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Element Fact
There are around 120 known elements. Of these, 91 elements occur naturally on Earth. The rest no longer exist or are found only in traces as intermediate decay products alongside with other radioisotopes.

Rhenium, Re

rhenium sample

Atomic number: 75
Atomic mass: 186.207(1)
Natural abundance: 0.0007 ppm
185Re (184.952956) - 37.4%
187Re (186.955751) - 62.6%

History and Production

From Latin Rhenus, meaning Rhine. It was discovered in 1925 by W. Noddack, I. Tacke and O. Berg in a sample of gadolinite, molybdenite and platinum ores. They were able to extract only 1 g of the metal out of 660 kg of molybdenite. It was also independently discovered by F.H. Loring and J.F.G. Druce in manganese compounds. In fact it was the last naturally occuring element to be discovered. It is now recovered from the flue dust produced in the roasting of molybdenum sulfide ores. It is used in spectrometer filaments, furnace heater windings, thermocouples (Re-W up to 2200C) and electrical contacts. It is also used as a catalyst in hydrogenation and dehydrogenation processes such as petroleum refining.

Physical Data

The metal is lustrous and silvery white. It is the second highest melting point (after tungsten) metal. It is widely spread but very rare in earth, about 0.0007 ppm and does not occur free in nature, nor as any specific mineral. It is usually associated with molybdenite ores (up to 0.2%).

Interatomic distance: 274.2 pm
Melting point: 3186C
Boiling point: 5596C
Thermal conductivity/Wm-1K-1: 47.9 (27C)
Density/kgm-3: 21020 (20C), 18900 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 769.9 kJ/mol
Gibbs free energy of formation: 724.6 kJ/mol
Entropy: 188.9 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Xe] 4f14 5d5 6s2
Term symbol: 6S5/2
Electron affinity: 14.4728 kJ/mol   Electronegativity (Pauline): 1.70
Ionization energy (first, second, third): 755.818, -, - kJ/mol

Chemical properties

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