Synthetic element

A synthetic element is one of 24 chemical elements that do not occur naturally on Earth: they have been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, they are called "synthetic", "artificial", or "man-made". The synthetic elements are those with atomic numbers 95–118, as shown in purple on the accompanying periodic table:[1] these 24 elements were first created between 1944 and 2010. The mechanism for the creation of a synthetic element is to force additional protons onto the nucleus of an element with an atomic number lower than 95. All synthetic elements are unstable, but they decay at a widely varying rate: their half-lives range from 15.6 million years to a few hundred microseconds.

  Synthetic elements
  Rare radioactive natural elements; often produced artificially

Seven other elements that were created artificially—and thus initially considered to be synthetic—were later discovered to exist in nature in trace quantities. The first, technetium, was created in 1937.[2] Plutonium, atomic number 94, first synthesized in 1940, is another such element. It is the element with the largest number of protons (and equivalent atomic number) to occur in nature, but it does so in such tiny quantities that it is far more practical to synthesize it. Plutonium is extremely well-known due to its use in atomic bombs and nuclear reactors.[3] No elements with an atomic number greater than 99 have any uses outside of scientific research, since they have extremely short half-lives, and thus have never been produced in large quantities.

Properties

Any elements with atomic number greater than 94 present at the formation of the earth about 4.6 billion years ago have decayed sufficiently rapidly into lighter elements relative to the age of Earth that any atoms of these elements that may have existed when the Earth formed have long since decayed.[4][5] Atoms of synthetic elements now present on Earth are the product of atomic bombs or experiments that involve nuclear reactors or particle accelerators, via nuclear fusion or neutron absorption.[6]

Atomic mass for natural elements is based on weighted average abundance of natural isotopes that occur in Earth's crust and atmosphere. For synthetic elements, the isotope depends on the means of synthesis, so the concept of natural isotope abundance has no meaning. Therefore, for synthetic elements the total nucleon count (protons plus neutrons) of the most stable isotope, i.e. the isotope with the longest half-life—is listed in brackets as the atomic mass.

History

Technetium

The first element discovered through synthesis was technetium—its discovery being definitely confirmed in 1937.[7] This discovery filled a gap in the periodic table, and the fact that no stable isotopes of technetium exist explains its natural absence on Earth (and the gap).[8] With the longest-lived isotope of technetium, 97Tc, having a 4.21-million-year half-life,[9] no technetium remains from the formation of the Earth.[10][11] Only minute traces of technetium occur naturally in the Earth's crust—as a spontaneous fission product of uranium-238 or by neutron capture in molybdenum ores—but technetium is present naturally in red giant stars.[12][13][14][15]

Curium

The first discovered purely synthetic element was curium, synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso by bombarding plutonium with alpha particles.[16][17][18][19]

Eight others

The discoveries of americium, berkelium, and californium followed soon. Einsteinium and fermium were discovered by a team of scientists led by Albert Ghiorso in 1952 while studying the radioactive debris from the detonation of the first hydrogen bomb.[20] The isotopes discovered were einsteinium-253, with a half-life of 20.5 days, and fermium-255, with a half-life of about 20 hours. The discoveries of mendelevium, nobelium, and lawrencium followed.

Rutherfordium and dubnium

During the height of the Cold War, teams from the Soviet Union and the United States independently discovered rutherfordium and dubnium. The naming and credit for discovery of these elements remained unresolved for many years, but eventually shared credit was recognized by IUPAC/IUPAP in 1992. In 1997, IUPAC decided to give dubnium its current name honoring the city of Dubna where the Russian team made their discoveries since American-chosen names had already been used for many existing synthetic elements, while the name rutherfordium (chosen by the American team) was accepted for element 104.

The last thirteen

Meanwhile, the American team had discovered seaborgium, and the next six elements had been discovered by a German team: bohrium, hassium, meitnerium, darmstadtium, roentgenium, and copernicium. Element 113, nihonium, was discovered by a Japanese team; the last five known elements, flerovium, moscovium, livermorium, tennessine, and oganesson, were discovered by Russian–American collaborations and complete the seventh row of the periodic table.

List of synthetic elements

The following elements do not occur naturally on Earth. All are transuranium elements and have atomic numbers of 95 and higher.

Element nameChemical
Symbol		Atomic
Number		First definite
synthesis
AmericiumAm951944
CuriumCm961944
BerkeliumBk971949
CaliforniumCf981950
EinsteiniumEs991952
FermiumFm1001952
MendeleviumMd1011955
LawrenciumLr1031961
NobeliumNo1021966
RutherfordiumRf1041966 (USSR), 1969 (US) *
DubniumDb1051968 (USSR), 1970 (US) *
SeaborgiumSg1061974
BohriumBh1071981
HassiumHs1081984
MeitneriumMt1091982
DarmstadtiumDs1101994
RoentgeniumRg1111994
CoperniciumCn1121996
NihoniumNh1132003–4
FleroviumFl1141999
MoscoviumMc1152003
LivermoriumLv1162000
TennessineTs1172010
OganessonOg1182002
* Shared credit for discovery.

Other elements usually produced through synthesis

All elements with atomic numbers 1 through 94 occur naturally at least in trace quantities, but the following elements are often produced through synthesis. Technetium, promethium, astatine, neptunium, and plutonium were discovered through synthesis before being found in nature.

Element nameChemical
Symbol		Atomic
Number		First definite
discovery
TechnetiumTc431937
PromethiumPm611945
PoloniumPo841898
AstatineAt851940
FranciumFr871939
ActiniumAc891902
ProtactiniumPa911913
NeptuniumNp931940
PlutoniumPu941940

References
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