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About Francium

Francium Bohr

Francium is the second rarest and the most unstable naturally occurring element on the periodic table; only astatine is rarer. A product of a disintegration of actinium, which undergoes beta-disintegration 99% of the time, francium is so highly radioactive that its most stable isotope (Francium-233, formerly known as actinium-K) has a half-life of merely 22 minutes. As such, only 20-30 grams of the element are present at any given time in the earth’s crust, limited to trace amounts in uranium and thorium ores.

Francium can be produced in the laboratory via bombardment of thorium with protons or radium with neutrons, but only in small quantities--the largest amount ever synthesized was a cluster of 30,000 atoms. The element has never been observed in bulk; with the lowest electronegativity of any element on the periodic table, it would immediately vaporize due to the extreme heat of decay. Thus, scientists estimate that francium’s theoretical properties are similar to the other members of the alkali metals family. There are no commercial applications for francium because of its instability.

Dmitri Mendeleev predicted the existence of Francium in the 1870's, calling it “eka-caesium” because of its similarity to cesium (“eka” meaning one element down on the periodic table). The element was discovered by French chemist Marguerite Catherine Perey of the Curie Institute in 1939 while analyzing the decay of actinium; named for her country of origin, Francium would become the last naturally-occurring element to be discovered rather than being synthesized in a laboratory.

Francium Properties

Francium Bohr ModelFrancium is a S-Block, Group 1, Period 7 element. The number of electrons in each of Francium's shells is 2,8,18,32,18,8,1 and its electronic configuration is 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p6 7s1. In its elemental form francium's CAS number is 7440-73-5. The francium atom has a radius of 270.pm and it's Van der Waals radius is 348.pm. Francium was discovered by Marguerite Perey of the Curie Institute in Paris, France in 1939 although its existence was predicted by Mendeleev during the 1870's.

Francium, formerly known as eka-caesium and actinium K, is the second rarest naturally occurring element, the first being Astatine. Francium has the lowest electronegativitiy of all known elements and it was the last element discovered in nature. Outside of the laboratory, only trace amounts of francium can be found in uranium and thorium ores. Out of all of the naturally occurring elements, francium is the most unstable. Due to its rarity and instability, commercial applications for francium do not exist. Francium information, including technical data, properties, research, and other useful facts are discussed below. Scientific facts such as the atomic structure, ionization energy, conductivity and thermal properties are also included.

Symbol: Fr
Atomic Number: 87
Atomic Weight: 223
Element Category: alkali metal
Group, Period, Block: 1, 7, s
Color: silver-gray/metallic
Other Names: N/A
Melting Point: 21°C, 69.8°F, 294.15 K
Boiling Point: Unknown
Density: Unknown
Liquid Density @ Melting Point: N/A
Density @ 20°C: 1.873 g/cm3
Density of Solid: 2900 (estimated) kg·m3
Specific Heat: N/A
Superconductivity Temperature: N/A
Triple Point: 2.177 K, 5.043 kPa
Critical Point: 5.1953 K, 0.22746 MPa
Heat of Fusion (kJ·mol-1): about 2
Heat of Vaporization (kJ·mol-1): about 65
Heat of Atomization (kJ·mol-1): about 64
Thermal Conductivity: 15 W·m1·K1
Thermal Expansion: N/A
Electrical Resistivity: 3 µ (calculated)·m
Tensile Strength: N/A
Molar Heat Capacity: N/A
Young's Modulus: N/A
Shear Modulus: N/A
Bulk Modulus: N/A
Poisson Ratio: N/A
Mohs Hardness: N/A
Vickers Hardness: N/A
Brinell Hardness: N/A
Speed of Sound: N/A
Pauling Electronegativity: 0.7
Sanderson Electronegativity: N/A
Allred Rochow Electronegativity: 0.86
Mulliken-Jaffe Electronegativity: 0.68 (s orbital)
Allen Electronegativity: N/A
Pauling Electropositivity: 3.3
Reflectivity (%): N/A
Refractive Index: N/A
Electrons: 87
Protons: 87
Neutrons: 136
Electron Configuration: 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p6 7s1
Atomic Radius: N/A
Atomic Radius,
non-bonded (Å):
3.48
Covalent Radius: 260 pm
Covalent Radius (Å): 2.42
Van der Waals Radius: 348 pm
Oxidation States: 1 (strongly basic oxide)
Phase: Solid
Crystal Structure: cubic body-centered
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) 46.892
1st Ionization Energy: 380 kJ·mol-1
2nd Ionization Energy: N/A
3rd Ionization Energy: N/A
CAS Number: 7440-73-5 
EC Number: N/A
MDL Number: N/A
Beilstein Number: N/A
SMILES Identifier: [Fr]
InChI Identifier: InChI=1S/Fr
InChI Key: KLMCZVJOEAUDNE-UHFFFAOYSA-N
PubChem CID: 6328145
ChemSpider ID: 4886484
Earth - Total: N/A
Mercury - Total: N/A
Venus - Total: N/A
Earth - Seawater (Oceans), ppb by weight: N/A
Earth - Seawater (Oceans), ppb by atoms: N/A
Earth -  Crust (Crustal Rocks), ppb by weight: N/A
Earth -  Crust (Crustal Rocks), ppb by atoms: N/A
Sun - Total, ppb by weight: N/A
Sun - Total, ppb by atoms: N/A
Stream, ppb by weight: N/A
Stream, ppb by atoms: N/A
Meterorite (Carbonaceous), ppb by weight: N/A
Meterorite (Carbonaceous), ppb by atoms: N/A
Typical Human Body, ppb by weight: N/A
Typical Human Body, ppb by atom: N/A
Universe, ppb by weight: N/A
Universe, ppb by atom: N/A
Discovered By: Marguerite Perey
Discovery Date: 1939
First Isolation: Marguerite Perey (1939)

Francium Isotopes

Francium has no stable isotopes.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
199Fr 199.00726(4) 16(7) ms Unknown 1/2+# N/A 1510.04 -
200Fr 200.00657(8) 24(10) ms a to 196At 3+# N/A 1518.12 -
201Fr 201.00386(8) 67(3) ms a to 196At; ß+ to 201Rn (9/2-) N/A 1526.2 -
202Fr 202.00337(5) 290(30) ms a to 197At; ß+ to 202Rn (3+) N/A 1534.28 -
203Fr 203.000925(17) 0.55(2) s a to 198At; ß+ to 203Rn (9/2-)# N/A 1542.36 -
204Fr 204.000653(26) 1.7(3) s a to 199At; ß+ to 204Rn (3+) N/A 1550.44 -
205Fr 204.998594(8) 3.80(3) s a to 200At; ß+ to 205Rn (9/2-) N/A 1567.83 -
206Fr 205.99867(3) ~16 s ß+ to 206Rn; a to 201At (2+,3+) N/A 1575.91 -
207Fr 206.99695(5) 14.8(1) s a to 202At; ß+ to 207Rn 9/2- N/A 1583.99 -
208Fr 207.99714(5) 59.1(3) s a to 203At; ß+ to 208Rn 7+ N/A 1592.07 -
209Fr 208.995954(16) 50.0(3) s a to 204At; ß+ to 209Rn 9/2- N/A 1600.15 -
210Fr 209.996408(24) 3.18(6) min a to 206At; EC to 210Rn 6+ 4.4 1608.23 -
211Fr 210.995537(23) 3.10(2) min a to 207At; EC to 211Rn 9/2- 4 1616.3 -
212Fr 211.996202(28) 20.0(6) min a to 208At; EC to 212Rn 5+ 4.6 1624.38 -
213Fr 212.996189(8) 34.6(3) s a to 209At; EC to 213Rn 9/2- 4 1632.46 -
214Fr 213.998971(9) 5.0(2) ms a to 210At (1-) N/A 1640.54 -
215Fr 215.000341(8) 86(5) ns a to 211At 9/2- N/A 1639.3 -
216Fr 216.003198(15) 0.70(2) µs a to 212At; EC to 216Rn (1-) N/A 1647.38 -
217Fr 217.004632(7) 16.8(19) µs a to 213At 9/2- N/A 1655.46 -
218Fr 218.007578(5) 1.0(6) ms a to 214At 1- N/A 1663.54 -
219Fr 219.009252(8) 20(2) ms a to 215At 9/2- N/A 1671.62 -
220Fr 220.012327(4) 27.4(3) s a to 216At; ß- to 220Ra 1+ N/A 1670.38 -
221Fr 221.014255(5) 4.9(2) min a to 217At; ß- to 221Ra; 14C 5/2- 1.58 1678.46 -
222Fr 222.017552(23) 14.2(3) min ß- to 222Ra 2- 0.63 1686.54 -
223Fr 223.0197359(26) 22.00(7) min a to 219At 3/2(-) 1.17 1694.62 -
224Fr 224.02325(5) 3.33(10) min ß- to 224Ra; 1- 0.4 1693.38 -
225Fr 225.02557(3) 4.0(2) min ß- to 225Ra 3/2- 1.07 1701.46 -
226Fr 226.02939(11) 49(1) s ß- to 226Ra 1- 0.071 1709.54 -
227Fr 227.03184(11) 2.47(3) min ß- to 227Ra 1/2+ 1.5 1708.3 -
228Fr 228.03573(22)# 38(1) s ß- to 228Ra 2- N/A 1716.38 -
229Fr 229.03845(4) 50.2(4) s ß- to 229Ra (1/2+)# N/A 1724.46 -
230Fr 230.04251(48)# 19.1(5) s ß- to 230Ra N/A N/A 1723.22 -
231Fr 231.04544(50)# 17.6(6) s ß- to 231Ra (1/2+)# N/A 1731.3 -
232Fr 232.04977(69)# 5(1) s ß- to 232Ra N/A N/A 1739.38 -