Fluorine

Fluorine, ₉F
	Liquid fluorine (at extremely low temperatures)
General properties
Pronunciation	/ˈflʊəriːn, -ɪn/; (FLOOR-een, -in); /ˈflɔːriːn, -ɪn/; (FLOR-een, -in);
Allotropes	alpha, beta
Appearance	gas: very pale yellow; liquid: bright yellow; solid: alpha is opaque, beta is transparent
Standard atomic weight (Ar, standard)	18.998403163(6)
Fluorine in the periodic table
	oxygen ← fluorine → neon
Atomic number (Z)	9
Group	group 17 (halogens)
Period	period 2
Element category	diatomic nonmetal
Block	p-block
Electron configuration	[He] 2s2 2p5
Electrons per shell	2, 7
Physical properties
Phase at STP	gas
Melting point	53.48 K (−219.67 °C, −363.41 °F)
Boiling point	85.03 K (−188.11 °C, −306.60 °F)
Density (at STP)	1.696 g/L
when liquid (at b.p.)	1.505 g/cm3
Triple point	53.48 K, 90 kPa
Critical point	144.41 K, 5.1724 MPa
Heat of vaporization	6.51 kJ/mol
Molar heat capacity	Cp: 31 J/(mol·K) (at 21.1 °C); Cv: 23 J/(mol·K) (at 21.1 °C)
Atomic properties
Oxidation states	−1 (oxidizes oxygen)
Electronegativity	Pauling scale: 3.98
Ionization energies	1st: 1681 kJ/mol; 2nd: 3374 kJ/mol; 3rd: 6147 kJ/mol; (more);
Covalent radius	64 pm
Van der Waals radius	135 pm
	Spectral lines
	Spectral lines
Miscellanea
Crystal structure	cubic
Thermal conductivity	0.02591 W/(m·K)
Magnetic ordering	diamagnetic (−1.2×10−4)
CAS Number	7782-41-4
History
Naming	after the mineral fluorite, itself named after Latin fluo (to flow, in smelting)
Discovery	André-Marie Ampère (1810)
First isolation	Henri Moissan(June 26, 1886)
Named by	Humphry Davy
Main isotopes of fluorine
ε (3%)	18O
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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.

Among the elements, fluorine ranks 24th in universal abundance and 13th in terrestrial abundance. Fluorite, the primary mineral source of fluorine which gave the element its name, was first described in 1529; as it was added to metal ores to lower their melting points for smelting, the Latin verb fluo meaning "flow" gave the mineral its name. Proposed as an element in 1810, fluorine proved difficult and dangerous to separate from its compounds, and several early experimenters died or sustained injuries from their attempts. Only in 1886 did French chemist Henri Moissan isolate elemental fluorine using low-temperature electrolysis, a process still employed for modern production. Industrial production of fluorine gas for uranium enrichment, its largest application, began during the Manhattan Project in World War II.

Owing to the expense of refining pure fluorine, most commercial applications use fluorine compounds, with about half of mined fluorite used in steelmaking. The rest of the fluorite is converted into corrosive hydrogen fluoride en route to various organic fluorides, or into cryolite which plays a key role in aluminium refining. Organic fluorides have very high chemical and thermal stability; their major uses are as refrigerants, electrical insulation and cookware, the last as PTFE (Teflon). Pharmaceuticals such as atorvastatin and fluoxetine also contain fluorine, and the fluoride ion inhibits dental cavities, and so finds use in toothpaste and water fluoridation. Global fluorochemical sales amount to more than US$15 billion a year.

Fluorocarbon gases are generally greenhouse gases with global-warming potentials 100 to 20,000 times that of carbon dioxide. Organofluorine compounds persist in the environment due to the strength of the carbon–fluorine bond. Fluorine has no known metabolic role in mammals; a few plants synthesize organofluorine poisons that deter herbivores.