Ruthenium Facts – Ru or Atomic Number 44

Ruthenium Facts

Ruthenium (Ru or atomic number 44) is a transition metal that belongs to the platinum group on the periodic table. It has remarkable hardness, resistance to corrosion, and versatility in various industrial applications. You encounter this element in daily life in electrical contacts and in certain pens.

Discovery, Naming, and Isolation

Ruthenium was discovered by Russian scientist Karl Ernst Claus in 1844 at Kazan State University. He named it after Ruthenia, the Latin name for Russia. However, there was some uncertainty surrounding its discovery. Polish chemist Jedrzej Sniadecki claimed to have discovered it in 1807 but later withdrew his claim due to inconclusive evidence.

Claus isolated ruthenium from platinum ore residues, a process that involved dissolving the ore in aqua regia, precipitating platinum and palladium, and then treating the remaining solution with ammonium chloride to precipitate ruthenium as ammonium ruthenium chloride. Finally, the ruthenium was reduced to its metallic form using hydrogen.

Allotropes, Appearance, and Properties

Ruthenium has a shiny, silvery-white appearance. It exists in several allotropes. The most stable allotrope at room temperature is the hexagonal close-packed (hcp) structure. It is a hard and brittle metal with a high melting point of 2334°C and a boiling point of 4150°C. However, ruthenium starts a downward trend in melting and boiling point in the 4d transition metals because its 4d subshell is more than half full. Because of this, electrons don’t participate in metallic bonding as readily as when the subshell is less than half full.

Like other platinum group metals, ruthenium is chemically inert and resists corrosion, even at high temperatures. It forms various oxidation states, with +2 and +4 being the most common. Ruthenium is the only 4d transition metal that displays the +8 oxidation state. It exhibits catalytic properties, particularly in the presence of hydrogen and oxygen.

Element Group and Period

Ruthenium is part of the platinum group metals (PGMs) in group 8 (VIII) of the periodic table, period 5. It is a d-block element with partially filled d-orbitals.


Natural ruthenium consists of seven stable isotopes: 96Ru, 98Ru, 99Ru, 100Ru, 101Ru, 102Ru, and 104Ru. The most abundant of these is 102Ru, accounting for 31.6% of the elements natural abundance.

There are also 34 synthetic radioisotopes. 106Ru is notable for its use in medical applications. This isotope also results from uranium or plutonium fission.

Abundance and Sources

Ruthenium is relatively rare, with an estimated abundance in the Earth’s crust of 0.001 ppm. It is primarily a byproduct of nickel and platinum mining, particularly from ores such as pentlandite. Major sources include:

  • South Africa: Largest producer of ruthenium, mainly from platinum ores.
  • Russia: Significant reserves in the Ural Mountains.
  • North America: Minor production in Canada.


Purification of ruthenium involves multiple steps:

  1. Dissolution in Aqua Regia: The acid dissolves platinum group metals so they can be isolated.
  2. Precipitation with Ammonium Chloride: Ruthenium precipitates out as ammonium ruthenium chloride.
  3. Reduction: Reducing the chloride with hydrogen gas yields pure ruthenium metal.

Uses of Ruthenium

Ruthenium’s applications are diverse, ranging from electronics to catalysis.

  • Electroplating: Historically important for electroplating electrical contacts to enhance durability.
  • Alloys: Combines with platinum to improve hardness and corrosion resistance.
  • Stains: The compound ruthenium red is a biological stain for pectin and mucopolysaccharides. Ruthenium tetroxide reacts with fats and exposes latent fingerprints.
  • Electronics: In chip resistors and electrical contacts due to its excellent conductive properties.
  • Catalysis: Acts as a catalyst in chemical reactions, including ammonia synthesis and hydrogenation processes.
  • Pens: Some fountain pen nibs use ruthenium-iridium alloys.
  • Medicine: 106Ru finds use in radiation therapy for eye tumors.
  • Solar Cells: Ruthenium complexes increase efficiency in dye-sensitized solar cells.

Biological Role, Health Effects, and Toxicity

Ruthenium has no known essential biological role in humans. However, it has potential therapeutic uses, particularly in cancer treatment. Some ruthenium compounds are toxic if inhaled or ingested in large amounts, causing respiratory and skin irritation. Ruthenium does not pose a significant environmental threat, but it accumulates in organisms over time.

Key Ruthenium Facts for Scientists

Atomic Number44
Atomic Weight101.07
Group8 (VIII)
Electron Configuration[Kr] 4d7 5s1
Electrons per Shell2, 8, 18, 15, 1
State at Room TemperatureSolid
Melting Point2334°C
Boiling Point4150°C
Density12.36 g/cm³
Heat of Fusion38.59 kJ/mol
Heat of Vaporization619 kJ/mol
Molar Heat Capacity24.06 J/mol·K
Oxidation States-4, -2, 0, +1, +2, +3, +4, +5, +6, +7, +8
First Ionization Energy710 kJ/mol
Second Ionization Energy1620 kJ/mol
Third Ionization Energy2747 kJ/mol
Atomic Radius134 pm
Covalent Radius146 pm
Crystal StructureHexagonal close-packed (hcp)
Thermal Conductivity117 W/m·K
Electrical Resistivity71 nΩ·m
Magnetic OrderingParamagnetic
Young’s Modulus447 GPa
Shear Modulus173 GPa
Mohs Hardness6.5


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