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Before the development of the modern periodic table, there were other attempts to arrange the elements in a useful way. For example, Döbereiner arranged groups of three elements with similar properties into ‘triads'. Newlands and Mendeleev arranged the elements in order of increasing relative atomic mass.
Some attempts at arranging the elements were more successful than others. Newlands did not leave any space for undiscovered elements but Mendeleev did. Using his table, Mendeleev was able to successfully predict the properties of three elements that were not yet discovered.
Johann Wolfgang Döbereiner (13 December 1780 – 24 March 1849) was a German chemist who is best known for work that foreshadowed the periodic law for the chemical elements and inventing the first lighter, which was known as the Döbereiner's lamp. He became a professor of chemistry and pharmacy at the University of Jena.
Döbereiner reported trends in certain properties of selected groups of elements. For example, the average atomic mass of lithium and potassium was close to the atomic mass of sodium. A similar pattern was found with calcium, strontium, and barium, with sulphur, selenium, and tellurium, and also with chlorine, bromine, and iodine. Moreover, the densities for some of these triads followed a similar pattern. These sets of elements became known as "Döbereiner's triads".
Dimitri Ivanovich Mendeleev (8 Feb 1834-2 Feb 1907)
He was a Russian chemist. He as ereator of the first version of the periodic table of elements... Using the table he could predict even the properties of elements which were not known in those days.
Mendeleeve also investigated the composition of oil fields and helped to establish first oil refinery in Russia. The crater Mendeleev on the moon and the element number 101 mendelevium were named after him to show respect to his work.
Dimitri Mendeleev
Julius Lother Meyer (19 Aug 1830 11 Apr 1895)
He was German chemist. He was competitor of Mendeleev to draw up the first periodic table. He showed that if the atomic weights are plotted against atomic volumes, the curve obtained shows series of maxima and minimum. The most electropositive elements are at the peak of the curve in the order of their atomic weights.
Julius Lother Meyer
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