History of Elements Classification Schemes

1817
According to Van Spronsen, the first observation of a relationship betwwen the atomic weights (equivalent weight) of elements was made by Johann Wolfgang Dobereiner, of the University of Jena. He found three-member groups of analgous element (triads), for which the equivalent weight of the middle element was the arithmetic mean of the weights of the other members of the triad. He concluded that this relationship must reflect some general principle--which he could not identify.

1827
Leopold Gmelin, University of Heidelberg, expands Dobereiner's triads--again in 1843 and 1852. He was the only other well-known chemist to study this relationship before 1850.

1845
Oliver Gibbs, Rumford professor at Harvard, classifies elements on the equivalents, isomorphism (crystalline form), combining relationships, and types of compounds.

1850
Max von Pettenkofer, Universiyt of Munich, revives Prout's hypothesis of primary matter. Prout believed that all elements were whole number multiples of hyddrogen. Hence, elements would not be indivisible, but have a smaller unit of structure. Pettenkofer expanded Dobereiner's triads. He noted that similar elements formed and arithmetic series and the difference between elements in each series was 8 or a multiple of 8.

1851
Jean Baptisite Dumas, Sorbonne, compared families of elemnts with families of organic comounds. He revived Prout's hypothesis and further refined his system to involve complicated arithmetic progresssions.

1852
Peter Kremers added to Dobereiner's triads. He surmised that four was the atomic weight of a basic element. Multiplication by an odd number yielded a metalloid, even-numbered weights related to non-metals.

1853
John Gladstone's analogies fell into three categories--elements with identical weights, those with weights that are multiples of each other, and those in triads.

1854-55
Josiah Cooke, Harvard, based his system on more than atomic weight--he used isomorphism, electronegativity, physical properties, chemical reactions. His system, like the others, failed to establish a continuous system including all the elemtns because ot the underlying idea that elements could be built up from some simpler form.

1857
Ernst Lessen, Wiesbaden, believed that all elements except niobium could fit into triads. The attempt to classify all elements was encouraging, the results difficult to justify.

William Odling constructs a grouping based on analgous properties. He finds a relationship between four of his thirteen groups.

1860
Matthew Lea, Philadelphia, finds new relationships between atomic weights, even considering negative atomic weights. He attempts to show that the sums and differences of atomic weights gave the numbers 44 or 45. He attempts to predict atomic weights for elements not yet discovered.

1862
Van Spronsen considers this to be the birth year of the periodic system--he lists six discoverers, including Mendeleev. In 1862, Alexander de Chancourtois presented a system showing periodicity as a function of atomic weight in a three-dimensional representation. His Vis Tellurique, so named because tellurium was at the center, was a spiral encompassing a cylinder (also known as the telluric screw).

1865
John Newlands constructs a system of classification based on octaves. His use of atomic weights did not reflect the precision available. His work was ridiculed as having no more basis than if he had chosen an alphabetical listing as a classification.

Odling revises his system to contain 57 elements (Newlands had only used 24), and arranges them in order of increasing atomic weight. Definite groups and subgroups aand gaps in the series (which may have been predictions of undiscovered elements) were the main features of this system. However, he could not explain the relationships his table showed, assuming it would have to include valence.

1867
Gustavus Hinrichs, Iowa State, stated that the properties of of chemical elements are functions of thier weights. He proposed a spiral chart and also had vacant spaces.

1868
As early as 1864, Julius Lothar Meyer, University of Tubingen, presented a system based on valence, but he could not include all known elements. Eventually he did include them all, but he was not published until 1872, after Mendeleev. He is acknowledged as an independent discovere of the periodic law with Mendeleev. He never doubted the indivisibility of the atom, and showed that properties were functions of atomic weight, such as atomic volume.

1869
Dmitri Mendeleev uses the advantage of recent developments--precise atomic weights (Cannizzaro) and the large sample of known elements (67) to create a system of classifciation based on atomic weight. He was aware of these predecessors: Kremers, Gladstone, Lenssen, Dumas, and Pettenkofer. He knew nothing of the more important work of Newlands, Odling, Hinrichs, and Meyer at the time he formulated his table. Not only did he use relationships between elements with similar properties, but he also discovered relationships between elements with dissimilar properties. Whether or not Mendeleev used cards to sort his elements (his affinity for the card game patience is documented), he wrote a table which recognized bidirectional relationships, both horizontally and vertically. His predictions of the physical and chemical properties of undiscovered elements provided the experimental verification that made his theory accepted in just a few years. The discovery of gallium, germainiu, and scandium brought acceptance where a purely theoretical base for the table could not.

Bibliography

Primary Sources Secondary Sources