical (Electronic) Theory of the Course of Organic Reactions, Institute of Chemistry, London, 1932, pp. 12-15 W. B. Jensen, The Lewis Acid-Base Concepts, Wiley-Interscience, New York, 1980, pp. 58-59. 

However, the protolytic theory cannot explain the distinctly acid or base properties of numerous substances which are not able to either split-off or accept a proton. This stimulated G. N. Lewis (1923) to a different generalization of the notion of acids and bases. According to the Lewis theory a base is a substance which is the donor of a free electron pair, whereas, acid can bond a free electron pair of another particle and thus, it is its acceptor. Neutralization of an acid by base is conditioned by the formation of coordination (donor-acceptor) bond. The Lewis theory is of importance particularly in the chemistry of coordination compounds where all central... 

A much more general classification was made possible by the Lewis acid-base theory, which has also proved of great value in coordination chemistry. In... 

The acid-base concept, either in the limited interpretation of the Bronsted-Lowry theory or in the more general sense of the Lewis theory, is one of the most useful classification schemes in chemistry and a tool for systematizing the relationship between structure and reactivity. In this section we examine how this general concept can be applied to solid surfaces [29], From the most general (Lewis) point of view, a surface is classified as acidic (electron acceptor) or basic (electron donor) according to the direction of net electron transfer that results in the formation of new chemical bonds with an adsorbed molecule. 

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