The First International Congress of Chemists took place in September 1860 in Karlsruhe, Germany to review scientific matters that there was little agreement to. Following this congress led to the development of the periodic table of elements. Top contributors to the periodic table included Staislao Cannizzaro, Dmitri Mendeleev, Henry Gwyn-Jeffreys Moseley, John William Strutt, William Ramsay, Friedrich Ernst Dorn, and Glenn Seaborg. Stanislao Cannizzaro, born in 1826 and died in 1910, was an Italian chemist.
He presented a method to measure atomic masses and to interpret the results of the measurements. Cannizzaro’s method aided scientists into agreeing standard values for atomic masses. The scientists then searched for relationships among atomic masses and other properties of the elements. Dmitri Mendeleev, born in 1834, was a Russian chemist, and is sometimes considered as the ‘father of the Periodic Table’. Mendeleev was in the process of writing a chemistry textbook and he wanted to organize the elements according to their properties.
Mendeleev created a table where elements with similar properties were grouped together. Mendeleev’s table left several empty spaces because there were elements that had not been discovered yet. Then in 1871, Mendeleev predicted the existence and properties of three elements. His predictions were a success and it led to scientists accepting his periodic table. Henry Gwyn-Jeffreys Moseley, born in 1887, was an English scientist that discovered that atomic number, not atomic mass, was the basis for the organization of the Periodic Table.
Moseley and Rutherford performed multiple experiments on 38 metals and Moseley discovered a pattern in which the positive charge of the nucleus increased by one unit from one element to the next when the elements are arranged as they are in the Periodic Table. His studies also led to the modern definition of atomic number and it provided justification for Mendeleev’s ordering of the Periodic Table by properties rather than just by atomic mass. Mendeleev’s Periodic Table did not include noble gases because at that time it was not discovered then.
The English physicists John William Strutt and William Ramsay discovered four of he noble gases. Argon and helium were discovered by the two scientists in 1894. To fit argon and helium into the table, they proposed a new group that was placed between Group 17 and Group 1. Then, krypton and xenon were discovered by Ramsay in 1898. Radon, the final noble gas, was discovered in 1900 by a German scientist named Friedrich Ernst Dorn. Glenn Seaborg was an American scientist and he discovered all the transuranic elements from 94 to 102. With this discovery, he was the last person to majorly change the Periodic Table by placing the actinide series below the lanthanide series.
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