Ruthenium
Ruthenium is a chemical element with 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 inert to most other chemicals.
Identity
- Atomic mass
- 101.072 u
- Category
- Transition metals
- Group
- 8
- Period
- 5
- Block
- d
- Oxidation States
- +2, +3, +4, +6, +8
- Phase (25 °C)
- Solid
- Appearance
- silvery white metallic
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d7
- Short configuration
- [Kr] 4d7 5s1
- Electrons per shell
- 2, 8, 18, 15, 1
- Electronegativity (Pauling)
- 2.20
- Electron affinity
- 101 kJ/mol
- 1st ionization energy
- 710 kJ/mol
- Ionization energies
- 710 · 1620 · 2747 kJ/mol
Physical properties
- Melting point
- 2333.8 °C (2607 K)
- Boiling point
- 4149.9 °C (4423 K)
- Density
- 12.45 g/cm³
- Molar heat capacity
- 24.1 J/(mol·K)
Chemical behavior of ruthenium
Ruthenium is a group 8 transition metal with symbol Ru and atomic number 44. It is a hard silvery-white platinum-group metal, resistant to heat and corrosion. Its states range from +2 to +8, with +3 and +4 the most common; volatile RuO4 shows +8. It hardens platinum, catalyzes metathesis and serves electronics.
Reactivity
Ru + 3 Cl2 -> RuCl4
Ruthenium reacts with chlorine to form ruthenium tetrachloride, a bluish-gray solid that is one of its compounds.
Ru + 4 HNO3 -> RuO4 + 4 NO2 + H2O
Ruthenium reacts with concentrated nitric acid, releasing nitrogen dioxide and forming ruthenium tetroxide.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Ruthenium tetroxide | RuO4 | Orange solid; getter precursor and oxidizing agent |
| Ruthenium(III) chloride | RuCl3 | Bluish-gray solid; getter and reagents precursor |
| Ruthenium(II) chloride | RuCl2 | Reddish solid; getter precursor and used in organic synthesis |
Electron shell distribution
View in the atom builderIsotopes
Natural ruthenium has seven stable isotopes: ruthenium-102 (31.6 %), ruthenium-104 (18.6 %), ruthenium-101 (17.1 %), ruthenium-99 (12.8 %), ruthenium-100 (12.6 %), ruthenium-96 (5.5 %) and ruthenium-98 (1.9 %). Ruthenium-106, a fission product with ~374-day half-life, is used in eye-plaque radiotherapy.
Occurrence and production
Trace platinum-group element (ppb level) in cooperite, laurite and nickel-copper sulfide ores. Main supply is a by-product of platinum mining in South Africa and Russia, plus Canada and Zimbabwe, refined from anode slimes and residues.
History and origin of the name
Karl Ernst Claus isolated it in 1844 at Kazan from Ural platinum residues and named it from Ruthenia, Latin for Rus/Russia. Earlier claims by Berzelius and Osann had not held; Claus proved a distinct element and mapped its compounds.
Applications and relevance of ruthenium
Uses of the element
Hardens platinum and palladium for wear-resistant electrical contacts, pen nibs and jewelry. Thin films and alloys serve chip resistors, hard disks and chip interconnects needing stability.
Uses of its compounds
Complexes catalyze olefin metathesis for pharma and polymers; dioxide coats dimensionally stable anodes for chlorine; dyes sensitize experimental solar cells; tetroxide stains electron-microscopy specimens.
Health, safety and environment
Biological role
Ruthenium is not essential. Low-oxidation complexes are moderately toxic if ingested or inhaled; high-oxidation tetroxide is strongly irritant and volatile. No nutritional requirement; anticancer complexes remain experimental drugs.
Safety
Metal is stable, but RuO4 vapors attack eyes, skin and airways and can explode with organics. Handle chlorides and powders with ventilation, gloves and eye protection; store tetroxide cold, isolated and in tiny amounts.
Environment
Platinum-group mining carries land, water and energy costs. Ruthenium is scarce and persistent; recycling contacts, catalysts and electronic scrap cuts primary demand and dispersal.
Frequently asked questions about Ruthenium
Why did olefin-metathesis catalysts win a Nobel Prize?
Ruthenium carbenes reshuffle carbon-carbon double bonds cleanly to build pharma, polymer and fine-chemical molecules. Grubbs-type catalysts tolerate many groups and air better than early systems. Recognized with the 2005 chemistry Nobel shared for metathesis.
What does ruthenium oxide do in electrochemical technology?
Conductive RuO2-based coatings line anodes for chlorine production and other electrolysis, lowering overpotential and lasting in harsh brines. Related hydrous oxides show large capacitance studied for supercapacitors. Composition and microstructure set performance.
Is ruthenium studied against cancer?
Yes. Ruthenium complexes are tested as possible anticancer agents for distinct DNA and protein interactions versus platinum drugs. Lab activity is only a start: safety and efficacy need preclinical and clinical trials. None is a routine treatment.
Why is ruthenium tetroxide both useful and feared?
Volatile RuO4 strongly oxidizes and stains fatty tissue black, fixing microscopy samples crisply. Same volatility and oxidizing power make vapors fiercely irritant and risky with organics, so only trained labs use micro-amounts under containment.
Why is ruthenium used in electronics?
Metal and dioxide give conductive, stable thin films with tunable resistance. Found in chip resistors, contacts and microelectronic stacks. Wear resistance aids durability; cost and compatibility with neighbors decide each design.
Why add ruthenium to platinum alloys?
It raises hardness and wear resistance while keeping corrosion resistance. Useful for sliding electrical contacts, specialty parts and some jewelry. Proportion balances hardness, conductivity, workability and price.
What use does ruthenium have in solar cells?
Ruthenium bipyridyl-type dyes absorb visible light and inject electrons in dye-sensitized cells. Tunable chemistry made them research benchmarks. Commercial fate hinges on efficiency, stability, cost and rival photovoltaics.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.