Usanovich acid-base definition

The various acid-base definitions are summarized in the Venn diagram (Fig. 2.1). From this it can be seen that the Usanovich definition subsumes the Lewis definition, which in turn subsumes all other definitions (i.e. Arrhenius, Bronsted-Lowry, Germann-Cady-Elsey, Lux-Flood). 

An example of the different points of view and different tastes in the matter of acid-base definitions was provided to one of the authors in graduate school while attending lectures on acid-base chemistry from two professors. One Felt that the solvent system was very useful, but that the Lewis concept went too far because it included coordination chemistry. The second used Lewis concepts in all of his work, but felt uncomfortable with the Usanovich definition because it included redox chemistry To the latter s credit, however, he realized that the separation was an artificial one, and he suggested the pyridine oxide example given above. 

The Usanovich theory is the most general of all acid-base theories. According to Usanovich (1939) any process leading to the formation of a salt is an acid-base reaction. The so-called positive-negative definition of Usanovich runs as follows. 

The Usanovich definition of acids and bases has not been widely used, probably because of (I) the relative inaccessibility of the original to non-Russian-reading chemists and (2) the awkwardness and circularity of Usanovich s original definition. The Usanovich definition includes all reactions of Lewis acids and bases and extends the latter concept by removing the restriction that the donation or acceptance of electrons be as shared pairs. The complete definition is as follows An add is any chemical species which reacts with bases, gives up cations, or accepts anions or electrons, and, conversely, a base is any chemical species which reacts with acids, gives up anions or electrons, or combines with cations. Although perhaps unnecessarily complicated, this definition simply includes all Lewis acid-base reactions plus redox reactions, which may consist of complete transfer of one or more electrons. Usanovich also stressed unsaturation involved in certain acid-base reactions ... 

Almost all of the reactions that the practicing inorganic chemist observes in the laboratory take place in solution. Although water is the best-known solvent, it is not the only one of importance to the chemist. The organic chemist often uses nonpolar solvents such as carbon tetrachloride and benzene to dissolve nonpolar compounds. These are also of interest to the inorganic chemist and, in addition, polar solvents such as liquid ammonia, sulfuric acid, glacial acetic acid, sulfur dioxide, and various nonmetal halides have been studied extensively. The study of solution chemistry is intimately connected with acid-base theory, and the separation of this material into a separate chapter is merely a matter of convenience. For example, nonaqueous solvents are often interpreted in terms of the solvent system concept, the formation of solvates involve acid-base interactions, and even redox reactions may be included within the Usanovich definition of acid-base reactions. 

Since Arrhenius, definitions have extended the scope of what we mean by acids and bases. These theories include the proton transfer definition of Bronsted-Lowry (Bronsted, 1923 Lowry, 1923a,b), the solvent system concept (Day Selbin, 1969), the Lux-Flood theory for oxide melts, the electron pair donor and acceptor definition of Lewis (1923, 1938) and the broad theory of Usanovich (1939). These theories are described in more detail below. 

The theory of general relativity is a universal theory and is believed to apply to all objects in the universe. The theory of relativity is useful and universal because it relates to phenomena that pervade the cosmos and it is intellectually compelling to have a theory that is as unified as possible. However, universal chemical theories, such as Usanovich s concepts of acids and bases may be less useful they can become so all-encompassing as to lack definition and hence fail to clarify the area of science under consideration. It Includes many reactions, such as redox reactions, which can perhaps best be considered as a separate type of reaction involving electron transfer. 

In the same spirit of generalization that characterized Lewis s approach, let s take an extraordinarily bold step and define a base as follows a base is an electron. In a similarly bold way, let s define an acid as the absence of an electron in an atom or molecule s electron cloud. I shall call that absence a hole, so the proposal is that an acid is a hole and a base is an electron. You can t get more fundamental than that These definitions are closely related to the more elaborate proposals made by the Russian chemist M. Usanovich in 1938 and which I warmed over elsewhere some time ago. ... 

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