iridium

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

Description

The name iridium is appropriate, for its salts are highly coloured. Iridium is white, similar to platinum, but with a slight yellowish cast. It is very hard and brittle, making it very hard to machine, form, or work. It is the most corrosion resistant metal known, and was used in making the standard metre bar of Paris, which is a 90% platinum-10% iridium alloy. This metre bar has since been replaced as a fundamental unit of length (see Krypton).

Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN.

General information

Discoveror: Smithson Tennant, Antoine Fourcroy, Louis Vanquelin, Hippolyte Collet-Descotils
Date discovered: 1803
Discovered at: England, France
Meaning of name: From the Greek word "iris" meaning "rainbow"

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m^-3: 22650
Molar volume/cm³: 8.52

Radii /pm

Atomic: 180
Covalent (single bond):
Pauling radius for the ion [Ir]^-: no data

Valence shell orbital radius maxima (R_max)

orbital	s	p	d	f
radius	151.5	no data	67.8	20.7

Electronegativities

Both values are quoted on the Pauling scale.

Pauling: 2.20
Allred Rochow: 1.55

Crystal Structure

structure: ccp (cubic 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: 2739
boiling point: 4701

Enthalpies /kJ mol^-1

fusion: 26.4
vaporization: 560

single bond enthalpies:

Ir-F	Ir-Cl	Ir-Br	Ir-I	Ir-Ir
no data	no data	no data	no data	no data

Ionization enthalpies /kJ mol^-1

Number	Enthalpy
1st	880

Isotopes

This section gives some data for naturally occurring isotopes.

Nominal mass	Accurate mass	% natural abundance
191Ir	190.960584 (4)	37.3 (5)
193Ir	192.962917 (4)	62.7 (5)

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