OsmiumConsortium

Osmium was discovered by Smithson Tennant (England) in 1803. The origin of the name comes from the Greek word osme meaning smell. It is hard fine black powder or hard, lustrous, blue-white metal. Unaffected by air, water and acids. Characteristic acrid, chlorine like odour due to tetroxide compound. Osmium tetroxide highly toxic.

TRANSITION ELEMENT: IRON GROUP

Relative atomic mass:

190.23(3)

Electron configuration:

1s²2s²p⁶3s²p⁶d¹⁰4s²p⁶d¹⁰f¹⁴5s²p⁶d⁶6s²

Oxidation state:

2,3,4,6,8

Electronegativities:

2.2

Atomic radius:

133.8 pm

Standard state (20 °C):

solid

Density (g dm^-3):

22590 (293 K) 20100 (m.p.)

Molar volume (cm³ mol^-1):

8.42 (293 K) 9.46 (m.p.)

Thermal conductivity:

87.6 W m^-1 K^-1

Electrical resistivity (20 °C):

9.5 μΩcm

THERMAL PROPERTIES

Melting point:

3033 °C

Heat of fusion:

29.3 kJ mol^-1

Boiling point:

5012 °C

Heat of vaporization:

738.06 kJ mol^-1

Critical temperature:

12427 °C

Heat of atomization:

791 kJ mol^-1

IONIZATION ENERGIES AND ABUNDANCE

1st ionization energy:

814.17 kJ mol^-1

Abundance of element (Earth’s crust):

0.005 ppm

ISOTOPES

Isotopes

Relative atomic mass

Abundance (%)

¹⁸⁴Os

183.952491(3)

0.02(1)

¹⁸⁶Os

185.953838(3)

1.58(30)

¹⁸⁷Os

186.955748(3)

1.6(3)

¹⁸⁸Os

187.955836(3)

13.3(7)

¹⁸⁹Os

188.958145(3)

16.1(8)

¹⁹⁰Os

189.958445(3)

26.4(12)

¹⁹²Os

191.961479(4)

41.0(8)

MINERALS AND USES

Osmium is obtained from the same ores as platinum. Used to tip gold pen points, instrument pivots, to make electric light filaments. Used for high temperature alloys and pressure bearings. Very hard and resists corrosion better than any other.

REDUCTION POTENTIALS

Balanced half-reaction

E^o / V

Annotation

Os²⁺ + 2e^- Os(s)

+0.85

1 mol dm^-3 HCl

OsO₂(s) + 2H₂O + 4e^- Os(s) + 4OH^-

- 0.15

 

OsO₄(s) + 8H⁺ + 8e^- Os(s) + 4H₂O

+0.85

 

OsO₄(s) + 8H⁺ + 6Cl^- + 4e^- OsCl₆^2- + 4H₂O

+1.0

 

HOsO₅^- + 2e^- OsO₄^2- + OH^-

+0.3

 

OsO₄^2- + 2H₂O + 2e^- OsO₂(s) + 4OH^-

+0.1

 

OsCl₆^2- + e^- OsCl₆^3-

+0.85

 

OsCl₆^3- + e^- Os²⁺ + 6Cl^-

+0.4

 

OsCl₆^3- + 3e^- Os(s) + 6Cl^-

+0.71

 

More information can be found at http://www.ktf-split.hr/periodni/en/os.html