Francium was discovered in 1939. It is very unstable alkali metal and considered the second rarest element in the earth crust.
History and Discovery
Francium was discovered by Marguerite Perey in 1939, who was studying the decay of actinium-227 by negative beta decay to an isotope of thorium and by alpha emission into an isotope of Francium-223, which was known as actinium. Dmitri Mendeleev predicted the existence of element based on the gap in the periodic table in 1870. Perey suggested the name francium after France and this name was adopted by the IUPAC (International Union of Pure and Applied Chemistry) in 1949. Francium is the last natural element to be discovered [1].
Francium
| Periodic Table Classification | Group 1 Period 7 |
|---|---|
| State at 20C | Solid (predicted) |
| Color | Silver-gray-metallic (presumed) |
| Electron Configuration | [Rn] 7s1 |
| Electron Number | 87 |
| Proton Number | 87 |
| Electron Shell | 2, 8, 18, 32, 18, 8, 1 |
| Density | 0.00 g.cm-3 at 20°C |
| Atomic number | 87 |
| Atomic Mass | 223 g.mol -1 |
| Electronegativity according to Pauling | >0.79 |
Occurrence
Francium is formed by radioactive decay of actinium, and artificially made by bombarding thorium with protons. It is naturally present in uranium and consider the second rarest element in the earth crust. It exists in short-lived radioactive forms and cannot be isolated in pure stable form. It is estimated that less than 30 grams of francium occur at any time in the earth crust.
Physical Characteristics
Francium is the shiny metal in its pure state and exist in liquid form at room temperature rather than a solid. Francium belongs to alkali group of the periodic table so its physical properties are similar with alkali group elements. Its melting point is about 27oC and its boiling point is 677oC, but both have uncertainty due to high radioactivity and is extremely rare in nature. Francium is heaviest known metal of alkali group. Its atomic number is 87 and atomic mass is 223 [2].
Chemical Characteristics
Francium chemical properties are similar with caesium. It has slightly higher ionization energy and electron affinity than caesium. It is the least electronegative element so it is chemically reactive alkali metal. And readily loses it outer shell to become Nobel element. Like alkali metals it is readily oxidized in air and vigorously react with water. It exit in +1 oxidation state. It has slightly higher ionization energy than cesium. Nearly all francium salts are water soluble.
Significance and Uses
- There are no commercial applications due to its instability and rarity in nature.
- Francium has been used in research purpose only [3].
Health Hazards
Francium has no known biological role in human life. Its toxicity is just due to its radioactivity, that can cause damage to cells and nuclear material.
Isotopes of Francium
The longest-lived isotope of francium is Fr-223, which has a half-life of only 22 minutes. Thirty four artificial isotopes with atomic masses from 199 to 232 because natural isotope of francium cannot be concentrated. All isotopes decay into astatine, radium or radon.
REFERENCES
[1]. https://www.britannica.com/science/francium
[2]. http://www.newworldencyclopedia.org/entry/Francium
[3]. Winter, Mark. “Uses”. Francium. The University of Sheffield. Retrieved March 25, 2007.