Fluorine
Reactive nonmetal · Period 2 · Group 17 · p-block
The most reactive element, tamed into Teflon
- Atomic mass
- 18.998 u
- State at 25 °C
- Gas
- Electronegativity
- 3.98
- Melting point
- -219.7 °C
- Boiling point
- -188.1 °C
- Configuration
- [He] 2s2 2p5
Fluorine, explained
Overview
Fluorine is one electron short of a noble gas configuration ([He]2s2 2p5), and its small atom holds that missing electron's place very close to the nucleus. It is the most electronegative element (3.98) and the strongest elemental oxidizing agent. The F-F bond in the pale yellow F2 molecule is unusually weak, about 159 kJ/mol, because lone pairs on the two small atoms repel each other. Weak bond plus strong pull on electrons means fluorine reacts with almost every element, including the noble gases xenon and krypton, often with flames.
The paradox of fluorine is that once bonded, it is extremely stable. The carbon-fluorine bond is the strongest single bond in organic chemistry, so fluorocarbons such as PTFE (Teflon) resist heat and chemicals, and so-called PFAS 'forever chemicals' persist in the environment for decades. Fluoride ions convert hydroxyapatite in tooth enamel into the more acid-resistant fluorapatite. Most fluorine comes from the mineral fluorite, CaF2, and the gas itself is still made much as it was first isolated: by electrolysis of potassium fluoride dissolved in hydrogen fluoride.
Discovery
Fluorite was used as a smelting flux by the 1500s, and Georgius Agricola named it in 1529 from the Latin fluere, to flow. Isolating the element took most of the 19th century; several chemists were poisoned or injured by hydrogen fluoride. On 26 June 1886, Henri Moissan finally produced fluorine gas by electrolysing potassium fluoride in liquid hydrogen fluoride at low temperature in a platinum apparatus, earning the 1906 Nobel Prize in Chemistry.
- Where it’s found
- Fluorine is mined mainly as fluorite (CaF2), with smaller amounts from fluorapatite; the free element is produced by electrolysis of molten KF·2HF.
- What it’s used for
- Non-stick coatings
- Fluoride toothpaste
- Uranium enrichment
- Refrigerant gases
- Aluminium smelting flux
- Fluorinated drugs
- In living things
- Fluoride is not considered essential, but small amounts strengthen tooth enamel and reduce decay; excess causes dental and skeletal fluorosis. Fluorine gas and hydrogen fluoride are highly toxic.
- Safety
- Fluorine gas is extremely toxic and corrosive and ignites many materials on contact. Hydrofluoric acid penetrates skin and binds calcium in tissues, so even small burns can cause deep damage and dangerous changes in heart rhythm.
How it compares
Where Fluorine sits among all 118 elements on the trends that shape the table.
- Electronegativity3.98Pauling
#1 of 100 elements with data
- Ionization energy1,680kJ/mol
#3 of 104 elements with data
- Atomic radius50pm
#94 of 95 elements with data
- Electron affinity328kJ/mol
#2 of 109 elements with data
- Density0.002g/cm³
#109 of 114 elements with data
- Melting point53.5K
#107 of 110 elements with data
- Density
- 1.7 g/L
- Atomic radius
- 50 pm
- Covalent radius
- 64 pm
- Molar heat
- —
- Appearance
- —
- Discovered by
- André-Marie Ampère
Inside the atom
9 electrons arranged in 2 shells: 2 · 7.
Orbital diagram
1s2 2s2 2p5 · shorthand [He] 2s2 2p5
- 1s2
- 2s2
- 2p5
Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Fluorine bonds.
Ionization energies
Signature reactions
The chemistry Fluorine is known for.
Redox · Synthesis
Hydrogen and fluorine
Hydrogen and fluorine react explosively on mixing, even at -200 °C, without needing a spark. The product, hydrogen fluoride, has one of the strongest single bonds known, which explains the huge energy release. This violence is a direct consequence of fluorine's weak F-F bond.
Conditions: explosive even in the dark at low temperature
Acid-base · Etching
Etching glass with hydrofluoric acid
Hydrofluoric acid dissolves silica, the main component of glass, by forming volatile silicon tetrafluoride. It is used to frost light bulbs, etch decorative glass and clean silicon wafers in chip fabrication. Because of this, HF cannot be stored in glass bottles.
Conditions: room temperature
Ion exchange
Fluoride hardening of tooth enamel
Fluoride ions replace hydroxide ions in hydroxyapatite, the mineral of tooth enamel, forming fluorapatite. Fluorapatite dissolves less readily in the acids produced by mouth bacteria. This is the chemistry behind fluoride toothpaste and water fluoridation.
Conditions: fluoride from toothpaste or water
Where you’ll meet it
Fluorite
Fluorite, calcium fluoride, is the main source of fluorine and comes in nearly every colour.
Photo: Wikimedia Commons
Toothpaste
Most toothpastes contain sodium fluoride or similar compounds that help enamel resist decay.
Photo: Wikimedia Commons
Non-stick pan
Non-stick cookware is coated with PTFE, a polymer whose surface is sheathed in fluorine atoms.
Photo: Wikimedia Commons
Cryolite
This sodium aluminium fluoride mineral from Greenland was once essential for smelting aluminium.
Photo: Wikimedia Commons
Research
No research on Fluorine yet
When Bhavya publishes a project that studies Fluorine, it will be linked here.