Development of the Periodic Table

Topics: Periodic table, Chemical element, Chemistry Pages: 6 (2342 words) Published: April 22, 2013
It’s a rarity that we should come across a laboratory, classroom, chemistry textbook or lecture theatre that doesn’t contain a periodic table of the elements. It required the immense research and determination of the scientist Dmitri Mendeleev to show us that all elements followed a natural form and provided us with the first decent periodic table. There are 111 elements recognised today by IUPAC and they are arranged in the periodic table in horizontal groups and vertical periods. The eight groups consist of the alkali metals, the alkaline earth metals, the transition elements, metalloids, non-metals, the halogens and the nobel gases. The development of the periodic table first began with Antoine Lavoisier. His job as a privatised tax-collector helped finance his scientific research. He was the first scientist to classified the elements into four groups. These groups consisted of gases, metals, non-metals and metal oxides. In 1789, he proposed the Law of Conservation of Mass. This law stated that the mass of the products of a chemical reaction is equal to the reactants. This led to the “chemical revolution” and sparked interest amongst other scientists which, in turn, led to the periodic table that we know of today. In 1817 Johann Dobereiner saw became aware that the atomic weight of strontium was exactly half of the sum of the atomic weights of calcium and barium, which were elements that possessed similar properties. It took Dobereiner another twelve years to propose the Law of the Triads, after extensive research into finding the triads of the halogen group and the alkali metal group. In 1829 he proposed that nature contained triads of elements, with the middle element showing properties that were an average of the other two elements when ordered by atomic weight. Slowly, Dobereiners views began to be taken up by other chemists who tried to complete the unfinished triads, as further knowledge of the elements was gained. Dobereiner’s triads played an important role in Gmelin’s Hand Book of Chemistry, but besides their importance in this publication not much notice was taken of the triads until much later on. The first scientist to arrange the elements in a periodic system was not actually a chemist, but a geologist. Beguyer de Chancourtois proposed a three-dimensional representation of the list of known elements wrapped around a cylinder in a helical graph. Elements that appeared on the same vertical line on the cylinder had similar properties. His helical graph also contained compounds and ions as well as elements so Beguyer de Chantcourtois’ work was disregarded until the work of Mendeleev. In 1862, John Newlands wrote a paper in which he arranged the fifty-six known elements into eleven groups based on similar physical properties. He noted that many of the elements with similarities differed by some multiple of eight in their atomic weights. Newlands found his work unpublished by the Royal Society as there were many criticisms made about his classification of the elements. John Newlands left no places in the table for undiscovered elements which altered the flexibility of the scheme. He didn’t evaluate the best values for the atomic weights, which was a serious omission according to Mendeleev. Some of the elements didn’t obey the scheme, the metals Mn, Ti and Fe aren’t of any resemblance to the non-metals P, Si and s which are placed eight elements before them. He was so convinced of his Law that he tried to force the elements to fit into this system Newlands believed that the system of the octaves would remain valid despite the number of elements that should be discovered. His work was ignored and forgotten until the work of Mendeleev had become famous. Both Dmitri Mendeleev and Lothar Meyer produced similar results concerning the periodic table even though they worked independently of each other. Meyer constructed an abbreviated version of the periodic table, with only half if the known elements...
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