Ununhexium

Ununhexium, artificially produced radioactive chemical element; symbol Uuh; at. no. 116; mass number of most stable isotope 292; m.p., b.p., sp. gr., and valence unknown. Situated in Group 16 of the periodic table, it is expected to have properties similar to those of polonium and tellurium.

In 1999 a research team at the Lawrence Berkeley National Laboratory in Calif. bombarded lead-208 atoms with high-energy krypton-86 ions to create, apparently, ununoctium (element 118) atoms. The Uuo-293 isotope that they synthesized emitted an alpha particle to decay into Uuh-289, which has a life-life of about 0.6 millisecond, which then emitted an alpha particle to decay into ununquadium (element 114). Although the Berkeley laboratory retracted its claim for creating ununoctium in 2001, other research teams have since created ununhexium directly. No name has yet been adopted for element 116, which is therefore called ununhexium, from the Latin roots un for one and hex for six, under a convention for neutral temporary names proposed by the International Union of Pure and Applied Chemistry (IUPAC) in 1980.

Ununhexium

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Element 116, also called ununhexium (Uuh), chemical element with atomic number 116. Each ununhexium atom has a nucleus, or inner core, containing particles called neutrons and protons (see Atom). The number of protons in the nucleus of an atom determines the element’s atomic number. The nucleus of an atom of ununhexium, therefore, contains 116 protons. Ununhexium has never been found in nature but can be produced in the laboratory by nuclear fusion (a process in which a chemical element with larger atoms is produced by fusing together two smaller atoms of other elements).

Scientists at the Joint Institute for Nuclear Research in Dubna, Russia, created the first atom of ununhexium in mid-2001. They produced ununhexium by using a machine called a particle accelerator to accelerate calcium atoms to a very high velocity and then smashing them into atoms of the element curium. In a very small percentage of these collisions, an atom of calcium combines with an atom of curium to form an isotope of ununhexium called ununhexium-292. Isotopes are varieties of an element that all contain the same number of protons in their cores but contain different numbers of neutrons. Ununhexium-292 contains 116 protons and 176 neutrons (116 + 176 = 292). The Dubna scientists have since produced additional atoms of the element, but their discovery has not yet been confirmed by another laboratory.

Atoms that contain many more than 200 protons and neutrons tend to be unstable and split apart into atoms of elements containing fewer protons and neutrons. This decay is called spontaneous fission, a process in which the atom breaks into smaller “daughter” components. In general, the more particles a nucleus contains, the quicker it tends to decay. Like most of the other known atoms with large numbers of particles packed into their nuclei, ununhexium-292 breaks down very quickly, taking an average of only about 76 milliseconds to decay.

Scientists have been unable to examine ununhexium’s chemical properties because of the limited amount of ununhexium-292 that has been produced and its short life span. Scientists suspect, however, that ununhexium’s properties will turn out to resemble those of the naturally occurring element polonium (Po). Ununhexium belongs to Group 16 (or VIa), a column of the periodic table that also contains polonium. Elements in the same group of the periodic table often share similar properties (a pattern known as the periodic law).

The International Union of Pure and Applied Chemistry has not yet approved permanent names to several recently discovered elements, including ununhexium. Ununhexium is a temporary name based on the element’s atomic number that uses Latin prefixes for the digits of the atomic number (un = 1, hex = 6) followed by the suffix -ium.