Francium

Francium is the heaviest alkali metal, in the same family as sodium and cesium, and would likely be among the most reactive metals of all, if enough could ever be gathered. Its longest-lived form, francium-223, has a half-life of only about 22 minutes. Tiny traces form in uranium ores, making it one of the rarest natural elements.

Marguerite Perey discovered it in 1939 at the Curie Institute in Paris while studying the decay of actinium, and named it after France. It was the last element discovered in nature rather than made in a lab. Scientists now create francium by firing beams of nuclei at gold, then trap small clouds of its atoms with lasers to study atomic physics.