ELEMENTLE

Element 9 · Halogen

Fluorine

Period 2 · Group 17

Fluorine is a chemical element with symbol F and atomic number 9. It is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. As the most electronegative element, it is extremely reactive:almost all other elements, including some noble gases, form compounds with fluorine.

Three reasons Fluorine stands out

  1. 1

    Used in toothpaste.

  2. 2

    It is the most chemically reactive element known, capable of corroding through glass.

  3. 3

    The non-stick coating on frying pans is a compound made with this element.

Chemistry at its most aggressive

Fluorine pulls on shared electrons more strongly than any other element. The pure gas attacks substances that seem inert, including glass, yet tightly bound fluorides can be stable enough for toothpaste and non-stick coatings. Its usefulness comes from controlling an element that is extraordinarily difficult to isolate.

Fluorine at a glance
Atomic number / protons9
SymbolF
Family (Elementle)Halogen
Classification (PubChem)Halogen
Period2
Group17
Atomic mass (u)18.99840316
Standard stateGas
Electron configuration[He]2s2 2p5
Reported oxidation states-1
Electronegativity (Pauling)3.98
Atomic radius (pm)135
First ionization energy (eV)17.423
Electron affinity (eV)3.339
Density (g/cm³)0.001696
Melting point53.53 K (-219.62 °C)
Boiling point85.03 K (-188.12 °C)
Discovery (PubChem)1670

Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.

Sources & further reading

PubChem: Fluorine · Fluorine on Wikipedia

The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.