|
|
| General |
| Name, Symbol, Number | Osmium, Os, 76 |
| Chemical series | transition metals |
| Group, Period, Block | 8 (VIIIB)[?], 6 , d |
| Density, Hardness | 22610 kg/m3, 7 |
| Appearance | bluish grey |
| Atomic Properties |
| Atomic weight | 190.23 amu |
| Atomic radius (calc.) | 130 (185) pm |
| Covalent radius | 128 pm |
| van der Waals radius | no data |
| Electron configuration | [Xe]4f145d66s2 |
| e- 's per energy level | 2, 8, 18, 32, 14, 2 |
| Oxidation states (Oxide) | ±0.7 (mildly acidic) |
| Crystal structure | hexagonal |
| Physical Properties |
| State of matter | Solid (--) |
| Melting point | 3306 K (5491 °F) |
| Boiling point | 5285 K (9054 °F) |
| Molar volume | 8.42 ×10-3 m3/mol |
| Heat of vaporization | 627.6 kJ/mol |
| Heat of fusion | 31.8 kJ/mol |
| Vapor pressure | 2.52 Pa at 3300 K |
| Speed of sound | 4940 m/s at 293.15 K |
| Miscellaneous |
| Electronegativity | 2.2 (Pauling scale) |
| Specific heat capacity | 130 J/(kg*K) |
| Electrical conductivity | 10.9 106/m ohm |
| Thermal conductivity | 87.6 W/(m*K) |
| 1st ionization potential | 840 kJ/mol |
| 2nd ionization potential | 1600 kJ/mol |
| Most Stable Isotopes |
| iso | NA | half-life | DM | DE MeV | DP |
| 184Os | 0.02% | >5.6 E13 y | | | |
| 186Os | 1.58% | >2.0 E15 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 |
| 192Os | 41.0% | Os is stable with 116 neutrons |
| 194Os | {syn.} | 6 y | β- | 0.097 | 194Ir |
|
| SI units & STP are used except where noted. |
Osmium 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, if not the heaviest metal known and 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
ball point pen tips, electrical contacts and in other applications where extreme durability and hardness are needed.
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 (Os
O4), 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 heaviest 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 for iridium versus 22661 for osmium. Definitive selection between the two is therefore not possible at this time. It's just too close to call.
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.
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 are very hard and along with other platinum group metals is almost entirely used in alloys employed in the tips of
ball point pens,
phonograph needles, instrument pivots, and electrical contacts.
Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for microscope slides. An alloy of 90% platinum and 10% osmium (90/10) is used in surgical implants[?] such as pacemakers and replacement pulmonary[?] valves.
Osmium (
Greek osme meaning "a smell") was discovered in
1803 by
Smithson Tennant[?] in London, England along with
iridium in the residue of dissolving
platinum in
aqua regia.
This transition metal is found in
iridiosmium[?] a naturally occurring alloy of iridium and osmium and in
platinum-bearing river sands in the
Ural Mountains,
North, and
South America. It is 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.
Osmium tetroxide OsO
4
Osmium has seven naturally-occurring
isotopes, 5 of which are stable: Os-187, Os-188, Os-189, Os-190, and (most abundant) Os-192. Os-184, Os-186 have absurdly long
half lifes and for practical purposes can be consided to be stable as well. Os-187 is the daughter of
rhenium-187 (
half-life 4.56 x 10
10 years) and is most often measured in a Os-187/Os-186 ratio. This ratio, as well as the
Re-187/Os-187 ratio, have been used extensively in dating terrestrial as well as
meteoric rocks. 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.
Osmium tetraoxide is highly toxic. Airborne concentrations of osmium as low as 10
7 g/
m³ can cause
lung congestion,
skin or
eye damage.
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