Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactive, as it reacts with all other elements except for the light inert gases.

Among the elements, fluorine ranks 24th in universal abundance and 13th in terrestrial abundance. Fluorite, the primary mineral source of fluorine which gave the element its name, was first described in 1529; as it was added to metal ores to lower their melting points for smelting, the Latin verb fluo meaning 'flow' gave the mineral its name. Proposed as an element in 1810, fluorine proved difficult and dangerous to separate from its compounds, and several early experimenters died or sustained injuries from their attempts. Only in 1886 did French chemist Henri Moissan isolate elemental fluorine using low-temperature electrolysis, a process still employed for modern production. Industrial production of fluorine gas for uranium enrichment, its largest application, began during the Manhattan Project in World War II.

Owing to the expense of refining pure fluorine, most commercial applications use fluorine compounds, with about half of mined fluorite used in steelmaking. The rest of the fluorite is converted into corrosive hydrogen fluoride en route to various organic fluorides, or into cryolite, which plays a key role in aluminium refining. Molecules containing a carbon–fluorine bond often have very high chemical and thermal stability; their major uses are as refrigerants, electrical insulation and cookware, and PTFE (Teflon). Pharmaceuticals such as atorvastatin and fluoxetine contain C−F bonds. The fluoride ion from dissolved fluoride salts inhibits dental cavities, and so finds use in toothpaste and water fluoridation. Global fluorochemical sales amount to more than US$69 billion a year.

Fluorocarbon gases are generally greenhouse gases with global-warming potentials 100 to 23,500 times that of carbon dioxide, and SF6 has the highest global warming potential of any known substance. Organofluorine compounds often persist in the environment due to the strength of the carbon–fluorine bond. Fluorine has no known metabolic role in mammals; a few plants and sea sponges synthesize organofluorine poisons (most often monofluoroacetates) that help deter predation.

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Atomic properties

Standard atomic weight18.9984 ±5·10-9
Atomic mass18.9984 u

Atomic radii

Radius (empirical)50 pm
Radius (calculated)42 pm
Covalent radius64 pm
Van der Waals radius135 pm

Atomic shell

Electron configurationHe 2s2 2p5
Ionization energy(1st) 17.42282 eV
(2nd) 34.97081 eV
(3rd) 62.70798 eV
(4th) 87.175 eV
(5th) 114.249 eV
(6th) 157.16311 eV
(7th) 185.1868 eV
Shell model

Physical properties

Density0.001696 g·cm−3 (273 K)
Molar volumesolid: 1.12·10-5 m3·mol−1


Melting point53.48 K
Boiling point85.03 K
Liquid range31.55 K
Triple point53.48 K @ 0.252 kPa
Critical point144.4 K @ 5.172 MPa


Melting enthalpy0.26 kJ·mol-1
Enthalpy of vaporization3.27 kJ·mol-1
Binding energy79 kJ·mol-1

Heat and conductivity

Thermal conductivity0.0279 W·m-1·K-1


Magnetic susceptibility-1.201·10-4 cm3·mol−1

Optical properties

Refractive index1

Chemical properties

Basicitystrongly acidic
Oxidation state-1
Standard potential2.87 V (F + e- → F-)


Pauling scale3.98
Sanderson scale4
Allred-Rochow scale4.1
Mulliken scale3.91
Allen scale4.193
Ghosh-Gupta scale10.03 eV
Boyd-Edgecombe scale4
Nagle scale4.23
Pearson absolute negativity10.41 eV

Other properties

Natural occurrenceprimordial
Crystal structureSimple cubic
Goldschmidt Classificationlithophile
Superconductorwithout transition tempperature
Price/kg2 ±0.16 USD

Natural abundances

400 ppb ≈ 4.02·1012 M☉
500 ppb ≈ 9.94·1011 Mt
89,000 ppb ≈ 89 g
Earth’s crust
540,000 ppb ≈ 1.49·107 Mt
1,300 ppb ≈ 1.78 Mt
Flowing water
100 ppb ≈ 1.6 Gt
Human body
37,000 ppb ≈ 2.59 g