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Fluorine                                                                                                 

Standard Sate: gas at 298 K 

Color: pale yellow            

Fluorine is a Group 17 element. Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with practically all organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. Until World War 2, there was no commercial production of elemental fluorine. Atom bomb projects and nuclear energy applications made it necessary to produce large quantities of fluorine since isotopes of uranium can be separated through the gas diffusion of UF₆. Reasonably safe handling techniques for fluorine are now available and one can transport liquid fluorine by the ton. Compounds of fluorine with noble gases such as xenon, radon, and krypton are known. Elemental fluorine and the fluoride ion (in quantity) are highly toxic.

(F),

most reactive chemical element, lightest member of the halogen
elements, or Group VIIa of the periodic table.

Under ordinary conditions fluorine is a gas a little heavier than air,
with a pale yellow colour; inhalation except in very low concentrations
is dangerous. Upon cooling, fluorine becomes a yellow liquid.
Fluorine occurs combined in the widely distributed mineral fluorite
(calcium fluoride, fluorspar), its chief source, in the minerals cryolite
and fluorapatite, and in small amounts in seawater, bones, and teeth.
Not a rare element, it makes up about 0.065 percent of the Earth's
crust. Only one isotope occurs in nature, stable fluorine-19.

Fluorine is difficult to isolate from its compounds, and in fact it is
impossible to free it by chemical means. No other element is powerful
enough, as an oxidizing agent, to replace it. The French chemist Henri
Moissan first isolated fluorine in 1886 by electrolysis of anhydrous
hydrogen fluoride (HF), in which potassium hydrogen fluoride (KHF2)
had been dissolved to make it conduct a current. Elemental fluorine
of high purity is prepared commercially by Moissan's procedure. The
elemental gas is used as an oxidizer in rocket fuels and to prepare
fluorides.

Fluorine, composed of two-atom molecules (F2), combines with all
other elements except helium, neon, and argon to form ionic or
covalent fluorides. Its chemical activity can be attributed to its
extreme ability to attract electrons (it is the most electronegative
element) and to the small size of its atoms. The oxidation state of -1 is
the only one observed in fluorine compounds. Because of the small
size of the fluoride ion (F-), it forms many stable complexes with
positive ions; for example, hexafluorosilicate(IV) (SiF62-) and
hexafluoroaluminate(III) (AlF63-).

One of the principal industrial compounds of fluorine is hydrogen
fluoride, obtained by treating fluorite with sulfuric acid. It is employed
in the preparation of numerous inorganic and organic fluorine
compounds of commercial importance, e.g., sodium aluminum fluoride
(Na3AlF6), used as an electrolyte in the electrolytic smelting of
aluminum metal; and uranium hexafluoride (UF6), utilized in the
gaseous diffusion process of separating uranium-235 from
uranium-238 for reactor fuel. A solution of hydrogen fluoride gas in
water is called hydrofluoric acid, large quantities of which are
consumed in industry for cleaning metals and for polishing, frosting,
and etching glass.

Boron trifluoride (BF3) and antimony trifluoride (SbF3), like hydrogen
fluoride, are important catalysts for organic reactions; cobalt
trifluoride (CoF3) and chlorine trifluoride (ClF3) are useful fluorinating
agents; and sulfur hexafluoride (SF6) is used as a gaseous electrical
insulator. Sodium fluoride (NaF) is used to treat dental caries and is
often added in small amounts to fluoride-deficient water supplies
(fluoridation) to reduce tooth decay.

Elemental fluorine, often diluted with nitrogen, reacts with
hydrocarbons to form corresponding fluorocarbons in which some or
all hydrogen has been replaced by fluorine. The resulting compounds
are usually characterized by great stability, chemical inertness, high
electrical resistance, and other valuable physical and chemical
properties. This fluorination may be accomplished also by treating
organic compounds with cobaltic fluoride or by electrolyzing their
solutions in anhydrous hydrogen fluoride. Useful plastics with
non-sticking qualities, such as polytetrafluoroethylene ([CF2CF2)x];
known by the commercial name Teflon), are readily made from
unsaturated fluorocarbons. Organic compounds containing chlorine,
bromine, or iodine are fluorinated to produce compounds such as
dichlorodifluoromethane (Cl2CF2), the coolant used in most household
refrigerators and air conditioners. atomic number 9 atomic weight
18.9984 melting point -219.62 C (-363.32 F) boiling point -188 C
(-306 F) density (1 atm, 0 C) 1.696 g/litre oxidation states -1
electronic config. 2-7 or 1s22s22p5

"fluorine" Encyclop�dia Britannica Online.

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