Periodic Table of the Chemical Elements: From Mendeleev to Moseley
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).
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)
KeywordsSulfide Cobalt Cadmium CdCl Iodine
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