Fluorine

HALOGEN · GROUP 17 · PERIOD 2
9
F
Fluorine
18.998

Atomic Data

Atomic Number9
SymbolF
Atomic Weight18.998 u
Density (STP)1.696 g/L
Melting Point−219.67 °C (53.48 K)
Boiling Point−188.12 °C (85.03 K)
Electronegativity3.98 (Pauling)
Electron Config.1s² 2s² 2p⁵
Oxidation States−1
Phase at STPGas
CategoryHalogen
Period / Group2 / 17
CAS Number7782-41-4

Electron Configuration

F K L

1s2 2s2 2p5

Shell n Subshell Electrons Cumulative
K 1 1s 2 2
L 2 2s 2 4
L 2 2p 5 9
Total 7 9

Isotopes of Fluorine

Fluorine has only one stable isotope, fluorine-19, which accounts for 100% of naturally occurring fluorine. This makes fluorine monoisotopic — a useful property in NMR spectroscopy and mass spectrometry. All other fluorine isotopes are radioactive and have short half-lives.

Isotope Symbol Protons Neutrons Abundance Stability
Fluorine-19 ¹⁹F 9 10 100% Stable
Fluorine-18 ¹⁸F 9 9 Trace Radioactive (t½ = 109.77 min)

Abundance & Occurrence

Fluorine is the 13th most abundant element in Earth's crust at about 585 ppm, concentrated in the mineral fluorite (CaF2, also called fluorspar), the principal commercial source. Other significant minerals include fluorapatite (Ca5(PO4)3F), found in phosphate rock used for fertiliser production, and cryolite (Na3AlF6), historically important in aluminium smelting. Fluorine never occurs in elemental form in nature owing to its extreme reactivity. China, Mexico, Mongolia, and South Africa are the major producers of fluorspar.

World Fluorspar Reserves by Country (approx. %)

China
57%
Mexico
17%
Mongolia
9%
South Africa
7%
Other
10%

Global Fluorine Demand by Sector (approx. %)

Aluminium
36%
Fluorochemicals
30%
Fluorine compounds
20%
Other (ceramics, nuclear)
14%

Discovery & History

1529
Georgius Agricola — Described the use of fluorspar (CaF2) as a flux in metal smelting in De Re Metallica. The name fluorspar comes from Latin fluere (to flow), referring to its use in lowering the melting point of ores.
1813
Humphry Davy — Proposed that a new element was present in hydrofluoric acid (HF), naming it fluorine. Numerous chemists subsequently attempted to isolate elemental fluorine — several died from the toxic HF vapours generated in the process, earning fluorine the reputation as the most dangerous element to isolate.
1886
Henri Moissan — Successfully isolated fluorine gas on 26 June 1886 by electrolyising liquid hydrogen fluoride at low temperature in a platinum cell with platinum-iridium electrodes. The 73-year search for a method to isolate fluorine earned Moissan the 1906 Nobel Prize in Chemistry.
1938
Roy Plunkett (DuPont) — Accidentally discovered polytetrafluoroethylene (PTFE, later trademarked Teflon) when a sample of tetrafluoroethylene polymerised in its storage cylinder. PTFE's extraordinary chemical inertness and non-stick properties made it one of the most commercially important fluorine compounds.
1940s–1950s
Manhattan Project & Cold War — Uranium hexafluoride (UF6) became the key compound for uranium isotope separation in gaseous diffusion plants. Fluorine chemistry underpinned both the US and Soviet nuclear weapons programmes and the subsequent development of civilian nuclear power.

Safety & Handling

  • Extreme corrosivity and toxicity: Elemental fluorine gas is one of the most dangerous chemicals in existence. It reacts violently with water, organic materials, and almost every metal and non-metal. It causes immediate, severe chemical burns to all tissues on contact, and even brief inhalation causes fatal pulmonary oedema.
  • Hydrofluoric acid (HF) — penetrating burn hazard: HF is the primary handling form of fluorine in industry. Unlike most acids that cause surface burns, HF penetrates skin painlessly and then attacks underlying bone, releasing toxic fluoride ions into the bloodstream. Even 1% body-surface-area burns from concentrated HF can be fatal. Immediate treatment with calcium gluconate gel is required.
  • Fluorine gas handling requirements: Fluorine gas must be handled in purpose-built nickel or Monel alloy equipment that forms a passive fluoride surface layer. Standard stainless steel, glass, and most polymers are rapidly attacked. Personnel require full chemical-protective suits, supplied-air respirators, and face shields.
  • Fluoride compounds: Sodium fluoride and other soluble fluoride salts are acutely toxic by ingestion above ~5 mg/kg. Chronic excessive fluoride intake causes dental fluorosis (mottling of enamel) and skeletal fluorosis (bone thickening and joint pain). Water fluoridation at recommended levels (0.7 ppm) is well below harmful thresholds.
  • PFAS environmental persistence: Per- and polyfluoroalkyl substances (PFAS) used in industrial applications are essentially non-biodegradable and have been detected in drinking water, wildlife, and human blood globally. Several PFAS are linked to serious health effects including cancer, immunosuppression, and hormonal disruption.

Real-World Uses

  • PTFE (Teflon) production — Polytetrafluoroethylene (PTFE) is produced by polymerising tetrafluoroethylene (TFE), itself made from fluorite and chloroform. PTFE's extreme chemical inertness, non-stick surface, and low friction make it indispensable in cookware coatings, pipe linings for corrosive chemicals, seals in chemical plants, and wire insulation. The global fluoropolymer market exceeds $10 billion annually.
  • Uranium enrichment — Natural uranium is converted to uranium hexafluoride (UF6), a gas at slightly elevated temperature, for isotope separation. Centrifuges or gaseous diffusion processes exploit the small mass difference between ²³⁵UF6 and ²³⁸UF6 to enrich ²³⁵U for nuclear fuel and weapons.
  • Toothpaste fluoridation — Sodium fluoride (NaF), sodium monofluorophosphate (MFP), or stannous fluoride at 1,000–1,500 ppm in toothpaste converts tooth enamel hydroxyapatite to the harder, more acid-resistant fluorapatite. Regular use reduces cavity incidence by roughly 25% compared to non-fluoride toothpaste.
  • Refrigerants (HFCs and HFOs) — Hydrofluorocarbons (HFCs) such as R-134a replaced ozone-depleting CFCs in air conditioners and refrigerators following the Montreal Protocol. Next-generation hydrofluoroolefins (HFOs) like R-1234yf have very low global-warming potential and are now the standard refrigerant in new vehicle air conditioning systems.
  • Semiconductor etching — Fluorine compounds including hydrogen fluoride (HF), nitrogen trifluoride (NF3), and sulfur hexafluoride (SF6) are central to semiconductor manufacturing. HF etches silicon dioxide selectively; NF3 is used to clean chemical vapour deposition chambers; SF6 plasma is used in deep reactive ion etching (DRIE) of silicon microstructures.
  • Fluorine-18 PET imaging — Fluorine-18 (half-life 109.8 min), a positron emitter, is the most widely used radioisotope in medical positron emission tomography (PET). Incorporated into fluorodeoxyglucose (FDG), it enables imaging of metabolically active tissues including tumours, providing critical diagnostic information in oncology, neurology, and cardiology.

Downloadable Resources

Free periodic table reference sheets for classrooms, study sessions, and laboratory use.

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Frequently Asked Questions

Why is fluorine the most electronegative element?

Fluorine has the highest electronegativity (3.98 on the Pauling scale) of any element because it combines the smallest atomic radius of any halogen with seven valence electrons — meaning it needs only one more electron to complete its octet. Its compact nucleus exerts an exceptionally strong attractive force on shared electrons, making it the most powerful electron acceptor in covalent bonding. No other element can oxidise fluorine.

Why is fluoride added to toothpaste and drinking water?

Fluoride ions (F−) react with the hydroxyapatite in tooth enamel to form fluorapatite, which is harder and more resistant to acid attack from bacteria. In toothpaste, fluoride compounds at 1,000–1,500 ppm provide effective cavity protection. Community water fluoridation at 0.7 ppm is endorsed by the WHO and CDC as safe and effective for reducing dental decay across populations.

What is Teflon and why is it non-stick?

Teflon is the brand name for polytetrafluoroethylene (PTFE), a fluoropolymer made by polymerising tetrafluoroethylene (CF2=CF2). PTFE's non-stick property arises from the extreme strength of the C–F bond and fluorine's electron cloud, which shields the carbon backbone from interaction with other molecules. PTFE is resistant to virtually every chemical except molten alkali metals and fluorine gas itself.

How was fluorine isolated?

Isolating fluorine was one of the hardest challenges in 19th-century chemistry. Because fluorine reacts violently with water, glass, and most metals, every attempt to liberate it failed — and several chemists were killed or injured. Henri Moissan finally succeeded in 1886 by electrolyising liquid hydrogen fluoride (HF) in a platinum apparatus at −23°C, earning him the 1906 Nobel Prize in Chemistry.

What are PFAS chemicals and why are they concerning?

PFAS (per- and polyfluoroalkyl substances) are synthetic fluorinated compounds used in non-stick cookware, food packaging, firefighting foams, and waterproof textiles. The extreme strength of the C–F bond makes PFAS essentially non-biodegradable — they persist in the environment and in human tissues for decades, earning the nickname ‘forever chemicals.’ Epidemiological studies link PFAS exposure to thyroid disorders, immune suppression, certain cancers, and developmental effects. Regulatory agencies worldwide are progressively restricting their use.