Osmium (Os)


  • Symbol: Os
  • Atomic Number: 76
  • Atomic Weight: 190.23
  • Element Classification: Transition Metal
  • Discovered By: Smithson Tennant
  • Discovery Date: 1803
  • Name Origin: Greek: ‘osme’ (smell), referring to the strong odor of its volatile oxide
  • Density(g/cc): 22.59
  • Melting Point: 3033°C
  • Boiling Point: 5012°C
  • Appearance: Bluish-white, hard, brittle metal
  • Atomic Radius(pm): 135


Osmium was discovered in 1803 by the English chemist Smithson Tennant. Tennant discovered osmium in the residue left when crude platinum was dissolved in aqua regia (a mixture of hydrochloric and nitric acid). He identified osmium by the distinct smell of its volatile oxide, from which the element’s name is derived, meaning “smell” in Greek. The discovery of osmium occurred simultaneously with the discovery of iridium, as both elements were found in the insoluble residue of dissolved platinum ores.

Relation to Other Elements

Osmium is a member of the platinum group metals (PGMs), which includes platinum, palladium, rhodium, ruthenium, and iridium. These metals share similar physical and chemical properties, such as high melting points, resistance to corrosion and wear, and catalytic abilities. Osmium is distinguished by having the highest density of all naturally occurring elements and an extremely high melting point, making it exceptionally hard and brittle.

Natural Occurrence

Osmium is one of the least abundant elements in the Earth’s crust. It is found in nature alloyed with other platinum group metals in alluvial deposits and within nickel and copper ores. The primary sources of osmium are the nickel-bearing ores found in the Sudbury region of Canada, the Ural Mountains in Russia, and in South Africa. The extraction of osmium is challenging due to its rarity and the complex processing required to separate it from other metals.


Osmium has a few specialized applications, which are primarily due to its extreme density and hardness:

  • Alloys: Osmium is alloyed with other platinum group metals to create extremely hard and durable materials used in fountain pen tips, electrical contacts, and other applications requiring wear-resistant materials.
  • Catalysis: Like other PGMs, osmium is used as a catalyst in chemical reactions, although its use is less common due to its rarity and toxicity.
  • Research: Osmium tetroxide (OsO₄) is used in biological staining for electron microscopy to provide high contrast images of cellular structures. However, its toxicity requires careful handling.

The discovery of osmium expanded the understanding of platinum group metals, contributing to advancements in materials science and technology. Despite its limited applications and the challenges associated with its toxicity, osmium plays a unique role in specialized fields due to its exceptional properties.

Rhenium (Re)

Iridium (Ir)