engines to lower its freezing point so
that it does not solidify at sub-zero
temperatures. The commonest antifreeze is *ethane-1,2-diol (ethylene
glycol).
antigorite See serpentine.
anti-isomer See isomerism.
antiknock agent A petrol additive
that inhibits preignition (‘knocking’)
in internal-combustion engines. Antiknock agents work by retarding
combustion chain reactions. The
commonest, lead(IV) tetraethyl,
causes environmental pollution, and
its use is being discouraged.
antimonic compounds Compounds of antimony in its +5 oxidation state; e.g. antimonic chloride is
antimony(V) chloride (SbCl 5 ).
antimonous compounds Compounds of antimony in its +3 oxidation state; e.g. antimonous chloride is
antimony(III) chloride (SbCl 3 ).
antimony Symbol Sb. An element
belonging to *group 15 (formerly VB)
of the periodic table; a.n. 51; r.a.m.
121.75; r.d. 6.68; m.p. 630.5°C; b.p.
1750°C. Antimony has several allotropes. The stable form is a bluishwhite metal. Yellow antimony and
black antimony are unstable nonmetallic allotropes made at low temperatures. The main source is
stibnite (Sb 2 S 3 ), from which antimony is extracted by reduction with
iron metal or by roasting (to give the
oxide) followed by reduction with
carbon and sodium carbonate. The
main use of the metal is as an alloying agent in lead-accumulator plates,
type metals, bearing alloys, solders,
Britannia metal, and pewter. It is also
an agent for producing pearlitic cast
iron. Its compounds are used in
Ûame-prooÜng, paints, ceramics,
enamels, glass dyestuffs, and rubber
technology. The element will burn in
air but is unaffected by water or dilute acids. It is attacked by oxidizing
acids and by halogens. It was Ürst reported by Tholden in 1450.
A
• Information from the WebElements site
antioxidants Substances that slow
the rate of oxidation reactions. Various antioxidants are used to preserve
foodstuffs and to prevent the deterioration of rubber, synthetic plastics,
and many other materials. Some antioxidants act as chelating agents to
sequester the metal ions that catalyse
oxidation reactions. Others inhibit
the oxidation reaction by removing
oxygen free radicals. Naturally occurring antioxidants include *vitamin E
and β-carotene; they limit the cell
and tissue damage caused by foreign
substances, such as toxins and pollutants, in the body.
antiparallel spins Neighbouring
spinning electrons in which the
*spins, and hence the magnetic moments, of the electrons are aligned in
the opposite direction. Under some
circumstances the interactions between magnetic moments in atoms
favour *parallel spins, while under
other conditions they favour antiparallel spins. The case of antiferromagnetism (see magnetism) is an example
of a system with antiparallel spins.
antiperiplanar See torsion angle.
anti-Stokes radiation Electromagnetic radiation occurring in the
*Raman effect, which is of much
lower intensity than the Rayleigh
scattering in which the frequency of
the radiation is higher than that of
the incident light, i.e. displaced towards shorter wavelengths. If the frequency of the original light is ν, the
frequency of the anti-Stokes radiation is ν + ν k , where ν k is the frequency of the rotation or vibration of
the molecule. The spectral lines asso41
anti-Stokes radiation
a
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that it does not solidify at sub-zero
temperatures. The commonest antifreeze is *ethane-1,2-diol (ethylene
glycol).
antigorite See serpentine.
anti-isomer See isomerism.
antiknock agent A petrol additive
that inhibits preignition (‘knocking’)
in internal-combustion engines. Antiknock agents work by retarding
combustion chain reactions. The
commonest, lead(IV) tetraethyl,
causes environmental pollution, and
its use is being discouraged.
antimonic compounds Compounds of antimony in its +5 oxidation state; e.g. antimonic chloride is
antimony(V) chloride (SbCl 5 ).
antimonous compounds Compounds of antimony in its +3 oxidation state; e.g. antimonous chloride is
antimony(III) chloride (SbCl 3 ).
antimony Symbol Sb. An element
belonging to *group 15 (formerly VB)
of the periodic table; a.n. 51; r.a.m.
121.75; r.d. 6.68; m.p. 630.5°C; b.p.
1750°C. Antimony has several allotropes. The stable form is a bluishwhite metal. Yellow antimony and
black antimony are unstable nonmetallic allotropes made at low temperatures. The main source is
stibnite (Sb 2 S 3 ), from which antimony is extracted by reduction with
iron metal or by roasting (to give the
oxide) followed by reduction with
carbon and sodium carbonate. The
main use of the metal is as an alloying agent in lead-accumulator plates,
type metals, bearing alloys, solders,
Britannia metal, and pewter. It is also
an agent for producing pearlitic cast
iron. Its compounds are used in
Ûame-prooÜng, paints, ceramics,
enamels, glass dyestuffs, and rubber
technology. The element will burn in
air but is unaffected by water or dilute acids. It is attacked by oxidizing
acids and by halogens. It was Ürst reported by Tholden in 1450.
A
• Information from the WebElements site
antioxidants Substances that slow
the rate of oxidation reactions. Various antioxidants are used to preserve
foodstuffs and to prevent the deterioration of rubber, synthetic plastics,
and many other materials. Some antioxidants act as chelating agents to
sequester the metal ions that catalyse
oxidation reactions. Others inhibit
the oxidation reaction by removing
oxygen free radicals. Naturally occurring antioxidants include *vitamin E
and β-carotene; they limit the cell
and tissue damage caused by foreign
substances, such as toxins and pollutants, in the body.
antiparallel spins Neighbouring
spinning electrons in which the
*spins, and hence the magnetic moments, of the electrons are aligned in
the opposite direction. Under some
circumstances the interactions between magnetic moments in atoms
favour *parallel spins, while under
other conditions they favour antiparallel spins. The case of antiferromagnetism (see magnetism) is an example
of a system with antiparallel spins.
antiperiplanar See torsion angle.
anti-Stokes radiation Electromagnetic radiation occurring in the
*Raman effect, which is of much
lower intensity than the Rayleigh
scattering in which the frequency of
the radiation is higher than that of
the incident light, i.e. displaced towards shorter wavelengths. If the frequency of the original light is ν, the
frequency of the anti-Stokes radiation is ν + ν k , where ν k is the frequency of the rotation or vibration of
the molecule. The spectral lines asso41
anti-Stokes radiation
a
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