and *cryolite (Na 3 AlF). The element is
obtained by electrolysis of a molten
mixture of potassium Ûuoride and
hydrogen Ûuoride. It is used in the
synthesis of organic Ûuorine compounds. Chemically, it is the most reactive and electronegative of all
elements. It is a highly dangerous element, causing severe chemical
burns on contact with the skin. The
element was identiÜed by Scheele in
1771 and Ürst isolated by Moissan in
1886.
A
• Information from the WebElements site
Ûuorite (Ûuorspar) A mineral form
of calcium Ûuoride, CaF 2 , crystallizing in the cubic system. It is variable
in colour; the most common Ûuorites
are green and purple (blue john), but
other forms are white, yellow, or
brown. Fluorite is used chieÛy as a
Ûux material in the smelting of iron
and steel; it is also used as a source of
Ûuorine and hydroÛuoric acid and in
the ceramic and optical-glass industries.
Ûuorite structure A type of ionic
crystal structure in which the cations
have an expanded face-centred cubic
arrangement with the anions occupying both types of tetrahedral hole.
The cations have a coordination
number of 8 and the anions have a
coordination number of 4. Examples
of compounds with this structure are
CaF 2 , BaCl 2 , and PbO 2 .
The antiÛuorite structure is the opposite arrangement, with anions in
the fcc array with coordination number 8 and cations in the tetrahedral
holes with coordination number 4.
Examples of the antiÛurite structure
are K 2 O, Li 2 O, Na 2 O, K 2 S, and Na 2 S.
A
• An interactive version of the structure
Ûuorocarbons Compounds obtained by replacing the hydrogen
atoms of hydrocarbons by Ûuorine
atoms. Their inertness and high stability to temperature make them
suitable for a variety of uses as oils,
polymers, etc. See also chlorofluorocarbon; halon.
5-Ûuorouracil (5-FU) A Ûuorine derivative of the pyrimidine uracil. It is
used in chemotherapy where it inhibits the cell’s ability to synthesize
DNA. It is often used in a treatment
regime along with cisplatin.
Ûux 1. A substance applied to the
surfaces of metals to be soldered to
inhibit oxidation. 2. A substance
used in the smelting of metals to assist in the removal of impurities as
slag.
Ûuxional molecule A molecule
that undergoes alternate very rapid
rearrangements of its atoms and thus
only has a speciÜc structure for a
very short period of time. For example, the molecule ClF 3 has a T-shape
at low temperatures (–60°C); at room
temperature the Ûuorine atoms
change position very rapidly and appear to have identical positions.
foam A dispersion of bubbles in a
liquid. Foams can be stabilized by
*surfactants. Solid foams (e.g. expanded polystyrene or foam rubber)
are made by foaming the liquid and
allowing it to set. See also colloids.
foaming agent (blowing agent) A
substance used to produce a liquid or
solid foam (e.g. an expanded plastic).
Physical agents are compressed
gases; chemical foaming agents are
substances that release gas under certain conditions (e.g. sodium hydrogencarbonate).
Fokker–Planck equation An
equation in *nonequilibrium statistical mechanics that describes a superposition of a dynamic friction
(slowing-down) process and a diffufluorite
230
f
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obtained by electrolysis of a molten
mixture of potassium Ûuoride and
hydrogen Ûuoride. It is used in the
synthesis of organic Ûuorine compounds. Chemically, it is the most reactive and electronegative of all
elements. It is a highly dangerous element, causing severe chemical
burns on contact with the skin. The
element was identiÜed by Scheele in
1771 and Ürst isolated by Moissan in
1886.
A
• Information from the WebElements site
Ûuorite (Ûuorspar) A mineral form
of calcium Ûuoride, CaF 2 , crystallizing in the cubic system. It is variable
in colour; the most common Ûuorites
are green and purple (blue john), but
other forms are white, yellow, or
brown. Fluorite is used chieÛy as a
Ûux material in the smelting of iron
and steel; it is also used as a source of
Ûuorine and hydroÛuoric acid and in
the ceramic and optical-glass industries.
Ûuorite structure A type of ionic
crystal structure in which the cations
have an expanded face-centred cubic
arrangement with the anions occupying both types of tetrahedral hole.
The cations have a coordination
number of 8 and the anions have a
coordination number of 4. Examples
of compounds with this structure are
CaF 2 , BaCl 2 , and PbO 2 .
The antiÛuorite structure is the opposite arrangement, with anions in
the fcc array with coordination number 8 and cations in the tetrahedral
holes with coordination number 4.
Examples of the antiÛurite structure
are K 2 O, Li 2 O, Na 2 O, K 2 S, and Na 2 S.
A
• An interactive version of the structure
Ûuorocarbons Compounds obtained by replacing the hydrogen
atoms of hydrocarbons by Ûuorine
atoms. Their inertness and high stability to temperature make them
suitable for a variety of uses as oils,
polymers, etc. See also chlorofluorocarbon; halon.
5-Ûuorouracil (5-FU) A Ûuorine derivative of the pyrimidine uracil. It is
used in chemotherapy where it inhibits the cell’s ability to synthesize
DNA. It is often used in a treatment
regime along with cisplatin.
Ûux 1. A substance applied to the
surfaces of metals to be soldered to
inhibit oxidation. 2. A substance
used in the smelting of metals to assist in the removal of impurities as
slag.
Ûuxional molecule A molecule
that undergoes alternate very rapid
rearrangements of its atoms and thus
only has a speciÜc structure for a
very short period of time. For example, the molecule ClF 3 has a T-shape
at low temperatures (–60°C); at room
temperature the Ûuorine atoms
change position very rapidly and appear to have identical positions.
foam A dispersion of bubbles in a
liquid. Foams can be stabilized by
*surfactants. Solid foams (e.g. expanded polystyrene or foam rubber)
are made by foaming the liquid and
allowing it to set. See also colloids.
foaming agent (blowing agent) A
substance used to produce a liquid or
solid foam (e.g. an expanded plastic).
Physical agents are compressed
gases; chemical foaming agents are
substances that release gas under certain conditions (e.g. sodium hydrogencarbonate).
Fokker–Planck equation An
equation in *nonequilibrium statistical mechanics that describes a superposition of a dynamic friction
(slowing-down) process and a diffufluorite
230
f
www.AzShimi.ir www.AzShimi.com