Francium
alkali metal · period 7 · group 1 (alkali metals (and hydrogen)) · s-block
Francium is a chemical element with the symbol Fr and atomic number 87. Prior to its discovery, it was referred to as eka-caesium.
What the numbers say
At standard temperature and pressure Francium is a solid, sitting in period 7, group 1 of the s-block.
Its melting point of 300 K (27 °C) is the 96th highest of the 110 elements with a measured value — mid-range among the elements.
Pauling electronegativity is 0.79. Paired with oxygen (3.44) that is a difference of 2.65, which puts the bond predominantly ionic — expect a stable oxide ceramic.
First identified in 1939.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Fr — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 18 · N 32 · O 18 · P 8 · Q 1
Properties
| Atomic number | 87 |
|---|---|
| Atomic mass | 223 u |
| Series | alkali metal |
| Group | 1 |
| Period | 7 |
| Block | s-block |
| Phase at STP | Solid |
| Melting point | 300 K (27 °C) |
| Boiling point | 950 K (677 °C) |
| Electronegativity (Pauling) | 0.79 |
| Electron configuration | [Rn] 7s¹ |
| Oxidation states | 1 |
| Discovered | 1939 |
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See Fr in context with all 118 elements.
Working with francium in a real design?
Ask the materials chat how Fr behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.