FRANCIUM

(Fr), heaviest chemical element of Group Ia in the periodic table, the alkali metal group. It exists only in short-lived radioactive forms. Natural francium cannot be isolated in visible, weighable amounts, for only about 30 grams (about one ounce) occurs at any time in the crust of the Earth. Marguerite Perey discovered francium (1939) while studying actinium-227, which decays by negative beta decay (electron emission) to an isotope of thorium (thorium-227) and by alpha emission (about 1 percent) into an isotope of francium (francium-223) that was formerly called actinium K (AcK) and is a member of the actinium decay series. Though it is the longest-lived isotope of francium, francium-223 has a half-life of only 21 minutes. Isotopes of francium with masses between 204 and 224 have been artificially prepared, and, because natural francium cannot be concentrated, it too is prepared by neutron irradiation of radium to produce actinium, which decays to produce traces of francium. The chemistry of francium can be studied only by methods designed for trace quantities. In all respects its observed behaviour, including valence of one, is that to be expected of an alkali element filling a place just below cesium in the periodic table of the elements. atomic number 87 stablest isotope (223) valence 1 electronic config. 2-8-18-32-18-8-1 or (Rn) 7s1