Osmium Facts – Element 76 Symbol Os

Osmium Element Facts
Osmium is the densest metal, plus it is extremely hard.

Osmium is an extremely hard and dense metallic element with symbol Os and atomic number 76. Although it is a rare element, you encounter it in daily life in ballpoint pens and electrical contacts.

Key Osmium Facts

  • Name: Osmium
  • Atomic Number: 76
  • Element Symbol: Os
  • Atomic Mass: 190.23
  • Element Group: Group 8
  • Period: Period 6
  • Block: d-block
  • Electron Configuration: [Xe] 4f14 5d6 6s2
  • Appearance: Silvery blue metal


English chemist Smithson Tennant discovered osmium and iridium in a sample of platinum ore in 1803. He found osmium in the residue left after dissolving the ore in aqua regia (a mixture of nitric and hydrochloric acid). This residue contained a dark-colored powder, which he investigated further.

He distinguished osmium by its distinct, pungent odor from the oxide that formed. This characteristic led to the naming of the element from the Greek word “osme,” meaning smell.

Appearance and Properties

Osmium is a bluish-white, lustrous metal in its pure form. It’s incredible density of 22.59 g/cm³ makes it the densest naturally occurring element. It is the least compressible metallic element. Osmium has a high melting point (3033 °C) and boiling point (5012 °C), signifying its strong metallic bonds. Its hardness also contributes to its resistance to wear and abrasion.

Osmium Isotopes

Osmium has seven natural isotopes. Of there, five are stable: 187Os, 188Os, 189Os, 190Os, 192Os. The most abundant isotope is 192Os. 184Os undergoes alpha decay and has a half-life of 1013 years. 186Os has such a long half-life that is essentially stable.

Abundance and Sources

Osmium is one of the rarest elements in the Earth’s crust, with an abundance around 50 parts per trillion. It usually occurs as an alloy with other platinum group metals in deposits of minerals like osmiridium and iridosmine. Nickel and copper deposits are another source of the element. Also, the element occurs in some meteorites. The largest producers of osmium are South Africa, Russia, and Canada, typically from processing nickel and platinum ores.

Osmium Uses

Osmium’s primary applications leverage its hardness and resistance to wear. It finds use in alloys for fountain pen nibs, electrical contacts, phonograph styluses, and other components where durability is crucial. 187Os is useful in dating geological formations and meteorites. Osmium tetroxide, a compound of osmium, is used in microscopy, staining biological samples, and organic synthesis.

Powdered osmium absorbs hydrogen atoms, making the element a candidate for a metal-hydride battery. Osmium coatings are highly reflective, especially in the ultraviolet portion of the spectrum. This is useful for UV spectrometers. However, osmium mirrors react with oxygen in air, rapidly damaging their surface.

Electron Levels of an Osmium Atom

Oxidation States

Osmium exhibits several oxidation states, ranging from -4 to +8 (-4, -2, -1, 0, +1, +2, +3, +4, +5, +6, +7, +8). The +2, +3, +4, and +8 states are the most common and stable. The +8 oxidation state is one of the highest of any element (although iridium has a +9 state). Osmium tetroxide (OsO4) is a prime example of the +8 oxidation state. Na2[Os(CO4)] is an example of the -2 oxidation state.

Health Effects and Toxicity

Like most rare metals, osmium has no known biological role. The pure metal is not very reactive and does not pose much risk. However, its compounds, especially osmium tetroxide, are highly toxic and volatile. Osmium reacts in air and forms the oxide, which poses risks to the eyes, lungs, and skin. The risk is especially high when dealing with the powdered metal. Adequate safety measures are essential when handling osmium and its compounds.

Atomic Data and Physical Properties

For scientists and chemistry enthusiasts, here’s a comprehensive table of key osmium facts:

PropertyOsmium Fact
Atomic Number76
Atomic Weight190.23
Electron Configuration[Xe] 4f¹⁴ 5d⁶ 6s²
Electrons per Shell2, 8, 18, 32, 14, 2
State at Room TemperatureSolid
Melting Point3033 °C
Boiling Point5012 °C
Density22.59 g/cm³
Heat of Vaporization378 kJ/mol
Heat of Fusion31 kJ/mol
Molar Heat Capacity24.7 J/(mol·K)
Oxidation States-4, -2, -1, 0, +1, +2, +3, +4, +6, +7, +8
Ionization Energies1st: 840 kJ/mol, 2nd: 1600 kJ/mol
Atomic Radius135 pm
Covalent Radius144 pm
Crystal StructureHexagonal close-packed (hcp)
Thermal Conductivity87.6 W/(m·K)
Shear Modulus222 GPa
Bulk Modulus462 GPa
Mohs Hardness7
Magnetic OrderingParamagnetic

Interesting Osmium Facts

Here are some interesting and unusual facts about osmium:

  • Stinky Element: Osmium reacts in air and forms osmium tetroxide, which has an acrid odor similar to chlorine with a hint of garlic.
  • Color-Changing Oxide: Osmium tetroxide (OsO4) changes from colorless to yellow at room temperature and then to red as osmates form.
  • Rare Meteorite Component: Osmium occurs in some meteorites, providing insights into the early solar system’s formation.
  • Catalytic Properties: Osmium is a catalyst in some chemical reactions, such as the process of synthesizing ammonia in the Haber process.
  • Historical Significance in Lighting: Due to its high melting point, osmium was used to create filaments for the very first light bulbs.
  • Superconductivity: Osmium becomes superconductive at very low temperatures.
  • Use in Forensic Science: Osmium tetroxide detects fingerprints. It reacts with fatty oils present in fingerprints, making them more visible.
  • Extreme Properties: Osmium is the hardest element, least compressible metal, and one of the rarest metal.
  • Potential in Nanotechnology: Osmium has applications in nanotechnology, including in high-density data storage systems.
  • Impact on Jewelry Industry: Alloys of osmium are extremely hard and durable, making them suitable for high-end jewelry pieces, especially in combination with other platinum-group metals.
  • UV Reflector: Several shuttle missions carried osmium-coated mirrors. However, oxygen radicals in low Earth orbit damaged their surfaces.
  • Space Exploration: Due to its resistance to corrosion and high-density properties, osmium has potential applications in space exploration equipment and spacecraft.


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  • Cynn, Hyunchae; Klepeis, J. E.; Yeo, C. S.; Young, D. A. (2002). “Osmium has the Lowest Experimentally Determined Compressibility”. Physical Review Letters. 88 (13): 135701. doi:10.1103/PhysRevLett.88.135701
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  • Peters, Stefan T.M.; Münker, Carsten; Becker, Harry; Schulz, Toni (2014). “Alpha-decay of 184Os revealed by radiogenic 180W in meteorites: Half life determination and viability as geochronometer”. Earth and Planetary Science Letters. 391: 69–76. doi:10.1016/j.epsl.2014.01.030
  • Tennant, S. (1804). “On Two Metals, Found in the Black Powder Remaining after the Solution of Platina”. Philosophical Transactions of the Royal Society. 94: 411–418. doi:10.1098/rstl.1804.0018