Transuranium element
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In chemistry, transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, the atomic number of uranium.
Of the elements with atomic numbers 1 to 92, all but four (43-technetium, 61-promethium, 85-astatine, and 87-francium) occur in easily detectable quantities on earth, having stable, or very long half life isotopes, or are created as common products of the decay of Uranium.
All of the elements with higher atomic numbers, however, have been first discovered artificially, and other than plutonium and neptunium, none occur naturally on earth. They are all radioactive, with a half-life much shorter than the age of the Earth, so any atoms of these elements, if they ever were present at the earth's formation, have long since vanished, other than trace amounts of Neptunium and Plutonium formed in some Uranium rich rock, and small amounts which escaped atmospheric tests of atomic weapons. The Np and Pu generated are from spontaneous fission in uranium ore with two subsequent beta decays (U-238 → U-239 → Np-239 → Pu-239).
Those that can be found on earth now are artificially generated synthetic elements, via nuclear reactors or particle accelerators. The half lives of these elements show a general trend of decreasing with atomic number. There are exceptions, however, including Dubnium and several isotopes of Curium. Further anomalous elements in this series have been predicted by Glenn T. Seaborg, and are categorised as the Island of stability.
Transuranic elements that have not been discovered, or have been discovered but are not yet officially named, use IUPAC's systematic element names. The naming of transuranic elements is a source of controversy.
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Discovery and naming of transuranium elements
The majority of the transuranium elements were produced by two groups:
- A group at the University of California, Berkeley, under three different leaders:
- Edwin Mattison McMillan, first to produce a transuranium element:
- Glenn T. Seaborg, next in order, who produced:
- 94. plutonium, Pu, named after the planet Pluto, following the same naming rule as it follows neptunium and Pluto follows Neptune in the planetary sequence.
- 95. americium, Am, named because it is an analog to europium, and so was named after the continent where it was first produced.
- 96. curium, Cm, named after Pierre and Marie Curie, famous scientists who separated out the first radioactive elements.
- 97. berkelium, Bk, named after the city of Berkeley, where the university is located.
- 98. californium, Cf, named after the state of California, where the university is located.
- Albert Ghiorso, who had been on Seaborg's team when they produced curium, berkelium, and californium, took over as director to produce:
- 99. einsteinium, Es, named after the great physicist Albert Einstein.
- 100. fermium, Fm, named after Enrico Fermi, the physicist who produced the first controlled chain reaction.
- 101. mendelevium, Md, named after the Russian chemist Dmitry Ivanovich Mendeleev, one of the two men who developed the periodic table of the chemical elements.
- 102. nobelium, No (see below).
- 103. lawrencium, Lr, named after Ernest O. Lawrence, a physicist best known for his development of the cyclotron, and the person for whom the Lawrence Livermore National Laboratory (which hosted the creation of these transuranium elements) were named.
- 104. rutherfordium, Rf, named after Ernest Rutherford, who was responsible for the concept of the atomic nucleus.
- 105. An element for which the Berkeley group proposed the name hahnium, after Otto Hahn, the first chemist to detect evidence of nuclear fission, but which is now named dubnium, Db (see below).
- 106. seaborgium, Sg, named after Glenn T. Seaborg. This name caused controversy because Seaborg was still alive, but eventually became accepted by international chemists.
- A group at the Gesellschaft für Schwerionenforschung (Society for Heavy Ion Research) in Darmstadt, Hessen, Germany, under Peter Armbruster, who prepared:
- 107. bohrium, Bh, named after the Danish physicist Niels Bohr, important in the elucidation of the structure of the atom. The group had first suggested the name nielsbohrium, but the ultimately accepted name is bohrium.
- 108. hassium, Hs, named after the Latin form of the name of Hesse, the German Bundesland where this work was performed.
- 109. meitnerium, Mt, named after Lise Meitner, a German physicist who was one of the earliest scientists to become involved in the study of nuclear fission.
- 110. darmstadtium, Ds named after Darmstadt, Germany. Where the Gesellschaft für Schwerionenforschung is situated which discovered the element.
- 111. roentgenium, Rg named after Wilhelm Roentgen, discoverer of the X-Ray
- 112. This element has not yet been given a name.
Now-obsolete claims of discovery
Two other groups had worked on the preparation of transuranium elements, but their original reports have since been discredited:
- A group at the Nobel Institute in Sweden, which claimed to have produced element 102, and named it nobelium, in honor of Alfred Nobel, inventor of dynamite and donor of the endowment for the Nobel Prizes. The name "nobelium" was ultimately agreed upon, though their production is no longer accepted.
- A group at the Joint Institute for Nuclear Research in Dubna in Russia (then the Soviet Union) who claimed to have produced:
- 104, which they named kurchatovium after the Soviet chemist Igor Kurchatov.
- 105. Although their claim is not accepted, the name dubnium is now official for this element, named after the city where they worked. They originally proposed nielsbohrium for this element.
- 106. seaborgium
- 107. bohrium
List of the transuranic elements:
93 neptunium Np
94 plutonium Pu
95 americium Am
96 curium Cm
97 berkelium Bk
98 californium Cf
99 einsteinium Es
100 fermium Fm
101 mendelevium Md
102 nobelium No
103 lawrencium Lr
104 rutherfordium Rf
105 dubnium Db
106 seaborgium Sg
107 bohrium Bh
108 hassium Hs
109 meitnerium Mt
110 darmstadtium Ds
111 roentgenium Rg
112 ununbium Uub*
113 ununtrium Uut*
114 ununquadium Uuq*
115 ununpentium Uup*
116 ununhexium Uuh*
*The existence of these elements has been confirmed, however the names and symbols given are provisional as no names for the elements have been agreed on.
See also
- Bose-Einstein condensate (also known as Superatom)
- Super-heavy atom
- Island of stabilityja:超ウラン元素