Francium

1 · Identity

Symbol, number

Fr, 87

Oxidation states in water

+1 (book entry); never measured in water

Note

Identity from the book entry; nothing measured in water.

Sources

Identity

Name and symbol

Francium, Fr

Atomic number

87 protons

Position

group 1 · period 7 · s-block · alkali metal

CAS number

7440-73-5

Atomic structure

Atomic mass

223 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s¹
[Rn] 7s¹

Electrons per shell

2, 8, 18, 32, 18, 8, 1

Valence electrons

1 outer shell

Physical properties

State at room temperature

Solid

Melting point

300 K (26.85 °C)

Boiling point

680 K (406.85 °C)

Density

not in sources

Appearance

not in sources

Thermal conductivity

15 W/(m·K)

Electrical resistivity

3 µΩ·m

Electrical conductivity

333,333.333 S/m

Crystal structure

body-centered cubic

Molar heat capacity

not in sources

Chemical properties

Oxidation states

+1

Electronegativity

0.67 (Allen Scale)

Ionisation energy

3.9 eV
1st 380 kJ/mol

Electron affinity

0.47 eV

Atomic radius

empirical 260, covalent 260, van der Waals 348 pm

Ionic radius

Fr⁺ 180 pm

Reactivity

The heaviest alkali metal (7s1) and the second most electropositive element after caesium, but its longest-lived isotope lasts 22 minutes and no more than about 30 g exist in the crust at once, so bulk francium has never been seen; every fact about its chemistry comes from tracer solutions of the Fr+ ion coprecipitated with caesium salts.

with water

Not known: no bulk sample has ever existed to test, though by analogy with caesium the reaction would be explosive; in water francium is simply the soluble Fr+ ion.

with oxygen, air

Not known: no oxidation of the metal has been observed; the oxide is predicted to disproportionate to the peroxide and the metal, and the superoxide FrO2 to be more covalent than its lighter congeners.

with acids

Not known for the metal; francium salts are handled only in solution, where the perchlorate, iodate, picrate, tartrate, chloroplatinate and silicotungstate coprecipitate with the caesium salts and the rest stay dissolved.

with halogens

Not known: the halides are expected to be white, water-soluble solids formed from the elements, but none has been made by direct reaction.

Typical compounds

• FrClO₄ francium perchlorate tiny amounts coprecipitated with caesium perchlorate

Occurrence, production and use

Crustal abundance

Not Applicable

Oceanic abundance

Not Applicable

Occurrence and sources

• transient decay product in actinium and uranium ore detected in purified actinium; made artificially from radium or thorium

Extraction, production

Neutron bombardment of radium in a reactor, or proton bombardment of thorium

no equation printed

Uses

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

Safety, toxicity

not in sources

Discovery and name

Discovered by

Marguerite Perey

Discovered

1939

First isolated

not in sources

Named by

not in sources

Origin of the name

after France, homeland of the discoverer

Francium was discovered in 1939 by Marguerite Perey, a physicist at the Curie Institute in Paris, France (Fig. IUPAC.87.1). 223Fr (with a half-life of 22 min) occurs naturally in uranium minerals as a result of actinium decay. However, it is estimated that no more than approximately 30 g of francium is present in the Earth’s crust at any time. Francium can be produced artificially for research by bombarding thorium with protons. Francium was named in honor of Perey’s home country, France [575], [576], [577]. Francium has no known isotopic applications outside of scientific research.