ElementsWhat is fluorine?
Fluorine is a pale yellow gas and the most reactive of all elements. It attacks almost everything, even glass. In nature it is found only in minerals such as fluorite.
What is fluorine used for?
Fluoride in toothpaste, non-stick coatings such as PTFE, refrigerant gases, and processing uranium for nuclear fuel.
Where the name comes from
From the Latin word fluere, to flow. The mineral fluorspar was used to make metal ores melt and flow more easily.
Key facts
- Symbol
- F
- Atomic number
- 9
- Atomic mass
- 18.99840316 u
- Family
- Halogen
- Period
- 2
- Group
- 17
- Block
- p
- State at room temperature
- Gas
- Melting point
- -219.6 °C (53.53 K, -363 °F)
- Boiling point
- -188.1 °C (85.03 K, -307 °F)
- Density
- 0.001696 g/cm³ (as a gas at 0 °C)
- Electrons per shell
- 2, 7
- Electron configuration
- [He]2s2 2p5
- Common oxidation states
- -1
- Electronegativity (Pauling)
- 3.98
- First ionisation energy
- 17.423 eV
- Electron affinity
- 3.339 eV
- Atomic radius (van der Waals)
- 135 pm
- Discovered
- 1886
Place in the periodic table
Fluorine is element number 9. It sits in period 2 (row 2) of the periodic table, in group 17 (column 17), and belongs to the p-block. Just before it comes oxygen (8), and just after it comes neon (10). In the same column, chlorine is below it. Elements in one column tend to behave alike.
Family: Halogens.
Physical properties
At room temperature fluorine is a gas. It melts at -219.6 °C and boils at -188.1 °C, so it stays liquid over a range of 32 degrees. One litre of the gas weighs about 1.696 grams at 0 °C and normal pressure. That is heavier than air, which weighs about 1.29 grams a litre. It has the 4th lowest melting point of all elements.
Inside the atom
An atom of fluorine has 9 protons in its nucleus and, when neutral, 9 electrons around it. The electrons are arranged in 2 shells: 2, 7. The outermost shell holds 7 electrons. Written in full, the electron configuration is [He]2s2 2p5.
Its electronegativity on the Pauling scale is 3.98, the highest of all. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 17.423 electronvolts (about 1,681 kilojoules per mole). One mole of fluorine weighs 18.99840316 grams, so a single gram contains about 3.17 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains fluorine with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.