Francium
Francium is an extremely rare, intensely radioactive alkali metal and one of the least stable elements found in nature — every atom of it decays away within minutes of forming. It exists on Earth only as a fleeting byproduct of the radioactive decay of heavier elements like uranium and actinium, and at any given moment, the total amount present across the entire planet is thought to be less than an ounce.
- Group · Period
- 1 · 7
- At room temp
- solid
- Melts at
- 300 K
- Density
- Not yet available
- Discovered
- 1939
Uses
Francium has no practical commercial or industrial applications — it’s simply too rare, too radioactive, and too short-lived for that to be feasible. Its only real use is in fundamental scientific research: physicists occasionally produce minuscule numbers of francium atoms, sometimes using laser trapping techniques to hold a handful of atoms in place just long enough to study them, in order to learn about atomic structure and test predictions in physics. Because francium sits at the very bottom of the alkali metal group, studying its properties, however briefly, also helps scientists understand trends across that entire group of elements.
History
Francium was discovered in 1939 by French physicist Marguerite Perey while she was working at the Curie Institute in Paris, studying the decay products of actinium. She identified a new radioactive element that had eluded earlier researchers because it exists in such minute, fleeting quantities, and she named it francium in honor of her home country. It was the last element found in nature, rather than created artificially in a lab, and its discovery closed out the search for naturally occurring elements that had driven chemistry for well over a century.
Fun facts
- Francium's longest-lived isotope has a half-life of only about 22 minutes, meaning any sample of it vanishes almost as quickly as it forms.
- Scientists estimate that less than 30 grams of francium exist naturally in the Earth's crust at any given moment, across the whole planet.
- Francium was the last naturally occurring element to be discovered, found in France in 1939 by physicist Marguerite Perey, who named it after her home country.
Frequently asked questions
Why is francium so rare if it's a natural element?
Francium only forms as one step in the radioactive decay chains of heavier elements, and it decays away itself almost as fast as it's produced, with a longest half-life of roughly 22 minutes. Because it never accumulates, only a tiny, constantly refreshed trace of it exists in nature at any one time.
Has anyone ever seen a visible sample of francium?
No — francium decays so quickly and exists in such tiny quantities that a sample large enough to see with the naked eye has never been produced. It also generates so much heat relative to its mass through radioactive decay that a large enough sample would likely vaporize itself instantly.
What is francium used for?
Essentially nothing outside of scientific research. Because it's so unstable and scarce, francium has no commercial or industrial applications — its main value is to physicists who study it in tiny, carefully trapped quantities to learn more about atomic structure and fundamental physics.
Isotopes
37 known isotopes
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| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Fr-212 | — | 20.0 m | Electron capture / beta-plus decay (57%), Alpha decay (43%) | -3,516 keV | 7,766.85 keV | 3.80 × 10-19 eV |
| Fr-222 | — | 14.2 m | Beta-minus decay (100%) | 16,378.1 keV | 7,690.95 keV | 5.35 × 10-19 eV |
| Fr-223 | — | 22.00 m | Beta-minus decay (99.994%), Alpha decay (0.006%) | 18,382.33 keV | 7,683.67 keV | 3.46 × 10-19 eV |
Show all 37 isotopes
| Fr-197 | — | 0.6 ms | Alpha decay (100%) | 10,253.97 keV | 7,673.76 keV | 7.60 × 10-13 eV |
| Fr-198 | — | 15 ms | Alpha decay (100%) | 9,577.7 keV | 7,679.19 keV | 3.04 × 10-14 eV |
| Fr-199 | — | 12 ms | Alpha decay (0%), Electron capture / beta-plus decay | 6,771.39 keV | 7,695.26 keV | 3.80 × 10-14 eV |
| Fr-200 | — | 49 ms | Alpha decay (100%) | 6,133.58 keV | 7,700.33 keV | 9.31 × 10-15 eV |
| Fr-201 | — | 63 ms | Alpha decay (100%) | 3,588.57 keV | 7,714.84 keV | 7.24 × 10-15 eV |
| Fr-202 | — | 0.30 s | Alpha decay (100%) | 3,101.54 keV | 7,719.01 keV | 1.52 × 10-15 eV |
| Fr-203 | — | 0.55 s | Alpha decay (100%) | 876.41 keV | 7,731.71 keV | 8.30 × 10-16 eV |
| Fr-204 | — | 1.8 s | Alpha decay (92%), Electron capture / beta-plus decay (8%) | 607.31 keV | 7,734.69 keV | 2.53 × 10-16 eV |
| Fr-205 | — | 3.90 s | Alpha decay (98.5%), Electron capture / beta-plus decay (1.5%) | -1,309.82 keV | 7,745.69 keV | 1.17 × 10-16 eV |
| Fr-206 | — | 16 s | Alpha decay (84%), Electron capture (16%) | -1,246.86 keV | 7,746.96 keV | 2.85 × 10-17 eV |
| Fr-207 | — | 14.8 s | Alpha decay (95%), Electron capture / beta-plus decay (5%) | -2,849.02 keV | 7,756.27 keV | 3.08 × 10-17 eV |
| Fr-208 | — | 59.1 s | Alpha decay (89%), Electron capture / beta-plus decay (11%) | -2,664.93 keV | 7,756.9 keV | 7.72 × 10-18 eV |
| Fr-209 | — | 50.5 s | Alpha decay (89%), Electron capture / beta-plus decay (11%) | -3,782.14 keV | 7,763.75 keV | 9.03 × 10-18 eV |
| Fr-210 | — | 3.18 m | Alpha decay (60%), Electron capture / beta-plus decay (40%) | -3,343.51 keV | 7,763.12 keV | 2.39 × 10-18 eV |
| Fr-211 | — | 3.10 m | Alpha decay (80%), Electron capture (20%) | -4,140.31 keV | 7,768.36 keV | 2.45 × 10-18 eV |
| Fr-213 | — | 34.17 s | Alpha decay (99.44%), Electron capture / beta-plus decay (0.56%) | -3,554.2 keV | 7,768.45 keV | 1.34 × 10-17 eV |
| Fr-214 | — | 5.5 ms | Alpha decay (100%) | -958.33 keV | 7,757.74 keV | 8.30 × 10-14 eV |
| Fr-215 | — | 86 ns | Alpha decay (100%) | 318.14 keV | 7,753.26 keV | 5.31 × 10-9 eV |
| Fr-216 | — | 0.70 us | Alpha decay (100%), Electron capture (2e-7%) | 2,971.02 keV | 7,742.45 keV | 6.52 × 10-10 eV |
| Fr-217 | — | 22 us | Alpha decay (100%) | 4,314.66 keV | 7,737.78 keV | 2.07 × 10-11 eV |
| Fr-218 | — | 1.1 ms | Alpha decay (100%) | 7,059.44 keV | 7,726.71 keV | 4.15 × 10-13 eV |
| Fr-219 | — | 24 ms | Alpha decay (100%) | 8,616.94 keV | 7,721.18 keV | 1.90 × 10-14 eV |
| Fr-220 | — | 27.4 s | Alpha decay (99.65%), Beta-minus decay (0.35%) | 11,482.33 keV | 7,709.74 keV | 1.67 × 10-17 eV |
| Fr-221 | — | 4.9 m | Alpha decay (100%), Beta-minus decay (0.1%) | 13,277.25 keV | 7,703.26 keV | 1.55 × 10-18 eV |
| Fr-224 | — | 3.33 m | Beta-minus decay (100%) | 21,748.61 keV | 7,670.37 keV | 2.28 × 10-18 eV |
| Fr-225 | — | 3.95 m | Beta-minus decay (100%) | 23,820.6 keV | 7,662.94 keV | 1.93 × 10-18 eV |
| Fr-226 | — | 49 s | Beta-minus decay (100%) | 27,520.54 keV | 7,648.38 keV | 9.31 × 10-18 eV |
| Fr-227 | — | 2.47 m | Beta-minus decay (100%) | 29,682.45 keV | 7,640.72 keV | 3.08 × 10-18 eV |
| Fr-228 | — | 38 s | Beta-minus decay (100%) | 33,384.22 keV | 7,626.37 keV | 1.20 × 10-17 eV |
| Fr-229 | — | 50.2 s | Beta-minus decay (100%) | 35,668.25 keV | 7,618.34 keV | 9.09 × 10-18 eV |
| Fr-230 | — | 19.1 s | Beta-minus decay (100%) | 39,486.77 keV | 7,603.71 keV | 2.39 × 10-17 eV |
| Fr-231 | — | 17.6 s | Beta-minus decay (100%) | 42,080.58 keV | 7,594.5 keV | 2.59 × 10-17 eV |
| Fr-232 | — | 5.5 s | Beta-minus decay (100%) | 46,072.83 keV | 7,579.35 keV | 8.30 × 10-17 eV |
| Fr-233 | — | 0.9 s | Beta-minus decay (100%), Beta-minus, neutron emission | 48,920.05 keV | 7,569.24 keV | 5.07 × 10-16 eV |