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Element Fact
In 1961, the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis of atomic weight, which has a mass of exactly 12.000 atomic mass unit.

Rhodium, Rh

rhodium sample

Atomic number: 45
Atomic mass: 102.90550(2)
Natural abundance: 0.0001 ppm
103Rh (102.90550) - 100%

History and Production

From the Greek rhodon, meaning rose. It was discovered in 1803 by W.H. Wollaston from the residue after crude platinum ore has been dissolved in aqua regia. The name was given due to the rose-coloration of its salt in water. It is obtained from anode slimes in the electrolytic refinement of other metals such as copper or nickel. Aqua regia is added to remove platinum, palladium and gold, and after a series of chemical treatment rhodium is sepearated as powder or sponge. It is used as a catalyst for hydrogenation process. It alloys with platinum and palladium for furnace windings, thermocouple elements, electrodes and laboratory cricubles. The alloy is also used in wear and corrosion resistant electrical contact.

Physical Data

It is silvery white, lustrous and very hard. It is very rare, and is usually occurred native with other platinum metals in river sands and also in the copper-nickel sulfide deposits ores of Sudbury in Ontario.

Interatomic distance: 269 pm
Melting point: 1964C
Boiling point: 3695C
Thermal conductivity/Wm-1K-1: 150 (27C)
Density/kgm-3: 12410 (20C), 10650 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 556.9 kJ/mol
Gibbs free energy of formation: 510.8 kJ/mol
Entropy: 185.8 J/mol K
Heat capacity: 21.0 J/mol K

Electronic data

Electronic configuration: [Kr] 4d8 5s1
Term symbol: 4F9/2
Electron affinity: 109.7039 kJ/mol   Electronegativity (Pauline): 2.28
Ionization energy (first, second, third): 719.67, 1744.46, 2996.84 kJ/mol

Chemical properties

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