Ruthenium is the chemical element with symbol Ru and atomic number 44. It is a rare, hard, silvery member of the platinum-group metals. Ruthenium is valued for catalysis, electrical contacts, chip resistors, electrochemical coatings and its ability to harden platinum and palladium alloys.
Ruthenium quick facts
| Property | Value |
| Symbol | Ru |
| Atomic number | 44 |
| Relative atomic mass | 101.07 |
| Group | 8 |
| Period | 5 |
| Block | d-block |
| Density | 12.1 g/cm³ |
| Melting point | 2333°C |
| Boiling point | 4147°C |
| Electron configuration | [Kr] 4d⁷ 5s¹ |
| Common oxidation states | +2, +3, +4 |
| CAS number | 7440-18-8 |
| Key natural isotopes | ¹⁰¹Ru, ¹⁰²Ru, ¹⁰⁴Ru |
Position and chemistry
Ruthenium is in group 8, period 5 and the d-block. Its electron configuration is [Kr] 4d⁷ 5s¹. Ruthenium supports many oxidation states and rich coordination chemistry, which contributes to its usefulness as a catalyst.
See the complete CleverlySmart periodic table.
Physical properties
Ruthenium is hard, brittle, corrosion-resistant and has a high melting point. It is one of the rarest platinum-group metals and usually occurs together with platinum, palladium, osmium, iridium and rhodium rather than in concentrated standalone deposits.
Important ruthenium compounds
- Ruthenium dioxide (RuO₂): an electrically conductive oxide used in electrodes, resistors and electrochemical coatings.
- Ruthenium tetroxide (RuO₄): a volatile, powerful oxidising compound that is highly hazardous.
- Ruthenium coordination complexes: widely studied in homogeneous catalysis, photochemistry, solar-energy research and medicinal chemistry.
Occurrence and production
Ruthenium occurs in platinum-group mineral deposits and in some nickel and copper ores. It is generally recovered as a by-product during the refining of platinum-group metals or nickel. Separation is challenging because the platinum-group elements have related chemical behaviour.
Uses of ruthenium
- Electronics: ruthenium compounds and films are used in chip resistors, electrical contacts and specialised semiconductor processes.
- Electrochemical electrodes: RuO₂-containing coatings are used on durable anodes for chlorine production and other electrochemical processes.
- Catalysts: ruthenium compounds catalyse hydrogenation, oxidation, ammonia-related processes and many organic reactions.
- Alloys: small amounts harden platinum and palladium and improve wear resistance in contacts and jewellery alloys.
- Energy research: ruthenium complexes have been studied for dye-sensitised solar cells and photochemical water-splitting systems.
Ruthenium isotopes
Natural ruthenium contains seven stable isotopes, including ⁹⁶Ru, ⁹⁸Ru, ⁹⁹Ru, ¹⁰⁰Ru, ¹⁰¹Ru, ¹⁰²Ru and ¹⁰⁴Ru. Radioactive ruthenium isotopes are also produced in nuclear fission and are relevant to nuclear-waste and environmental monitoring.
For broader isotope data, see the CleverlySmart isotope table.
Biological role and safety
Ruthenium has no known essential biological role. Metallic ruthenium is relatively inert, but some compounds are hazardous. Ruthenium tetroxide is particularly dangerous because it is volatile, strongly oxidising and toxic.
Discovery and name
Ruthenium was definitively isolated and characterised in 1844 by Karl Ernst Claus. The name comes from Ruthenia, a Latin name associated with Russia.
Frequently asked questions
Is ruthenium a precious metal?
It is a platinum-group metal and is rare and valuable, although market terminology and pricing differ from gold, silver, platinum and palladium.
Why is ruthenium useful as a catalyst?
Its multiple oxidation states and flexible coordination chemistry allow ruthenium complexes to facilitate many bond-breaking and bond-forming reactions.
Ruthenium in catalysis and electronics
Ruthenium is a versatile platinum-group metal used in both homogeneous and heterogeneous catalysis. Ruthenium complexes are central to important reactions such as olefin metathesis, while supported ruthenium catalysts are studied for hydrogenation, ammonia chemistry and energy applications.
Ruthenium dioxide (RuO₂) is electrically conductive and chemically robust. It is used in specialised electrodes, thick-film resistors and electrochemical devices. Thin ruthenium layers are also important in some semiconductor and data-storage technologies.
Hardening platinum-group alloys
Small amounts of ruthenium can harden platinum and palladium alloys, improving wear resistance for electrical contacts and other precision components. As with other platinum-group metals, commercial ruthenium is usually recovered as a by-product during nickel, copper and platinum refining.
Frequently asked questions
Is ruthenium rarer than gold?
Yes. Ruthenium is much less abundant in Earth’s crust and is produced in far smaller quantities.
Are ruthenium compounds hazardous?
Hazards depend on the compound. Ruthenium tetroxide, for example, is volatile, strongly oxidising and particularly dangerous, while many other ruthenium materials are less reactive.
