Synthetic element


Synthetic element

In chemistry, a synthetic element is a chemical element that is too unstable to occur naturally on Earth, and therefore has to be created artificially. So far 30 synthetic elements have been discovered—that is, synthesized. Six of them are "quasi-synthetic"—meaning that they occur naturally on Earth in trace quantities and generally have to be produced artificially,—and 24 are "fully synthetic"—meaning that they do not occur naturally on Earth at all, and can only be produced artificially. Of all the synthetic elements, plutonium—first synthesized in 1940—is the one best known to lay people, because of its use in atomic bombs and nuclear reactors.

Contents

Properties

Synthetic elements are radioactive and decay very rapidly into lighter elements—possessing half-lives so short, relative to the age of the Earth (which formed 4.54 billion years ago), that any atoms of these elements that may have existed when the Earth formed have long since decayed. Because of this, atoms of synthetic elements only occur on Earth as the product of experiments that involve nuclear reactors or particle accelerators, via nuclear fusion or neutron absorption.

Atomic mass for natural life is based on weighted average abundance of natural isotopes that occur in the 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 nucleus 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.

(Note: Just because an element is radioactive does not mean it is synthetic. For instance, uranium and thorium have no stable isotopes but occur naturally in the Earth's crust and atmosphere; therefore, neither are synthetic. Unstable elements such as polonium, radium, and radon—which form through the decay of uranium and thorium—are also found in nature, despite their short half-lives.)

History

The first element discovered through synthesis was technetium—its discovery being definitely confirmed in 1936. 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). With the longest-lived isotope of technetium, Tc-98, having a 4.2 million year half-life, no technetium remains from the formation of the Earth. 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.

List of synthetic elements

Quasi-synthetic elements

All elements with atomic numbers 1 through 94, including these, are naturally occurring at least in trace quantities.

Element name Chemical
Symbol
Atomic
Number
First definite
synthesis
Technetium Tc 43 1936
Promethium Pm 61 1945
Astatine At 85 1940
Francium Fr 87 1939
Neptunium Np 93 1940
Plutonium Pu 94 1940

Fully synthetic elements

All elements in the following categories do not occur naturally on Earth, and have atomic numbers of 95 and higher.

Transuranium elements

Element name Chemical
Symbol
Atomic
Number
First definite
synthesis
Americium Am 95 1944
Curium Cm 96 1944
Berkelium Bk 97 1949
Californium Cf 98 1950
Einsteinium Es 99 1952
Fermium Fm 100 1952

Transfermium elements

Element name Chemical
Symbol
Atomic
Number
First definite
synthesis
Mendelevium Md 101 1955
Nobelium No 102 1966
Lawrencium Lr 103 1961

Transactinide elements

Element name Chemical
Symbol
Atomic
Number
First definite
synthesis
Rutherfordium Rf 104 1969
Dubnium Db 105 1968 (USSR)/
1970 (USA) *
Seaborgium Sg 106 1974
Bohrium Bh 107 1981
Hassium Hs 108 1984
Meitnerium Mt 109 1982
Darmstadtium Ds 110 1994
Roentgenium Rg 111 1994
Copernicium Cn 112 1996

(* The United States and Soviet Union made discoveries of Dubnium independently and were given shared credit by IUPAC/IUPAP in 1992. In 1997, IUPAC decided to give the element its current name—a name suggested by the Russians—since American-chosen names had already been used for many existing synthetic elements.)

Recently observed synthetic elements

Note: Names and symbols for these elements are provisional.

Element name Chemical
Symbol
Atomic
Number
First definite
synthesis
Ununtrium Uut 113 2003
Ununquadium Uuq 114 1999
Ununpentium Uup 115 2003
Ununhexium Uuh 116 2000
Ununseptium Uus 117 2010
Ununoctium Uuo 118 2002

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