Francium is the rarest naturally occurring element on Earth. Scientists think there may be only 30 g of francium in Earth's rocks. Francium atoms are created when radioactive elements decay. Francium can be extracted from radioactive minerals such as thorite and uraninite, which contain small amounts of this element. Even so, to date, the largest sample of the metal made contained only 300,000 atoms, and lasted only a few days. Francium has no known uses outside of research.
Summary of properties (Fr)
| Atomic weight | [223] |
| Discoverer (year) | Perey, Marguerite (1939) |
| Natural form | metallic solid (-) |
| Electron configuration | [Rn] 7s1 |
| Melting point (ºC) | 27 |
| Boiling point (ºC) | 677 |
| Abundance in earth's crust (ppm) | <0.001 |
| Isotope (abundance) | |
| Density g/cm3 | |
| Van der Waals radius (pm) | 348 |
| Covalent radius (pm) | 242 |
| Electronegativity (Pauling) | 0.7 |
| Vaporization enthalpy (kJ/mol) | - |
| Enthalpy of fusion (kJ/mol) | - |
| Specific heat capacity (J/g·K) at 25ºC and 1 atm | - |
| Thermal conductivity (W/cm·K) at 25ºC and 1 atm | - |
| Oxidation state | +1 |
| Electron affinity (eV) | 0.46 |
| 1st Ionization potential (eV) | 4.0727 |
