Chemical Elements, plutonium to samarium,
Chart 6 of 8

plutonium | polonium | potassium | praseodymium | promethium | protactinium | radium | radon | rhenium | rhodium | roentgenium | rubidium | ruthenium | rutherfordium | samarium

This is the sixth of eight groups of chem elements available in this cross-reference searches.

The Chemical Elements Chart is here.

The Chemical-Elements Table Index is here.

Symbol: Pu
Atomic number: 94
Year discovered: 1940
Discovered by: Glenn Theodore Seaborg (1912-1999), American physicist and co-workers; Arthur Charles Wahl and Joseph W. Kennedy, Edwin Mc Millan

Additional information:
  • Plutonium was synthesized by Seaborg, McMillan, Kennedy, and Wahl in 1940 by deuteron bombardment of uranium in a cyclotron (a device used to accelerate atomic particles) at Berkeley, California, USA.
  • Plutonium was the second transuranium element of the actinide series to be discovered.
  • In 1808, plutonium was suggested as a name for element 56 but Sir Humphrey Davy’s original name of barium for element 56 still stands.
  • Plutonium occurs in nature in very small concentrations in uranium-bearing ores.
  • Such plutonium was first detected, in Canadian pitchblende, by Seaborg and Morris L. Perlman in 1942.
  • The main use of plutonium is in the production of nuclear (atomic) energy.
  • It is a chemical element that is important in nuclear engineering and in the history of atomic weapons.
Name in other languages:
French: plutonium
German: Plutonium
Italian: plutonio
Spanish: plutonio

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Symbol: Po
Atomic number: 84
Year discovered: 1898
Discovered by: Marie Sklodowska Curie (1867-1934), Polish-born French chemist; and Pierre Curie (1859-1906), French chemist in Paris.

Additional information:
  • Marie Curie discovered that although pure uranium compounds were always radioactive only to the extent that uranium was present, some uranium ores produced far more radioactivity than could be accounted for by the uranium present.
  • It seemed to her that the ores must contain other elements (in small quantities or they would have been discovered earlier) that were much more intensely radioactive than uranium.
  • In July, 1898, the Curies detected such an element, which they called “polonium” in honor of Marie Curie’s native land.
  • It required several tons of pitchblende to produce very small amounts of polonium.
  • Polonium is used in nuclear physics as a source of alpha radiation that is practically exempt from penetrating rays.
  • Irène Curie (1900-1956) and her husband Frédéric Joliet-Curie (1900-1958), discovered artificial radioactivity in1934 by bombarding aluminum, boron, and magnesium with alpha rays of Po.
  • While working as her mother’s assistant, Irène met Frédéric Joliet, another assistant and they were married in 1926.
  • Since Marie and Pierre Curie had no sons and since Joliot did not wish that eminent name of Curie to die out, he changed his name to Joliot-Curie.
  • When ill health forced her mother to retire, Irène succeeded to her post of professor at the Sorbonne in Paris.
  • Marie had taken over the post when Pierre was killed, the first woman ever to hold such a position at the Sorbonne.
  • Irène and Frédéric worked together (just as her parents had done) on further researches into radioactivity.
  • Both died in Paris, Irène on March 17, 1956, at the age of 52 (of leukemia, like her mother, probably induced by overexposure to energetic radiation) and Frédéric on August 14, 1958, at the age of 58.
  • Mixtures of polonium with beryllium and other light elements are used as sources of neutrons.
  • Polonium also has been used to ionize air, mainly in order to avoid the accumulation of electrostatic charges.
  • For the detection of polonium and radium, Marie Curie (her husband by then having been run over and killed by a horse-drawn vehicle) received the Nobel Prize for chemistry in1911.
Name in other languages:
French: polonium
German: Polonium
Italian: polonio
Spanish: polonio

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Symbol: K
Atomic number: 19
Year discovered: 1807
Discovered by: Sir Humphry Davy (1778-1829), an English chemist.

Additional information:
  • Until the 18th century, no distinction was made between potassium and sodium.
  • This was because early chemists did not recognize that “vegetable alkali”, potassium carbonate (coming from deposits in the earth) and “mineral alkali”, sodium carbonate (derived from wood ashes) are distinct from each other. Eventually a distinction was made.
  • Potassium was isolated, in 1807, by Sir Humphry Davy, who obtained it through the electrolysis of very dry molten caustic potash (potassium hydroxide).
  • It was known that an electric current would break up water molecules into hydrogen and oxygen when more customary chemical methods failed.
  • Davy was interested in the problem and he constructed a battery with over two hundred fifty metallic plates, the strongest ever built up to that time.
  • On October 6, 1807, he passed an electric current through molten potassium carbonate and liberated a metal, which he called potassium.
  • Sir Davy coined the word “potassium”, a Latinized version of “potash”.
  • Potassium was the first metal isolated by electrolysis.
  • Davy isolated sodium by a similar procedure later in 1807.
  • Potassium is one of the most reactive of the metallic elements.
  • This property is illustrated when it is dropped into water; hydrogen is displaced and both the hydrogen and the potassium burst into flame, burning with a violet colored flame that usually culminates in a slight explosion.
  • To put it another way, little globules of shining metal, when added to water, tear the water molecules apart as the metal recombines with oxygen, and the liberated hydrogen is heated to the point where it bursts into flames.
  • It is important for the nutrition of plants, and its compounds are contained in most plant and animal tissues.
  • In the first decade of the 15th century, potassium salts were being produced in Scotland from the ashes of seaweed.
Name in other languages:
French: potassium
German: Kalium
Italian: potassio
Spanish: potasio

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Symbol: Pr
Atomic number: 59
Year discovered: 1885
Discovered by: Carl Auer, Freiherr von Welsbach (1858-1929), an Austrian chemist

Additional information:
  • In 1885, Carl Auer von Welsbach separated an “earth” called didymia, obtained from the mineral samarskite, into two earths, praseodymia and neodymia; which resulted in salts of different colors.
  • It is oxidized slowly by air at room temperature and reacts rapidly with hot water, liberating hydrogen.
  • A mixture of praseodymium and neodymium is used as coloring in the goggles worn by glassblowers and welders.
  • The name of this element is a shortened variant of praeseodidymium (“green didymium”, because of the green color of the salts).
Name in other languages:
French: praséodyme
German: Praseodym
Italian: praseodimio
Spanish: praseodimio

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Symbol: Pm
Atomic number: 61
Year discovered: 1945
Discovered by: Charles Du Bois Coryell (born 1912), J.A. Marinsky, and L.E. Glendenin.

Additional information:
  • A number of investigators in the past had claimed to have proven the existence of element 61 in naturally occurring rare earths; among the names they applied were illimium and florentium.
  • A group at Ohio State University (USA) claimed element 61 in experiments involving its synthesis in a cyclotron, but again the evidence did not satisfy everyone.
  • In 1947, Marinsky, Glendenin, and Coryell, at the Oak Ridge, Tennesee, research site, made the first chemical identification of promethium by use of ion-exchange chromatography on residues in a nuclear reactor.
  • The name of promethium is derived from Prometheus, who in Greek mythology stole fire from heaven (the gods) and gave it to mankind; an appropriate name, since the element comes from the fierce fires of the atomic furnace.
  • Although promethium salts have been used for miniature batteries, the main use of the element is for research.
Name in other languages:
French: prométhium
German: Promethium
Italian: prometio
Spanish: prometio

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Symbol: Pa
Atomic number: 91
Year discovered: 1913 and 1917.
Discovered by: Kasimir Fajans (1887-1975) and O. H. Göring, in 1913; and by Otto Hahn (1879-1968), German physical chemist, and co-worker, Lise Meitner (1878-1968), Austrian physicist; in 1917, in Germany; as well as Frederick Soddy (1877-1956), and John A. Cranston, in England.

Additional information:
  • This was previously known as “protoactinium”; so called because, by the loss of an alpha particle, it forms “actinium”.
  • Protactinium is found in pitchblende and ores from Zaire and it is one of the rarest and most expensive naturally occurring elements.
  • Protactinium was identified by Fajans and Göring in 1913 who named the new element brevium (“brief”).
  • The metal itself was not isolated until 1934 when Aristid Grosse developed two methods.
  • One involved reduction of the pentoxide with a stream of electrons in a vacuum and the second involved heating iodide under vacuum.
Name in other languages:
French: protactinium
German: Protactinium
Italian: protoattinio
Spanish: protactinio

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Symbol: Ra
Atomic number: 88
Year discovered: 1898
Discovered by: Marie Sklodowska Curie (1867-1934), Polish-born French chemist and Pierre Curie (1859-1906), French chemist and an assistant, G. Bémont, at the Sorbonne in Paris.

Additional information:
  • Marie Curie began the investigation of the new field of radiations produced by uranium (she coined the word “radioactivity”) and showed that it was indeed the uranium atom that was the source of the radiations.
  • Pierre Curie, recognizing the talent of his wife, abandoned his own researches and joined her in her work.
  • The Curies discovered that although pure uranium compounds were always radioactive only to the extent that uranium was present, some uranium ores produced far more radioactivity than could be accounted for by the uranium present.
  • It seemed to them that the ores must contain other elements (in small quantities or they would have been discovered earlier) that were much more intensely radioactive than uranium.
  • Radium was discovered, in 1898, by Marie and Pierre Curie in pitchblende (or uraninite) from North Bohemia.
  • In 1911, Marie alone was awarded the Nobel Prize for Chemistry for the discovery of polonium and radium.
  • She was the only one to receive the award because her husband, Pierre, was killed in a traffic accident in 1906 having been run over by a horse-drawn vehicle.
  • Radium was isolated, in 1911, by Mme. Curie and André-Louis Debierne (1874-1949) by the electrolysis of a solution of pure radium chloride, employing a mercury cathode.
  • Marie Curie died of leukemia in Haute Savoie, France, on July 4, 1934; most probably as a result of so much exposure to radiation during her research over the years.
  • On distillation in an atmosphere of hydrogen, this amalgam yielded pure radium.
  • The uses of radium all result from its radiations; the most important of these has been in medicine, principally for the treatment of cancer.
  • Radium has been mixed, in small concentrations, with a paste of zinc sulfide to make a luminescent paint for watch, clock, meter dials, and signs which must be read in the dark.
  • Fluorescent paints activated by ultraviolet radiation are replacing radium paints in airplane panel meters.
Name in other languages:
French: radium
German: Radium
Italian: radio
Spanish: radio

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Symbol: Rn
Atomic number: 86
Year discovered: 1900
Discovered by: Friedrich Ernst Dorn (1848-1916), a German physicist.

Additional information:
  • Friedrich Ernst Dorn, while studying the radium that the Curies had discovered, found in 1900 that it gave off not only radiations but a gas that was itself radioactive.
  • The gas was called “radium emanation” at first, but on closer study it turned out to be a noble gas, the sixth one, and was named “radon”.
  • Dorn, apparently also called it “niton” after “the element radium” (radon was called “niton” because it was based on the Latin word, nitens, meaning “shining, bright, glittering”).
  • Because of its transient existence, radon is found only in conjunction with a source of radium.
  • The atmosphere contains traces of radon near the ground as a result of seepage from soil and rocks, all of which contain minute quantities of radium.
Name in other languages:
French: radon
German: Radon
Italian: radon (emanio)
Spanish: radón

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Symbol: Re
Atomic number: 75
Year discovered: 1925
Discovered by: Walter Karl Friedrich Noddack (1893-1960), German chemist and Ida Eva Tacke (1896-?), German chemist.

Additional information:
  • Although they did not know it at the time, Noddack and Tacke (they were married the next year) had discovered the eighty-first and last element that possessed stable isotopes.
  • They also announced the discovery of element 43 at the same time as that of rhenium, which they called “masurium”, after a district in eastern Germany.
  • In this case; however, their observations were mistaken.
  • Rhenium was detected in platinum ores and columbite.
  • The metal and its alloys have found limited application as fountain-pen points, high-temperature thermocouples, catalysts, electrical contact points, instrument-bearing points, and in electric components.
Name in other languages:
French: rhénium
German: Rhenium
Italian: renio
Spanish: renio

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Symbol: Rh
Atomic number: 45
Year discovered: 1803 or 1804
Discovered by: William Hyde Wollaston (1766-1828), a British chemist.

Additional information:
  • William Hyde Wollaston discovered rhodium in crude platinum ore from South America rather soon after his discovery of another element, palladium.
  • He dissolved the ore in aqua regia (a mixture of hydrochloric and nitric acids), neutralized the acid with sodium hydroxide, and precipitated the platinum by treatment with ammonium chloride, as ammonium chloroplatinate.
  • Palladium was then removed as palladium cyanide by treatment with mercuric cyanide.
  • The remaining material was a red material containing rhodium chloride salts from which rhodium metal was obtained by reduction with hydrogen gas.
  • The surface of rhodium has a high reflectivity for light and is not corroded or tarnished by air at room temperature.
  • It is frequently electroplated onto metal objects and polished to give permanent attractive surfaces for jewelry and other decorative purposes.
  • The black tarnish of silver is prevented by the use of rhodium plate.
  • It also is particularly important as an element for the preparation of “silvered” surfaces for reflectors of searchlights and motion-picture projectors.
  • Rhodium is almost as resistant as iridium to chemical attack by acids.
  • This massive metal is not dissolved by hot concentrated nitric or hydrochloric acid or even by aqua regia which dissolves gold and platinum.
Name in other languages:
French: rhodium
German: Rhodium
Italian: rodio
Spanish: rodio

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Symbol: Rg
Atomic number: 111
Year discovered: 1994
Discovered by: S. Hofmann, V. Ninov, F. P. Hessberger, P. Armbruster, H. Folger, G. Münzenberg, H. J. Schott, A. G. Popeko, A. V. Yeremin, A. N. Andreyev, S. Saro, R. Janik, M. Lein, and others at GSI in Darmstadt, Germany.

Additional information:
  • Röntgen, or Roentgen, was born on March 27, 1845, in Lennkep, Prussia (now Remscheid, Germany) and died on February 10, 1923 in Munich, Germany.
  • Wilhelm Conrad Röntgen, as a German physicist, discovered X-rays on 8 November 1895, a new type of rays to which he gave this name in view of their uncertain nature.
  • Their use has subsequently revolutionized medicine, found wide application in technology, and heralded the age of modern physics, which is based on atomic and nuclear properties.
  • In 1901, six years after their discovery, the benefit of X-rays to mankind was so evident that Roentgen was awarded the first Nobel Prize in Physics.
  • His discovery of "x-rays" significantly contributed to modern physics and revolutionized diagnostic medicine.
  • Röntgen studied at the Polytechnic in Zürich and then was professor of physics at the universities of Strasbourg (1876-79), Giessen (1879-88), Würzburg (1888-1900), and Munich (1900-20).
  • His research also included work on elasticity, capillary action of fluids, specific heats of gases, conduction of heat in crystals, absorption of heat by gases, and piezoelectricity.
  • Röntgen determined that because the X-rays were not deflected by a magnet, they could not be a form of cathode rays.
  • He speculated that instead the X-rays might be longitudinal electromagnetic waves.
  • The possible medical use of X-rays was realized almost immediately.
  • Unlike other discoveries where the practical applications follow only after decades, physicians were using X-rays within months to inspect internal damage without surgery.
  • Today we know that X-rays are high energy, transverse electromagnetic waves similar to other forms of light.
  • Electromagnetic radiation ranges from high energy, short wave-length gamma and X-rays, through ultraviolet light, visible light, and infrared, to low energy, and long wave-length radio waves.
  • Despite the fact that Röntgen discovered nearly all the properties of X-rays within the first few weeks of investigation, the temporary name he used (X-rays) for the sake of brevity remains the name that is still generally used today (except in Germany where they usually refer to a "Röntgen" examination or report).
  • Element 111 was synthesized exactly 100 years after Roentgen's discovery.
  • To honor Wilhelm Conrad Roentgen, the name, roentgenium, was proposed for the element with atomic number 111.
  • The name roentgenium for the element of atomic number 111 (with symbol Rg) was officially approved as of November 1, 2004.
Name in other languages:
French: roentgenium
German: roentgenium or Röntgenium
Italian: roentgenium
Spanish: roentgenium

You will find a special Röntgen biography,
if you want to know more about him.

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Symbol: Rb
Atomic number: 37
Year discovered: 1861
Discovered by: Gustav Robert Kirchhoff (1824-1887), a German physicist; and Robert Wilhelm Bunsen (1811-1899), a German chemist.

Additional information:
  • Rubidium was discovered, in 1861, spectroscopically by Robert Bunsen and Gustav Kirchoff as an impurity associated with samples of the mineral lepidolite (a form of mica).
  • In their report, made in 1861, Bunsen and Kirchhoff told how they named the new element: “The magnificent dark red color of these rays of the new alkali metal led us to give this element the name rubidium and the symbol Rb from ‘rubidus’, which, with the ancients, served to designate the deepest red.”
  • Rubidium was discovered, in 1861, spectroscopically by Robert Bunsen and Gustav Kirchoff as an impurity associated with samples of the mineral lepidolite (a form of mica).
  • A modern cesium atomic clock can tell time accurately to 15 digits behind the decimal point; however, these machines are running up against the limits of technology and physics.
  • In the search for something even more accurate, as of the year 2000, a research team from the United States and another from France have succeeded independently of each other in creating rubidium-run atomic clocks that have the potential to exceed the cesium standard.
  • The Laboratoire Primaire du Temps et des Fréquences (LPTF) in Paris holds the current world record of an inaccuracy of 1.1X1015, which means in practical terms that its clock would lose one second every 30 million years.
  • Scientists now believe that they can exceed the short-term stability of cesium clocks by a factor of 10.
  • Promising experiments using single ions and laser-cooled rubidium atoms suggest the potential for one day achieving measurements of the second up to 17 or 18 digits behind the decimal point.
  • Apparently, so far, there is no technical application for such a high level of precision; however, that would not stop any number of radio astronomers or cutting-edge researchers from immediately acquiring such an instrument the moment it becomes available.

  • —The information in the last six paragraphs (above) is based on an article in the Frankfurter Allegemeine Zeitung; titled “Atomic Clocks? Yes, Please! Subatomic Particles Drive World’s Most Accurate Timekeepers” by Max Rauner; November 3, 2000; Page 8.

Name in other languages:
French: rubidium
German: Rubidium
Italian: rubidio
Spanish: rubidio

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Symbol: Ru
Atomic number: 44
Year discovered: 1844
Discovered by: Karl Karlovich Klaus (1796-1864) [also spelled: Carl Ernst Claus and Carl Carlovich Claus], Russian chemist of German descent.

Additional information:
  • Ruthenium was isolated, in 1844, by Karl Karlovich Klaus, who obtained ruthenium from the part of crude platinum that is insoluble in aqua regia.
  • It is possible that a Polish chemist Jedrzej Sniadecki had in fact isolated ruthenium from some platinum ores a little earlier than this in 1807, but his work was apparently not ratified, because he withdrew his claims. He called it “vestium”.
  • The name, ruthenium, was selected by G. W. Osann, in 1828, when he made a premature announcement of the discovery of the element in platinum ore from the Ural Mountains.
  • Although Osann’s announcement was never confirmed, Claus kept the name for this element.
Name in other languages:
French: ruthénium
German: Ruthenium
Italian: utenio
Spanish: utenio

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Symbol: Rf
Atomic number: 104
Year discovered: 1969
Discovered by: Albert Ghiorso (born July 15, 1915) and co-workers at the University of California, Berkeley, USA.

Additional information:
  • In 1964, scientists at Dubna, Russia, claimed discovery of element 104 and suggested the name “kurchatovium” and the symbol Ku in honor of Igor Vasilyevich Kurchatov (1903-1960), who led the team that developed the Soviet nuclear bomb.
  • In 1969, an American group at Berkeley, California, reported the formation of isotopes for Element 104.
  • They also indicated that they were unable to reproduce the earlier Russian synthesis from 1964.
  • The Americans proposed “rutherfordium” (Rf) for the new element in honor of the New Zealand physicist, Ernest R. Rutherford.
  • Rutherfordium (Rf) is now the preferred IUPAC name for Element 104.
  • This element was previously called unnilquadium, Ung, which is the Latin equivalent for the number “104”; but it was changed because scientists, and others, thought it was too complicated to remember.
  • In addition to unnilquadium (Ung), the proposed names for Element 104 before the official name was chosen by the International Union of Pure and applied Chemistry were rutherfordium (Rf) and kurchtovium (Ku); as indicated above in the first paragraph.
  • Ernest Rutherford (1871-1937) was a New Zealand physicist and winner of the Nobel Prize in Chemistry in 1908.
  • His research in radiation and atomic structure were basic to later 20th-century developments in nuclear physics.
  • Rutherford, together with J. Chadwick and C. Ellis, wrote Radiations from Radioactive Substances (1930), an authoritative reference about radiation.
  • Dated March 29, 1999, Time magazine had a special issue called, “The Century’s Greatest Minds” in which the publisher did not mention several renowned scientists.
  • As a result, the Monday, March 29, 1999, issue of USA Today had the following article:
  • “New Zealand scientists are upset at the omission of the so-called ‘father of nuclear science,’ Sir Ernest Rutherford, from Time magazine’s series on the most influential people of the 20th century, The Sunday Star-Times reported. Rutherford, born in New Zealand in 1871, won the Nobel Prize for chemistry in 1908 for his discoveries on the nature of the atom and is widely regarded as the founder of nuclear physics.”
Name in other languages:
French: rutherfordium
German: Rutherfordium
Italian: rutherfordio
Spanish: rutherfordio

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Symbol: Sm
Atomic number: 62
Year discovered: 1879
Discovered by: Paul-Émile Lecoq de Boisbaudran (1838-1912), a French chemist.

Additional information:
  • Samarium was discovered spectroscopically by its sharp absorption lines, in 1853, by Jean Charles Galissard de Marignac in an “earth” called didymia.
  • The element was isolated, in 1879, by Lecoq de Boisbaudran from the mineral samarskite, named in honor of a Russian mine official, Colonel Samarski, and which therefore gave samarium its name.
Name in other languages:
French: samarium
German: Samarium
Italian: samario
Spanish: samario

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