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44 technetiumRutheniumrhodium


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
Physical properties
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)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2588 2811 3087 3424 3845 4388
Atomic properties
Crystal structure hexagonal
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
Poisson ratio 0.30
Mohs hardness 6.5
Brinell hardness 2160 MPa
CAS registry number 7440-18-8
Notable isotopes
Main article: Isotopes of ruthenium
iso NA half-life DM DE (MeV) DP
96Ru 5.52% Ru is stable with 52 neutrons
97Ru syn 2.9 d ε - 97Tc
γ 0.215, 0.324 -
98Ru 1.88% Ru is stable with 54 neutrons
99Ru 12.7% Ru is stable with 55 neutrons
100Ru 12.6% Ru is stable with 56 neutrons
101Ru 17.0% Ru is stable with 57 neutrons
102Ru 31.6% Ru is stable with 58 neutrons
103Ru syn 39.26 d β- 0.226 103Rh
γ 0.497 -
104Ru 18.7% Ru is stable with 60 neutrons
106Ru syn 373.59 d β- 0.039 106Rh

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.


Occurrence and isolation

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.

Notable characteristics

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.


  • Ruthenium is a highly effective hardener in alloys with platinum and palladium, and such alloys are used to make electrical contacts that are resistant to severe wear.
  • 0.1 percent ruthenium is added to titanium to improve its corrosion resistance a hundredfold.
  • For wear resistance, fountain pen nibs are often tipped with alloys containing ruthenium. For instance, from 1944 onward, the famous Parker 51 fountain pen was outfitted with the "RU" nib, a 14-carat gold nib tipped with 96.2% percent ruthenium, 3.8 percent iridium.
  • Ruthenium and its compounds are versatile catalysts. For instance, hydrogen sulfide (H2S) can be split by light in the presence of an aqueous suspension of cadmium sulfide (CdS) particles loaded with ruthenium dioxide. This may be a useful method of removing H2S from oil refining and other industrial processes.
  • Organometallic complexes of ruthenium (carbene and allenylidene complexes) have recently been found as highly efficient catalysts for certain chemical reactions (called olefin metathesis) that have important applications in organic and pharmaceutical chemistry.
  • Recently, large organometallic complexes of ruthenium have been found to exhibit anti-tumor activity, and a new group of anti-cancer medicines is now in the stage of clinical trials.
  • Ruthenium red, [(NH3)5Ru-O-Ru(NH3)4-O-Ru(NH3)5]6+, is a biological stain used to visualize polyanionic areas of membranes.
  • Some ruthenium complexes absorb light throughout the visible spectrum and are being actively studied for their potential in solar energy technologies.
  • Ruthenium may also be used in advanced, high-temperature, single-crystal superalloys, with applications that include the turbine blades of jet engines.


  • Ruthenium(III) chloride or ruthenium trichloride (RuCl3): This compound can be found in the anhydrous and hydrated forms, both of which are dark brown or black solids. The name "ruthenium(III) chloride" more commonly refers to the hydrate, RuCl3xH2O (where x may vary but usually equals three). The hydrate is a commonly used starting material for many hundreds of chemical compounds.
  • Ruthenium tetroxide (RuO4): This is a yellow, diamagnetic substance made up of molecules that are tetrahedral in shape. It is quite volatile, as expected for a small, electrically neutral, symmetrical oxide. It can oxidize virtually any hydrocarbon. It is used in organic syntheses to oxidize alkynes to 1,2-diketones and primary alcohols to carboxylic acids. RuO4 is highly toxic and readily explodes at slightly elevated temperatures. For this reason, most laboratories do not synthesize it directly but use an anionic derivative from a salt of "TPAP" [tetrapropylammonium perruthenate (Pr4N+ RuO4-)].

Organometallic compounds

Ruthenium readily forms organometallic compounds in which its atoms are directly bonded to carbon atoms. These compounds tend to be darker in color and react more quickly than osmium compounds.

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.

See also


  • Canterford, J.H., and R. Colton. 1968. Halides of the Second and Third Row Transition Metals. London: Wiley-Interscience.
  • Chang, Raymond. Chemistry, 9th ed. New York: McGraw-Hill Science/Engineering/Math, 2006. ISBN 0073221031
  • Cotton, F. Albert and Wilkinson, Geoffrey. 1980. Advanced Inorganic Chemistry, 4th ed. New York: Wiley. ISBN 0-471-02775-8
  • Cotton, S.A. 1997. Chemistry of the Precious Metals. Chapman & Hall. ISBN 0-7514-0413-6
  • Greenwood, N.N. and Earnshaw, A. 1998. Chemistry of the Elements, 2nd Edition. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
  • Ruthenium Los Alamos National Laboratory. Retrieved December 7, 2007.

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