   #copyright

Osmium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                76               rhenium ← osmium → iridium
                Ru
                ↑
                Os
                ↓
                Hs

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                       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] 4f^14 5d^6 6s^2
                                   Electrons per shell 2, 8, 18, 32, 14, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 22.61 g·cm^−3
                                      Liquid density at m.p. 20 g·cm^−3
                                                     Melting point 3306  K
                                                    (3033 ° C, 5491 ° F)
                                                      Boiling point 5285 K
                                                    (5012 ° C, 9054 ° F)
                                         Heat of fusion 57.85 kJ·mol^−1
                                     Heat of vaporization 738 kJ·mol^−1
                           Heat capacity (25 °C) 24.7 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 3160 3423 3751 4148 4638 5256

                                                         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^−1·K^−1
                        Thermal expansion (25 °C) 5.1 µm·m^−1·K^−1
                               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
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of osmium

                             iso    NA    half-life   DM  DE ( MeV)   DP
                            ^184Os 0.02% >5.6×10^13 y α   2.966     ^180W
                            ^185Os syn   93.6 d       ε   1.013     ^185Re
                            ^186Os 1.58% 2.0×10^15 y  α   2.822     ^182W
                            ^187Os 1.6%  Os is stable with 111 neutrons
                            ^188Os 13.3% Os is stable with 112 neutrons
                            ^189Os 16.1% Os is stable with 113 neutrons
                            ^190Os 24.6% Os is stable with 114 neutrons
                            ^191Os syn   15.4 d       β^- 0.314     ^191Ir
                            ^192Os 41.0% Os is stable with 116 neutrons
                            ^193Os syn   30.11 d      β^- 1.141     ^193Ir
                            ^194Os syn   6 y          β^- 0.097     ^194Ir

                                                                References

   Osmium ( IPA: /ˈɒzmiəm/) is a chemical element in the periodic table
   that has the symbol Os and atomic number 76. A hard brittle blue-gray
   or blue-black transition metal in the platinum family, osmium is one of
   the densest natural elements and is used in some alloys with platinum
   and iridium. The extraordinary density of osmium is a consequence of
   the lanthanide contraction. 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 in other applications where extreme durability
   and hardness are needed.

Notable characteristics

   Osmium in a metallic form is extremely dense, blue white, brittle and
   lustrous even at high temperatures, but proves to be extremely
   difficult to make. Powdered osmium is easier to make, but powdered
   osmium exposed to air leads to the formation of osmium tetroxide
   (OsO[4]), which is toxic. The oxide is also a powerful oxidizing agent,
   emits a strong smell and boils at 130° C.

   Due to its very high density osmium is generally considered to be the
   densest known element, narrowly defeating iridium. However,
   calculations of density from the space lattice may produce more
   reliable data for these elements than actual measurements and give a
   density of 22650 kg/m^3 for iridium versus 22610 kg/m^3 for osmium.
   Definitive selection between the two is therefore not possible at this
   time. If one distinguishes different isotopes, then the heaviest
   ordinary substance would be ^192Os.

   Osmium also has a very low compressibility. Correspondingly, its bulk
   modulus is extremely high -- commonly quoted as 462GPa, which is higher
   than that of diamond but lower than that of ADNR or aggregated diamond
   nanorods -- although there is some debate in the academic community
   about whether it is in fact this high. A paper by Cynn et al published
   in 2002 reported that osmium had this bulk modulus, based on an
   experimental result; but several subsequent authors have cast doubt
   upon this (for example Sahu et al in Sept 2005, who refer also to other
   such papers - see References section).

   This metal has the highest melting point and the lowest vapor pressure
   of the platinum family. Common oxidation states of osmium are +4 and
   +3, but oxidation states from +1 to +8 are observed.

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 OsO[4] 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 an Austrian chemist - Auer von Welsbach - developed the Oslamp
   with a filament made of osmium, which he introduced commercially in
   1902. After only a few years, osmium was replaced by the more stable
   metal tungsten (originally known as Wolfram). Tungsten has the highest
   melting point of any metal, and using it in light bulbs increases the
   luminous efficacy and life of incandescent lamps.

   The light bulb manufacturer OSRAM (founded in 1906 when three German
   companies; Auer-Gesellschaft, AEG and Siemens & Halske combined their
   lamp production facilities), derived its name from the elements of
   OSmium and wolfRAM.

History

   Osmium ( Greek osme meaning "a smell") was discovered in 1803 by
   Smithson Tennant and William Hyde Wollaston in London, England.

   Wollaston and Tennant were looking for a way to purify platinum by
   dissolution of native platinum ore in aqua regia. Large amounts of
   insoluble black powder remained as a byproduct of this operation.

   Wollaston concentrated on 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.

Occurrence

   Turkey with 127,000 tons has the world's largest known reserve of
   osmium. Bulgaria also has substantial reserves of about 2500 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. It also occurs in
   nickel-bearing ores found in the Sudbury, Ontario region with other
   platinum group metals. Even though the quantity of platinum metals
   found in these ores is small, the large volume of nickel ores processed
   makes commercial recovery possible.

Value

   Osmium is quite valuable, costing about US $100 per gram (g). One of
   the stable isotopes, ^187Os is worth about $25000 per gram.

Compounds

   See also osmium compounds. Osmium tetroxide OsO[4]

Isotopes

   Osmium has seven naturally-occurring isotopes, 5 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 10^10 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.

Precautions

   Osmium tetroxide is highly toxic. Airborne low concentrations of osmium
   can cause lung congestion, skin or eye damage.
   Retrieved from " http://en.wikipedia.org/wiki/Osmium"
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   with only minor checks and changes (see www.wikipedia.org for details
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