Francium
Element 87 · Alkali Metal
Francium sits at the bottom of group 1, below cesium, and is the second-rarest naturally occurring element. It is intensely radioactive: the longest-lived isotope, francium-223, has a half-life of only about 22 minutes, so no visible sample has ever been collected. Its chemistry is predicted to mirror the other alkali metals, forming +1 ions in salts, but almost nothing has been measured directly because it vanishes as it is made.
Key facts
| Atomic number | 87 |
|---|---|
| Atomic weight | [223] |
| Category | Alkali Metal |
| Group / Period | 1 / 7 |
| Block | s |
| Electron configuration | [Rn] 7s1 |
| Common oxidation states | +1 |
| State at STP | Solid |
| Electronegativity | 0.7 |
| Density | 1.87 g/cm3 (estimated) |
| Melting point | 27 °C (estimated) |
| Boiling point | 677 °C (estimated) |
Occurrence
Francium occurs only in trace amounts as a decay product of actinium-227 in uranium ores. At any moment the entire Earth's crust holds on the order of 30 grams, spread invisibly through rock.
Applications
Fundamental research on atomic structure and relativity effects
Production in particle accelerators for spectroscopy studies
No commercial or industrial uses exist
Common compounds
- Francium chloride (predicted, FrCl)
- Francium hydroxide (predicted, FrOH)
Francium was discovered in 1939 by Marguerite Perey at the Curie Institute in Paris, making it the last naturally occurring element to be found.
Data source: IUPAC standard atomic weights 2021