Name: Francium
Symbol: Fr
Atomic Number: 87
Atomic Weight: 223.000000
Family: Alkali Metals
CAS RN: 7440-73-5
Description: Metallic, very rare and radioactive.
State (25C): Solid
Oxidation states: +1
Valence Electrons: 7s1

Boiling Point:  950K, 677C, 1251F
Melting Point:
300K, 27C, 81F
Electrons Energy Level: 2, 8, 18, 32, 18, 8, 1
Isotopes: 32 (None Stable)
Heat of Vaporization: unknown
Heat of Fusion: 9.39 kJ/mol
Density: unknown
Specific Heat: unknown
Atomic Radius: unknown
Ionic Radius: 1.8
Electronegativity: 0.7 (Pauling); 0.86 (Allrod Rochow)
The existence of Francium was predicted by Dmitri Mendeleev in the 1870's and he presumed it would have chemical and physical properties similar to Cesium. Numerous historical claims to the discovery of element 87 were made resulting in the names Russium, Virginium, and Moldavium.

This element, which was named for France, was discovered in 1939 by Marguerite Perey, who was an assistant to Marie Curie, at the Curie Institute in Paris.   There was a British team working to be the first to discover this element at the same time as a French team. The British team wanted to name the element 'Britium' - the French team discovered it first and named it after their country.

Francium was the last element discovered in nature. Originally named Actinium K, it occurs as a result of Actinium's alpha decay and can be artificially made by bombarding Thorium with protons.  It is the heaviest alkali metal, but the next element to be discovered will most likely be an alkali metal even heavier than it.

Francium is a highly radioactive alkali metal that is found in very small amounts in Uranium and Thorium ores.  It is also notable for having the lowest electronegativity and electron affinity of all the elements.

Francium is the last of the known alkali metals and does not occur to any significant extent in nature.  All known isotopes are radioactive and have short half-lives (21.8 minutes is the longest).

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


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


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.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10
6s2 6p6

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.


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.


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


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.

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Isotope Atomic Mass Half-Life
Fr200   19 ms
Fr201 201.004 48 ms
Fr202 202.003 0.34 seconds
Fr203 203.001 0.55 seconds
Fr204 204.001 1.7 seconds
Fr205 204.999 3.85 seconds
Fr206 205.998 15.9 seconds
Fr207 206.997 14.8 seconds
Fr208 207.9971 59.1 seconds
Fr209 208.9959 50 seconds
Fr210 209.9964 3.18 minutes
Fr211 210.9955 3.10 minutes
Fr212 211.9962 20 minutes
Fr213 212.9962 34.6 seconds
Fr214 213.999 5 ms
Fr215 215.0003 86 ns
Fr216 216.0032 0.70 us
Fr217 217.0046 22 us
Fr218 218.0076 1 ms
Fr219 :219.00924 20 ms
Fr220 220.0123 27.4 seconds
Fr221 221.0143 4.9 minutes
Fr222 222.0175 14.2 minutes
Fr223 223.0197 21.8 minutes
Fr224 224.0232 3.33 minutes
Fr225 225.0256 4 minutes
Fr226 226.0293 49 seconds
Fr227 227.032 2.47 minutes
Fr228 228.036 38 seconds
Fr229 229.038 50 seconds
Fr230 230.043 19.1 seconds
Fr231 231.045 17.5 seconds

atom.gif (700 bytes)

Francium Data


Atomic Structure

Atomic Radius (): unknown
Atomic Volume cm3/mol : unknown
Covalent Radius: unknown
Crystal Structure: Cubic body centered
Ionic Radius: 1.8

Chemical Properties

Electrochemical Equivalents: 8.3209 g/amp-hr
Electron Work Function: unknown
Electronegativity: 0.7 (Pauling); 0.86 (Allrod Rochow)
Heat of Fusion: 9.39 kJ/mol
Incompatibilities: unknown
First Ionization Potential: 3.83
Second Ionization Potential: unknown
Third Ionization Potential: unknown
Valence Electron Potential(-eV): 8
Ionization Energy (eV): 3.9 eV

Physical Properties

Atomic Mass Average: 223
Boiling Point: 950K, 677C, 1251F
Melting Point: 300K, 27C, 81F
Heat of Vaporization: unknown
Coefficient of Lineal Thermal Expansion/K-1: N/A
Electrical Conductivity: 0.03 106/cm
Thermal Conductivity: 0.15 W/cmK
Density: unknown
Elastic Modulus (Bulk): unknown
Elastic Modulus (Rigidity): unknown
Elastic Modulus Youngs: unknown
Enthalpy of Atomization: 71 kJ/mole @ 25C
Enthalpy of Fusion: unknown
Enthalpy of Vaporization: unknown
Hardness Scale (Brinell): unknown
Hardness Scale (Mohs): unknown
Hardness Scale (Vickers): unknown
Flammability Class: unknown
Molar Volume: unknown
Optical Reflectivity: unknown
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: unknown
Vapor Pressure: unknown
Estimated Crustal Abundance: unknown
Estimated Oceanic Abundance: unknown

(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