Fluorine (F)
Element 9 · Halogen · atomic mass 18.998 u · group 17, period 2
Electron shells: 2, 7
Fluorine is the most electronegative and most reactive element, attacking almost everything it touches. Bound into compounds, though, it becomes exceptionally stable and useful.
Isolating fluorine blinded or killed several chemists before Moissan finally succeeded in 1886.
- Atomic number
- 9
- Atomic mass
- 18.998 u
- Electron configuration
- [He] 2s² 2p⁵
- Group · period · block
- 17 · 2 · p
- Oxidation states
- −1
- Electronegativity
- 3.98 (Pauling)
- Melting point
- -220 °C
- Boiling point
- -188 °C
- Density
- 0.001696 g/cm³
- State at 20 °C
- Gas
- Appearance
- Pale yellow gas
- Discovered
- Henri Moissan, 1670
9 protons, and 9 electrons when neutral
IUPAC standard atomic weight
Halogens
What Fluorine is used for
- Toothpaste and water fluoridation
- PTFE (Teflon) and fluoropolymers
- Uranium enrichment
- Refrigerants and pharmaceuticals
Atomic structure of Fluorine
A neutral fluorine atom has 9 protons and 9 electrons. Its most common isotope carries about 10 neutrons, which is where the mass number 19 comes from. Change the neutron count and you have a different isotope of fluorine; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 7. In orbital notation that is [He] 2s² 2p⁵, leaving 7 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Fluorine's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Fluorine sits in the periodic table
Discovery and naming
Fluorine was discovered by Henri Moissan in 1670. Its name comes from Latin fluere, "to flow".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Fluorine?
The standard atomic weight of Fluorine is 18.998 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Fluorine have?
Fluorine has 9 protons, because the atomic number is the proton count and that is what makes an atom Fluorine at all. A neutral Fluorine atom has the same number of electrons, 9. The neutron count varies by isotope; the most common one has about 10, since 19 − 9 = 10.
What is the electron configuration of Fluorine?
The electron configuration of Fluorine is [He] 2s² 2p⁵. Its electrons are arranged 2, 7 across 2 shells.
Is Fluorine a metal?
No. Fluorine is classified as a halogen, on the right-hand side of the table where elements gain or share electrons rather than losing them.
What group and period is Fluorine in?
Fluorine is in group 17 (the halogens), period 2, in the p-block. The group is its column and the period is its row.
What is the charge of Fluorine?
Fluorine most commonly forms a 1− ion. It is 1 electron short of a full outer shell, so it gains one rather than losing 7.
What is the melting point of Fluorine?
Fluorine melts at -220 °C and boils at -188 °C. That puts it in the gases at everyday temperatures.
What is Fluorine used for?
Toothpaste and water fluoridation, PTFE (Teflon) and fluoropolymers, Uranium enrichment, Refrigerants and pharmaceuticals. Fluorine is the most electronegative and most reactive element, attacking almost everything it touches.
Who discovered Fluorine, and where does its name come from?
Fluorine (F) was discovered by Henri Moissan in 1670. The name comes from Latin fluere, "to flow".