referred to as gas-phase electrophoresis.
ionophore A relatively small hydrophobic molecule that facilitates
the transport of ions across lipid
membranes. Most ionophores are
produced by microorganisms. There
are two types of ionophore: channel
formers, which combine to form a
channel in the membrane through
which ions can Ûow; and mobile ion
carriers, which transport ions across
a membrane by forming a complex
with the ion.
ion pair A pair of oppositely
charged ions produced as a result of
a single ionization; e.g.
HCl → H
+ + Cl
– .
Sometimes a positive ion and an electron are referred to as an ion pair, as
in
A → A
+ + e
–
.
ion pump A type of *vacuum
pump that can reduce the pressure
in a container to about 1 nanopascal
by passing a beam of electrons
through the residual gas. The gas is
ionized and the positive ions formed
are attracted to a cathode within
the container where they remain
trapped. The pump is only useful at
very low pressures, i.e. below about
1 micropascal. The pump has a limited capacity because the absorbed
ions eventually saturate the surface
of the cathode. A more effective
pump can be made by simultaneously producing a Ülm of metal by
ion impact (sputtering), so that
fresh surface is continuously produced. The device is then known as
a sputter-ion pump.
IP See ionization potential.
IR See infrared radiation.
iridium Symbol Ir. A silvery metallic *transition element (see also platinum metals); a.n. 77; r.a.m. 192.20;
r.d. 22.42; m.p. 2410°C; b.p. 4130°C.
It occurs with platinum and is
mainly used in alloys with platinum
and osmium. The element forms a
range of iridium(III) and iridium(IV)
complexes. It was discovered in 1804
by Smithson Tennant (1761–1815).
A
• Information from the WebElements site
iron Symbol Fe. A silvery malleable
and ductile metallic *transition element; a.n. 26; r.a.m. 55.847; r.d.
7.87; m.p. 1535°C; b.p. 2750°C. The
main sources are the ores *haematite
(Fe 2 O 3 ), *magnetite (Fe 3 O 4 ), limonite
(FeO(OH) n H 2 O), ilmenite (FeTiO 3 ),
siderite (FeCO 3 ), and pyrite (FeS 2 ).
The metal is smelted in a *blast furnace to give impure *pig iron, which
is further processed to give *cast
iron, *wrought iron, and various
types of *steel. The pure element has
three crystal forms: alpha-iron, stable
below 906°C with a body-centredcubic structure; gamma-iron, stable
between 906°C and 1403°C with a
nonmagnetic face-centred-cubic
structure; and delta-iron, which is
the body-centred-cubic form above
1403°C. Alpha-iron is ferromagnetic
up to its Curie point (768°C). The element has nine isotopes (mass numbers 52–60), and is the fourth most
abundant in the earth’s crust. It is required as a trace element (see essential element) by living organisms.
Iron is quite reactive, being oxidized
by moist air, displacing hydrogen
from dilute acids, and combining
with nonmetallic elements. It forms
ionic salts and numerous complexes
with the metal in the +2 or +3 oxidation states. Iron(VI) also exists in the
ferrate ion FeO 4
2– , and the element
also forms complexes in which its oxidation number is zero (e.g. Fe(CO) 5 ).
A
• Information from the WebElements site
ionophore
292
i
www.AzShimi.ir www.AzShimi.com
ionophore A relatively small hydrophobic molecule that facilitates
the transport of ions across lipid
membranes. Most ionophores are
produced by microorganisms. There
are two types of ionophore: channel
formers, which combine to form a
channel in the membrane through
which ions can Ûow; and mobile ion
carriers, which transport ions across
a membrane by forming a complex
with the ion.
ion pair A pair of oppositely
charged ions produced as a result of
a single ionization; e.g.
HCl → H
+ + Cl
– .
Sometimes a positive ion and an electron are referred to as an ion pair, as
in
A → A
+ + e
–
.
ion pump A type of *vacuum
pump that can reduce the pressure
in a container to about 1 nanopascal
by passing a beam of electrons
through the residual gas. The gas is
ionized and the positive ions formed
are attracted to a cathode within
the container where they remain
trapped. The pump is only useful at
very low pressures, i.e. below about
1 micropascal. The pump has a limited capacity because the absorbed
ions eventually saturate the surface
of the cathode. A more effective
pump can be made by simultaneously producing a Ülm of metal by
ion impact (sputtering), so that
fresh surface is continuously produced. The device is then known as
a sputter-ion pump.
IP See ionization potential.
IR See infrared radiation.
iridium Symbol Ir. A silvery metallic *transition element (see also platinum metals); a.n. 77; r.a.m. 192.20;
r.d. 22.42; m.p. 2410°C; b.p. 4130°C.
It occurs with platinum and is
mainly used in alloys with platinum
and osmium. The element forms a
range of iridium(III) and iridium(IV)
complexes. It was discovered in 1804
by Smithson Tennant (1761–1815).
A
• Information from the WebElements site
iron Symbol Fe. A silvery malleable
and ductile metallic *transition element; a.n. 26; r.a.m. 55.847; r.d.
7.87; m.p. 1535°C; b.p. 2750°C. The
main sources are the ores *haematite
(Fe 2 O 3 ), *magnetite (Fe 3 O 4 ), limonite
(FeO(OH) n H 2 O), ilmenite (FeTiO 3 ),
siderite (FeCO 3 ), and pyrite (FeS 2 ).
The metal is smelted in a *blast furnace to give impure *pig iron, which
is further processed to give *cast
iron, *wrought iron, and various
types of *steel. The pure element has
three crystal forms: alpha-iron, stable
below 906°C with a body-centredcubic structure; gamma-iron, stable
between 906°C and 1403°C with a
nonmagnetic face-centred-cubic
structure; and delta-iron, which is
the body-centred-cubic form above
1403°C. Alpha-iron is ferromagnetic
up to its Curie point (768°C). The element has nine isotopes (mass numbers 52–60), and is the fourth most
abundant in the earth’s crust. It is required as a trace element (see essential element) by living organisms.
Iron is quite reactive, being oxidized
by moist air, displacing hydrogen
from dilute acids, and combining
with nonmetallic elements. It forms
ionic salts and numerous complexes
with the metal in the +2 or +3 oxidation states. Iron(VI) also exists in the
ferrate ion FeO 4
2– , and the element
also forms complexes in which its oxidation number is zero (e.g. Fe(CO) 5 ).
A
• Information from the WebElements site
ionophore
292
i
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