Atomic number 44

Ruthenium

Ru
+ phase
− phase

Shells Orbitals 4d 5s

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44 electrons in 5 shells: 2, 8, 18, 15, 1.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 5
Group: 8
Block: d
Standard atomic weight: 101.07(2) Da
Electron configuration: [Kr] 4d⁷ 5s¹
Phase at 25 °C: solid
Melting point: 2334 °C
Boiling point: 4150 °C
Density: 12.1 g/cm³
Electronegativity (Pauling): 2.2
Discovered: 1844, Karl Karlovich Klaus

Neighbours in the table

Tc Rh

Ruthenium entered chemistry as a mistake that turned out half right. In 1827, Los Alamos reports, Berzelius and Gottfried Osann studied what was left after crude platinum from the Ural mountains dissolved in the acid mixture aqua regia. Berzelius saw nothing unusual, but Osann announced three new metals and called one of them ruthenium; IUPAC’s atomic-weights commission (CIAAW) dates his claim to 1828. In 1844 Karl Karlovich Klaus found Osann’s oxide badly impure, with a new metal inside it. Klaus drew 6 g of it from the part of the ore that aqua regia would not dissolve.

Ruthenium’s configuration, [Kr] 4d⁷ 5s¹, sets seven 4d electrons and a single 5s electron outside a krypton core, for shells of 2, 8, 18, 15 and 1. Such irregularities come, Chem1 explains, from the very small energy differences between some orbitals, which can let their usual order reverse. In that account, d electrons let transition metals take several valences. Los Alamos lists oxidation states, bookkeeping numbers counted as if each bond were ionic, from −4 to +8. At least eight have turned up in compounds, with +2, +3 and +4 the usual ones.

Where it is found

Jefferson Lab estimates ruthenium at 1 × 10⁻³ milligrams per kilogram of Earth’s crust and 7 × 10⁻⁷ milligrams per litre of seawater. Los Alamos finds the metal native, as uncombined metal, mixed with the other platinum metals, in ores from the Urals and from North and South America. Small but commercial amounts also sit in the mineral pentlandite from the nickel-mining district around Sudbury, Ontario, and in deposits in South Africa.

Most ruthenium is a byproduct of mining and refining platinum, Jefferson Lab says, with more coming out of Sudbury’s nickel operations. Commercial isolation is a complex chemical process. Its final step reduces ammonium ruthenium chloride with hydrogen and leaves a powder, which is then made into solid metal by powder metallurgy or by argon-arc welding.

South Africa leads the world in mined material containing the platinum-group metals, according to the US Geological Survey, and holds 63,000,000 kilograms of the group’s reserves. American imports of ruthenium ran at 18,000 kilograms in 2021 and fell to an estimated 10,000 kilograms in 2024.

Why it matters

A trace of ruthenium changes titanium. Adding 0.1 per cent of it improves the corrosion resistance of titanium a hundredfold, Los Alamos reports. Alloying is the element’s main use, Jefferson Lab says. Los Alamos counts ruthenium among the most effective hardening additions to platinum and palladium. Those hardened alloys become electrical contacts built for severe wear, and they also go into jewellery.

The metal is a versatile catalyst, Los Alamos says: a substance that speeds a reaction without being used up. One example uses light: in water, cadmium sulfide particles carrying ruthenium dioxide split hydrogen sulfide, H₂S. Los Alamos suggests this might one day help remove H₂S from oil refining. A ruthenium–molybdenum alloy is said to become superconducting, carrying current with no electrical resistance, at 10.6 K, about −263 °C.

The isotopes carry their own uses. Radioactive ruthenium-106 treats melanoma of the eye, Los Alamos notes. Stable ruthenium-100 forms through the double beta decay of molybdenum-100, a rare, very slow decay with a half-life of 7.1 × 10¹⁸ years. That half-life can put a ceiling on the mass of the electron neutrino, a neutral, weakly interacting subatomic particle, IUPAC’s isotope notes say. Ruthenium-104 serves as the target for making rhodium-105, a radioisotope with a half-life of about 35 hours.

Properties

Properties of ruthenium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	44
Standard atomic weight	101.07(2) Da	Da	IUPAC/CIAAW 2024
Melting point	2334 °C	°C	Los Alamos: 2334 °C
Boiling point	4150 °C	°C	Los Alamos: 4150 °C
Density	12.1 g/cm³	g/cm³
Electronegativity (Pauling)	2.2
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁷
Phase at 25 °C	solid

Safety

Metallic ruthenium is generally nontoxic, Haz-Map says in PubChem’s safety record, but it is not free of hazard. Among the company reports to the European Chemicals Agency that give a hazard classification, about half class the element as a flammable solid, signal word Danger. Some add long-lasting harm to aquatic life. Haz-Map also records allergic reactions to the platinum-group metals in susceptible people. Fuller detail on its classification sits in the PubChem Laboratory Chemical Safety Summary for ruthenium.

Questions

Where does the name ruthenium come from?

From Ruthenia, the Latin name for Russia, on Los Alamos's page; IUPAC's atomic-weights commission (CIAAW) calls it the old name of Russia. Gottfried Osann thought his sample held three new metals, pluranium, ruthenium and polinium, according to CIAAW, but the sample was impure. The Polish chemist Jedrzej Sniadecki had produced ruthenium in 1807 but withdrew his claim when others could not repeat his results, Jefferson Lab records. Karl Karlovich Klaus discovered it in 1844.

How many stable isotopes does ruthenium have?

Seven, in Jefferson Lab's count, with mass numbers 96, 98 to 102, and 104 in IUPAC's isotope notes. Ruthenium-102 is the most common, at 31.55 per cent of the natural element in the abundances of IUPAC's atomic-weights commission (CIAAW). Ruthenium and molybdenum in Earth's silicates lie on the same isotopic mixing line as most meteorites, IUPAC notes. That supports the idea that Earth was built from material of one unchanging isotopic mix.

How is ruthenium used to treat eye cancer?

Through its radioactive isotope ruthenium-106. Plaque brachytherapy, a small radiation source held against the eye, uses it to control uveal melanoma, a tumour of the eye's middle layer, while keeping the eye, IUPAC's isotope notes say. The IAEA's evaluation gives ruthenium-106 a half-life of 371.8 days, with every decay a beta-minus emission.

Is ruthenium metal toxic?

Haz-Map, in PubChem's safety record, calls the platinum-group metals generally nontoxic in the metallic state, though susceptible people can develop allergic reactions to them. The hazard classification is mixed: of the company reports to the European Chemicals Agency that give hazard codes, 49.9% list it as a flammable solid, while 120 of all 455 reports (26.4%) find it meets no hazard criterion of the Globally Harmonized System (GHS). The details are in PubChem's Laboratory Chemical Safety Summary for ruthenium.