Symbol	Rh
Atomic number	45
Atomic mass	102.91 g.mol -1
Electronegativity according to Pauling	2.2
Density	12.4 g.cm-3 at 20°C
Melting point	1970 °C
Boiling point	3727 °C
Isotopes	9
Electronic shell	[ Kr ] 4d8 5s1
Energy of first ionisation	742 kJ.mol -1
Standard Potential	0.6 V

Rhodium

Rhodium, together with ruthenium, palladium, osmium, iridium, and platinum form a group of elements referred to as the platinum group metals (PGM).

Rhodium metal is lustrous and silvery white. Rhodium has a higher melting point and lower density than platinum. It has a high reflectance and is hard and durable. Upon heating it turns to the oxide when red and at higher temperatures turns back to the element. Rhodium it is unaffected by air and water up to 600 C. It is insoluble in most acids, including aqua regia, but is dissolved in hot concentrated sulfuric acid and it is attacked by molten alkalis.

Applications

Most metal (85%) goes into catalytic converters for cars. The major use of the metal is in alloys with platinum and iridium, giving improved high-temperature strength and oxidation resistance. These alloys are used in furnace windings, pen nibs, phonograph needles, high-temperature thermocouple and resistance wires, electrodes for aircraft spark plugs, bearings and electrical contacts.
The metal itself,is used to plate jewelry and the reflectors of searchlights, due to its brilliance and resistance to tarnish,
It is also a highly useful catalyst in a number of industrial processes, such as the BP-Monsanto process.

Rhodium in the environment

Rodhium occurs as rare deposits of the uncombined metal, for example in Montana, USA and in rare minerals. The metal, which is available commercialy, comes as a by product of the refining of certain copper and nickel ores which can contain up to 0.1% rhodium. Most rhodium comes from South Africa and Russia, and world production is around 16 toone per year. Estimated reserves are 3.000 tonnes.

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