|Name, Symbol, Number||Ruthenium, Ru, 44|
|Chemical series||transition metals|
|Group, Period, Block||8, 5, d|
|Appearance||silvery white metallic
|Atomic mass||101.07(2) g/mol|
|Electron configuration||[Kr] 4d7 5s1|
|Electrons per shell||2, 8, 18, 15, 1|
|Density (near r.t.)||12.45 g/cm³|
|Liquid density at m.p.||10.65 g/cm³|
|Melting point||2607 K
(2334 °C, 4233 °F)
|Boiling point||4423 K
(4150 °C, 7502 °F)
|Heat of fusion||38.59 kJ/mol|
|Heat of vaporization||591.6 kJ/mol|
|Heat capacity||(25 °C) 24.06 J/(mol·K)|
|Oxidation states||2, 3, 4, 6, 8
(mildly acidic oxide)
|Electronegativity||2.2 (Pauling scale)|
|Ionization energies||1st: 710.2 kJ/mol|
|2nd: 1620 kJ/mol|
|3rd: 2747 kJ/mol|
|Atomic radius||130 pm|
|Atomic radius (calc.)||178 pm|
|Covalent radius||126 pm|
|Electrical resistivity||(0 °C) 71 nΩ·m|
|Thermal conductivity||(300 K) 117 W/(m·K)|
|Thermal expansion||(25 °C) 6.4 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 5970 m/s|
|Speed of sound (thin rod)||(r.t.) 447 m/s|
|Shear modulus||173 GPa|
|Bulk modulus||220 GPa|
|Brinell hardness||2160 MPa|
|CAS registry number||7440-18-8|
Ruthenium (chemical symbol Ru, atomic number 44) is a rare, hard, white metal. It is a member of the platinum group of elements and is found associated with platinum ores. Chemically, it is relatively inert.
This element is a highly effective hardener and wear-resistant agent in alloys with platinum and other metals. Such alloys are used to make electrical contacts and fountain pen nibs. It is sometimes alloyed with gold in jewelry. In addition, ruthenium, its inorganic compounds, and organometallic complexes are versatile catalysts for diverse chemical reactions.
This element is generally found in ores with the other platinum group metals in the Ural Mountains of western Russia and in parts of North and South America. Small but commercially important quantities are also found in the mineral pentlandite (iron-nickel sulfide) extracted from Sudbury, Ontario (Canada), and in deposits of pyroxenite rock (containing silicate minerals) in South Africa.
This metal is commercially isolated through a complex chemical process in which hydrogen is used to reduce ammonium ruthenium chloride, yielding a powder. The powder is then consolidated by powder metallurgy techniques or by argon-arc welding.
It is also possible to extract ruthenium from spent nuclear fuel, which contains an average of two kilograms of ruthenium per metric ton. Ruthenium produced in such a way contains radioactive isotopes, some with a half-life of up to 373.59 days. Therefore this ruthenium has to be stored for at least ten years in a secured area to allow it to become stable.
Jöns Berzelius and Gottfried Osann nearly discovered ruthenium in 1827. They obtained crude platinum (from alluvial deposits in the Ural Mountains), treated it with aqua regia (a 3:1 mixture of concentrated hydrochloric acid and nitric acid), and examined the insoluble residues. Berzelius did not detect any unusual elements, but Osann thought he found three new metals and named them pluran, ruthen, and polin.
Later, in 1844, Karl Klaus demonstrated that Osann had obtained impure ruthenium oxide and went on to isolate the new element from platinum ore. For his work, Klaus is generally credited as the discoverer of ruthenium. Klaus named the element after Ruthenia, a latinized name for Russia, in recognition of the work of Osann and in honor of his own birthland—Klaus was born in Tartu, which was then a part of the Russian Empire.
It is also possible that Polish chemist Jedrzej Sniadecki isolated this element from platinum ores in 1807. He called it vestium. His work, however, was never confirmed and he later withdrew his discovery claim.
Ruthenium is classified as a transition metal. In the periodic table, it lies in period five just ahead of rhodium and palladium and is closely related to the latter two elements. In addition, it is situated in group eight (former group 8B), between iron and osmium.
A hard, white metal, ruthenium does not tarnish at normal temperatures, but under certain conditions it oxidizes explosively. It has four crystal modifications. It is a member of the platinum group and is relatively inert. It is not attacked by acids but dissolves in fused (molten) alkalis. Halogens can attack it at high temperatures. Small amounts of ruthenium can increase the hardness of platinum and palladium. Also, the corrosion resistance of titanium can be increased markedly by adding a small amount of ruthenium.
This metal can be plated by either electrodeposition or thermal decomposition methods. An alloy of ruthenium and molybdenum has been found to be superconductive at 10.6 K. The oxidation states of ruthenium range from +1 to +8, and -2 is known, but the most common oxidation states are +2, +3, and +4.
Seven stable isotopes of ruthenium have been found in nature: 96Ru, 98Ru, 99Ru, 100Ru, 101Ru, 102Ru, and 104Ru. Among the radioactive isotopes, the three with the longest half-lives are: 106Ru, with a half-life of 373.59 days; 103Ru, with a half-life of 39.26 days; and 97Ru, with a half-life of 2.9 days. Many other radioactive isotopes are known, with atomic mass numbers ranging from 87 to 120, but their half-lives are much shorter.
The ruthenium organometallic compound easiest to make is RuHCl(CO)(PPh3)3. This compound has two forms (yellow and pink) that are identical when in solution but different in the solid state.
Grubbs' catalyst and Roper's complex are two of the important organometallic catalysts based on ruthenium. Another organometallic compound, called bis(2,4-dimethylpentadienyl)ruthenium, can be readily synthesized at high yields and can be used for the vapor-phase deposition of metallic ruthenium and to catalyze chemical reactions.
Ruthenium plays no known biological role but it strongly stains human skin. It may be carcinogenic and may bioaccumulate in bone. The compound ruthenium tetroxide (RuO4), similar to osmium tetroxide, is highly toxic and may explode.
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