Francium

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Francium is a chemical element in the periodic table that has the symbol Fr and atomic number 87. This is a highly radioactive alkali metal that is found in very small amounts in uranium and thorium ores.

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Characteristics

This element, which was named for France, was discovered in 1939 by Marguerite Perey of the Curie Institute in Paris. Francium is the heaviest alkali metal and occurs as a result of actinium's alpha decay and can be artificially made by bombarding thorium with protons.

Even though it naturally occurs in uranium minerals, it has been estimated that there might be less than 30 grams of francium in the earth's crust at any one time, making it possibly one of the rarest elements in the crust, along with astatine. It is also the most unstable element among the first 101 and has the highest equivalent weight of any element. Francium is the least electronegative of all the known elements, with caesium as its runner up.

There are 41 known isotopes of francium, the most of any element. With a 22-minute half life, the longest lived isotope of this element is ²²³Fr which is a daughter isotope of ²²⁷Ac and is the only isotope of francium that occurs naturally. All known isotopes of francium are highly unstable, therefore knowledge of the properties of this element only comes from radiochemical procedures.

A small number of pictures of francium have been taken, but only of at the most 350,000 atoms at a time. The images were made by trapping the atoms and using a special fluorescent imaging camera. The atoms were produced by a nuclear transformation with a particle accelerator at the State University of New York at Stony Brook. ¹⁸O nuclei are accelerated to an energy of 100 MeV, to have sufficient energy to fuse with a gold nucleus and create nuclei of francium. The Fr nuclei last for typically three minutes, and must be trapped and observed before they decay.

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