- Osmium (Os) is a dense, hard, bluish-white transition metal with atomic number 76, located in Group 8 of the periodic table, alongside iron, ruthenium, and iridium.
- Its electron configuration is [Xe] 4f¹⁴ 5d⁶ 6s², showing its placement in the d-block. Each atom of osmium contains seventy-six protons, seventy-six electrons, and a varying number of neutrons depending on the isotope.
- Natural osmium consists of seven stable isotopes, with osmium-192 (¹⁹²Os) being the most abundant.
- Osmium was discovered in 1803 by English chemist Smithson Tennant, alongside iridium, while analyzing the insoluble residues from dissolving platinum ore in aqua regia. The element was named after the Greek word osme, meaning “smell,” due to the pungent, chlorine-like odor of osmium tetroxide (OsO₄), one of its most notable compounds.
- Physically, osmium is extraordinary for its density, which ranges between 22.59 and 22.61 g/cm³, making it one of the densest naturally occurring elements—slightly denser than iridium. It is a brittle metal with a high melting point of 3,033 °C (5,491 °F) and a boiling point of 5,012 °C (9,054 °F). Osmium has a distinctive bluish-silver luster and remains stable under normal atmospheric conditions.
- Chemically, osmium is highly resistant to corrosion and oxidation at room temperature. However, when finely divided, it readily reacts with oxygen to form osmium tetroxide (OsO₄), a highly toxic and volatile compound with strong oxidizing properties. Osmium exhibits multiple oxidation states, ranging from –2 to +8, with +4 and +8 being the most common. OsO₄ is especially significant, as it is widely used in microscopy as a staining agent and fixative for biological tissues due to its ability to bind lipids and enhance contrast under electron microscopes.
- Osmium is primarily used in applications that require extreme durability and hardness. Alloys of osmium with iridium, ruthenium, and platinum are used for fountain pen nibs, electrical contacts, and instrument pivots, where long-term wear resistance is critical. In the medical field, osmium tetroxide has applications in histology and pathology, though its toxicity requires careful handling. Osmium compounds are also used as catalysts in chemical reactions, particularly in organic synthesis.
- Biologically, osmium has no essential role in life processes and is highly toxic in its oxidized form. Osmium tetroxide can cause severe damage to the eyes, skin, and respiratory system even at very low concentrations, making it one of the most hazardous compounds in laboratory chemistry.
- Environmentally, osmium is one of the rarest elements in Earth’s crust, with an average abundance of about 1 part per 10 million. It is usually found in platinum ores and nickel-copper deposits, often occurring together with other platinum-group metals. Major sources include Russia, South Africa, and Canada. Due to its rarity and the risks associated with its toxicity, osmium is not widely used compared to other platinum-group metals, though it remains valuable in specialized fields.
