osmium

• Description
• General information
• Physical data
• Radii
• Electronegativities
• Solid state structure
• Temperatures
• Enthalpies
• Ionization Enthalpies
• Isotopes
• Further information

Description

Osmium metal is lustrous, bluish white, extremely hard, and brittle even at high temperatures. It has the highest melting point and lowest vapour 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 oxidising 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 m^-3 can cause lung congestion, skin damage, or eye damage.

General information

Discoveror: Smithson Tennant
Date discovered: 1803
Discovered at: England
Meaning of name: From the Greek word "osme" meaning "smell"

Physical data

Standard state: solid at 298 K
Colour: bluish grey
Density of solid at ambient temperature/kg m^-3: 22610
Molar volume/cm³: 8.42

Radii /pm

Atomic: 185
Covalent (single bond):
Pauling radius for the ion [Os]^-: no data

Valence shell orbital radius maxima (R_max)

orbital	s	p	d	f
radius	155.5	no data	70.6	21.3

Electronegativities

Both values are quoted on the Pauling scale.

Pauling: 2.2
Allred Rochow: 1.52

Crystal Structure

structure: hcp (hexagonal close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.

Temperatures (/K)

melting point: 3306
boiling point: 5285

Enthalpies /kJ mol^-1

fusion: 31.0
vaporization: 628

single bond enthalpies:

Os-F	Os-Cl	Os-Br	Os-I	Os-Os
no data	no data	no data	no data	no data

Ionization enthalpies /kJ mol^-1

Number	Enthalpy
1st	840

Isotopes

This section gives some data for naturally occurring isotopes.

Nominal mass	Accurate mass	% natural abundance
184Os	183.952488 (4)	0.02 (1)
186Os	185.953830 (4)	1.58 (30)
187Os	186.955741 (3)	1.6 (1)
188Os	187.955830 (3)	13.3 (2)
189Os	188.958137 (4)	16.1 (3)
190Os	189.958436 (4)	26.4 (4)
192Os	191.961467 (4)	41.0 (3)

Further Information

• Additional information about WebElements 1.2.2
• This is a licensed copy (here is the full list) of WebElements 1.2.2 and contains a subset of the material contained within the main version of WebElements (version 2)
• For further information please try WebElements version 2
• Sheffield Chemdex: perhaps the largest internet chemistry directory
• Sheffield Chemputer: interactive chemistry calculators on the WWW