fráncium

Francium is a chemical element with the symbol Fr and atomic number 87. It is an alkali metal, belonging to group 1 of the periodic table. Francium is extremely rare and radioactive, with its most stable isotope, francium-223, having a half-life of only 22 minutes. It is the second rarest naturally occurring element in the Earth's crust, after astatine.

Francium was discovered in 1939 by Marguerite Perey in France, hence its name. It was found as a decay product of actinium. Due to its extreme rarity and short half-life, francium has no significant industrial or commercial applications. Its primary relevance is in scientific research, particularly in atomic physics and spectroscopy.

All isotopes of francium are highly radioactive. Francium-223 is the most common isotope and decays into astatine-223 or radium-223. The chemical properties of francium are predicted to be similar to those of cesium, but its radioactivity makes it very difficult to study these properties in detail. Because of its scarcity and instability, only minuscule amounts of francium have ever been produced or isolated. Its detection is challenging due to the intense radiation it emits.