dmitri mendeleev arranged the periodic table by atomic mass.
dmitri mendeleev arranged the periodic table by atomic mass.
who arranged the periodic table by atomic mass?
dmitri mendeleev
russian chemist dmitri mendeleev arranged the elements by atomic mass, corresponding to relative molar mass. it is sometimes said that he played "chemical solitaire" on long train journeys, using cards with various facts about the known elements. mendeleev used the trends he saw to suggest that atomic weights of some elements were incorrect and accordingly changed their placing: for instance, he figured there was no place for a trivalent uranium with the mass of 120 in his work, and he doubled both the atomic weight and valency of uranium, suggesting it was a hexavalent element with the atomic weight of 240. mendeleev also figured some spots in his ordering had no element to match, and he left gaps on account of future discoveries of these elements, using the elements before and after those missing ones to predict their properties. in 1869, he finalized his first work and had it published. mendeleev also sent it to a number of well-known chemists, including meyer; this preceded meyer's first comprehensive periodic table which he published a few months later, acknowledging mendeleev's priority. mendeleev continued to improve his ordering; in 1870, it gained a tabular shape, and in 1871, it was titled "periodic table". some changes also occurred with new revisions, with some elements changing positions.
history of the periodic table
before moseley's discovery, the atomic numbers (or elemental number) of an element had been thought of as a semi-arbitrary sequential number, based on the sequence of atomic masses, but modified somewhat where chemists found this modification to be desirable, such as by the russian chemist, dmitri ivanovich mendeleev. in his invention of the periodic table of the elements, mendeleev had interchanged the orders of a few pairs of elements in order to put them in more appropriate places in this table of the elements. for example, the metals cobalt and nickel had been assigned the atomic numbers 27 and 28, respectively, based on their known chemical and physical properties, even though they have nearly the same atomic masses. in fact, the atomic mass of cobalt is slightly larger than that of nickel, which would have placed them in backwards order if they had been placed in the periodic table blindly according to atomic mass. moseley's experiments in x-ray spectroscopy showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the periodic table correctly by moseley's objective measurements of their atomic numbers. hence, moseley's discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their x-ray spectra.
henry moseley