Fr 87

Francium (Fr)

alkali-metal

Period: 7 Group: 1 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Rn] 7s¹

Melting point

26.85 °C (300 K)

Boiling point

N/A

Density

1870 kg/m³

Oxidation states

Electronegativity (Pauling)

0.7

Ionization energy (1st)

Discovery year

1939

Atomic radius

N/A

Details

Name origin Named for France, the nation of its discovery.

Discovery country France

Discoverers Marguerite Derey

Francium is the heaviest known alkali metal and a member of group 1. All of its isotopes are radioactive, and the element occurs naturally only as fleeting decay products in uranium and thorium series minerals. Its chemistry is expected and partly observed to resemble an extremely electropositive form of caesium, dominated by the +1 oxidation state. Because the longest-lived isotope, ²²³Fr, has a half-life of only about 22 minutes, francium has no bulk technological role.

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.

Francium was discovered by Marguerite Catherine Perey, a French chemist, in 1939 while analyzing actinium's decay sequence. 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. Francium's most stable isotope, francium-223, has a half-life of about 22 minutes. It decays into radium-223 through beta decay or into astatine-219 through alpha decay.

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 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.

Read about Francium on Wikipedia

Images

Properties

Physical

Covalent radius 260 pm

Van der Waals radius 348 pm

Density

Phase at STP solid

Melting point 26.85 °C

Crystal structure bcc

Chemical

Electronegativity (Pauling) 0.7

Electronegativity (Allen) 0.67

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states +1

Valence electrons 1

Electron configuration

Electron configuration (semantic)

Thermodynamic

Heat of fusion 0.02072861 eV

Heat of vaporization 0.67367985 eV

Heat of sublimation 0.74622998 eV

Heat of atomization 0.74622998 eV

Nuclear

Stable isotopes 0

Mass number (most stable) 223

Discovery year 1939

Abundance

N/A

Reactivity

N/A

Crystal Structure

N/A

Electronic Structure

Electrons per shell 2, 8, 18, 32, 18, 8, 1

Identifiers

CAS number 7440-73-5

Term symbol

InChI InChI=1S/Fr

InChI Key KLMCZVJOEAUDNE-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 87

Electrons 87

Charge Neutral

Configuration Fr: 7s¹

[Rn] 7s¹

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

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

↑↓

2/2

↑↓

14/14

↑↓

10/10

↑↓

6/6

↑

1/2 1↑

Total electrons: 87 Unpaired: 1

Atomic model

Protons 87

Neutrons 128

Electrons 87

Mass number 215

Stability Radioactive

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

No stable isotopes.

Mass number	Atomic mass (u)	Natural abundance	Half-life
233 Radioactive	233.05264 ± 0.00032	N/A	900 ms
216 Radioactive	216.0031899 ± 0.0000045	N/A	700 ns
203 Radioactive	203.0009407 ± 0.0000067	N/A	550 ms
202 Radioactive	202.00332 ± 0.000055	N/A	372 ms
215 Radioactive	215.0003418 ± 0.0000076	N/A	90 ns

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 1.9 °C below melting point (26.85 °C)

Melting point 26.85 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid / Gas

Melting

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

26.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.02072861 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.67367985 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

0.74622998 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

1870 kg/m³

At standard conditions

Current density Calculated

1870 kg/m³

At standard conditions

Atomic Spectra

Showing 10 of 87 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Fr I	0	149	149	149

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Fr I	0	123
Fr II	+1	2
Fr III	+2	2
Fr IV	+3	2
Fr V	+4	2
Fr VI	+5	2
Fr VII	+6	2
Fr VIII	+7	2
Fr IX	+8	2
Fr X	+9	2

NIST Levels Holdings →

87 Fr 223

Francium — Atomic Orbital Visualizer

[Rn]7s1

Energy levels 2 8 18 32 18 8 1

Oxidation states +1

HOMO 7s n=7 · l=0 · m=0

Francium — Atomic Orbital Visualizer Preview

Three.js loads only on request

87 Fr 223

Francium — Crystal Structure Visualizer

Crystal structure data not available

Crystal structure: bcc

Ionic Radii

Charge	Coordination	Spin	Radius
+1	6	N/A	180 pm

Compounds

223.020 u

221.014 u

223.020 u

222.018 u

220.012 u

Isotopes (5)

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
233 Radioactive	233.05264 ± 0.00032	N/A	900 ms	β- =100%β-n ?
216 Radioactive	216.0031899 ± 0.0000045	N/A	700 ns	α =100%β+ ?
203 Radioactive	203.0009407 ± 0.0000067	N/A	550 ms	α ≈100%β+ ?
202 Radioactive	202.00332 ± 0.000055	N/A	372 ms	α ≈100%β+ ?
215 Radioactive	215.0003418 ± 0.0000076	N/A	90 ns	α =100%

233 Radioactive

Atomic mass (u) 233.05264 ± 0.00032

Natural abundance N/A

Half-life 900 ms

Decay mode

β- =100%β-n ?

216 Radioactive

Atomic mass (u) 216.0031899 ± 0.0000045

Natural abundance N/A

Half-life 700 ns

Decay mode

α =100%β+ ?

203 Radioactive

Atomic mass (u) 203.0009407 ± 0.0000067

Natural abundance N/A

Half-life 550 ms

Decay mode

α ≈100%β+ ?

202 Radioactive

Atomic mass (u) 202.00332 ± 0.000055

Natural abundance N/A

Half-life 372 ms

Decay mode

α ≈100%β+ ?

215 Radioactive

Atomic mass (u) 215.0003418 ± 0.0000076

Natural abundance N/A

Half-life 90 ns

Decay mode

α =100%

Spectral Lines

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
422.56552 nm	N/A	Fr I	emission	7s 2S → 8p 2P*	Measured	NIST
432.53607 nm	N/A	Fr I	emission	7s 2S → 8p 2P*	Measured	NIST
494.61573 nm	N/A	Fr I	emission	7p 2P* → 20d 2D	Measured	NIST
495.91444 nm	N/A	Fr I	emission	7p 2P* → 19d 2D	Measured	NIST
496.90308 nm	N/A	Fr I	emission	7p 2P* → 20s 2S	Measured	NIST
497.49878 nm	N/A	Fr I	emission	7p 2P* → 18d 2D	Measured	NIST
498.7192 nm	N/A	Fr I	emission	7p 2P* → 19s 2S	Measured	NIST
499.45999 nm	N/A	Fr I	emission	7p 2P* → 17d 2D	Measured	NIST
500.99176 nm	N/A	Fr I	emission	7p 2P* → 18s 2S	Measured	NIST
501.92929 nm	N/A	Fr I	emission	7p 2P* → 16d 2D	Measured	NIST
503.88964 nm	N/A	Fr I	emission	7p 2P* → 17s 2S	Measured	NIST
505.10105 nm	N/A	Fr I	emission	7p 2P* → 15d 2D	Measured	NIST
507.66912 nm	N/A	Fr I	emission	7p 2P* → 16s 2S	Measured	NIST
509.27532 nm	N/A	Fr I	emission	7p 2P* → 14d 2D	Measured	NIST
512.73622 nm	N/A	Fr I	emission	7p 2P* → 15s 2S	Measured	NIST
514.93307 nm	N/A	Fr I	emission	7p 2P* → 13d 2D	Measured	NIST
519.7664 nm	N/A	Fr I	emission	7p 2P* → 14s 2S	Measured	NIST
522.89168 nm	N/A	Fr I	emission	7p 2P* → 12d 2D	Measured	NIST
529.95916 nm	N/A	Fr I	emission	7p 2P* → 13s 2S	Measured	NIST
534.64166 nm	N/A	Fr I	emission	7p 2P* → 11d 2D	Measured	NIST
539.61762 nm	N/A	Fr I	emission	7p 2P* → 20d 2D	Measured	NIST
539.6469 nm	N/A	Fr I	emission	7p 2P* → 20d 2D	Measured	NIST
541.15779 nm	N/A	Fr I	emission	7p 2P* → 19d 2D	Measured	NIST
541.19321 nm	N/A	Fr I	emission	7p 2P* → 19d 2D	Measured	NIST
542.37083 nm	N/A	Fr I	emission	7p 2P* → 20s 2S	Measured	NIST
543.03716 nm	N/A	Fr I	emission	7p 2P* → 18d 2D	Measured	NIST
543.08061 nm	N/A	Fr I	emission	7p 2P* → 18d 2D	Measured	NIST
544.53524 nm	N/A	Fr I	emission	7p 2P* → 19s 2S	Measured	NIST
545.36417 nm	N/A	Fr I	emission	7p 2P* → 17d 2D	Measured	NIST
545.4185 nm	N/A	Fr I	emission	7p 2P* → 17d 2D	Measured	NIST
545.63748 nm	N/A	Fr I	emission	7p 2P* → 12s 2S	Measured	NIST
547.24565 nm	N/A	Fr I	emission	7p 2P* → 18s 2S	Measured	NIST
548.29545 nm	N/A	Fr I	emission	7p 2P* → 16d 2D	Measured	NIST
548.36447 nm	N/A	Fr I	emission	7p 2P* → 16d 2D	Measured	NIST
550.70515 nm	N/A	Fr I	emission	7p 2P* → 17s 2S	Measured	NIST
552.06365 nm	N/A	Fr I	emission	7p 2P* → 15d 2D	Measured	NIST
552.15244 nm	N/A	Fr I	emission	7p 2P* → 15d 2D	Measured	NIST
553.17161 nm	N/A	Fr I	emission	7p 2P* → 10d 2D	Measured	NIST
555.22268 nm	N/A	Fr I	emission	7p 2P* → 16s 2S	Measured	NIST
557.02549 nm	N/A	Fr I	emission	7p 2P* → 14d 2D	Measured	NIST
557.14445 nm	N/A	Fr I	emission	7p 2P* → 14d 2D	Measured	NIST
561.28917 nm	N/A	Fr I	emission	7p 2P* → 15s 2S	Measured	NIST
563.7589 nm	N/A	Fr I	emission	7p 2P* → 13d 2D	Measured	NIST
563.92284 nm	N/A	Fr I	emission	7p 2P* → 13d 2D	Measured	NIST
569.72475 nm	N/A	Fr I	emission	7p 2P* → 14s 2S	Measured	NIST
571.87464 nm	N/A	Fr I	emission	7p 2P* → 11s 2S	Measured	NIST
573.24676 nm	N/A	Fr I	emission	7p 2P* → 12d 2D	Measured	NIST
573.48185 nm	N/A	Fr I	emission	7p 2P* → 12d 2D	Measured	NIST
585.3491 nm	N/A	Fr I	emission	7p 2P* → 9d 2D	Measured	NIST
587.29 nm	N/A	Fr I	emission	7p 2P* → 11d 2D	Measured	NIST
587.64619 nm	N/A	Fr I	emission	7p 2P* → 11d 2D	Measured	NIST
600.95745 nm	N/A	Fr I	emission	7p 2P* → 12s 2S	Measured	NIST
609.52762 nm	N/A	Fr I	emission	7p 2P* → 10d 2D	Measured	NIST
610.10952 nm	N/A	Fr I	emission	7p 2P* → 10d 2D	Measured	NIST
618.5596 nm	N/A	Fr I	emission	6d 2D → 20p 2P*	Measured	NIST
618.7831 nm	N/A	Fr I	emission	6d 2D → 20p 2P*	Measured	NIST
621.0658 nm	N/A	Fr I	emission	6d 2D → 19p 2P*	Measured	NIST
621.3414 nm	N/A	Fr I	emission	6d 2D → 19p 2P*	Measured	NIST
621.98126 nm	N/A	Fr I	emission	7p 2P* → 10s 2S	Measured	NIST
624.178 nm	N/A	Fr I	emission	6d 2D → 18p 2P*	Measured	NIST
624.5235 nm	N/A	Fr I	emission	6d 2D → 18p 2P*	Measured	NIST
626.3009 nm	N/A	Fr I	emission	6d 2D → 20p 2P*	Measured	NIST
628.1118 nm	N/A	Fr I	emission	6d 2D → 17p 2P*	Measured	NIST
628.5529 nm	N/A	Fr I	emission	6d 2D → 17p 2P*	Measured	NIST
628.8704 nm	N/A	Fr I	emission	6d 2D → 19p 2P*	Measured	NIST
632.0616 nm	N/A	Fr I	emission	6d 2D → 18p 2P*	Measured	NIST
632.9403 nm	N/A	Fr I	emission	7p 2P* → 11s 2S	Measured	NIST
633.1901 nm	N/A	Fr I	emission	6d 2D → 16p 2P*	Measured	NIST
633.7661 nm	N/A	Fr I	emission	6d 2D → 16p 2P*	Measured	NIST
636.0957 nm	N/A	Fr I	emission	6d 2D → 17p 2P*	Measured	NIST
639.9141 nm	N/A	Fr I	emission	6d 2D → 15p 2P*	Measured	NIST
640.6887 nm	N/A	Fr I	emission	6d 2D → 15p 2P*	Measured	NIST
641.3044 nm	N/A	Fr I	emission	6d 2D → 16p 2P*	Measured	NIST
648.2027 nm	N/A	Fr I	emission	6d 2D → 15p 2P*	Measured	NIST
648.421 nm	N/A	Fr I	emission	7p 2P* → 9d 2D	Measured	NIST
649.103 nm	N/A	Fr I	emission	6d 2D → 14p 2P*	Measured	NIST
649.4876 nm	N/A	Fr I	emission	7p 2P* → 9d 2D	Measured	NIST
650.1812 nm	N/A	Fr I	emission	6d 2D → 14p 2P*	Measured	NIST
650.7242 nm	N/A	Fr I	emission	7p 2P* → 8d 2D	Measured	NIST
657.633 nm	N/A	Fr I	emission	6d 2D → 14p 2P*	Measured	NIST
662.174 nm	N/A	Fr I	emission	6d 2D → 13p 2P*	Measured	NIST
663.746 nm	N/A	Fr I	emission	6d 2D → 13p 2P*	Measured	NIST
671.054 nm	N/A	Fr I	emission	6d 2D → 13p 2P*	Measured	NIST
681.787 nm	N/A	Fr I	emission	6d 2D → 12p 2P*	Measured	NIST
684.222 nm	N/A	Fr I	emission	6d 2D → 12p 2P*	Measured	NIST
691.204 nm	N/A	Fr I	emission	6d 2D → 12p 2P*	Measured	NIST
694.8987 nm	N/A	Fr I	emission	7p 2P* → 10s 2S	Measured	NIST
713.491 nm	N/A	Fr I	emission	6d 2D → 11p 2P*	Measured	NIST
717.615 nm	N/A	Fr I	emission	6d 2D → 11p 2P*	Measured	NIST
717.98664 nm	N/A	Fr I	emission	7s 2S → 7p 2P*	Measured	NIST
723.811 nm	N/A	Fr I	emission	6d 2D → 11p 2P*	Measured	NIST
728.5892 nm	N/A	Fr I	emission	7p 2P* → 8d 2D	Measured	NIST
730.9713 nm	N/A	Fr I	emission	7p 2P* → 8d 2D	Measured	NIST
744.1976 nm	N/A	Fr I	emission	7p 2P* → 9s 2S	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Van der Waals Radii

Truhlar

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

Phase Transitions & Allotropes

Melting point

294.15 K

Oxidation State Categories

+1 main

Advanced Reference Data

Crystal Radii Detail (1)

Charge	CN	Spin	r_crystal (pm)	Origin
1	VI		194	Ahrens (1952) ionic radius,

Isotope Decay Modes (60)

Isotope	Mode	Intensity
197	A	100%
198	A	100%
199	A	100%
199	B+	—
200	A	100%
200	B+	—
200	B+SF	—
201	A	100%
201	B+	—
202	A	100%

X‑ray Scattering Factors (516)

Energy (eV)	f₁	f₂
10	—	0.05044
10.1617	—	0.06059
10.3261	—	0.07277
10.4931	—	0.08938
10.6628	—	0.11712
10.8353	—	0.15347
11.0106	—	0.20109
11.1886	—	0.26349
11.3696	—	0.40321
11.5535	—	0.63759

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

Not Applicable

References (1)

[5] Francium https://education.jlab.org/itselemental/ele087.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

Not Applicable

References (1)

[5] Francium https://education.jlab.org/itselemental/ele087.html

References

(9)

1 PubChem

Data deposited in or computed by PubChem

Visit source

2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

Visit source License

3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Francium

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

Visit source License

4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

Visit source License

License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Francium

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

Visit source License

License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Francium

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

Visit source License

7 NIST Physical Measurement Laboratory

Francium

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

Visit source License

8 PubChem Elements

Francium

This section provides all form of data related to element Francium.

License

9 PubChem Elements

Francium

The element property data was retrieved from publications.

License

Last updated: May 1, 2026