Francium is a highly radioactive alkali metal that was discovered in 1939 and is the second least abundant element in nature. It has only one electron in its valence shell like other alkali metals and decays into astatine, radium, and radon. Francium has a melting point of 300K and boiling point of 950K with a density of 1870 kg/m3, but there are no commercial applications due to its scarcity and instability, being only used for research in biology and atomic structure.