| Symbol | Os |
| Atomnummer | 76 |
| Gruppe | 8 (Jerngruppe) |
| Periode | 6 |
| Blok | d |
| Klassifikation | Overgangsmetal |
| Udseende | Silvery, blue cast |
| Farve | Skifergrå |
| Antal protoner | 76 p+ |
| Antal neutroner | 114 n0 |
| Antal elektroner | 76 e- |
| Fase ved STP | Fast |
| Massefylde | 22.59 g/cm3 |
| Atommasse | 190.233 u |
| Smeltepunkt | 3306 K 3032.85 °C 5491.13 °F |
| Kogepunkt | 5285 K 5011.85 °C 9053.33 °F |
| Fordampningsvarme | 627.6 kJ/mol |
| Elektronegativitet (Pauling Scale) | 2.2 |
| Elektronaffinitet | 103.99 kJ/mol |
| Oxidationstrin | −4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8 (a mildly acidic oxide) |
| Ioniseringsenergier |
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| Opdagelse og første isolation | Smithson Tennant (1803) |
| Navngivet af | Smithson Tennant |
Opdagelse af osmium Osmium was discovered in 1803 by Smithson Tennant and William Hyde Wollaston in London, England. The discovery of osmium is intertwined with that of platinum and the other metals of the platinum group. Platinum reached Europe as platina ("small silver"), first encountered in the late 17th century in silver mines around the Chocó Department, in Colombia. The discovery that this metal was not an alloy, but a distinct new element, was published in 1748. Chemists who studied platinum dissolved it in aqua regia (a mixture of hydrochloric and nitric acids) to create soluble salts. They always observed a small amount of a dark, insoluble residue. Joseph Louis Proust thought that the residue was graphite. Victor Collet-Descotils, Antoine François, comte de Fourcroy, and Louis Nicolas Vauquelin also observed iridium in the black platinum residue in 1803, but did not obtain enough material for further experiments. In 1803, Smithson Tennant analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids and obtained a volatile new oxide, which he believed was of this new metal—which he named ptene, from the Greek word πτηνος (ptènos) for winged. However, Tennant, who had the advantage of a much larger amount of residue, continued his research and identified two previously undiscovered elements in the black residue, iridium and osmium. He obtained a yellow solution by reactions with sodium hydroxide at red heat. After acidification he was able to distill the formed OsO4. He named it osmium after Greek osme meaning "a smell", because of the ashy and smoky smell of the volatile osmium tetroxide. Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804. | |