Unitary Theory

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Unitary Theory


a system of views in 19th-century chemistry based on the concept that the molecule is a unified whole made up of atoms of the chemical elements. The unitary theory took shape in the 1830’s and 1840’s in the works of J. Dumas, A. Laurent, and, in particular, C. Gerhardt, who set forth the theory in his Introduction to the Study of Chemistry According to the Unitary System (1848; Russian translation, 1859). The theory challenged the generally accepted dualistic theory of J. Berzelius, which regarded chemical compounds as combinations of two distinct constituents bearing opposite electrical charges. The inability of this theory to account for reactions involving the substitution of chlorine for hydrogen in organic compounds was one of the principle reasons for the theory’s abandonment.

The historical significance of the unitary theory lies in its clear distinction between the concepts of atom, molecule, and equivalent and its introduction of Avogadro’s law and “two-volume” formulas, that is, formulas using the H2 molecule as the unit of comparison. In addition, the theory made possible correct values for many elements and corrections of formulas for the elements’ compounds. The basic principles of the unitary theory were accepted in 1860 at an international congress of chemists held in Karlsruhe.


Faershtein, M. G. Istoriia ucheniia o molekule v khimii (do 1860 g.). Moscow, 1961. Pages 243–66, 283–352.


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