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Since antiquity, around the 400s BC, in ancient Greece,they have used the words "element" and "atom" to describe the differences between different parts of the material and to designate the smallest parts that make up matter.
In the eighteenth century, the great French chemist Antoine Lavoiser, in his " 'Traité élémentaire de Chimie (Elementary Treatise of Chemistry), published in 1789, divided the 33 elements known in his time, in four groups according to chemical properties: gases, non-metals, metals, and earth.
In the nineteenth century, in 1869 German scientist Johann Döbereiner noted that similar elements have similar atomic masses. He eleborat the so-called Law of triads which consist of dividing the items into groups of three similar elements, the middle element properties being deduced from the properties of the most difficult element and the easiest item.
Examples of triads in this table: lithium, sodium and potassium, sulfur, selenium and tellurium and chlorine, bromine and iod.Cercetătorul French Chancourtois made a cylindrical table of elements to show a periodic recurrence properties of chemical elements. In 1865, another researcher who attempted classification of items was Englishman John Newlands, professor in the School of Medicine in London.
He placed the items in a table consists of 7 columns in order of increasing atomic mass. He pointed out that elements with similar properties occur at intervals of 8 elements and eleborat so-called Law of octaves.
Other contributions to the classification of chemical elements, were also brought by English scientist William Olding, in 1864 and German scientist Julius Lothar Meyer in 1868.
W. Olding has made a table very similar to that made later by Mendeleev. The groups are arranged horizontally and the elements are arranged in order of atomic mass. In the tables were left blanks for undiscovered elements.
German chemist Julius Lothar Meyer made a table of chemical elements in 1864, then a second version in 1868, where the elements were arranged in order of atomic mass. Mayer published his work much later than Mendeleev, so could not prevail in this area. It seems that the two chemists, Meyer and Mendeleev discovered the periodic system of elements simultaneously.
He who is widely accepted as the discoverer of the periodic system of elements was modern Russian chemist Dmitri Ivanovich Mendeleev. The final version of the system periodically in 1871 has left spaces suggesting that other chemical elements will be discovered later. Element 101 was named after Dmitri Ivanovich Mendeleev (1834-1907), who discovered the "Periodic System" arranged in tabular form and continuously improved between 1868 and 1871.
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