44 Ru Ruthenium 101.07
Transition metal d-block Period 5 Group 8

Ruthenium

Ru · Element 44 · Transition metal

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A platinum-group metal that hardens its neighbours and catalyses ammonia synthesis.

State at 20°C Solid
Atomic mass 101.07 u
Electron configuration[Kr] 4d⁷ 5s¹
43Tc All 118 45Rh

Structure

The ruthenium atom

Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.

Orbital cloud

Measured values

Property sheet

Every bar shows where ruthenium sits among all 118 elements for that property.

Physical

Density 12.45 g/cm³ 74%
Melting point 2607 K 93%
Boiling point 4423 K 89%
Specific heat 0.238 J/g·K
Thermal conductivity 117 W/m·K 85%

Atomic

Atomic radius 134 pm 21%
Covalent radius 146 pm
Van der Waals radius 207 pm

Electronic

Electronegativity 2.2 78%
Ionisation energy 710.1 kJ/mol 52%
Electron affinity 101.3 kJ/mol 68%

Occurrence

Abundance in crust 0.001 mg/kg 32%

Identity

SymbolRu
Atomic number44
Atomic mass101.07 u
CategoryTransition metal
Blockd
Crystal structurehexagonal close-packed
Oxidation states-2, 0, +1, +2, +3, +4, +5, +6, +7, +8
Discovered1844
Discovered byKarl Ernst Klaus

Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.

Same element, different neutrons

Isotopes of ruthenium

All ruthenium atoms have the same number of protons, 44, and differ only in their number of neutrons: those variants are its isotopes. The most common, Ru-102, has 58 neutrons and makes up 31.55% of natural ruthenium.

Isotopes of ruthenium found in nature, with their share of the natural element, and well-known radioactive ones
ISOTOPE Neutrons Natural Abundance Half-life Decay Mode
Ru-96 52 5.54% Stable —
Ru-98 54 1.87% Stable —
Ru-99 55 12.76% Stable —
Ru-100 56 12.60% Stable —
Ru-101 57 17.06% Stable —
Ru-102 most common 58 31.55% Stable —
Ru-104 60 18.62% Stable —
Ru-106 62 — 371.8 days β⁻

The classroom shortcut, rounded atomic mass minus atomic number, gives 57 for ruthenium, but the most common ruthenium atom has 58 neutrons: the atomic mass, 101.07, is an average over all natural isotopes.

Decay modes

β⁻
beta-minus decay

Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.

Size, to scale

How big is a ruthenium atom?

Radius 134 pm — that is 0.134 nm, so about 3.73 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Ruthenium is liquid over a 1816 K window, from 2607 K to 4423 K.

Where it sits

Position in the table

Ruthenium sits in period 5, group 8. Everything in group 8 shares the same outer-electron count, which is why they behave so similarly.

Other transition metals

21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 39Y 40Zr 41Nb 42Mo 43Tc 45Rh
All transition metals

The story

What ruthenium is, and how we found it

Ruthenium (Ru) is element 44, a hard, brittle, silvery-white metal and one of the six platinum group metals, with rhodium, palladium, osmium, iridium and platinum. It sits in group 8, below iron. It melts at 2,334 °C (2,607 K) and has a density of 12.45 g/cm³. At room temperature ruthenium resists acids, even aqua regia, but it is attacked by molten alkalis with oxidizers.

Atomic structure and isotopes

Ruthenium has 44 electrons in five shells, arranged 2, 8, 18, 15, 1, with the configuration [Kr] 4d⁷ 5s¹. It shows more oxidation states than most elements, up to +8 in ruthenium tetroxide; the most common are +2, +3 and +4.

Natural ruthenium is a mix of seven stable isotopes, the most abundant being ruthenium-102, at about 32%. The radioactive isotope ruthenium-106, with a half-life of about one year, is a product of uranium fission.

The discovery of ruthenium

Claims from platinum residues

In 1808 the Polish chemist Jędrzej Śniadecki reported a new metal, which he called vestium, in South American platinum ore, and in 1828 Gottfried Osann in Tartu reported ruthenium and other new metals in platinum from the Urals. Neither claim could be confirmed.

Klaus identifies ruthenium (1844)

In 1844 Karl Ernst Klaus (also written Claus), a professor at Kazan University, worked through the residues left after platinum was extracted from Ural ore. He isolated a new metal, showed that it was distinct from the known platinum metals, and kept Osann's name ruthenium, from Ruthenia, the Latin name for the Rus' lands (Russia).

The last platinum metal

Ruthenium was the last of the six platinum group metals to be identified, about 40 years after palladium, rhodium, osmium and iridium.

Applications

What ruthenium is used for

Electronics

  • Chip resistors: thick-film resistors made with ruthenium dioxide are found on almost every circuit board.
  • Hard disk drives: a very thin ruthenium layer in the recording media helps store data at high density.
  • Contacts and chips: ruthenium plates electrical contacts, and chip makers are adopting it for the finest wiring layers of advanced processors.

Chemistry and industry

  • Chlorine production: titanium electrodes coated with ruthenium and titanium oxides are the standard anodes for making chlorine and caustic soda from brine.
  • Catalysts: ruthenium catalysts are used in some ammonia plants, in hydrogenation, and in olefin metathesis, the reaction of the Grubbs catalysts recognized by the 2005 Nobel Prize in Chemistry.

Alloys

Small additions of ruthenium harden platinum and palladium for jewelry and electrical contacts, improve the corrosion resistance of titanium, and strengthen some nickel superalloys used for jet engine turbine blades.

In everyday life

Ruthenium is hidden inside electronics, in the chip resistors on circuit boards and in hard disk drives. It also appears in jewelry, as a hardener in platinum alloys and as a dark gray plating, and in the hard tips of some fountain pen nibs.

Where it comes from

Natural occurrence

0.001 mg/kg of Earth's crust · more abundant than 32% of elements

Abundance

Ruthenium is one of the rarest elements in Earth's crust, at about 0.001 parts per million. It occurs in natural alloys with the other platinum group metals and in rare minerals such as laurite (ruthenium sulfide).

Production

Ruthenium is recovered as a byproduct of platinum and nickel refining. Most comes from the Bushveld Complex in South Africa, with smaller amounts from Russia, Zimbabwe and Canada. Annual production is only a few tens of tonnes.

Handling

Safety

Health hazards

Ruthenium metal is inert and of low toxicity. The danger is ruthenium tetroxide (RuO₄), a volatile, highly toxic and strongly oxidizing compound that can form when ruthenium or its compounds meet strong oxidizers. Its vapor damages the eyes and lungs, and it can explode on contact with organic matter.

Other hazards

Many ruthenium compounds stain the skin and are irritants. Radioactive ruthenium-106 from nuclear fuel reprocessing is a radiation hazard; in 2017 traces of it were detected in the air across Europe, from an unreported release that investigators traced to the southern Urals.

Safe handling

  • Handle ruthenium compounds and powders in a fume hood, with gloves and eye protection.
  • Keep ruthenium away from strong oxidizers such as hypochlorite, permanganate and periodate, which can generate the tetroxide.

Keep exploring

Use ruthenium in the tools

Quick answers

Ruthenium: common questions

What is ruthenium?

Ruthenium (symbol Ru) is element 44 on the periodic table, a transition metal in period 5, group 8. A platinum-group metal that hardens its neighbours and catalyses ammonia synthesis. At room temperature it is a solid.

What is the electron configuration of ruthenium?

Ruthenium's ground-state electron configuration is [Kr] 4d⁷ 5s¹, giving 5 occupied shells with the distribution 2, 8, 18, 15, 1.

What are the melting and boiling points of ruthenium?

Ruthenium melts at 2607 K (2333.9 °C) and boils at 4423 K (4149.9 °C). That puts it among the most refractory elements — it stays solid at temperatures that vaporise most metals.

What is the atomic mass of ruthenium?

The standard atomic weight of ruthenium is 101.07 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How many neutrons does ruthenium have?

The most common ruthenium atom, Ru-102, has 58 neutrons: its mass number, 102, minus its atomic number, 44. It makes up 31.55% of natural ruthenium. The classroom shortcut, rounded atomic mass (101.07) minus atomic number, gives 57 instead, because the atomic mass is an average over all natural isotopes of ruthenium.

How dense is ruthenium?

Ruthenium has a density of 12.45 g/cm³. Water is 1.0 g/cm³, so a block of ruthenium is about 12.5× heavier.

What is the electronegativity of ruthenium?

Ruthenium has a Pauling electronegativity of 2.2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.

Who discovered ruthenium, and when?

Ruthenium was discovered in 1844 by Karl Ernst Klaus. Origin of the name: Latin Ruthenia, Russia.

How common is ruthenium on Earth?

Ruthenium makes up about 0.001 mg/kg of the Earth's crust — genuinely rare, which is why it is expensive.

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