Synthetic element

Synthetic elementsRare radioactive natural elements; often artificially producedNatural radioactive elements

In chemistry, a synthetic element is a chemical element that does not occur naturally on Earth, and can only be created artificially. So far, 24 synthetic elements (those with atomic numbers 95-118) have been created. All are unstable, decaying with half-lives ranging from 15.6 million years to a few hundred microseconds.

Five other elements were first created artificially, and therefore considered synthetic, although they were later found to occur naturally (in trace amounts); among them plutonium —first synthesized in 1940—, the best known of the profane, due to its use in atomic bombs and nuclear reactors.

On December 31, 2015, a team of researchers from the Japanese Riken center confirmed the identification of element number 113 of the periodic table, of a synthetic nature and with the provisional name of ununtrium.

Properties

Synthetic elements are radioactive and quickly decay into other light elements. They have half-lives so short compared to the age of the Earth (which formed about 4.6 billion years ago), that any atom of these elements that might be existed when the planet was formed has long since disintegrated. Atoms of synthetic elements are only produced on Earth by experiments involving nuclear reactors or particle accelerators, via nuclear fusion or mass neutron absorption.

The atomic mass for natural life is based on the weighted average abundance of naturally occurring isotopes in the Earth's crust and atmosphere. For synthetic elements, the isotope depends on the means of synthesis, so the concept of natural isotopic abundance is meaningless. Therefore, for synthetic elements the total nucleus count (protons and neutrons) of the most stable isotope, that is, the isotope with the longest half-life are listed as atomic mass in braces ([ ]).

Not all radioactive elements are synthetic. For example, uranium and thorium do not have stable isotopes, but occur naturally in the Earth's crust and atmosphere. Other unstable elements, such as polonium, radium, and radon—formed through the decay of uranium and thorium—also occur in nature, despite their short half-lives. Plutonium is an outlier: its half-life, depending on the isotope, can be as long as 80.8 million years. (The main isotope of plutonium in use has a half-life of 24,100 years.)

History

The first element discovered through synthesis was technetium (its discovery was definitively 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 void). Having the longest-lived isotope of technetium, Tc-98, a half-life of 4.2 million years, no technetium remains since 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—although technetium occurs naturally in red giant stars. The first synthetic element discovered was curium, synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso by bombarding plutonium with alpha particles. Discoveries of americium, berkelium, and californium soon followed. Einsteinium and fermium were discovered by a team of scientists led by Albert Ghiorso in 1952, while they were studying the radioactive remains of the detonation of the first hydrogen bomb. 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 came later. During the height of the Cold War, the Soviet Union and the United States independently discovered rutherfordium and dubnium. Its naming and discovery credit remained unresolved for many years, but joint credit was finally recognized by IUPAC/IUPAP in 1992. In 1997, IUPAC decided to give dubnium its current name after the city of Dubná—where the Russian team made their discoveries—as the names chosen by the Americans had already been used for many existing synthetic elements, while the name "rutherfordium" (chosen by the American team) was accepted for element 104.

No element with an atomic number greater than 99 has any use outside of scientific research, as they have a very short half-life.

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.

Other elements generally produced through synthesis

All elements with atomic numbers from 1 to 94 occur naturally, at least in trace amounts, but the following elements are generally produced through synthesis. Except for polonium and francium, all of them were discovered through synthesis before being found in nature.