Bronsted’s concept

Cations at the surface possess Lewis acidity, i.e. they behave as electron acceptors. The oxygen ions behave as proton acceptors and are thus Bronsted bases. This has consequences for adsorption, as we will see. According to Bronsted s concept of basicity, species capable of accepting a proton are called a base, while a Bronsted acid is a proton donor. In Lewis concept, every species that can accept an electron is an acid, while electron donors, such as molecules possessing electron lone pairs, are bases. Hence a Lewis base is in practice equivalent to a Bronsted base. However, the concepts of acidity are markedly different. 

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. 

Hydrogen was recognized as the essential element in acid by Davy after his work on hydrohalic acid. Theories of acid and base have played an important role ever since. The electrolytic dissociation theory of Arrhenius and Ostwald, the introduction of the pH scale for hydrogen-ion concentrations by Sorensen, the theory of acid-base titration and the use of indicators, and Bronsted s concept of acid and conjugate base as proton donors and acceptors are other landmarks in the recognition of hydrogen as an acid. 

Here is a simple didactic example that I owe to Briiggemann (see e.g. Bell 1974). Suppose we want to find out what Bronsted s concept of acid might be, along examples. For this purpose we consider the following set of attributes ... 

Unlike Arrhenius, Lowiy-Bronsted and Lewis acids and bases, the Usanovich s concept in a much broader sense includes all the oxidizing agents as acids and the reducing agents as bases, e.g.,... 

I. Definition of Basicity A. General Comments on the Acid-base Concept The current general definition of the acid-base concept is based on the definitions by Bronsted and Lewis. According to Bronsted s theory (1923) an acid-base interaction can be described by the general relation (1) ... 

The Bronsted-Lowry concept looks at the equilibrium reaction and ties the acid on the left to a base on the right, called a conjugate acid-base pair or, more simply, a conjugate pair. Suppose we were to consider an acid reacting with a compound in equilibrium with the acid s anion and the products, as... 

Fig. 5. The concept lattice connected with Bronsted s definition...

Since we have to read Hasse diagrams from bottom to top, the concept lattice visualizes that HC1 and H2S04 are the only acids in Bronsted s sense, that they dissociate water in contrast to all the other molecules of the lattice, and that they contain hydrogen. 

Earlier in this chapter we considered Arrhenius s concept of acids and bases An acid is a substance that produces ions when dissolved in water, and a base is a substance that produces OH ions. Although these ideas are fundamentally correct, it is convenient to have a more general definition of a base, which includes substances that do not contain OEI ions. Such a definition was provided by Johannes N. Bronsted (1879-1947) and Thomas M. Lowry (1874-1936), who defined acids and bases as follows ... 

The advantage of Tamele s concept is that it more clearly shows how the acid site associated with the aluminum ion is interconvertible to Lewis acid and Bronsted acid by removing or adding a water molecule ... 

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 ... 

The formation of the former direction is closely associated with the works of J.N. Bronsted, E.A. Guggenheim and G. Scatchard (1976), who in the 1920 s and 1930 s came up with the specific ion interaction theory. Based on this theory the Bronsted-Guggenheim-Scatchard model or specific ion interaction theory - SIT model was formed. It merges interaction of electrostatic and Coulomb forces of components in the solution in consideration of their individual properties. Laid in its basis were concepts of... 

The addition of acid to the solution leads to shifts in the equilibria that favor the aqua-form of the complex. Thus, Pfeiffer, in 1906, established the reversible transformation of aqua-complexes into hydroxo-complexes. Werner later used this observation in the development of add-base concepts in coordination chemistry.32 Werner s work in this field is now largely of historical interest but two points, emphasized by Werner, remain espedally noteworthy, i.e. the importance of solvent in add-base equilibria and that bases may be considered as proton acceptors. These statements were incorporated into the acid-base theory developed by Bronsted and Lowry in 1923. 

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