its crust), this chemical element may either occur in its free elemental form or compounded with platinum or other noble metals that share similar chemical properties (like the iridium-osmium alloy, i.e.osmiridium).įor commercial use, iridium is obtained as a by-product in the mining of nickel (sulfides), platinum, copper, and nickel ores. In the alluvial iridium deposits of the Earth’s thinnest layer (i.e. The very thin layer of iridium in Earth’s crust that dates from the Cretaceous period is considered to be evidence of a collision between Earth and an asteroid. In this way, iridium was deposited into the alluvium formations. In fact, some scientists believe that during the asteroid impact which led to the extinction of the dinosaurs, element 77 was disseminated throughout our planet along with an incredible amount of climate-changing gases that were released into the atmosphere upon impact. The sediment in the layers that do contain some iridium are traced to the end of the Cretaceous period. In fact, they contain larger amounts of the 77th element than Earth’s crust. In the Universe, a large percent of iridium occurs in meteors and asteroids. However, they failed in isolating iridium from the platinum ore solution residue. Vauquelin attempted performing similar experiments to Tennant’s. It should be noted that the French chemists H.V. On June 21, 1804, Tennant submitted his scientific evidence in a letter addressed to the Royal Society of London for Improving Natural Knowledge (today’s Royal Society) after which the new element iridium was officially recognized and assigned the atomic number 77 in the periodic table. In order to prove his claim, Tennant exposed the solution to alkalis and marine (hydrochloric) acid and purified the platinum ore, which helped him isolate two new chemicals – iridium and osmium. Since he previously managed to isolate graphite during the meteorite experiment, Tennant disagreed with his French colleague Joseph Louis Proust (1754 – 1826) who thought that the black residue from the platinum ore submerged in aqua regia was graphite, i.e. By diluting it in aqua regia, the British scientist obtained black residue from the platinum ore solution. In 1803, Tennant attempted an individual experiment on a crude platinum sample. In the meteorite analysis he conducted, Tennant exposed the sample to acid which resulted in graphite (plumbago). Prior to this, Tennant’s curiosity was sparked by the analysis of a 300-pound Cape of Good Hope iron meteorite in 1801. The 300-Pound Cape of Good Hope Iron Meteorite In the 17th century, this ore was introduced in Europe by the Spanish conquistadors, who had learned about – what was locally referred to as platina or “silverette” – on their South American exploits on the territory of today’s western Colombia. Ruthenium and osmium are the only elements that show lower reactivity than iridium.Īncient Ethiopians and various peoples from the South American continent were familiar with a type of platinum ore that contained traces of several chemical elements that are classified in the platinum family of the periodic table, such as ruthenium, rhodium, palladium, osmium, and iridium. Iridium is unaffected even by aqua regia. Being non-reactive with water, acids, silicates, molten metals, or air, this transition metal is able to resist corrosion better than any other metal in the periodic table of elements. Its crystal structure is cubic-face centered. Iridium has a specific gravity of 22.42 (17☌), an electronegativity of 2.2 according to Pauling, and the atomic radius according to van der Waals is 0.126 nm. Iridium reaches a boiling point at 4527☌, while its melting point is at 2450☌. However, when exposed to temperatures between 1,200° and 1,500° C (2,200° to 2,700° F), iridium becomes ductile and malleable. This member of the platinum family is also very brittle and dense in its metal form. Iridium is the hardest substance according to the classification of elements within Mendeleev’s system. It has an atomic mass of 192.2 g.mol -1 and electron configuration 4f 14 5d 7 6s 2. Located between osmium and platinum in the periodic table, the chemical element iridium is labeled with the symbol Ir and the atomic number 77. Rare, very heavy, soft, silvery-white metal Used with osmium to tip gold pen points, to make crucible and special containers, and in heat-resistant alloys S.Tenant, A.F.Fourcory, L.N.Vauquelin, H.V.Collet-Descoltils Chemical and Physical Properties of Iridium PropertyĪ lustrous, silver-white metal with a yellowish hue
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