Bohrium (BH)
Bohrium (Bh) is a synthetic, radioactive element with the atomic number 107. It was first produced in 1975 by a team led by Soviet physicist Yuri Oganessian at the Russian Joint Institute for Nuclear Research. This element is known for its extreme instability, with its most stable isotope, bohrium-270, having a half-life of only 61 seconds before decaying into dubnium-266. Although little is known about its physical characteristics, it is believed to have a silvery or metallic grey appearance and is categorized as a transition metal within Group 7 of the periodic table.
The element has been the subject of ongoing research, particularly in the fields of nuclear chemistry and the study of its compounds, such as the oxychloride BhO3Cl. Scientists have theorized that bohrium may exhibit chemical properties resembling those of its lighter homologues, rhenium and technetium. However, due to its rapid decay and the limited amounts produced, bohrium currently has no practical applications and has not been studied extensively for its potential effects on human health. The IUPAC officially recognized the name "bohrium" in 1997, resolving prior naming disputes associated with its discovery.
Subject Terms
Bohrium (BH)
- Element Symbol: Bh
- Atomic Number: 107
- Atomic Mass: 264
- Group # in Periodic Table: 7
- Group Name: Transition metals
- Period in Periodic Table: 7
- Block of Periodic Table: d-block
- Discovered by: Peter Armbruster, Gottfried Münzenberg (1981)
Bohrium, a radioactive element that is artificially produced in a laboratory, has an atomic number of 107 and symbol Bh. Because it is very unstable, little is known of its properties, but it is in all probability silvery or metallic grey. In Dubna in 1975, Soviet physicist Yuri Oganessian led a team at the Russian Joint Institute for Nuclear Research (JINR) that produced bohrium artificially for the first time. The group bombarded a fast moving cylinder coated with a thin layer of bismuth with chromium-54 ions that were fired tangentially at the cylinder; after employing this technique, the team detected the presence of the element. The next year, in 1976, the team formally submitted a claim that it had discovered this element.
In 1981, a subsequent attempt to produce the element was conducted at the Institute for Heavy Ion Research. (In German, the institute is named Gesellschaft für Schwerionenforschung [GSI]). Two of the GSI researchers, Peter Armbruster and Gottfried Münzenberg, also bombarded bismuth with chromium, and in doing so, the duo was successful in making five atoms of isotope bohrium-262. In the end, the International Union of Pure and Applied Chemistry (IUPAC) named the GSI team the official discoverer of bohrium.
Before it was isolated, bohrium was historically referred to as eka-rhenium. Nielsbohrium was the name suggested by the Germans after their own work yielded five atoms. They wanted to honor the Danish Nobel Prize–winning physicist Niels Bohr, but the Soviets had already recommended this name for element 105 (dubnium). Thus, a controversy arose as to what the elements from 101 to 109 were to be called. The IUPAC gave a temporary name unnilseptium (Uns) to element 107. A committee of IUPAC members suggested in 1994 that element 107 be named bohrium, but only in 1997 was it internationally recognized by this name.
The Paul Scherrer Institute (PSI) in Bern, Switerland; Berkeley Lab; and the University of California, Berkeley, have been collaborating with other institutions to study the chemistry of bohrium. The institutions these three groups have been working with include the University of Bern in Switzerland, GSI, the Flerov Laboratory in Russia, the Technical University of Dresden in Germany, and the Japan Atomic Energy Research Institute.
Physical Properties
The boiling and freezing points of bohrium are unknown. Atomic mass unit (amu) is the measure for the atomic masses of elements. Bohrium’s atomic mass is 262 amu. Bohrium has a thermal conductivity of +206 watts per meter kelvin. It belongs to Group 7 of the periodic table. The standard state of an element is its state at 298 K. Because the melting point of bohrium has not yet been determined, the standard state of the element is not yet known with certainty, but it is believed that it is a solid at 298 K. The element’s key isotope is bohrium-272. It belongs to the transition metals family. The weight of bohrium is greater than that of manganese, technetium, and rhenium.
Chemical Properties
Bohrium is a radioactive element and is not found naturally. Scientists created this element using the cold fusion method. Bohrium’s most stable isotope, bohrium-270, has a half-life of 61 seconds, after which it decays into dubnium-266. The numbers of electrons per shell are 2, 8, 18, 32, 32, 13, 2. Its valence electrons are believed to be 6d57s2, although a precise determination of the valence electrons has not yet been established. It has an electron configuration of 5f146d57s2. Bohrium and rhenium are homologous, but bohrium is the heavier homologue. Bohrium’s chemical properties can be compared to the chemistry of the other Group 7 elements, although its own chemical properties are only partly characterized.
Heinz W. Gäggeler of the University of Bern in Switzerland led a team of nuclear chemists who prepared a compound, BhO3Cl, from six isolated atoms of bohrium-267. When analyzing the decay products of this compound, the team was able to define the thermochemical properties of BhO3Cl. As a result, the team showed that bohrium appears to behave as might be predicted according to its position in the periodic table.
Since the Group 7 heavier elements form volatile heptoxides, bohrium too should form Bh2O7. Likewise, if it dissolves in water, it should form HBhO4. A range of oxyhalides are formed by rhenium and technetium from the halogens of the oxides; therefore, in theory, bohrium should also form the oxychloride BhO3Cl. The bohrium oxychloride formation may indicate eka-rhenium properties.
The oxychlorides of bohrium were passed through a chromatography column by Gäggeler and his team. The temperatures of the more volatile products of this process were lowered. At 180°C, the bohrium-267 compound was shown to be volatile. In other words, it behaved much like rhenium and technetium, its lighter homologues in Group 7 in the periodic table.
Radiochemists at PSI have used the Philips cyclotron to determine the volatility of bohrium, which is the heaviest Group 7 element of the periodic table whose chemistry has yet to be successfully investigated.
Applications
Bohrium is very unstable. It quickly forms other elements by decaying, and hence its effect on humans has not been studied. Bohrium is created only in small amounts, and, therefore, it has no uses. Even though it is an alpha emitter, it is not much of a radiation hazard because it has only a few atoms.
Bibliography
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"Bohrium." Periodic Table. Royal Society of Chemistry, n.d. Web. 1 Jan. 2016.
"Bohrium (Bh)." Encyclopaedia Britannica Online. Encyclopaedia Britannica Inc., 2016. Web. 1 Jan. 2016.
"Bohrium: the Essentials." WebElements. The University of Sheffield and WebElements, n.d. Web. 1 Jan. 2016.
Krebs, Robert E. The History and Use of Our Earth’s Chemical Elements: A Reference Guide. Westport: Greenwood, 1998.