Electrochemical dualism

In addition to atomism, the principal chemical theories of the nineteenth century included electrochemical dualism, the radical theory, the type theory, and the structure theory, the latter strongly identified with what chemists called the "law of linking" of carbon atoms. The valence theory evolved as a way of tying together the notions of chemical equivalence and chemical structure, and it carried along the old problem that some chemical elements (e.g., nitrogen) exhibit different combining values with another element in different circumstances. 

The roots of both chemical thermodynamics and contemporary kinetics both lie in the eighteenth-century ideas of chemical "affinity" and "force," transformed into nineteenth-century conceptions of "work" and "energy." Berthollet identified the fundamental difficulty for eighteenth-century theories of affinity in a critique that applied equally to early-nineteenth-century theories of electrochemical dualism. In "Recherches sur les lois de l affinite" (1799), Berthollet wrote,... 

The discussion and classification of reagents is masterful in identifying Ingold s new nomenclature and principles with more widely known oxidation-reduction and acid-base theory. The 1953 lectures at Cornell University, published as Structure and Mechanism in Organic Chemistry, follow this same strategy, showing how old classification schemes overlap with each other and how apparent inconsistencies disappear as old schemes are incorporated into the new one. Nineteenth-century Berzelian electrochemical dualism, revived by Lapworth and Robinson in the cationic/anionic schema, disappears into the electrophilic/nucleophilic language. 

The idea of electronegativity was bom as soon as chemists suspected that the formation of chemical compounds involved electrical forces (before the discovery of the electron) metals and nonmetals were seen to possess opposite appetites for the electrical fluid(s) of eighteenth century physics. This electrochemical dualism is most strongly associated with Berzelius [136], and is clearly related to our qualitative notion of electronegativity as the tendency of a species to attract electrons. Parr and Yang have given a sketch of attempts to quantify the idea [137]. Electronegativity is a central notion in chemistry. 

Berzelius s methodology had been derived from inorganic chemistry, and especially the chemistry of salts, and it was based on atomism and electrochemical dualism. It was remarkably successful in giving inorganic chemistry coherent shape, with formulas, affinities, and classification firmly in place. But inorganic chemistry, the chemistry that included salts and minerals, was much more easily handled than organic chemistry, the chemistry of those compound substances that exist in nature as constituents of animals or plants, or are derived from such constituents. The next chapter will explore problems and triumphs in the establishment of organic chemistry. 

In the decades when Avogadro s hypothesis was mostly gathering dust, Berzelius s electrochemical dualism was the most successful chemical theory in Europe. It explained the properties of elements and compounds, especially the chemical reactions they underwent, and Berzelius, looking at those properties and reactions, derived his own formulas for compounds. But, as Berzelius s critics from organic chemistry pointed out in the 1840s, different reactions suggest different formulas for one and the same substance, and that is not very satisfactory. What is more, the kinds of problem arising from Daltons simplicity... 

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