Science, Tech, Math › Science Osmium Facts - Element Number 76 or Os Chemical & Physical Properties of Osmium Share Flipboard Email Print Periodictableru Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 2019 Osmium is an extremely heavy silver-blue metal with atomic number 76 and element symbol Os. While most elements aren't know for the way they smell, osmium emits a characteristic unpleasant smell. The element and its compounds are highly toxic. Here is a collection of osmium element facts, including its atomic data, chemical and physical properties, uses, and sources. Osmium Basic Facts Atomic Number: 76 Symbol: Os Atomic Weight: 190.23 Discovery: Smithson Tennant 1803 (England), discovered osmium in residue remaining when crude platinum was dissolved in aqua regia Electron Configuration: [Xe] 4f14 5d6 6s2 Word Origin: from the Greek word osme, a smell or odor Isotopes: There are seven naturally-occurring isotopes of osmium: Os-184, Os-186, Os-187, Os-188, Os-189, Os-190, and Os-192. Six additional manmade isotopes are known. Properties: Osmium has a melting point of 3045 +/- 30 °C, boiling point of 5027 +/- 100°C, specific gravity of 22.57, with a valence usually +3, +4, +6, or +8, but sometimes 0, +1, +2, +5, +7. It is a lustrous blue-white metal. It is very hard and remains brittle even at high temperatures. Osmium has the lowest vapor pressure and highest melting point of the platinum group metals. Although solid osmium is unaffected by air at room temperature, the powder will give off osmium tetroxide, a strong oxidizer, highly toxic, with a characteristic odor (hence the metal's name). Osmium is slightly more dense than iridium, so osmium is often credited as being the heaviest element (calculated density ~ 22.61). The calculated density for iridium, based on its space lattice, is 22.65, though the element hasn't been measured as heavier than osmium. Uses: Osmium tetroxide can be used to stain fatty tissue for microscope slides and to detect fingerprints. Osmium is used to add hardness to alloys. It is also used for fountain pen tips, instrument pivots, and electrical contacts. Sources: Osmium is found in iridomine and platinum-bearing sands, such as those found in the Americas and Urals. Osmium may also be found in nickel-bearing ores with other platinum metals. Although the metal is difficult to make, the power can be sintered in hydrogen at 2000°C. Element Classification: Transition Metal Osmium Physical Data Density (g/cc): 22.57 Melting Point (K): 3327 Boiling Point (K): 5300 Appearance: blue-white, lustrous, hard metal Atomic Radius (pm): 135 Atomic Volume (cc/mol): 8.43 Covalent Radius (pm): 126 Ionic Radius: 69 (+6e) 88 (+4e) Specific Heat (@20°C J/g mol): 0.131 Fusion Heat (kJ/mol): 31.7 Evaporation Heat (kJ/mol): 738 Pauling Negativity Number: 2.2 First Ionizing Energy (kJ/mol): 819.8 Oxidation States: 8, 6, 4, 3, 2, 0, -2 Lattice Structure: Hexagonal Lattice Constant (Å): 2.740 Lattice C/A Ratio: 1.579 Return to the Periodic Table Sources Arblaster, J. W. (1989). "Densities of osmium and iridium: recalculations based upon a review of the latest crystallographic data" (PDF). Platinum Metals Review. 33 (1): 14–16.Chisholm, Hugh, ed. (1911). "Osmium". Encyclopædia Britannica. 20 (11th ed.). Cambridge University Press. p. 352.Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.