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.

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