fluorine

American  

[floor-een, -in, flawr-, flohr-] / ˈflʊər in, -ɪn, ˈflɔr-, ˈfloʊr- /

noun

Chemistry.

1. the most reactive nonmetallic element, a pale-yellow, corrosive, toxic gas that occurs combined, especially in fluorite, cryolite, phosphate rock, and other minerals. F; 18.9984; 9.

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fluorine British  

/ ˈflʊəriːn, ˈflʊərɪn /

noun

1. a toxic pungent pale yellow gas of the halogen group that is the most electronegative and reactive of all the elements, occurring principally in fluorspar and cryolite: used in the production of uranium, fluorocarbons, and other chemicals. Symbol: F; atomic no: 9; atomic wt: 18.9984032; valency: 1; density: 1.696 kg/m³; relative density: 1.108; freezing pt: –219.62°C; boiling pt: –188.13°C

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fluorine Scientific  

/ flr′ēn′ /

1. A pale-yellow, poisonous, gaseous element of the halogen group. It is highly corrosive and is used to separate certain isotopes of uranium and to make refrigerants and high-temperature plastics. It is also added in fluoride form to the water supply to prevent tooth decay. Atomic number 9; atomic weight 18.9984; melting point −223°C; boiling point −188.14°C; specific gravity of liquid 1.108 (at boiling point); valence 1.

2. See Periodic Table

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Etymology

Origin of fluorine

First recorded in 1805–15; fluor(ic) + -ine ¹

Compare meaning

How does fluorine compare to similar and commonly confused words? Explore the most common comparisons:

• fluorine vs. fluoride

Example Sentences

See Examples For:

fluorine

The fluorine atom served as a relatively clear indicator of how the molecule's vibrations relaxed over time.

From Science Daily ● Jul. 30, 2026

The researchers studied 3-fluoropyridine, a small ring-shaped molecule containing both nitrogen and fluorine atoms.

From Science Daily ● Jul. 30, 2026

It also released about 35 percent of the fluorine atoms originally bound within the chemicals, converting them into fluoride salts.

From Science Daily ● Jul. 20, 2026

That threshold falls to roughly 10 electron volts when fluorine is added and about 14 electron volts when oxygen is used.

From Science Daily ● Jun. 17, 2026

A poor pharmacist with little in the way of advanced apparatus, he discovered eight elements–chlorine, fluorine, manganese, barium, molybdenum, tungsten, nitrogen, and oxygen–and got credit for none of them.

From "A Short History of Nearly Everything" by Bill Bryson