ElementsWhat is francium?
Francium is a strongly radioactive metal. Its longest-lived form lasts only minutes, so only a few grams at most exist in the Earth's crust at any time.
What is francium used for?
No uses outside research.
Where the name comes from
From France, the home country of its discoverer, Marguerite Perey.
Key facts
- Symbol
- Fr
- Atomic number
- 87
- Atomic mass
- 223.01973 u
- Family
- Alkali metal
- Period
- 7
- Group
- 1
- Block
- s
- State at room temperature
- Solid
- Melting point
- 26.9 °C (300 K, 80 °F)
- Boiling point
- not measured
- Density
- not measured
- Electrons per shell
- 2, 8, 18, 32, 18, 8, 1
- Electron configuration
- [Rn]7s1
- Common oxidation states
- +1
- Electronegativity (Pauling)
- 0.7
- First ionisation energy
- 3.9 eV
- Electron affinity
- 0.47 eV
- Atomic radius (van der Waals)
- 348 pm
- Discovered
- 1939
Place in the periodic table
Francium is element number 87. It sits in period 7 (row 7) of the periodic table, in group 1 (column 1), and belongs to the s-block. Just before it comes radon (86), and just after it comes radium (88). In the same column, caesium is above it. Elements in one column tend to behave alike.
Family: Alkali metals.
Physical properties
At room temperature francium is a solid. Its melting point is about 26.9 °C. Its boiling point has not been measured reliably.
Inside the atom
An atom of francium has 87 protons in its nucleus and, when neutral, 87 electrons around it. The electrons are arranged in 7 shells: 2, 8, 18, 32, 18, 8, 1. The outermost shell holds 1 electron. Written in full, the electron configuration is [Rn]7s1.
Its electronegativity on the Pauling scale is 0.7. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 3.9 electronvolts (about 376 kilojoules per mole). One mole of francium weighs 223.01973 grams, so a single gram contains about 2.70 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains francium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.