- Francium (Fr) is a highly radioactive alkali metal with atomic number 87, positioned in Group 1 of the periodic table beneath cesium.
- It is the second-rarest naturally occurring element on Earth, after astatine, and is considered one of the least stable of the first 101 elements.
- Francium’s electron configuration is [Rn] 7s¹, consistent with its placement as an alkali metal. It has one hundred and seventeen neutrons (in its most stable isotope), eighty-seven protons, and eighty-seven electrons arranged in seven shells.
- The most stable isotope known is francium-223 (²²³Fr), which has a half-life of only about 22 minutes, decaying via alpha emission and beta decay. Because of its short half-life and extreme rarity, only trace amounts of francium exist at any given time in nature.
- Francium was discovered in 1939 by Marguerite Perey at the Curie Institute in Paris, France. Perey identified it while studying the decay products of actinium-227 (²²⁷Ac). She originally proposed the name catium, referring to its strongly electropositive character, but later agreed with the scientific community to honor her home country, naming it francium. It was the last element discovered in nature rather than synthesized in a laboratory.
- As an alkali metal, francium would be expected to exhibit chemical behavior similar to cesium and rubidium, though its properties are not well studied due to its instability. The +1 oxidation state is the only stable form predicted, forming ionic compounds such as francium chloride (FrCl) or francium hydroxide (FrOH). Theoretical studies suggest francium might be even more reactive than cesium, though relativistic effects may counter this trend slightly. In practice, no bulk samples of francium have ever been isolated, so these predictions remain theoretical.
- Francium has no known biological role. If it were ever introduced into biological systems, its intense radioactivity would make it highly radiotoxic, but its scarcity and rapid decay prevent this from being a real-world concern.
- Environmentally, francium occurs only in trace amounts as part of the natural decay chains of actinium and thorium. At any given moment, Earth is estimated to contain no more than about 20–30 grams of francium in total, dispersed within uranium and thorium ores. It has no practical applications, and its importance lies mainly in nuclear research and the history of its discovery.
