Francium is an element


Francium - chemical symbol Fr, atomic number 87 - is a radioactive, very rare and inconsistent chemical element of the 1st main group (alkali metals) of the periodic table.

Of the naturally occurring chemical elements on earth, the francium was the last to be discovered in 1939 and named after the homeland of the discoverer Marguerite Perey.

Due to the very short half-life of the natural francium nuclides of less than 20 minutes, very little is known about this element and its compounds.

Chemically, the Francium joins the other alkali metals in its properties.

Francium was discovered by Marguerite Perey in France (from whom the element takes its name) in 1939. It was the last element that was first found in nature and did not have to be synthetically produced for the first discovery.


Overview: General data on the Francium


The Fr atom - and thus the chemical element francium - is clearly defined by the 87 positively charged protons in the atomic nucleus. The same number of electrons ensures the electrical balance in the uncharged francium atom.

The nuclear building blocks of the neutrons ensure that there are differences between the atomic nuclei. These types of atoms are grouped under the term francium isotopes or francium nuclides (isotope data: see there). The relative atomic mass must be given for the Fr nucleus under consideration; generally the atomic weight of the most stable nuclide is chosen; in the case of the Francium, it is Ar = 223 g mol-1.


Electron configuration

symbolOZshort form1s2s2p3s3p3d4s4p4d4f5s5p5d5f6s6p6d6f7s7p
Fr.87[Rn] 7s122626102610142610261


Ionization energies

The following table lists the binding energies or the ionization energies IE, i.e. the energy required in electron volts (eV) to separate a specific electron from a francium atom.

1. IE: 4.072741 eV2. IE: eV3. IE: eV4. IE: eV5. IE: eV6. IE: eV


Electron binding energy

The following table lists the electron binding energies of the individual francium electrons in the respective orbitals. The values ​​are given in electron volts (eV).











Further data


For the chemistry of francium see also the explanations under francium compounds.


Chemical data


Material and physical properties of the Francium

The following table lists some physical data and material properties of the pure Francium. In this case it should be noted that many of the values ​​listed were estimated and, in the better case, calculated and not actually measured or observed.



Geochemistry, occurrence, distribution

223Fr is an intermediate product in the α-decay of 227Actinium and can be found in traces in uranium minerals. Francium does not occur more frequently than 1 atom per 1018 Uranium atoms. It is estimated that about 30 grams of the alkali metal are found in the entire earth's crust. This makes it the second rarest element on earth after astatine.


[1] - Marguerite Perey:
L'élément 87: AcK, dérivé de l'actinium.
In: Journal de Physique et le Radium, 1939, DOI 10.1051 / jphysrad: 019390010010043500.

[2] - Eric Scerri:
Finding francium.
In: Nature Chemistry, 2009, DOI 10.1038 / nchem. 430, open access.

[3] - Mary Virginia Orna:
My favorite element. Francium: Uranium's Daughter, Perey's Discovery.
In: Journal of Chemical Education, 2009, DOI 10.1021 / ed086p1364.


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Category: Chemical elements

Updated on 02.02.2020.


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