Rhodium is a chemical element with the symbol Rh and atomic number 45. It a hard silvery-white metal of the transition series. Due to its low contact resistance and resistance to corrosion, it is used as a contact material in the production of reed switches. Rhodium coated reed switches perform as well Ruthenium.
|Appearance||silvery white metallic|
|Standard atomic weight Ar, std(Rh)||102.90549(2)|
|Rhodium in the periodic table|
|Atomic number (Z)||45|
|Element category||Transition metal|
|Electron configuration||[Kr] 4d8 5s1|
|Electrons per shell||2, 8, 18, 16, 1|
|Phase at STP||solid|
|Melting point||2237 K (1964 °C, 3567 °F)|
|Boiling point||3968 K (3695 °C, 6683 °F)|
|Density (near r.t.)||12.41 g/cm3|
|when liquid (at m.p.)||10.7 g/cm3|
|Heat of fusion||26.59 kJ/mol|
|Heat of vaporization||493 kJ/mol|
|Molar heat capacity||24.98 J/(mol·K)|
|Oxidation states||−3, −1, 0, +1, +2, +3, +4, +5, +6 (an amphoteric oxide)|
|Electronegativity||Pauling scale: 2.28|
|Atomic radius||empirical: 134 pm|
|Covalent radius||142±7 pm|
|Spectral lines of rhodium|
|Crystal structure||face-centered cubic (fcc)|
|Speed of sound thin rod||4700 m/s (at 20 °C)|
|Thermal expansion||8.2 µm/(m·K) (at 25 °C)|
|Thermal conductivity||150 W/(m·K)|
|Electrical resistivity||43.3 nΩ·m (at 0 °C)|
|Magnetic susceptibility||+111.0·10−6 cm3/mol (298 K)|
|Young's modulus||380 GPa|
|Shear modulus||150 GPa|
|Bulk modulus||275 GPa|
|Vickers hardness||1100–8000 MPa|
|Brinell hardness||980–1350 MPa|
|Discovery and first isolation||William Hyde Wollaston (1804)|
|Main isotopes of rhodium|
Rhodium is a chemical element with the symbol Rh and atomic number 45. It is an ultra-rare, silvery-white, hard, corrosion-resistant, and chemically inert transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isotope, 103Rh. Naturally occurring rhodium is usually found as free metal, as an alloy with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals.
Rhodium is found in platinum or nickel ores together with the other members of the platinum group metals. It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds.
The element's major use (approximately 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converters in automobiles. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its appearance while sterling silver is often rhodium-plated for tarnish resistance. Rhodium is sometimes used to cure silicones; a two-part silicone in which one part containing a silicon hydride and the other containing a vinyl-terminated silicone are mixed. One of these liquids contains a rhodium complex.
Rhodium detectors are used in nuclear reactors to measure the neutron flux level. Other uses of rhodium include asymmetric hydrogenation used to form drug precursors and the processes for the production of acetic acid.