Roentgenium (Rg)

• Element Symbol: Rg
• Atomic Number: 111
• Atomic Mass: [282]
• Group # in Periodic Table: 11
• Group Name: Transition metals
• Period in Periodic Table: 7
• Block of Periodic Table: d-block
• Discovered by: Peter Armbruster, Gottfried Münzenberg (1994)

Roentgenium is an artificially produced radioactive element. With a chemical symbol of Rg, its atomic number is 111, and its relative atomic weight is variously reported as either 280 or 281. Its electronic configuration is [Rn] 5f¹⁴6d¹⁰7s¹, where Rn stands for the element radon. In the periodic table, roentgenium is positioned between the elements darmstadtium and copernicium in Period 7 of Group 11. This placement puts it in the transactinide group. A transactinide element is an element with an atomic number of 103 or more. Transactinides are all synthetic elements, including meitnerium, actinium, and others. Properties are determined by research, but the transactinides tend to decay so quickly that it is difficult to study or categorize them or to assign them to groups and/or blocks based on their properties. The short-lived nature of the transactinides, however, as well as their chemical properties make them dissimilar to those of the other elements in the periodic table.

Roentgenium was discovered on December 8, 1994, at the GSI Helmholtz Centre for Heavy Ion Research at Darmstadt, Germany by a group consisting of thirteen nuclear physicists. They bombarded bismuth-209 with the ions of nickel-64 in a device called the linear accelerator. This device produced three atoms of roentgenium-272 and a free neutron. This isotope of roentgenium had a half-life of about 1.5 milliseconds. A linear accelerator is a device that yields high-energy X-rays. It is frequently used in the management of oncology patients.

To ensure that the nickel ions penetrated bismuth’s nucleus, scientists carefully controlled the energy of collisions in the linear accelerator. If the nickel ions did not go fast enough and could not overcome the repulsive force between the positive nuclei, the ions would fly away upon contact with bismuth. On the other hand, if the nickel ions went too fast, a compound nucleus would undergo fission, and the complex of nickel ions and bismuth nucleus would fall apart. The bombardment needed just the right amount of energy to form roentgenium. Despite these difficulties, the scientists succeeded in producing three effective collisions to form the element with atomic number 111 and mass 272.

It was in 1995 that the discovery of element 111 was first reported in a newspaper. Only then was it given a provisional designation of unununium, with a symbol Uuu. This name was derived from its atomic number of 111. However, the element was not assigned a permanent name until 2003. The scientists at the RIKEN linear accelerator facility in Japan were given the right to permanently name unununium after they successfully made fourteen atoms of the isotope. They then proposed the name roentgenium to acknowledge the scientist Wilhelm Conrad Roentgen, who had discovered X-rays in 1895.

Physical Properties

The standard state of an element is defined as its state at 298 kelvin (K). Roentgenium is a solid at this temperature. Its melting point, boiling point, and density are unknown at this time. There is no confirmation yet regarding roentgenium’s appearance; however, it has been placed beneath copper, silver, and gold within the periodic table. Chemists have ventured some predictions about its properties; they have suggested that if roentgenium is ever seen, it will possibly appear silver in color and will be very unreactive. The oxidation states of roentgenium are predicted to be +3 and +5.

Chemical Properties

Roentgenium is a synthetically produced, highly radioactive element. Due to its location in the periodic table, its chemical properties are presumed to be similar to those of gold. Its most stable isotope is roentgenium-281, which has a half-life of roughly twenty-six seconds. The isotope decays through spontaneous fission. Spontaneous fission is a type of radioactive decay that takes place in elements with mass number of 230 or more. In this type of decay, the nucleus of an unstable atom splits into two nuclei of the same size.

Another isotope (namely, roentgenium-272) decays through alpha decay to form the atoms of the elements with atomic numbers 109, 107, 105, and 103 during the decay series (that is, meitnerium, bohrium, dubnium and lawrencium, respectively. After additional decay, roetgenium-272 is found to decay to the element with atomic number 101 (that is, mendelevium-252). Furthermore, when researchers created element 115 in 2004, they found roentgenium-280, which has a half-life of about 3.6 seconds, in element 115’s decay sequence.

Applications

Given the extremely short half-life of roentgenium, it is very difficult to study its characteristics. Only a few atoms have ever been produced. There are, therefore, no applications of roentgenium outside of fundamental research. Moreover, according to many scientists, roentgenium is most likely a very precious metal, although it exists for only a few seconds.

Roentgenium has a very short half-life. When enriched with gold (chemical symbol Au), its half-life increases exponentially. A study reviewed the effects of enrichment of heavy elements, mainly roentgenium, on natural gold. The study concluded that it is possible to augment roentgenium with purified gold by vaporizing the gold in a vacuum at about 63^ºC over its melting point.

Bibliography

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Greenwood, Norman N, and Alan Earnshaw. Chemistry of the Elements. 2nd ed. Portsmouth: Butterworth-Heinemann, 1997. Print.

Marinov, A., et al. "Enrichment of the Superheavy Element Roentgenium (Rg) in Natural Au." International Journal Of Modern Physics E: 20.11 (2011): 2391-401. Web. 5 Feb. 2016.

"Roentgenium." Questia. The Columbia University Press, n.d. Web. 5 Feb. 2016.

"Roentgenium." Periodic Table. Royal Society of Chemistry, n.d. Web. 4 Feb. 2016.

"Spontaneous Fission." Encyclopaedia Britannica. Encyclopaedia Britannica Inc., n.d. Web. 7 Feb, 2016.