Discoveries of the chemical elements
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The story of the discoveries of the chemical elements is presented here in chronological order. The elements are listed generally in the order in which they were first isolated as the pure element, rather than as a compound (some such as boron were known to be elements decades before they could be isolated from their compounds). The first few predate any written record.
Although Aluminium may have been isolated in Roman times (see Aluminium#History), its isolation is usually credited to Hans Christian Ørsted in 1825, and is listed under that date.
|Arsenic||1250||Albertus Magnus is believed to have been the first to isolate the element.|
|Antimony||1450||First described scientifically by Tholden|
|Bismuth||15th century?||May have been described in writings attributed to Basil Valentinus, definitively identified by Claude Geoffroy Junine in 1753|
|Zinc||1526||Identified as a unique metal by Paracelsus|
|Phosphorus||1669||Hening Brand, later described by Robert Boyle|
|Platinum||ca. 1741||Discovered independently by Antonio de Ulloa (published 1748) and Charles Wood.|
|Nickel||1751||Axel Fredrik Cronstedt|
Priestley's work on atmospheric gases resulted in his preparation of oxygen. As he was a believer in phlogiston, he didn't realise that he had prepared a new element, and thought that he had managed to prepare air free from phlogiston ("de-phlogisticated air"). However, he was the first to isolate oxygen, even if he didn't realise what he had:
|Chlorine||1774||Carl Wilhelm Scheele|
|Manganese||1774||Johan Gottlieb Gahn|
|Hydrogen||1776||Isolated and described by Henry Cavendish, named by Antoine Lavoisier|
|Molybdenum||1778||Carl Wilhelm Scheele|
|Tellurium||1782||Franz-Joseph Müller von Reichenstein|
|Tungsten||1783||Juan José Elhuyar and Fausto Elhuyar|
The next element was discovered just after the discovery of a new class of astronomical objects: the new element was named after the newly discovered asteroid, Ceres. The element was discovered nearly simultaneously in two laboratories, though it was later shown that Berzelius and Hisinger's cerium was actually a mixture of cerium, lanthanum and didymium.
|Cerium||1803||Martin Heinrich Klaproth; Jöns Jakob Berzelius and Hisinger|
|Rhodium||1803||William Hyde Wollaston|
|Palladium||1803||William Hyde Wollaston|
At this point, Sir Humphry Davy pioneered the use of electricity from the Voltaic pile to decompose the salts of alkali metals, and so a number of those metals were first prepared as the pure element: the beginning of the field of electrochemistry.
|Boron||1808||Joseph Louis Gay-Lussac & Louis-Jacques Thenard|
|Lithium||1817||Johan August Arfwedson|
|Cadmium||1817||Friedrich Strohmeyer Independently discovered by K.S.L Hermann|
|Selenium||1817||Jöns Jakob Berzelius|
|Silicon||1823||Jöns Jakob Berzelius|
|Aluminium||1825||Hans Christian Ørsted (may have been isolated in Roman times, see Aluminium#History)|
|Bromine||1826||Antoine Jérôme Balard|
|Thorium||1828||Jöns Jakob Berzelius|
|Beryllium||1828||Friedrich Wöhler. Independently discovered by A.A.B. Bussy|
The next element discovered when Mosander showed that the cerium isolated in 1803 by Berzelius was actually a mixture of cerium, lanthanum and so-called didymium (which was not actually one element, and was resolved into two in 1885).
|Lanthanum||1839-41||Carl Gustaf Mosander|
|Terbium||1843||Carl Gustaf Mosander|
|Erbium||1843||Carl Gustaf Mosander|
A number of elements were first identified by their spectroscopic emission lines: caesium and rubidium were discovered by Robert Bunsen and Gustav Kirchhoff analysing the spectrum of alkali salts. The unknown element with blue emission lines was named caesium; in purifying the salts of this new element, another element was discovered with a red emission line; this was called rubidium. They were shortly afterwards prepared as the pure salts by Bunsen. The bright green line of thallium caused it to be named from the Greek thallos, meaning a green shoot, and the indigo-blue line from certain specimens of zinc-blende gave the name indium to the new element so discovered:
|Caesium||1860||Robert Bunsen and Gustav Kirchoff|
|Rubidium||1860||Robert Bunsen and Gustav Kirchoff|
|Thallium||1861||Sir William Crookes|
|Indium||1863||Ferdinand Reich and Theodor Richter|
Another spectroscopic discovery, helium was found by astronomers as an emission line in the spectrum of the sun, hence its name from the Greek helios meaning sun. It was at first thought to be an unknown metallic element, and so the name was given the ending -ium to signify a metal. By the time it had been found on Earth and discovered to be the lightest of the noble gases, the name was fixed; by analogy with the other noble gases, the name should have ended in -on.
|Helium||1868||Independently by Pierre Jansen and Norman Lockyer|
The Periodic table and the prediction of new elements
In 1871, Mendeleev predicted, from the gaps in his newly-devised periodic table, that there should be three as yet undiscovered elements, which he named eka-boron, eka-aluminium, and eka-silicon. With Mendeleev's prediction of their existence and approximate chemical properties, the missing elements were found by French, Scandinavian, and German chemists, and named for their countries of discovery, as gallium, scandium, and germanium:
The 'didymium' isolated by Mosander in 1839 was shown to actually be two separate elements, praseodymium and neodymium:
|Praseodymium||1885||Carl Auer von Welsbach|
|Neodymium||1885||Carl Auer von Welsbach|
|Dysprosium||1886||Paul Emile Lecoq de Boisbaudran|
|Fluorine||1886||Joseph Henri Moissan|
Refrigeration technology advanced considerably during the 19th century, to the point where it was possible to liquefy atmospheric gases. A curious observation was made: Nitrogen prepared by chemical means from its compounds had a slightly lower molecular weight than nitrogen prepared by liquefaction from air. This was attributed as being due to the presence of a previously unsuspected gas, christened argon. This gas was the first representative found of a previously unsuspected new group in the periodic table, first known as the inert gases, now more commonly known as the noble gases.
|Argon||1894||Lord Rayleigh & Sir William Ramsay|
Once liquid argon could be prepared in quantity from air, small amounts of a further three noble gases could be separated from it by differences in boiling point. These new elements were named from the Greek words for, respectively, 'new', 'hidden', and 'foreign'.
|Neon||1898||Sir William Ramsay|
|Krypton||1898||Sir William Ramsay|
|Xenon||1898||Sir William Ramsay|
With the discovery of radioactivity, we have the classic work by the Curies that isolated a number of previously unknown elements:
|Radium||1898||Pierre Curie and Maria Sklodowska-Curie|
|Polonium||1898||Pierre Curie and Maria Sklodowska-Curie|
Another of the noble gases, radon had avoided discovery because its short radioactive half-life had meant it was present in air in vanishingly tiny quantities. Once radium was available in macroscopic quantities, the production of this radioactive noble gas was readily detected as a product of radium's radioactive decay.
|Radon||1898||Friedrich Ernst Dorn who called it nitron|
|Protactinium||1917||Kasimir Fajans, O. Göhring, Fredrich Soddy, John Cranston, Lise Meitner and Otto Hahn|
|Rhenium||1925||Walter Noddack and Ida Tacke|
At this point, all the stable elements existing on earth had been discovered, and most of the periodic table had been filled. A few gaps remained amongst the higher mass elements, but there remained a troublesome gap at element number 43, just below manganese in the table. The gaps were filled by the synthetic elements. Walter Noddack and Ida Tacke (later Ida Noddack) also believed to have found Technetium, which they called Masurium (after Masurien, an area in Germany). They were later proved wrong.
The so-called "synthetic" elements are unstable, with half-lives so "short" relative to the age of the earth that any atoms of that element that may have been present when the earth formed have long since completely decayed away. Hence they are only known on earth as the product of nuclear reactors, particle accelerators, or in the byproducts from nuclear explosions. The discovery of technetium finally filled in a puzzling gap in the periodic table, and the discovery that there were no stable isotopes of technetium explained its absence on earth: its 4.2 million years half-life meant that none remained from the time of formation of the earth.
|Francium (natural)||1939||Marguerite Derey|
All elements after this are synthetic:
|Astatine||1940||Dale R. Corson, K.R.Mackenzie, Emilio Segrè|