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Chemical element, symbol Rh and atomic number 45 / From Wikipedia, the free encyclopedia

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Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isotope, which is 103Rh. Naturally occurring rhodium is usually found as a free metal or 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.

Quick facts: Rhodium, Pronunciation, Appearance, Standard ...
Rhodium, 45Rh
Pronunciation/ˈrdiəm/ (ROH-dee-əm)
Appearancesilvery white metallic
Standard atomic weight Ar°(Rh)
  • 102.90549±0.00002
  • 102.91±0.01 (abridged)[1]
Rhodium in the periodic table


Atomic number (Z)45
Groupgroup 9
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d8 5s1
Electrons per shell2, 8, 18, 16, 1
Physical properties
Phase at STPsolid
Melting point2237 K (1964 °C, 3567 °F)
Boiling point3968 K (3695 °C, 6683 °F)
Density (near r.t.)12.41 g/cm3
when liquid (at m.p.)10.7 g/cm3
Heat of fusion26.59 kJ/mol
Heat of vaporization493 kJ/mol
Molar heat capacity24.98 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2288 2496 2749 3063 3405 3997
Atomic properties
Oxidation states−3[2], −1, 0, +1,[3] +2, +3, +4, +5, +6, +7[4] (an amphoteric oxide)
ElectronegativityPauling scale: 2.28
Ionization energies
  • 1st: 719.7 kJ/mol
  • 2nd: 1740 kJ/mol
  • 3rd: 2997 kJ/mol
Atomic radiusempirical: 134 pm
Covalent radius142±7 pm
Color lines in a spectral range
Spectral lines of rhodium
Other properties
Natural occurrenceprimordial
Crystal structure face-centered cubic (fcc)
Face-centered cubic crystal structure for rhodium
Speed of sound thin rod4700 m/s (at 20 °C)
Thermal expansion8.2 µm/(m⋅K) (at 25 °C)
Thermal conductivity150 W/(m⋅K)
Electrical resistivity43.3 nΩ⋅m (at 0 °C)
Magnetic orderingparamagnetic[5]
Molar magnetic susceptibility+111.0×10−6 cm3/mol (298 K)[6]
Young's modulus380 GPa
Shear modulus150 GPa
Bulk modulus275 GPa
Poisson ratio0.26
Mohs hardness6.0
Vickers hardness1100–8000 MPa
Brinell hardness980–1350 MPa
CAS Number7440-16-6
Discovery and first isolationWilliam Hyde Wollaston (1804)
Isotopes of rhodium
Main isotopes[7] Decay
abun­dance half-life (t1/2) mode pro­duct
99Rh synth 16.1 d β+ 99Ru
101Rh synth 4.07 y ε 101Ru
101mRh synth 4.343 d ε 101Ru
IT 101Rh
102Rh synth 207 d β+ 102Ru
β 102Pd
102mRh synth 3.742 y β+ 102Ru
IT 102Rh
103Rh 100% stable
105Rh synth 35.341 h β 105Pd
Symbol_category_class.svg Category: Rhodium
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Rhodium is found in platinum or nickel ores 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 (consuming about 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 to resist tarnishing. 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.[8]

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.

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