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He maintained that all elements were strictly individual, indestructible, and irreducible, yet he acknowledged the seeming challenge posed by chemical reactions. Unlike some of his contemporaries Mendeleev rejected the suggestion that the periodic system implied the existence of any form of primary matter of which all the elements were composed. But what really set Mendeleev’s contribution apart? From Simple Substances to Abstract Elementsīy organizing the elements as he did Mendeleev took a stand on the centuries-old question of the philosophical status of the elements. In the popular imagination the periodic system invariably and justifiably connects to his name, to the same extent that the theory of evolution connects to Darwin’s name and the theory of relativity to Einstein’s. Mendeleev’s version of the periodic table left the biggest impact on the scientific community, both at the time it was produced and thereafter. Notwithstanding these earlier scientists’ contributions to the idea of periodicity, Mendeleev remains the undisputed champion of the periodic system in the literal sense of its defense, propagation, and elaboration. THE DISAPPEARING SPOON PODCAST Tales of Love and Madness from the Periodic Table Hinrichs was intrigued that atomic spectral frequencies, like planetary distances, show whole number ratios, and he concluded that atomic spectra must therefore be an indication of atomic size. A more eccentric spiral periodic system was created by the Danish-born polymath Gustavus Hinrichs in 1864. In 18 two British chemists, John Newlands and William Olding (coincidentally, both born in the same London borough of Southwark), independently published periodic tables that used atomic weight to arrange the elements into groups with analogous properties. Periodic relationships could be seen by moving vertically down the screw. The French geologist Alexandre-Émile Béguyer de Chancourtois achieved the first true periodic system in 1862 by arranging the elements by atomic weight in a spiral line wrapped around a metal cylinder. His triads-which would eventually appear on the periodic table in vertical columns-represented the first step in fitting the elements into a system that would account for their chemical properties and reveal their physical relationships.īy the 1860s a number of scientists had moved beyond the triad concept to produce some very respectable periodic systems.
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Although Döbereiner worked with the rather crude approximations of atomic weight available at the time, he successfully identified four such groups: strontium, calcium, and barium bromine, iodine, and chlorine sodium, lithium, and potassium and selenium, sulfur, and tellurium. The elements in these groupings displayed an important numerical relationship to each other: the equivalent weight (an early substitute for atomic weight) of the middle element had the approximate mean of the values of the two flanking elements. In 1817 the German chemist Johann Wolfgang Döbereiner noticed the existence of groupings of elements in threes, subsequently called triads. The observation that certain types of elements prefer to combine with certain other types prompted early chemists to classify the elements in tables of chemical affinities. Mendeleev was hardly the first to arrive at a periodic system. Courtesy Edgar Fahs Smith Collection, Kislak Center for Special Collections, Rare Books and Manuscripts, University of Pennsylvania. Dmitri Ivanovich Mendeleev in his study at home in 1904.