Francium (Fr)

• Element Symbol: Fr
• Atomic Number: 87
• Atomic Mass: 223
• Group # in Periodic Table: 1
• Group Name: Alkali metals
• Period in Periodic Table: 7
• Block of Periodic Table: s-block
• Discovered by: Marguerite Catherine Perey (1939)

Francium is a highly radioactive alkali metal in the periodic table. The alkali metals are the elements in group 1, excluding hydrogen, and they include lithium, sodium, potassium, rubidium, and cesium. All alkali metals are explosively reactive with water, but cesium and francium are the most reactive. Francium is the heaviest alkali metal.

Russian chemist Dmitri Mendeleev predicted the existence of francium, or element 87, around seventy years before it was actually discovered. His diagram of elements included a spot for element 87. Mendeleev named this element eka-cesium, which means "one cesium." This name refers to the placement of element 87 one space below cesium in the periodic table.

A variety of scientists claimed to have discovered element 87 in the early years of the twentieth century, including scientists from Russia, England, Romania, France, and the United States. Many of these scientists studied x-rays of various minerals and compounds. Observed emission lines were hypothesized to be produced by element 87. However, the results from these observations could not be verified.

Element 87 was eventually discovered by French chemist Marguerite Perey in 1939. Perey worked in Marie Curie’s laboratory at the Radium Institute (now the Curie Institute) in Paris. She had been hired as a teenager to work as a technician for Curie herself. Many years of work had allowed Perey to become an expert in the purification of the element actinium from uranium ore. While working with an actinium sample in late 1938, Perey detected radiation emission that was more intense than previous samples she had worked with. Further chemical analysis of the sample allowed Perey to identify a new radioactive element. She named this element francium in honor of her home country, France. Francium was the last of the natural elements to be discovered.

Perey’s discovery of francium allowed her to pursue a PhD at the Sorbonne in Paris. She later headed the Department of Nuclear Chemistry at the University of Strasbourg, and she pursued research on the biological effects of francium. Some of her work focused on the use of francium as a tool to diagnose cancer. However, it became clear that francium was an element that could severely damage human health. Perey’s early exposure to francium had caused radiation to concentrate within her body. She developed bone cancer at an early age and lost her eyesight and parts of her hands due to radiation poisoning. Marguerite Perey eventually died from cancer at the age of sixty-five.

Perey was only one of many researchers to suffer severe health problems or early death due to exposure to radioactive elements. Those scientists who first discovered such elements did not recognize the potential hazards of radiation. Therefore, necessary safety precautions were not taken within laboratories. There are stories of technicians working in the Curie lab without gloves or other protective gear. Many of these technicians died young. Irène Joliot-Curie, Marie Curie’s daughter and a Nobel Prize winner in her own right, sometimes used mouth pipetting—that is, sucking liquid up into a tube using one’s mouth—to move solutions containing radioactive elements between containers. Joliot-Curie eventually contracted leukemia. Marie Curie herself carried around test tubes containing radium without proper shielding, and she died of anemia caused by radiation exposure. Even more than eighty years after her death, Marie Curie’s notebooks are still too radioactive to handle.

Physical Properties

Francium is hypothesized to be a soft, silvery metal that is solid in its standard state at 298 kelvins (K). However, a sample of francium large enough to detect these properties has never been produced. Most of francium’s physical properties are unknown due to the element’s rarity, its highly radioactive nature, and its extremely short half-life. Its estimated melting point is 27 degrees Celsius (°C). Its estimated boiling point is 680 °C. Its density, specific heat, thermal conductivity, electrical conductivity, resistivity, and magnetic type are all unknown.

Chemical Properties

Francium is explosively reactive with water. The radioactive decay of this element generates intense heat. Most of francium’s chemical properties are unknown. However, it is hypothesized that the physical and chemical properties of francium are similar to those of cesium.

Francium has an electron affinity of 44 kilojoules per mole (kJ/mol). This element has one valence electron. Its electronegativity is 0.7. Its ionization energy is 380 kJ/mol. It has one oxidation state, +1.

Francium has thirty-four known isotopes, all of which are radioactive and extremely short-lived. Their mass numbers range from 199 to 232. The shortest-lived isotopes of francium have half-lives of less than one minute. Its longest-lived isotope, francium-223, has a half-life of twenty-two minutes. This element has an electron configuration of [Rn]7s¹.

Applications

Francium is an extremely rare element, but it does exist in nature. Short-lived francium isotopes are produced through decay chains of other natural radioactive elements, such as actinium. Tiny amounts of francium may be found in some uranium ores. It is hypothesized that only thirty grams of natural francium exist on Earth at any one time. Of all the natural elements, francium is the least stable.

Francium can be produced synthetically in particle accelerators and nuclear reactors. In a particle accelerator, thorium is bombarded with protons to produce francium. In a reactor, radium is bombarded with neutrons to produce actinium, which then decays to produce francium.

Synthetic francium can only be produced in extremely small quantities. Due to the short half-lives of its isotopes, francium also disappears quickly after it has been produced. Even the longest-lived isotope has a half-life of less than thirty minutes. This short half-life has made it nearly impossible to determine francium’s physical and chemical properties. Its intense radiation has also impeded further study. Because francium is a strongly radioactive element that disappears quickly, it has no practical applications.

Bibliography

Aldersey-Williams, Hugh. Periodic Tales: A Cultural History of the Elements, from Arsenic to Zinc. New York: Viking, 2011. Print.

Dye, James L. "Francium (Fr)." Encyclopædia Britannica. Encyclopædia Britannica, 14 June 2013. Web. 25 Sept. 2015.

"Francium." Periodic Table. Royal Soc. of Chemistry, 2015. Web. 25 Sept. 2015.

Gray, Theodore. The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog, 2009. Print.

Greenwood, Veronique. "My Great-Great-Aunt Discovered Francium. And It Killed Her." New York Times Magazine. New York Times, 3 Dec. 2014. Web. 25 Sept. 2015.

Parsons, Paul, and Gail Dixon. The Periodic Table: A Visual Guide to the Elements. New York: Quercus, 2014. Print.

"Technical Data for Francium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 25 September 2015.