Fluorine (F)

Fluorine (symbol F) is the chemical element with atomic number 9: a halogen, a gas at 0 °C, with an atomic mass of 18.998 u. Discovered in 1886 (Henri Moissan).

Fluorine is the most reactive element on the table: it attacks almost everything, glass included. It injured or killed several chemists who tried to isolate it. Once combined, though, it becomes extraordinarily stable, which is the strength of Teflon but also the problem with “forever chemicals” (PFAS). In small doses, fluoride protects tooth enamel.

Key facts

Atomic number: 9
Symbol: F
French name: Fluor
Atomic mass: 18.998 u
Molar mass: 18.998 g/mol
Family: Halogens
Position: period 2, group 17, p-block
State at 0 °C: Gas
Melting point: -219.7 °C
Boiling point: -188.1 °C
Density: 0.0017 g/cm³
Electronegativity (Pauling): 3.98
First ionization energy: 1,681 kJ/mol
Atomic radius: 50 pm
Electron configuration: [He] 2s² 2p⁵
Abundance in Earth's crust: 585 ppm (13th most abundant element)
Indicative price: 2 $/kg (order of magnitude)
Radioactive: no
Discovery: 1886, Henri Moissan

Origin of the name

From the Latin fluere, to flow, after the mineral fluorite, used as a flux.

What does fluorine look like?

A very pale yellow gas with a sharp, pungent smell. It is so aggressive that it can make wood, rubber and even water burst into flame under certain conditions.

Where is fluorine found?

About 550 ppm of Earth's crust, always combined, mainly in fluorite. It is found in seawater and, as fluorides, in bones and teeth.

Natural sources

Fluorite (fluorspar)
Cryolite
Fluorapatite

How is fluorine produced?

About 9 million tonnes of fluorite are mined each year and treated with sulfuric acid to make hydrofluoric acid, the starting point for nearly all fluorine chemistry. Fluorine gas itself is produced by electrolysis, following the method pioneered by Moissan.

Top producers

China
Mexico
Mongolia
South Africa

What is fluorine used for?

Toothpastes and fluoridated water against tooth decay.
Non-stick and waterproof polymers (PTFE/Teflon).
Refrigerant gases in air conditioners and refrigerators.
Uranium enrichment (uranium hexafluoride).
Medicines: about one drug in five contains fluorine.
Aluminium production (cryolite as a flux).

In everyday life

Your toothpaste
A non-stick frying pan
The coolant in your fridge and air conditioner
Breathable waterproof jackets

Role in living things

Not strictly essential, fluoride binds into tooth enamel and makes it more resistant to acids from bacteria. Too much during childhood causes fluorosis (white or brown spots on teeth) and, at very high doses over long periods, bone damage.

Hazards of fluorine

Fluorine gas is extremely toxic and corrosive. Hydrofluoric acid is especially treacherous: it passes through skin without immediate pain and strips calcium from the body, which can cause cardiac arrest. PFAS, nearly indestructible fluorinated compounds, build up in the environment and the human body.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of fluorine

For more than seventy years, many chemists tried to isolate it, and several were badly poisoned: they became known as the “fluorine martyrs.” Frenchman Henri Moissan finally succeeded on June 26, 1886, by low-temperature electrolysis, a feat that helped earn him the 1906 Nobel Prize in Chemistry.

Did you know?

The word “fluorescence” comes from fluorite, a mineral that glows under ultraviolet light.
Teflon was discovered by accident in 1938 by Roy Plunkett at DuPont, who found a slippery white powder inside a gas cylinder that seemed empty.
Fluorine can even react with xenon and krypton, noble gases reputed to be inert.

Isotopes of fluorine

A single stable isotope, fluorine-19. Radioactive fluorine-18 is the most widely used isotope in PET imaging for tracking down cancers.

fluorine-18: radioactive, half-life 1.83 h. Attached to glucose (FDG), it lights up tumors in PET scans.
fluorine-19: 100% of natural fluorine, stable. Highly sensitive in NMR, handy for studying fluorinated drugs.

Common compounds

Sodium fluoride (NaF) · Fluorite (CaF₂) · Freon (CFC-12) (CCl₂F₂) · Sulfur hexafluoride (SF₆)

Related elements

Same family (halogens): Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At).

Same column (group 17): Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), Tennessine (Ts).