Osmium

Osmium - Os

CAS: 7440-04-2
Description:Fine black powder or hard blue-gray mass
Classification: Transition Metal
Date of Discovery: 1803
Discoverer: Smithson Tenant
Name Origin: Greek osmê, "odor" or "smell"

Atomic Number: 76
Number of Neutrons: 114
Atomic Mass: 190.23 amu
Melting Point: 3045.0 °C
Boiling Point: 5027.0 °C
Density (293 K): 22.4 g/cm³
Atomic volume: 8.49 cm³/mol
Electrical resistivity: 0.109 10^-6/cm

Thermal conductivity: 0.876 W/cmK
Enthalpy of atomization: 669 kJ/mol (est.)
Enthalpy of vaporization: 746.0 kJ/mol
Enthalpy of fusion: 31.80 kJ/mol
Specific heat capacity: 0.71 J/gK

Energy levels: 2-8-18-32-14-2
Electron configuration: [Xe]4f ¹⁴5d⁶6s²
Crystal Structure: Hexagonal
Atomic radius: 1.92 Å
Covalent radius: 1.26 Å
Oxidation States: 0 to +8, usually +3, +4, +6 and +8
Electronegativity, Pauling: 2.2
Electron affinity: 1.1 eV
First ionization energy: 8.7 eV
2nd ionization energy:
3rd ionization energy:
Polarizability: 8.5 10^-24cm³

Isotope	Natural Abundance	Atomic Mass	Half-life	Decay Mode	Spin
¹⁶²Os	161.984	1.9 ms
¹⁶³Os	162.982
¹⁶⁴Os	163.9779	0.04 s
¹⁶⁵Os	164.9765	0.07 s
¹⁶⁶Os	165.9718	0.18 s	⁺, EC;	0+
¹⁶⁷Os	166.9714	0.7 s	⁺, EC;
¹⁶⁸Os	167.96775	2.2 s	⁺, EC;	0+
¹⁶⁹Os	168.9671	3.3 s	⁺, EC;
¹⁷⁰Os	169.96357	7.1 s	⁺, EC;	0+
¹⁷¹Os	170.9630	8 s	⁺, EC;
¹⁷²Os	171.9601	19 s	⁺, EC;	0+
¹⁷³Os	172.9598	16 s	⁺, EC;
¹⁷⁴Os	173.9563	44 s	⁺, EC;	0+
¹⁷⁵Os	174.9570	1.4 m	⁺, EC
¹⁷⁶Os	175.9550	3.6 m	⁺, EC	0+
¹⁷⁷Os	176.9551	2.8 m	⁺, EC	(1/2-)
¹⁷⁸Os	177.9534	5.0 m	⁺, EC	0+
¹⁷⁹Os	178.9539	7 m	⁺, EC
¹⁸⁰Os	179.9524	21.5 m	⁺, EC	0+
^181mOs	1.75 h	EC	(1/2-)
¹⁸¹Os	180.9532	2.7 m	EC	(7/2-)
¹⁸²Os	181.95219	21.5 h	EC	0+
^183mOs	9.9 h	EC; IT	1/2-
¹⁸³Os	182.9531	13 h	EC	9/2+
¹⁸⁴Os	0.020(3)	183.952491	Stable	0+
¹⁸⁵Os	184.954043	93.6 d	EC	1/2-
¹⁸⁶Os	1.58(10)	185.953838	2.0 x 10¹⁵ y		0+
¹⁸⁷Os	1.6(1)	186.955748	Stable	1/2-
¹⁸⁸Os	13.3(2)	187.955836	Stable	0+
^189mOs	5.8 h	IT	9/2-
¹⁸⁹Os	16.1(3)	188.958145	Stable	3/2+
^190mOs	9.9 m	IT	10-
¹⁹⁰Os	26.4(4)	189.958445	Stable	0+
^191mOs	13.1 h	IT	3/2-
¹⁹¹Os	190.960928	15.4 d	^-	9/2-
^192mOs	6.0 s	IT	(10-)
¹⁹²Os	41.0(3)	191.961479	Stable	0+
¹⁹³Os	192.964148	30.5 h	^-	3/2-
¹⁹⁴Os	193.965179	6.0 y	^-	0+
¹⁹⁵Os	194.9681	6.5 m	^-
¹⁹⁶Os	195.96962	34.9 m	^-	0+
Discovered in 1803 by Tennant in the residue left when crude platinum is dissolved by aqua regia. Osmium occurs in iridosmine (Os,Ir) and in platinum-bearing river sands of the Urals, North America, and South America. It is also found in the nickel-bearing ores of Sudbury, Ontario, region along with other platinum metals. While the quantity of platinum metals in these ores is very small, the large tonnages of nickel ores processed make commercial recovery possible. The metal is lustrous, bluish white, extremely hard, and brittle even at high temperatures. It has the highest melting point and the lowest vapor pressure of the platinum group. The metal is very difficult to fabricate, but the powder can be sintered in a hydrogen atmosphere at a temperature of 2000 °C. The solid metal is not affected by air at room temperature, but the powdered or spongy metal slowly gives off osmium tetroxide, which is a powerful oxidizing agent and has a strong smell. The tetroxide is highly toxic, and boils at 130 °C (760 mm). Concentrations in air as low as 10^-7 g/m³ can cause lung congestion, skin damage, or eye damage. The tetroxide has been used to detect fingerprints and to stain fatty tissue for microscope slides. The metal is almost entirely used to produce very hard alloys, with other metals of the platinum group, for fountain pen tips, instrument pivots, phonograph needles, and electrical contacts. Natural osmium contains seven isotopes, one of which, ¹⁸⁶Os, is radioactive with a very long half-life. Thirty-four other isotopes and isomers are known, all of which are radioactive. The measured densities of iridium and osmium seem to indicate that osmium is slightly more dense than iridium, so osmium has generally been credited with being the heaviest known element. Calculations of the density from the space lattice, which may be more reliable for these elements than actual measurements, however, give a density of 22.65 for iridium compared to 22.61 for osmium. At present, therefore, we know either iridium or osmium is the heaviest element, but the data do not allow selection between the two. LINKS: Information, data sheet and standard forms Osmium Tetroxide: Chemicals for Microscopy Return Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.

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