Francium - chemistry.

Francium - chemistry. Francium, symbol Fr, radioactive metallic element that closely resembles cesium in chemical properties. In group 1 (or Ia) of the periodic table (see Periodic Law), francium is one of the alkali metals. The atomic number of francium is 87. Marguerite Perey of the Curie Laboratory of the Radium Institute of Paris discovered the element in 1939. The element was named after the country of France. Francium is produced when the radioactive element actinium disintegrates. Francium is naturally radioactive; its longest-lived isotope, francium-223 (also known as actinium-K) has a half-life of 22 minutes. It emits an extremely energetic beta particle of 1,100,000 electron volts (eV) energy when it decays. Isotopes ranging in atomic weights from 199 to 232 are known. Francium is the heaviest of the alkali metals; it is the most electropositive element. All its isotopes are radioactive and short-lived. The element is extremely rare, though atoms of francium have been detected in uranium ores. See also Radioactivity. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.