Francium (Fr)

Francium (Fr) is a chemical element with an atomic number of 87 in the periodic table of elements. It’s found in the amount of only 24.5 grams (0.86 ounces) at any time in Earth’s crust. Being a member of the alkali family group of the periodic table, this intensely radioactive substance is the heaviest chemical element of Group 1 (Ia). Francium has one valence electron in the s-orbital of the seventh energy level. 

Chemical and Physical Properties of Francium

Symbol of FranciumFr
Atomic Number87
Atomic Mass-223.0197
UsesSince its isotopes have such short half-lives there are no commercially significant compounds of francium.
DescriptionSilver-white metal. Intensely radioactive.
GroupAlkali Metal
Orbitals[Rn] 7s1
Crystal StructureCubic: Body centered
Covalent Radius
Atomic Radius
Atomic Volume
Name OriginNamed for France, the nation of its discovery.
Discovered ByMarguerite Derey
Oxidation States1
Melting Point21°C, 70°F, 294 K
Boiling Point650°C, 1202°F, 923 K
ColorPresumably silver-gray-metallic
Physical StateSolid at room temperature of 20°C
Half-lifeFrom 16(7) ms to 22 minutes
Van der Waals RadiusUnknown
Ionic RadiusUnknown
Most Characteristic Isotope223Fr
Electronic Shell[Rn] 7s1
The Energy of the First Ionization375 kJ.mol-1
Discovery DateIn 1939 by Marguerite Perey at the Curie Institute in Paris

With the periodic table symbol Fr, atomic number 87, the atomic mass of 223 g.mol-1, and electron configuration [Rn] 7s1, francium’s chemical properties by large resemble the properties of the other alkali metals (lithium, sodium, potassium, rubidium, and cesium). However, the ionization energy of francium is slightly higher than the one of caesium. In each energy level of its electron configuration, this alkali element carries one, two, eight, eighteen, thirty-two, and eighteen electrons, i.e. 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p6 7s1. 

Francium is an extremely rare alkali metal that reaches its boiling point at 650°C (1202°F, 923 K), while the melting point is achieved at 21°C (70°F, 294 K).  This member of the alkali family of elements in the periodic table has a +1 oxidation state and an electronegativity of 0.7 according to Pauling, whereas the atomic radius according to van der Waals is unknown.

How Was Francium Discovered?

Marguerite Catherine Perey (1909 – 1975) was a French physicist and a student of Marie Curie, employed at the Radium Institute of Paris. Perey was hired as an expert in isolation of the pure form of actinium by Marie Curie’s laboratory. In 1939, by performing the carefully planned procedures of actinium purification in her experimental trials, the French physicist noticed unusual radiation emitting from an actinium decay form. 

After a long and thorough observation, Perey decided to add caesium chloride to the purified sample of the radioactive substance. This caused actinium (89Ac) to lose two protons by emitting alpha particles. In this way, a new atom that has 87 protons was produced – francium (Fr). 

The element’s discovery was actually predicted by the great Russian chemist Dmitri Ivanovich Mendeleev (1834 – 1907). Namely, when Mendeleev postulated the periodic classification of the chemical elements, he had a practice of leaving empty spots in the table for the elements that he predicted should exist. His claims were made upon the basis of the unexplained radioactivity in minerals, i.e the new lines in their X-ray spectra. One of those empty spots was right beneath cesium, which in 1939 was taken by francium (Fr). 

How Did Francium Get Its Name?

Element 89 (francium) was named in honor of the country of its discovery, France. This is also the native country of the discoverer of francium, Marguerite Perey, as well as the second home country of Marie Curie – the Nobel Prize-winning French scientist and Perey’s mentor at the Radium Institute of Paris. 

Where Can You Find Francium?

The pure elemental form of francium occurs in nature as a result of an alpha disintegration of actinium (Ac). In most cases, it is found in uranium minerals. The bombardment of thorium with protons also produces atoms of francium. 

Francium in Everyday Life

Due to the small quantities available of this intensely radioactive substance, francium is mainly used in scientific research, for chemical trials and spectroscopic experiments, as well as for early diagnostics of various types of cancer. 

Most recently, francium found its application in several researches conducted at the Stony Brook University, New York, United States

How Dangerous Is Francium?

The alpha and beta particles that are emitted by this highly radioactive element readily attack the genetic material of the cells, which triggers their mutation. Exposure to any level of radiation can lead to severe types of cancer and fatal consequences. Such was the case of the discoverer of francium, Marguerite Perey. This distinguished French nuclear physicist practically fell victim to her eagerness in bringing this new element closer to the world of science. 

Environmental Effects of Francium

Being an extremely radioactive synthetically produced element, the isotopes of francium cannot be found free in nature and are characterised with an extremely short half-life. Hence, this substance has no harmful impact on the environment. 

Isotopes of Francium

Since all known isotopes of francium are extremely radioactive, there are no stable isotopes of this element. They all quickly decay into astatine, radium, and radon. The 223Fr isotope is the only naturally occurring isotope of francium. With a half-life of 22 minutes, francium-223 is also the longest-lived isotope of this chemical element. It decays into radium-223 through beta decay or into astatine-219 through alpha decay. 



[n 1]




ZNIsotopic mass (Da)


[n 2][n 3]



[n 4]




[n 5]




Spin and



[n 6][n 4]




Excitation energy[n 4]
199Fr 87112199.00726(4)16(7) ms  1/2+# 
200Fr 87113200.00657(8)24(10) msα196At3+# 
201Fr 87114201.00386(8)67(3) msα (99%)197At(9/2−) 
β+ (1%)201Rn
202Fr 87115202.00337(5)290(30) msα (97%)198At(3+) 
β+ (3%)202Rn
203Fr 87116203.000925(17)0.55(2) sα (95%)199At(9/2−)# 
β+ (5%)203Rn
204Fr 87117204.000653(26)1.7(3) sα (96%)200At(3+) 
β+ (4%)204Rn
205Fr 87118204.998594(8)3.80(3) sα (99%)201At(9/2−) 
β+ (1%)205Rn
206Fr 87119205.99867(3)~16 sβ+ (58%)206Rn(2+, 3+) 
α (42%)202At
207Fr 87120206.99695(5)14.8(1) sα (95%)203At9/2− 
β+ (5%)207Rn
208Fr 87121207.99714(5)59.1(3) sα (90%)204At7+ 
β+ (10%)208Rn
209Fr 87122208.995954(16)50.0(3) sα (89%)205At9/2− 
β+ (11%)209Rn
210Fr 87123209.996408(24)3.18(6) minα (60%)206At6+ 
β+ (40%)210Rn
211Fr 87124210.995537(23)3.10(2) minα (80%)207At9/2− 
β+ (20%)211Rn
212Fr 87125211.996202(28)20.0(6) minβ+ (57%)212Rn5+ 
α (43%)208At
213Fr 87126212.996189(8)34.6(3) sα (99.45%)209At9/2− 
β+ (.55%)213Rn
214Fr 87127213.998971(9)5.0(2) msα210At(1−) 
215Fr 87128215.000341(8)86(5) nsα211At9/2− 
216Fr 87129216.003198(15)0.70(2) µsα212At(1−) 
β+ (2×10−7%)216Rn
217Fr 87130217.004632(7)16.8(19) µsα213At9/2− 
218Fr 87131218.007578(5)1.0(6) msα214At1− 
219Fr 87132219.009252(8)20(2) msα215At9/2− 
220Fr 87133220.012327(4)27.4(3) sα (99.65%)216At1+ 
β (.35%)220Ra
221Fr 87134221.014255(5)4.9(2) minα (99.9%)217At5/2−Trace[n 7]
β (.1%)221Ra
CD (8.79×10−11%)207Tl



222Fr 87135222.017552(23)14.2(3) minβ222Ra2− 
223FrActinium K87136223.0197359(26)22.00(7) minβ (99.99%)223Ra3/2(−)Trace[n 8]
α (.006%)219At
224Fr 87137224.02325(5)3.33(10) minβ224Ra1− 
225Fr 87138225.02557(3)4.0(2) minβ225Ra3/2− 
226Fr 87139226.02939(11)49(1) sβ226Ra1− 
227Fr 87140227.03184(11)2.47(3) minβ227Ra1/2+ 
228Fr 87141228.03573(22)#38(1) sβ228Ra2− 
229Fr 87142229.03845(4)50.2(4) sβ229Ra(1/2+)# 
230Fr 87143230.04251(48)#19.1(5) sβ230Ra  
231Fr 87144231.04544(50)#17.6(6) sβ231Ra(1/2+)# 
232Fr 87145232.04977(69)#5(1) sβ232Ra  

Source: Wikipedia

List of Francium Compounds 

The common compounds of francium include the following combinations of chemical elements:

  • Francium Sulfide Fr2S   
  • Francium Dichromate Fr2Cr2O   
  • Francium Fluoride FrF      
  • Francium Bromide FrBr      
  • Francium Phosphide Fr3P     
  • Francium Chloride FrCl        
  • Francium Acetate FrC2H3O2      
  • Francium Carbonate Fr2CO3       
  • Francium Nitride Fr3N                
  • Francium Phosphate Fr3PO4              
  • Francium Oxide Fe2O4                                 
  • Francium Hydrogen Oxalate FrHC2O4               
  • Francium Selenide Fr2Se         
  • Francium Sulfate Fr2SO4                      
  • Francium Sulfite Fr2SO3                      
  • Francium Carbide Fr4C                           
  • Francium Telluride Fr2Te                               
  • Francium Permanganate FrMnO4                    
  • Francium Oxalate Fr2C2O4                              
  • Francium Nitrite FrNO2                                    
  • Francium Hydrogen Phosphate Fr2HPO4              
  • Francium Chlorite FrClO2                                         
  • Francium Hyposelenite Fr2SeO2                      
  • Francium Thiocyanate FrSCN       
  • Francium Bismuthate FrBiO3          
  • Francium Borate Fr3BO3      
  • Francium Chromate Fr2CrO4     
  • Francium Iodate FrIO3                  
  • Francium Metasilicate  Fr2SiO3                   
  • Francium Hydrogen Carbonate  FrHCO3             
  • Francium Hypochlorite FrClO        

5 Interesting Facts and Explanations

  1. Francium is the most unstable chemical of the first 101 elements in Mendeleev’s periodic system. 
  2. The natural form of francium cannot be isolated in visible amounts due to its scarcity in Earth’s crust. 
  3. Francium is the last natural element that has been discovered. It’s also the element with the highest equivalent weight of any other chemical. 
  4. After astatine (As), francium is the second rarest chemical element that has been traced in Earth’s crust. 
  5. This radioactive element is also considered to be the least electronegative of all the elements in the periodic table.