| In 1939 by Marguerite Perey at Curie's Institute in Paris was purifying actinium-227 when she detected β-emission produced by unknown isotope with a half-life of 21 minutes. More thorough research showed that the beta decay is detected not only for the main series Actinium- RadiumActinium - ActiniumX, but also by the lateral Actinium- Actinium K-Actinium X series. The element was first known as Actinium K. Chemical analyses showed that its properties were very close to those of eka-caesium. After the World War II which interrupted the research, Perey's results were confirmed. In 1946 it was named Francium, by Perey for her native country. |
| Alkali metal Francium does not have stable isotopes. 27 known radioactive isotopes have mass numbers from 202 to 229. Most long-lived radionuclides are 212Fr [half-life T1/2 20 min, α-decay (44%), electron capture (56%)] and 223Fr [half-life T1/2 21.8 min, β-decay (99.9%)]; the latter is a constituent part of natural actino-uranium. The Francium/Uranium ratio in Earth's crust is 4x10-16. Electron configuration: 5s25p65d106s26p67s1, oxidation number: +1; electronegativity: 0.7 (Pauling scale); atomic radius: 0.29 nm, Fr+ ion radius: 0.178 nm. |