Rhenium is very rare to find in nature. Only one atom in one billion in the earth's crust is a rhenium atom. It was discovered in Germany in 1925, and named after the Rhine river, it was the last non-radioactive stable element to be found. Rhenium has a very high melting point and can remain solid at extreme temperatures. This allows alloys made from this element to be used in very hot conditions, such as those found inside the tubes of X-ray machines, as well as rocket exhaust pipes and the jet engines of fighter jets.

Chemical properties

Rhenium’s chemistry is very similar to the chemistry of manganese. Rhenium forms colored oxides in several oxidation states: Re2O3 (black) ReO2 (brown) Re2O5 (blue) ReO3 (red) Re2O7 (yellow), in “+3”, “+4”, “+5”, “+6”, “+7” oxidation states, respectively.
As it is in group VIIA, its "+7" oxidation state is the preferred one. In addition, rhenium has been observed to exist in a “–1” oxidation state, which is exceptionally unusual for a metal.

Rhenium also forms a number of colored halides: ReI2 (black), Re3Cl9 (red), Re3Br9 (red-brown), Re3I9 (black), ReF4 (blue), ReCl4 (black), ReBr4 (red), ReI4 (black), ReF5 (green-yellow), ReCl5 (red-brown), ReBr5 (green-blue), ReF6 (yellow), ReCl6 (green-brown), ReF7 (yellow).

In addition, rhenium forms the perrhenate ion (ReO4), which in acidic solution, is a powerful oxidizing agent.

Summary of properties (Re)

Atomic weight186.207(1)
Discoverer (year)Noddack, Walter & Tacke, Ida (1925)
Natural formmetallic solid (hexagonal)
Electron configuration[Xe] 414 5d5 6s2
Melting point (ºC)3180
Boiling point (ºC)5627
Abundance in earth's crust (ppm)<0.001
Isotope (abundance)185Re (37.40), 187Re (62.60)
Density g/cm321.04
Van der Waals radius (pm)216
Covalent radius (pm)141
Electronegativity (Pauling)1.9
Vaporization enthalpy (kJ/mol)707.10
Enthalpy of fusion (kJ/mol)60.43
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.14
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.480
Oxidation state+7, +6, +4
Electron affinity (eV)0.15
1st Ionization potential (eV)7.8335

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