Francium Facts – Atomic Number 87 Element Symbol Fr

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Francium Element Facts
Francium (atomic number 87, element symbol Fr) is a radioactive metal. It’s very rare in nature, but occurs in uranium ores.

Francium is a radioactive element with atomic number 87 and element symbol Fr. While this alkali metal occurs naturally, it’s very rare. It’s also highly reactive and unstable, so it’s not an element you’ll encounter in daily life. It’s probably a silver-colored liquid metal at room temperature, but so little exists that no one knows for certain. Here is a collection of useful and interesting francium facts, including its discovery, sources, and hazards.

Electron Levels of a Francium Atom
Francium electron configuration

Basic Francium Facts

Name: Francium

Atomic Number: 87

Element Symbol: Fr

Group: Group 1

Period: Period 7

Block: s-block

Element Family: Alkali metal

Atomic Mass: [223]

Electron Configuration: [Rn] 7s1

Electrons per Shell: 2, 8, 18, 32, 18, 8, 1

Discovery: Marguerite Perey (1939)

Francium Discovery

The existence of francium was predicted based on the organization of the periodic table. Multiple research groups attempted to discover the element and at least four false discovery claims were made. Marguerite Perey of the Curie Institute in Paris officially discovered the element on January 7, 1939. Perey purified a sample of actinium-227 from uranium ore and noticed an unidentified decay product. After ruling out other possibilities, she noticed a product co-precipitated with cesium salts, leading her to suspect she had a new alkali metal. Francium was the last natural element to be discovered. All elements discovered since then have been synthesized.

Element Name Origin

Prior to its discovery, element 87 was called eka-cesium or eka-caesium. From 1925 up to the element’s official discovery in 1939, many scientists thought they had discovered francium. The names russium, alkalinium, virginium, and moldavium. But, these discoveries were either erroneous or else too incomplete. Marguerite Perey initially named the isotope she discovered actinium-K and proposed the element name catium (Cm), reflecting the element’s strength as a cation. However, her supervisor (Irène Joliot-Curie) opposed the name because she thought people would associate the element with felines rather than cations. Ultimately, Perey suggested the element name francium, after France. Initially, the element symbol was Fa, but it was changed to Fr.

Francium Isotopes

There are 34 known francium isotopes, ranging from atomic mass 199 to 232. Fr-221 and Fr-223 occur naturally. Francium-223 is the most stable isotope, with a half-life of 21.8 minutes. Fr-223 decays into radium-223 by beta decay. Francium-221 has a half-life of 4.8 minutes. Fr-221 decays into astatine-217 by alpha decay. To date, the least stable isotope to be synthesized is francium-215, which has a half-life of 0.12 microseconds.

Francium Uses

This sample of uraninite (formerly called pitchblende) contains thousands of francium-223 atoms at any given time.
This sample of uraninite (formerly called pitchblende) contains thousands of francium-223 atoms at any given time. (Rob Lavinsky, iRocks.com)

Francium is too unstable to have any commercial uses. Perey proposed using the element as a diagnostic aid for cancer, but the element causes cancer, so the application wasn’t practical. Because it’s possible to synthesize and trap francium, it’s used for spectroscopy experiments into energy levels and coupling constants for subatomic particles. Energy level transitions observed from francium have validated predictions made by quantum theory.

Natural Abundance and Sources

Only two francium isotopes occurs naturally: francium-223 and francium-221. Francium-223 results from the alpha decay of actinium-227, which in turn comes from the radioactive decay of uranium. Uranium and thorium ores, such as uraninite and thorite, contain trace amounts of francium. For every 1018 uranium atoms, there is only 1 francium atom. Francium-221 is even rarer than francium-223. Francium-221 is part of the neptunium decay chain. Scientists estimate that total mass of francium in the Earth’s crust is at most 30 grams at any given time.

Francium is synthesized using a fusion reaction. Bombarding a gold-197 target with oxygen-18 atoms can produce the isotopes Fr-209, Fr-201, and Fr-211. Other methods include neutron bombardment of radium, and proton or deuteron bombardment of thorium.

Biological Role and Toxicity

Francium has no biological role in any organism. It’s highly radioactive and reactive. Exposure to the element can cause cancer. Aside from the radioactivity, contact with the element would be dangerous because its reactivity would produce a chemical burn.

Physical Data

Density: 2.48 g/cm3 (estimated)

Melting Point: 281.0 K ​(8.0 °C, ​46.4 °F) (estimated)

Boiling Point: 890 K ​(620 °C, ​1150 °F) (estimated)

State at 20ºC: liquid (solid at 0ºC)

Atomic Data

Covalent Radius: 260 pm (extrapolated)

Van der Waals Radius: 348 pm (extrapolated)

Electronegativity: Pauling scale: >0.79

1st Ionization Energy: 393 kJ/mol

Oxidation States: +1

Magnetic Ordering: Paramagnetic

Crystal Structure: body-centered cubic (bcc) (extrapolated)

Interesting Francium Facts

  • Perey proposed the name catium for the element.
  • Francium was the last natural element to be discovered.
  • Too little francium has been isolated or synthesized to weigh it or even see it. However, francium atoms fluoresce so they may be indirectly observed by the light they release.
  • It’s likely a sample of francium would vaporize itself due to the heat produced by radioactive decay.
  • It is the second-rarest natural element, after astatine.
  • It is either the most electropositive or second-most electropositive element (after cesium). Its electronegativity value is predicted rather than known for sure.
  • Francium is the most reactive of the alkali metals. A hypothetical reaction between francium and water would be even more vigorous than the reaction between cesium and water.
  • Francium, like mercury, is likely a liquid metal at room temperature.
  • Perey was nominated five times for a Nobel Prize for her discovery of francium and work in radiochemistry, but she never won the prize.

References

  • Adloff, Jean-Pierre; Kauffman, George B. (2005). “Francium (Atomic Number 87), the Last Discovered Natural Element”. The Chemical Educator. 10 (5): 387–394. doi:10.1333/s00897050956a
  • Bonchev, Danail; Kamenska, Verginia (1981). “Predicting the Properties of the 113–120 Transactinide Elements”. Journal of Physical Chemistry. American Chemical Society. 85 (9): 1177–1186. doi:10.1021/j150609a021
  • Emsley, John (2001). Nature’s Building Blocks. Oxford: Oxford University Press. pp. 151–153. ISBN 978-0-19-850341-5.
  • Lavrukhina, A. K.; Pozdnyakov, A. A. (1970). Analytical Chemistry of Technetium, Promethium, Astatine, and Francium. Translated by R. Kondor. Ann Arbor–Humphrey Science Publishers. ISBN 978-0-250-39923-9.
  • Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics. 11. CRC. pp. 180–181. ISBN 0-8493-0487-3.