Francium (Fr)

Isotopes of Francium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin
Fr-210  209.99640  3.20 minutes  α to At-206; EC to Rn-210
Fr -211 210.99553  3.10 minutes  α to At-207; EC to Rn-211 9/2 
Fr-212 211.99618 20 minutes α to At-208; EC to Rn-212 5
Fr-213 212.99617 34.60 seconds α to At-209; EC to Rn-213 9/2
Fr-214 213.99895 0.0051 seconds α to At-210 1
Fr-215 215.00033 0.0000012 seconds α to At-211 9/2
Fr-216 216.00319 0.000007 seconds α to At-212; EC to Rn-216 No data available 
Fr-217 217.00462 0.00016 seconds α to At-213 9/2
Fr-218 218.00756 0.001 seconds α to At-214 1
Fr-219 219.00924 0.021 seconds α to At-215 9/2
Fr-220 220.01231 27.40 seconds α to At-216; β- to Ra-220 1
Fr-221 221.01425 4.80 minutes α to At-217; β- to Ra-221; C-14 5/2
Fr-222 222.01754 14.30 minutes β- to Ra-222 2
Fr-223 223.019733 22 minutes α to At-219; β- to Ra-223 3/2
Fr-224 224.02323 3 minutes β- to Ra-224 1
Fr-225 225.02561 3.90 minutes β- to Ra-225 3/2
Fr-226 226.0293 49 seconds β- to Ra-226 1
Fr-227 227.0318 2.48 minutes β- to Ra-227 1/2


Francium was discovered in 1939 by Marguerite Perey. It is named for France, where it was discovered. Its existence had been predicted during the 1870s by Mendeleev, who named it "eka-caesium," correctly predicting that its properties would resemble those of cesium.

Francium is the most unstable of the naturally-occurring elements. No weighable amount has ever been prepared. Preparing such a sample would be impossible, since the extreme heat of decay (the half-life of its longest-lived isotope is only 22 minutes) would immediately vaporize any viewable quantity of the element.

Due to its instability and rarity, there are no commercial applications for francium. It has been used for research purposes in the fields of biology and atomic structure. Its use as a potential diagnostic aid for various cancers has also been explored, but this application has been deemed impractical.

Properties of Francium

Name Francium 
Symbol Fr 
Atomic number 87 
Atomic weight 223 
Standard state Solid at 298 °K 
CAS Registry ID 7440-73-5 
Group in periodic table 1
Group name Alkali metal 
Period in periodic table
Block in periodic table s-block 
Color Metallic 
Classification Metallic 
Melting point 30 °C
Boiling point 598 °C
Thermal conductivity 15 (estimate) W/(m·K)
Electronegativity 0.7 
Heat of vaporization About 65 kJ·mol-1
Heat of fusion About 2 kJ·mol-1
Density of solid 2.9 (estimated) g/cm3
Electron configuration [Rn]7s
Oxidation state +1 

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