Rhodium is a chemical element with the symbol Rh and atomic number 45. A rare silvery-white hard transition metal and a member of the platinum group, rhodium is found in platinum ores and is used in alloys with platinum and as a catalyst. It is usually the most expensive precious metal, though it is sometimes surpassed by rhenium, depending on the market.
Rhodium is a hard silvery white and durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere at the melting point of rhodium, but on solidification the oxygen is released. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by acids: it is completely insoluble in nitric acid and dissolves slightly in aqua regia. A complete dissolution of rhodium in powder form is only obtained in sulfuric acid.
|Atomic number||45||Melting point /°C||1960|
|No. of naturally occurring isotopes||1||Boiling point /°C||3760|
|Metal radius(12-coordinate)/pm||134||ΔHf(monoatomic gas)/kJmol-1||556(+/-11)|
|Effective ionic radius(6-coord)/pm V||55||Electrical resistivity (20°C)/u,ohm cm||4.33|
|Effective ionic radius(6-coord)/pm IV||60||Ionization energy/kJmol-1 I||720|
|Effective ionic radius(6-coord)/pm III||66.5||Ionization energy/kJmol-1 II||1743|
|Electronegativity χ||2.2||Ionization energy/kJmol-1 III||2997|
|Temperature (oC) @Vap. Pressure||Techniques||Remarks|
|10-8 Torr||10-6 Torr||10-4 Torr||Electron Beam||Crucible||Coil||Boat|
|1277||1472||1707||Good||ThO2 & Vitreous Graphite||Tungsten||Tungsten|| EB Gun preferred|
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