Difference between revisions of "Osmium" - New World Encyclopedia
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== Notable characteristics == | == Notable characteristics == | ||
− | Osmium | + | Osmium is a [[transition metal]] that lies between [[rhenium]] and [[iridium]] in period 6 of the [[periodic table]]. It is thus a member of the [[platinum group]]* of [[metal]]s. In addition, it is located in group 8 (former group 8B), just below [[ruthenium]]. |
− | * The | + | In its metallic form, osmium is blue white, brittle, and lustrous even at high temperatures, but it is extremely difficult to make. It is easier to make osmium in a powdered form, but when this form is exposed to air, it is converted to [[osmium tetroxide]]* (Os[[oxygen|O]]<sub>4</sub>), which is toxic. The oxide is also a powerful [[oxidation|oxidizing]] agent, emits a strong smell and boils at 130°C. |
− | + | The measured [[density]] of osmium is higher than that of any other element, with a value slightly higher than that of [[iridium]]. Osmium is therefore often listed as the densest element known. On the other hand, when density is calculated based on the [[space lattice]]* structures of these elements, one obtains a value of 22,650 kilograms per cubic meter (kg/m³) for iridium, versus 22,610 kg/m³ for osmium. Based on these data, it is currently not possible to arrive at a firm conclusion about which of them is denser. If one were to distinguish between different isotopes, then the heaviest ordinary substance would be <sup>192</sup>Os. | |
− | Osmium | + | Osmium has the highest [[melting point]]* and the lowest [[vapor pressure]]* of the [[platinum family]]. It also has a very low [[compressibility]]* value. Common [[oxidation state]]s of osmium are +4 and +3, but observed oxidation states range from +1 to +8. |
− | + | === Isotopes === | |
− | + | Osmium has seven naturally occurring [[isotope]]s, five of which are stable: <sup>187</sup>Os, <sup>188</sup>Os, <sup>189</sup>Os, <sup>190</sup>Os, and (most abundant) <sup>192</sup>Os. The other two, <sup>184</sup>Os and <sup>186</sup>Os, have enormously long [[half life]]s and for practical purposes can be considered to be stable as well. <sup>187</sup>Os is the daughter of <sup>187</sup>[[rhenium|Re]] ([[half-life]] 4.56 x 10<sup>10</sup> years) and is most often measured in an <sup>187</sup>Os/<sup>188</sup>Os ratio. This ratio, as well as the <sup>187</sup>Re/<sup>187</sup>Os ratio, have been used extensively in dating terrestrial as well as [[meteorite|meteoric]] [[Rock (geology)|rock]]s. It has also been used to measure the intensity of continental weathering over geologic time. However, the most notable application of Os in dating has been in conjunction with [[iridium]], to analyze the layer of [[shocked quartz]] along the [[K-T boundary]] that marks the extinction of the [[dinosaur]]s 65 million years ago. | |
− | Osmium has seven naturally | + | |
+ | == Alloys and compounds == | ||
+ | |||
+ | * '''Iridiosmium''', '''iridosmium''', or '''osmium iridian''' (Os, Ir): This is an [[alloy]] of [[osmium]] and iridium. It occurs naturally as small, extremely hard, flat metallic grains with hexagonal crystal structure, and sometimes contains traces of [[platinum]], [[palladium]], [[rhodium]], and [[ruthenium]]. Iridiosmium has been used in making [[fountain pen]]* nibs. | ||
+ | |||
+ | * '''Osmiridium''': This is an [[alloy]] of [[osmium]] and iridium, with traces of [[platinum]] and [[rhodium]]. It is found in small amounts in nature, in [[mining|mine]]s of other [[platinum group metal]]*s. It can also be made artificially. It can be isolated by adding a piece to [[aqua regia]]*, which has the ability to dissolve [[gold]] and [[platinum]] but not osmiridium. This alloy is used in making [[surgery|surgical]] equipment and other high-wear devices. It was once used for [[fountain pen]]* nibs. | ||
+ | |||
+ | * '''[[Osmium tetroxide]]*''', '''osmium tetraoxide''', '''osmium(VIII) oxide''', or '''osmic acid''' (OsO<sub>4</sub>): When pure, the compound is colorless, but it is usually contaminated with a small amount of yellow-brown [[osmium dioxide]]* (OsO<sub>2</sub>), giving it a yellowish hue. OsO<sub>4</sub> is [[sublimation (chemistry)|sublimes]]* (changes from solid to gas) at [[room temperature]]* and has a characteristic odor similar to that of [[ozone]]. OsO<sub>4</sub> is highly poisonous, even at low exposure levels, and must be handled with appropriate precautions. In organic synthetic reactions, OsO<sub>4</sub> is widely used to oxidize [[alkene]]s to the dialcohols. In addition, it is used as a [[staining]]* agent in [[transmission electron microscopy]]*, [[scanning electron microscopy]]*, and optical microscopy. | ||
== Applications == | == Applications == | ||
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In 1898, Austrian chemist [[Carl Auer von Welsbach]]* developed the "Oslamp," with a filament made of osmium, which he introduced commercially in 1902. After a few years, however, osmium was replaced by the more stable metal [[tungsten]] (originally known as wolfram). | In 1898, Austrian chemist [[Carl Auer von Welsbach]]* developed the "Oslamp," with a filament made of osmium, which he introduced commercially in 1902. After a few years, however, osmium was replaced by the more stable metal [[tungsten]] (originally known as wolfram). | ||
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== Footnotes == | == Footnotes == |
Revision as of 18:38, 24 October 2006
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General | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Name, Symbol, Number | osmium, Os, 76 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Chemical series | transition metals | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Group, Period, Block | 8, 6, d | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Appearance | silvery, blue cast | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic mass | 190.23(3) g/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electron configuration | [Xe] 4f14 5d6 6s2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrons per shell | 2, 8, 18, 32, 14, 2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Physical properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Phase | solid | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Density (near r.t.) | 22.61 g/cm³ | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Liquid density at m.p. | 20 g/cm³ | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Melting point | 3306 K (3033 °C, 5491 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Boiling point | 5285 K (5012 °C, 9054 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of fusion | 57.85 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of vaporization | 738 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat capacity | (25 °C) 24.7 J/(mol·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Atomic properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Crystal structure | hexagonal | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Oxidation states | 8, 6, 4, 2, -2 (mildly acidic oxide) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electronegativity | 2.2 (Pauling scale) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ionization energies | 1st: 840 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2nd: 1600 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic radius | 130 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic radius (calc.) | 185 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Covalent radius | 128 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Miscellaneous | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Magnetic ordering | ? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrical resistivity | (0 °C) 81.2 nΩ·m | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal conductivity | (300 K) 87.6 W/(m·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal expansion | (25 °C) 5.1 µm/(m·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound (thin rod) | (20 °C) 4940 m/s | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Shear modulus | 222 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Poisson ratio | 0.25 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bulk modulus | 462 GPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mohs hardness | 7.0 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Brinell hardness | 3920 MPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CAS registry number | 7440-04-2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Notable isotopes | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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- For other uses, see Osmium (disambiguation).
Osmium (chemical symbol Os, atomic number 76) is a hard, brittle, blue-gray or blue-black transition metal in the platinum family. It is one of the densest natural elements[1] It is used in some alloys with platinum and iridium. Osmium is found native as an alloy in platinum ore and its tetroxide has been used to stain tissues and in fingerprinting. Alloys of osmium are employed in fountain pen tips, electrical contacts, and other applications where extreme durability and hardness are needed.
Occurrence and value
Turkey has the world's largest known reserve of osmium, estimated at 127,000 tons. Bulgaria also has substantial reserves, of about 2,500 tons. This transition metal is also found in iridiosmium, a naturally occurring alloy of iridium and osmium, and in platinum-bearing river sands in the Ural Mountains, and North and South America. Osmium also occurs in nickel-bearing ores found in the Sudbury, Ontario region, with other platinum group metals. Although the proportion of platinum metals in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.
Osmium is quite valuable, costing about US $100 per gram (g).[2] One of the stable isotopes, 187Os, is worth about $25,000 per gram.[3]
History
Osmium (from the Greek word osme, meaning "a smell") was discovered in 1803 by Smithson Tennant, while working with William Hyde Wollaston in London, England.
They were looking for a way to purify platinum by dissolving native platinum ore in aqua regia (a mixture of concentrated nitric and hydrochloric acids). A large amount of insoluble black powder remained as a byproduct of this operation.
Wollaston focused on analyzing the soluble portion and discovered palladium (in 1802) and rhodium (in 1804), while Tennant examined the insoluble residue. In the summer of 1803, Tennant identified two new elements: osmium and iridium. Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.
Notable characteristics
Osmium is a transition metal that lies between rhenium and iridium in period 6 of the periodic table. It is thus a member of the platinum group of metals. In addition, it is located in group 8 (former group 8B), just below ruthenium.
In its metallic form, osmium is blue white, brittle, and lustrous even at high temperatures, but it is extremely difficult to make. It is easier to make osmium in a powdered form, but when this form is exposed to air, it is converted to osmium tetroxide (OsO4), which is toxic. The oxide is also a powerful oxidizing agent, emits a strong smell and boils at 130°C.
The measured density of osmium is higher than that of any other element, with a value slightly higher than that of iridium. Osmium is therefore often listed as the densest element known. On the other hand, when density is calculated based on the space lattice structures of these elements, one obtains a value of 22,650 kilograms per cubic meter (kg/m³) for iridium, versus 22,610 kg/m³ for osmium. Based on these data, it is currently not possible to arrive at a firm conclusion about which of them is denser. If one were to distinguish between different isotopes, then the heaviest ordinary substance would be 192Os.
Osmium has the highest melting point and the lowest vapor pressure of the platinum family. It also has a very low compressibility value. Common oxidation states of osmium are +4 and +3, but observed oxidation states range from +1 to +8.
Isotopes
Osmium has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other two, 184Os and 186Os, have enormously long half lifes and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56 x 1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/187Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the K-T boundary that marks the extinction of the dinosaurs 65 million years ago.
Alloys and compounds
- Iridiosmium, iridosmium, or osmium iridian (Os, Ir): This is an alloy of osmium and iridium. It occurs naturally as small, extremely hard, flat metallic grains with hexagonal crystal structure, and sometimes contains traces of platinum, palladium, rhodium, and ruthenium. Iridiosmium has been used in making fountain pen nibs.
- Osmiridium: This is an alloy of osmium and iridium, with traces of platinum and rhodium. It is found in small amounts in nature, in mines of other platinum group metals. It can also be made artificially. It can be isolated by adding a piece to aqua regia, which has the ability to dissolve gold and platinum but not osmiridium. This alloy is used in making surgical equipment and other high-wear devices. It was once used for fountain pen nibs.
- Osmium tetroxide, osmium tetraoxide, osmium(VIII) oxide, or osmic acid (OsO4): When pure, the compound is colorless, but it is usually contaminated with a small amount of yellow-brown osmium dioxide (OsO2), giving it a yellowish hue. OsO4 is sublimes (changes from solid to gas) at room temperature and has a characteristic odor similar to that of ozone. OsO4 is highly poisonous, even at low exposure levels, and must be handled with appropriate precautions. In organic synthetic reactions, OsO4 is widely used to oxidize alkenes to the dialcohols. In addition, it is used as a staining agent in transmission electron microscopy, scanning electron microscopy, and optical microscopy.
Applications
Because of the extreme toxicity of its oxide, osmium is rarely used in its pure state and is instead often alloyed with other metals that are used in high-wear applications. Osmium alloys such as osmiridium are very hard and, along with other platinum group metals, is almost entirely used in alloys employed in the tips of fountain pens, phonograph needles, instrument pivots, and electrical contacts, as they can resist wear from frequent use.
Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for microscope slides. As a strong oxidant, it cross-links lipids by fixing biological membranes in place. Futhermore, osmium atoms are extremely electron dense, making OsO4 an important stain for transmission electron microscopy (TEM) studies of a wide range of biological materials. An alloy of 90% platinum and 10% osmium (90/10) is used in surgical implants such as pacemakers and replacement pulmonary valves.
The tetroxide (and a related compound, potassium osmate) are important oxidants for chemical synthesis, despite being very poisonous.
In 1898, Austrian chemist Carl Auer von Welsbach developed the "Oslamp," with a filament made of osmium, which he introduced commercially in 1902. After a few years, however, osmium was replaced by the more stable metal tungsten (originally known as wolfram).
Footnotes
- ↑ The two competitors for densest natural element are osmium and iridium. Currently, the dispute over which one is denser has not been resolved by the scientific community.
- ↑ http://www.engelhard.com/eibprices/DPCharts.aspx?MetalName=Osmium
- ↑ http://www.ecplaza.net/ecmarket/list.asp?cmd=search&keywords=osmium+187
ReferencesISBN links support NWE through referral fees
- Los Alamos National Laboratory - Osmium
- National Synchrotron Light Source - Science Highlights
- H Cynn, J E Klepeis, C S Yeo and D A Young, "Osmium has the Lowest Experimentally-Determined Compressibility", Phys. Rev. Lett. 88 #13 (2002).
- B R Sahu and L Kleinman, "Osmium Is Not Harder Than Diamond", Phys. Rev. B 72 (2005).
- Cotton, S. A. "Chemistry of Precious Metals," Chapman and Hall (London): 1997. ISBN 0-7514-0413-6.
- Berrisford, D. J.; Bolm, C.; Sharpless, K. B., "Ligand Accelerated Catalysis", Angewandte Chemie, International Edition English, 1995, volume 34, pp. 1059-1070.
External links
- WebElements.com - Osmium
- International Chemical Safety Card 0528
- NIOSH Pocket Guide to Chemical Hazards
- BBC report on bomb plot
- BBC What is Osmium tetroxide article
- Osmium Tetroxide: Molecule of the Month
- Chemical Reactions
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