Francium is an element that is highly unstable and has the shortest half-life of any element. It is the second-to-last element on the periodic table and is extremely rare in nature. Francium is highly reactive and can form compounds with many other
From Wikipedia
Francium is a chemical element; it has symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223, has a half-life of only 22 minutes. It is the second-most electropositive element, behind only caesium, and is the second rarest naturally occurring element. Francium's isotopes decay quickly into astatine, radium, and radon. The electronic structure of a francium atom is [Rn] 7s1; thus, the element is classed as an alkali metal.