Asynthetic element is a knownchemical element that does not occur naturally onEarth: it has been created by human manipulation offundamental particles in anuclear reactor, aparticle accelerator, or the explosion of anatomic bomb; thus, it is called "synthetic", "artificial", or "man-made". The synthetic elements are those with atomic numbers 95–118, as shown in purple on the accompanyingperiodic 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 into thenucleus of an element with anatomic number lower than 95. All known (see:Island of stability) synthetic elements are unstable, but theydecay at widely varying rates; thehalf-lives of their longest-lived isotopes range from microseconds to millions of years.
Five more elements that were first created artificially are strictly speaking notsynthetic because they were later found in nature in trace quantities:technetium (43Tc),promethium (61Pm),astatine (85At),neptunium (93Np), andplutonium (94Pu); although they are sometimes classified as synthetic alongside exclusively artificial elements.[2] The first, technetium, was created in 1937.[3] Plutonium, first synthesized in 1940, is another such element. It is the element with the largest number of protons (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 known mainly for its use in atomic bombs and nuclear reactors.[4]
No elements with atomic numbers 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.
All elements with atomic number greater than 94 decay quickly enough into lighter elements such that anyatoms of these that may have existed when the Earth formed (about 4.6 billion years ago) have long since decayed.[5][6] Synthetic elements now present on Earth are the product of atomic bombs or experiments that involvenuclear reactors orparticle accelerators, vianuclear fusion orneutron absorption.[7]
Atomic mass for natural elements is based on weighted average abundance of naturalisotopes inEarth'scrust andatmosphere. For synthetic elements, there is no "natural isotope abundance". Therefore, for synthetic elements the totalnucleon count (protons plusneutrons) of the most stableisotope, i.e., the isotope with the longesthalf-life—is listed in brackets as the atomic mass.
The first element to be synthesized, rather than discovered in nature, wastechnetium in 1937.[8] This discovery filled a gap in theperiodic table, and the fact that technetium has nostable isotopes explains its natural absence on Earth (and the gap).[9] With the longest-lived isotope of technetium,97Tc, having a4.21-million-year half-life,[10] no technetium remains from the formation of the Earth.[11][12] Only minute traces of technetium occur naturally in Earth's crust—as aproduct ofspontaneous fission of238U, or fromneutron capture inmolybdenum—but technetium is present naturally inred giant stars.[13][14][15][16]
The first entirely synthetic element to be made wascurium, synthesized in 1944 byGlenn T. Seaborg,Ralph A. James, andAlbert Ghiorso by bombardingplutonium withalpha particles.[17][18]
Synthesis ofamericium,berkelium, andcalifornium followed soon.Einsteinium andfermium were discovered by a team of scientists led byAlbert Ghiorso in 1952 while studying the composition ofradioactive debris from the detonation of the first hydrogen bomb.[19] The isotopes synthesized were einsteinium-253, with a half-life of 20.5 days, andfermium-255, with a half-life of about 20 hours. The creation ofmendelevium,nobelium, andlawrencium followed.
During the height of theCold War, teams from theSoviet Union and the United States independently createdrutherfordium anddubnium. The naming and credit for synthesis of these elements remainedunresolved for many years, but eventually, shared credit was recognized byIUPAC/IUPAP in 1992. In 1997, IUPAC decided to give dubnium its current name, honoring the city ofDubna where the Russian team worked since American-chosen names had already been used for many existing synthetic elements, while the namerutherfordium (chosen by the American team) was accepted for element 104.
Meanwhile, the American team had createdseaborgium, and the next six elements had been created by a German team:bohrium,hassium,meitnerium,darmstadtium,roentgenium, andcopernicium. Element 113,nihonium, was created by a Japanese team; the last five known elements,flerovium,moscovium,livermorium,tennessine, andoganesson, were created by Russian–American collaborations and complete the seventh row of the periodic table.
The following elements do not occur naturally on Earth. All aretransuranium elements and have atomic numbers of 95 and higher.
| 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 |
| Mendelevium | Md | 101 | 1955 |
| Nobelium | No | 102 | 1965 |
| Lawrencium | Lr | 103 | 1961 |
| Rutherfordium | Rf | 104 | 1969 (USSR and US) * |
| Dubnium | Db | 105 | 1970 (USSR and US) * |
| 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 |
| Nihonium | Nh | 113 | 2003–04 |
| Flerovium | Fl | 114 | 1999 |
| Moscovium | Mc | 115 | 2003 |
| Livermorium | Lv | 116 | 2000 |
| Tennessine | Ts | 117 | 2009 |
| Oganesson | Og | 118 | 2002 |
| *Shared credit for discovery. | |||
All elements withatomic numbers 1 through 94 occur naturally at least in trace quantities, but the following elements are often produced through synthesis.
| Element name | Chemical symbol | Atomic number | First definite discovery | Discovery in nature |
|---|---|---|---|---|
| Technetium‡ | Tc | 43 | 1937 | 1962 |
| Promethium‡ | Pm | 61 | 1945 | 1965[20] |
| Polonium | Po | 84 | 1898 | |
| Astatine‡ | At | 85 | 1940 | 1943 |
| Francium | Fr | 87 | 1939 | |
| Radium | Ra | 88 | 1898 | |
| Actinium | Ac | 89 | 1902 | |
| Protactinium | Pa | 91 | 1913 | |
| Neptunium‡ | Np | 93 | 1940 | 1952 |
| Plutonium‡ | Pu | 94 | 1940 | 1941–42[21] |
‡ These five elements were discovered through synthesis before being found in nature.