Rhenium is a chemical element with the symbol Re and atomic number 75.
It is a silvery-gray, heavy, third-row transition metal in group 7 of the
periodic table. With an estimated average concentration of 1 part per billion
(ppb), rhenium is one of the rarest elements in the Earth's crust. It has the
third-highest melting point and second-highest boiling point of any element at
5869 K. It resembles manganese and technetium chemically and is mainly
obtained as a by-product of the extraction and refinement of molybdenum and
copper ores. It shows in its compounds a wide variety of oxidation states
ranging from −1 to +7.
Discovered by Walter Noddack, Ida Tacke and Otto Berg in 1925, rhenium was the
last stable element to be discovered.