Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chemicals. Karl Ernst Claus, a Russian scientist of Baltic-German ancestry, discovered the element in 1844 at Kazan State University and named it in honor of Russia, using the Latin name Ruthenia. Ruthenium is usually found as a minor component of platinum ores; the annual production has risen from about 19 tonnes in 2009 to 35.5 tonnes in 2017. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. A minor application for ruthenium is in platinum alloys and as a chemical catalyst. A new application of ruthenium is as the capping layer for extreme-ultraviolet photomasks in semiconductor lithography. Ruthenium is generally found in ores with the other platinum-group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, and in pyroxenite deposits in South Africa.
Characteristics
Physical properties
Ruthenium, a polyvalent hard white metal, is a member of the platinum group and is in group 8 of the periodic table:
While other group 8 elements have two electrons in the outermost shell, in ruthenium the outermost shell has only one electron (the final electron is in a lower shell). This anomaly, which has no effect on chemical properties, is also observed in all other elements (except technetium) in the range of Z = 41–45.
Chemical properties Ruthenium has four crystal modifications and does not tarnish at ambient conditions; it oxidizes upon heating to 800 °C (1,070 K). Ruthenium dissolves in fused alkalis to give ruthenates (RuO42−). It is not attacked by acids (even aqua regia) but is attacked by sodium hypochlorite at room temperature, and halogens at high temperatures. Ruthenium is most readily attacked by oxidizing agents. Small amounts of ruthenium can increase the hardness of platinum and palladium. The corrosion resistance of titanium is increased markedly by the addition of a small amount of ruthenium. The metal can be plated by electroplating and by thermal decomposition. A ruthenium–molybdenum alloy is known to be superconductive at temperatures below 10.6 K. Ruthenium is the only 4d transition metal that can assume the oxidation state +8, and even then it is less stable there than the heavier congener osmium: this is the first group from the left of the table where the second- and third-row transition metals display notable differences in chemical behavior. Like iron but unlike osmium, ruthenium can form aqueous cations in its lower oxidation +2 and +3 states. Ruthenium is the first in a downward trend in the melting and boiling points and atomization enthalpy in the 4d transition metals after the maximum seen at molybdenum, because the 4d subshell is more than half full and the electrons are contributing less to metallic bonding. (Technetium, the previous element, has an exceptionally low value that is off the trend due to its half-filled [Kr]4d55s2 configuration, though it is not as far off the trend in the 4d series as manganese in the 3d transition series.) Unlike its lighter congener iron, ruthenium is mainly paramagnetic at room temperature. However, the metastable tetragonal phase of ruthenium, created as a thin film on single-crystal Mo, is ferromagnetic at room temperature. The reduction potentials in acidic aqueous solution for some common ruthenium species are shown below:
Isotopes
Naturally occurring ruthenium is composed of seven stable isotopes: 96, 98–102, 104. Additionally, 34 synthetic radioactive isotopes have been discovered. Of these radioisotopes, the most stable are 106Ru with a half-life of 371.8 days, 103Ru with a half-life of 39.245 days, and 97Ru with a half-life of 2.837 days. Fifteen other radioisotopes have been characterized, ranging from 85Ru to 125Ru. Most of these have half-lives that are less than 5 minutes; the exceptions are 94Ru (51.8 minutes), 95Ru (1.607 hours), and 105Ru (4.44 hours). The primary decay mode for isotopes lighter than the most abundant isotope, 102Ru, is electron capture to produce technetium, while the primary mode for heavier isotopes is beta emission to rhodium. 106Ru is a fission product of uranium or plutonium. High concentrations of this isotope detected in the atmosphere over Europe were associated with an alleged undeclared nuclear accident in Russia in 2017.
Occurrence
Ruthenium is found in about 100 parts per trillion in the Earth's crust, making it the 78th most abundant element. It is generally found in ores with the other platinum-group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, Canada, and in pyroxenite deposits in South Africa. The native form of ruthenium is a very rare mineral (Ir replaces part of Ru in its structure).
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