1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰f¹⁴ 5s²p⁶d¹⁰ 6s²p⁶ 7s¹

Characteristics

Even though it naturally occurs in Uranium minerals, it has been estimated that there might be only from 340 to 550 grams of Francium in the Earth's crust at any one time, making it the second rarest element in the crust, next to 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 Cesium as its runner up.

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 specia 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.

Occurrence

Although considered a natural element, scientists estimate that there is no more than one ounce of Francium in the earth's crust at one time.  Since there is so little naturally occurring Francium on earth, scientists must produce Francium in order to study it.  Francium can be produced by bombarding Thorium with protons or by bombarding Radium with neutrons.

Applications

Due to the small amounts produced and its short half-life, there are currently no uses for Francium outside of basic scientific research.

Isotopes

There are 32 known isotopes of Francium (with the mass number between 199 and 232), and 11 metastable states.  With a 21.8-minute half-life, the longest lived isotope of this element is ²²³Fr which is a daughter isotope of ²²⁷Ac and is one of two isotopes of Francium that occur naturally.  The second naturally occurring isotope of Francium is ²²⁴Fr, being the member of the Thorium radioactive series.  All known isotopes of Francium are highly unstable, therefore knowledge of the properties of this element only comes from radiochemical procedures.

Francium's most stable isotope, ²²³Fr, has a half-life of about 22 minutes.   It decays into ²²³Ra through beta decay or into ²¹⁹As through alpha decay.

(France) Discovered in 1939 by Mlle. Marguerite Perey of the Curie Institute, Paris. Francium, the heaviest known member of the alkali metals series, occurs as a result of an alpha disintegration of actinium. It can also be made by artificially by bombarding thorium with protons. While it occurs naturally in uranium minerals, there is probably less than an ounce of francium at any time in the total crust of the earth. It has the highest equivalent weight of any element, and is the most unstable of the first 101 elements of the periodic system. Thirty-three isotopes of francium are recognized. The longest lived 223Fr (Ac, K), a daughter of 227Ac, has a half-life of 22 min. This is the only isotope of francium occurring in nature. Because all known isotopes of francium are highly unstable, knowledge of the chemical properties of this element comes from radiochemical techniques. No weighable quantity of the element has been prepared or isolated. The chemical properties of francium most resemble cesium.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond