Periodic Table of the Chemical Elements: From Mendeleev to Moseley

Part of the Science & Technology Education Library book series (CTISE, volume 36)

From a history and philosophy of science perspective the periodic table of elements has generally been considered as a classification, system, table, law, and very rarely as a theory. According to a historian of chemistry: “From the 1870s Mendeleev's Periodic Table came to adorn every chemical lecture room; it compressed a great deal of knowledge into a small compass, meaning that the student no longer had to be burdened with a great load of unrelated brute facts” (Knight, 1998, p. xii). Another historian goes further by recognizing that the periodic table “has contributed much more than mere classification. It has been a conceptual tool which has predicted new elements, predicted unrecognized relationships, served as a corrective device, and fulfilled a unique role as a memory and organization device” (Ihde, 1969, p. ix). Van Spronsen (1969) presents a detailed account of various attempts to classify elements between 1817 and 1860. However, a major problem with such classifications was that the atomic weights were not yet determined correctly and nor were they understood well, because “Dalton's atomic theory was too recent to have been conclusively demonstrated” (van Spronsen, 1969, p. 95).

Most historians consider the International Congress held in Karlsruhe (3–5 September 1860) as crucial in the development of chemistry and the periodic table in particular. A circular (dated July 10, 1860) sent by the organizers of the Congress to most outstanding chemists of Europe outlined its objective as the need to reach a consensus on “[m]ore precise definitions of the concepts of atom, molecule, equivalent, atomicity, alkalinity, etc.; discussion on the true equivalents of bodies and their formulas; initiation of a plan for a rational nomenclature” (reproduced in De Milt, 1951, p. 421). Mendeleev attended the Congress and was greatly impressed by Cannizaro's contribution and in a letter dated September 7, 1860, he summarized an important achievement of the Congress:

It is decided to take a different understanding of molecules and atoms, considering as a molecule the amount of a substance entering a reaction and determining physical properties, and considering as an atom the smallest amount of a substance included in a molecule. Further, it reached an understanding about equivalents, considered as empirical, not depending on the understanding about atoms and molecules. (Reproduced in De Milt, 1951, p. 422)


Scientific Theory Periodic Table Atomic Weight Original Emphasis Inductive Generalization 
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© Springer Science + Business Media B.V. 2009

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