Rhenium, discovered in 1925, is the last discovered element with a stable isotope.
German chemists Walter Noddack, Ida Tacke, and Otto Berg identified element 75 through X-ray spectroscopy and named it rhenium, after the Rhine River. Rhenium is exceptionally rare and was found in platinum ore, columbite, gadolinite, and molybdenite. In 1928, the team extracted just 1 gram from 660 kilograms of molybdenite.
The discovery story has an earlier twist: Japanese chemist Masataka Ogawa reported “nipponium” in 1908, believing he had found element 43. Later analysis indicates that his sample contained rhenium, element 75, although the original claim was assigned incorrectly. Hafnium, discovered in 1923, was the previous stable element found.
Rhenium has two naturally occurring isotopes: stable rhenium-185 and very long-lived radioactive rhenium-187. Later discoveries, beginning with technetium, involved elements with no stable isotopes, making rhenium the conventional final member of the stable-isotope lineup.