Lewis Concept of Acids and Bases

Usanovich (1934) modified the Lewis concept of acid and base by removing the restriction of either donation or acceptance of the electron pair in a more generalized fashion. According to him ... 

The generalized Lewis concept of acids and bases also includes common proton-transfer reactions.1 Thus water acts as a base because one of the... 

Even more general is the Lewis concept of acids and bases a Lewis base has a lone pair available for formation of a coordinate bond, and a Lewis acid has a vacant acceptor orbital handy. This concept is applicable to reactions in the gas phase or in inert solvents (as discussed in the previous section) as well as to complex formation in solution and the acid/ base phenomena studied by Arrhenius, Br0nsted and Lowry. 

The Lewis concept of acids and bases (G. N. Lewis, 1923) interprets the combination of acids with bases in terms of the formation of a coordinate covalent bond. A Lewis acid can accept and share a lone pair of electPDns donated by a Lewis base. Because protons readily attach themselves to lone electron pairs, Lewis bases are also Biyinsted bases. Lewis acids, however, include a large number of substances in addition to proton donors for examjjle, metal ions, acidic oxides, or atoms. 

Skill 25.1 Compare the Arrhenius, Bronsted-Lowry, and Lewis concepts of acids and bases. 

The importance of the Lewis concept of acids and bases is that it can help explain reactions between molecules that are not strictly acids or bases, so it broadens the applicability to include nearly every reaction you can think of. 

SECTION 16.11 The Lewis concept of acids and bases emphasizes the shared electron pair rather than the proton. A Lewis acid is an electron-pair acceptor, and a Lewis base is an electron-pair donor. The Lewis concept is more general than the Bronsted Lowry concept because it can apply to cases in which the add is some substance other than H. ... 

The Lewis concept of acids and bases includes proton-transfer reactions all Bronsted-Lowry bases (proton acceptors) are also Lewis bases, and all Bronsted-Lowry acids (proton donors) are also Lewis acids. The Lewis model, however, is more general in that it is not restricted to proton-transfer reactions. 

In the first part of this chapter, we will discuss the Arrhenius, the Bronsted-Lowry, and the Lewis concepts of acids and bases.The Bronsted-Lowry and Lewis concepts apply to nonaqueous as well as aqueous solutions and also enlarge on the Arrhenius concept in other ways.This chapter expands on what you learned in Chapter 4 about acids and bases. 

The Lewis concept of acids and bases was discussed in Section 16.3. 

Scepticism about the quantitative usefulness of the Lewis concept of acids and bases is still frequently encountered in chemistry textbooks. We expect that this book will demonstrate that quantitative data exist for acid/base systems other than those involving proton donors and acceptors, and will encourage textbook authors to go beyond a mere qualitative presentation of the Lewis acid/base concepts. 

According to the Lewis concept of acids and bases the catalyst in this reaction behaves as an acid and the halide reacts as a base. Many other metallic halides catalyze this reaction in a similar manner. All of them can be shown to be acids by titrating with indicators in the proper solvent. 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

The Bronsted-Lowry theory focuses on the transfer of a proton from one species to another. However, the concepts of acids and bases have a much wider significance than the transfer of protons. Even more substances can be classified as acids or bases under the definitions developed by G. N. Lewis ... 

Each of the three definitions expands our concept of acids and bases. Arrhenius basic definition is adequate for understanding many of the properties of acids and bases. It is important to recognize, though, that acids and bases are not fixed labels that can be applied to a substance. Bronsted-Lowry and Lewis showed that acid-base characteristics are dependent on the reactions that take place between substances. A... 

In 1923, the same year in which Bronsted and Lowry defined acids and bases in terms of their proton donor/acceptor properties, the American chemist G. N. Lewis proposed an even more general concept of acids and bases. Lewis noticed... 

A still more general conception of acids and bases is possible (Lewis), in which bases are compounds or groups such as O2-, OH, H20, NH3, NH2- and F, with a free electron pair which can take part in a reaction (electron donors or nucleophilic compounds), for example, with a proton in bases regarded according to Bronsted s concept. 

The concept of acids and bases has been important since ancient times. It has been used to correlate large amounts of data and to predict trends. Jensen has described a useful approach in the preface to his book on the Lewis acid-base concept ... 

We shall find the Lewis concept of acidity and basicity fundamental to our understanding of organic chemistry. To make it clear that we are talking about this kind of acid or base, we shall often use the expression Lewis acid (or base) or sometimes acid (or base) in the Lewis sense. 

E. Concepts of Acids and Bases — Brpnsted-Lowry approaches, Lewis theory, solvent system approaches... 

These definitions describe the Lowry-Bronsted concept of acidity and basicity. The Lewis concept of acids and b s is more general, and may be useful for reactions in which protons are not involved. A Lewis acid is any substance that can accept electrons, and a Lewis base is any substance that can donate electrons. Small, high-charge metal ions such as Al + and Fe " are strong Lewis acids because they tend to complex with functional groups on molecules (Lewis bases) by accepting electrons from them ... 

In the simple theory based on Lewis concepts exemplified above, the key aspects are an empty orbital on one atom and a filled orbital (with a pair of electrons present, the lone pair) on the other. Many of the ligand species providing the lone pair are considered bases in the classical Brpnsted-Lowry concept of acids and bases (which has as its focus the transfer... 

A definite connection exists between the concepts of acids and bases and the idea of nucleophiles and their complementary substances, electrophiles. A Lewis acid is an electrophile, and a Lewis base is a nucleophile. Catalysis by enzymes, including their remarkable specificity, is based on these well-known chemical principles operating in a complex environment. 

A more general concept of acids and bases was introduced by Gilbert N. Lewis. The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction. According to this theory, a base is any substance that has an unshared pair of electrons (electron pair donor), and an acid is any substance that will attach itself to or accept a pair of electrons. 

Gilbert N. Lewis (1875-1946) introduced the theory of the electron pair that extended our understanding of covalent bonding and of the concept of acids and bases. It is in his honor that we often refer to an "electron dot" structure as a Lewis structure. 

The acid-base reaction theoi7 of adhesion has been proposed to explain a number of observed adhesive phenomena [7,8]. This theory is based on acid-base reactions at the surface. Initially, only the Bronsted concept of acid and bases were considered, but the more general current theory incorporates the Lewis acid (electron donor-acceptor) concept. The determination of the acidity or basicity of polymers is not as straightforward as might be accepted. Several approaches that have been used for this determination are described in [8]. 

Although the Bronsted concept of acids and bases focuses on the transfer of a proton, electron pairs are more fundamental to the process. Covalent bonds are formed or broken when a proton is transferred from one atom to another. To account for this possibihty, Gilbert N. Lewis proposed a definition of acids that focuses on electron pairs. A Lewis acid is an electron pair acceptor a Lewis base is an electron pair donor. This is a general definition of an acid and a base. For example, hydrochloric acid, a Bronsted acid, is also a Lewis acid because it contains a proton that accepts an electron pair. Ammonia is a Lewis base because it can act as an electron pair donor. However, many other species can serve as electron pair acceptors or donors. Consider the following general reaction between a Lewis acid and a Lewis base. 

Extending the Concept of Acids and Bases The Lewis Model... 

EXTENDING THE CONCEPT OF ACIDS AND BASES THE LEWIS MODEL... 

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