chemical element in the periodic table that has the symbol Fr and atomic number 87. This is a highly radioactive alkali metal that is found in uranium and thorium ores.
This element, which was named for France, was discovered in 1939 by Marguerite Perey of the Curie Institute in Paris. Francium is the heaviest alkali metal and occurs as a result of actinium's alpha decay and can be artificially made by bombarding thorium with protons.
Even though it naturally occurs in uranium minerals, it has been estimated that there might be less than one ounce of francium in the crust of the earth at any one time. It is the most unstable element among the first 101 and has the highest equivalent weight of any element.
There are 33 known isotopes of francium. At 22 minutes, the longest lived isotope of this element is Fr-223 which is a daughter isotope of Ac-227 and is the only isotope of francium that occurs naturally. All known isotopes of francium are highly unstable, therefore knowledge of the properties of this element only comes from radiochemical procedures.
No research team has produced a weighable quantity of francium nor has this element been prepared or isolated, and probably never will be. Chemically, the properties of francium are closest to those of caesium.