Francium

Francium is considered as the most unstable natural occurring element. Several scientists unsuccessfully claimed the discovery, but finally in the year 1939 Maguerite Perey was able to provide evidence and named it after her homeland France. The radioactivity is two million times higher than plutonium. Therefore it is impossible to produce visible amounts of it, the sample woud immediately evaporate because of the heat generated by its own radioactivity.