Francium is a chemical element with symbol Fr and atomic number 87. It used to be known as eka-caesium and actinium K. It is the second-least electronegative element, behind only caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon.
Three reasons Francium stands out
- 1
Highly radioactive, it's the second rarest naturally occuring element.
- 2
At any given moment, fewer than 30 grams of it are estimated to exist in the entire Earth's crust.
- 3
It gives up its single outer electron more readily than any other element, making it the most electropositive known.
A few moments at the bottom of group one
Francium is continually created and destroyed in uranium decay chains, leaving only trace amounts on Earth. Its longest-lived isotope survives for minutes, preventing anyone from collecting a visible sample. Experiments with trapped atoms test how an extremely heavy alkali metal follows—and departs from—group trends.