Periodic Table


Atomic number: 87
Atomic weight: 223
Symbol: Fr
Group number: 1
Electronic configuration: [Rn].7s1


Francium occurs as a result of a disintegration of actinium. Francium is found in uranium minerals, and can be made artificially by bombarding thorium with protons. It is the most unstable of the first 101 elements. The longest lived isotope, 223Fr, a daughter of 227Ac, has a half-life of 22 minutes. This is the only isotope of francium occurring in nature, but at most there is only 20-30 g of the element present in the earth's crust at any one time. No weighable quantity of the element has been prepared or isolated. There are 20 known isotopes.

General information

Discoveror: Marguerite Perey
Date discovered: 1939
Discovered at: France
Meaning of name: Named after "France"

Physical data

Standard state: solid at 298 K
Colour: metallic
Density of solid at ambient temperature/kg m-3: no data
Molar volume/cm3: no data

Radii /pm

Atomic: no data
Covalent (single bond):
Pauling radius for the ion [Fr]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius298.6no datano datano data


Both values are quoted on the Pauling scale.

Pauling: 0.7
Allred Rochow: 0.86

Crystal Structure


The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: no data
boiling point: 273

Enthalpies /kJ mol-1

fusion: 2.1
vaporization: 64

single bond enthalpies:
Fr-F Fr-Cl Fr-Br Fr-I Fr-Fr
no data no data no data no data no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Fr.html