Rhenium is a transition metal in Group VIIB (Group 7) and the 6th period. Other members of the group are manganese (Mn) and technetium (Tc). Re has oxidation numbers ranging from -1 to 7.
The element was not discovered until 1925. W. Noddack, I. Tacke (later Frau Noddack), and O. Berg found it in as sample of the mineral gadolinite and named it rhenium after the river Rhine.
In the solid state, the metal has a hexagonal closest packed structure.
The elements of Group VIIB have many contrasting features. Metallic Mn was isolated in 1774, but its compounds have been known and used for centuries. Rhenium also occurs naturally, but only in trace amounts; its estimated terrestial abundance is only 0.0007 ppm, similar to that of the platinum group metals. On the other hand, technetium is man-made, albeit in kilogram quantities.
The density of Re is exceeded only by that of platinum, osmium, and iridium, and its melting point is exceeded only by that of tungsten and carbon. The metal is silvery white.
Rhenium is now obtained chiefly from molybdenum sulfide ores in Arizona and Utah. Roasting in air converts the rhenium to the volatile oxide, Re2O7, which collects in flue dusts in the processing plant. (Note that osmium also form a volatile oxide, OsO4, and Tc2O7 is volatile.)
In spite of the scarcity of the element, its price ($540/100 g in 1991) is lower than that of most of the platinum group metals and comparable with the prices of the lanthanides.
If it were not for the scarcity of rhenium, it would find wide use as it has many desirable properties. It is very ductile and so is used in wire for filaments, furnace heater windings, and thermocouples. Further, because it has good wear resistance and withstands arc corrosion, it is used in electrical contacts.
Finally, over 95% of the rhenium is used in bimetallic Pt/Re catalysts to produce low-lead, high octane gasoline.