C
cacodyl An oily liquid,
(CH 3 ) 2 AsAs(CH 3 ) 2 . It has a characteristic odour of garlick and is poisonous.
Cacodyl was one of the Ürst organometallic compounds to be synthesized (by heating arsenic with
potassium acetate). The group
(CH 3 ) 2 As– is the cacodyl group.
cadmium Symbol Cd. A soft bluish
metal belonging to *group 12 (formerly IIB) of the periodic table; a.n.
48; r.a.m. 112.41; r.d. 8.65; m.p.
320.9°C; b.p. 765°C. The element’s
name is derived from the ancient
name for calamine, zinc carbonate
ZnCO 3 , and it is usually found associated with zinc ores, such as sphalerite (ZnS), but does occur as the
mineral greenockite (CdS). Cadmium
is usually produced as an associate
product when zinc, copper, and lead
ores are reduced. Cadmium is used in
low-melting-point alloys to make solders, in Ni–Cd batteries, in bearing
alloys, and in electroplating (over
50%). Cadmium compounds are used
as phosphorescent coatings in TV
tubes. Cadmium and its compounds
are extremely toxic at low concentrations; great care is essential where
solders are used or where fumes are
emitted. It has similar chemical properties to zinc but shows a greater tendency towards complex formation.
The element was discovered in 1817
by F. Stromeyer.
A
• Information from the WebElements site
cadmium cell See weston cell.
cadmium sulphide A waterinsoluble compound, CdS; r.d. 4.82.
It occurs naturally as the mineral
greenockite and is used as a pigment
and in semiconductors and Ûuorescent materials.
caesium Symbol Cs. A soft silverywhite metallic element belonging to
*group 1 (formerly IA) of the periodic
table; a.n. 55; r.a.m. 132.905; r.d.
1.88; m.p. 28.4°C; b.p. 678°C. It occurs in small amounts in a number
of minerals, the main source being
carnallite (KCl.MgCl 2 .6H 2 O). It is obtained by electrolysis of molten caesium cyanide. The natural isotope is
caesium–133. There are 15 other
radioactive isotopes. Caesium–137
(half-life 33 years) is used as a gamma
source. As the heaviest alkali metal,
caesium has the lowest ionization potential of all elements, hence its use
in photoelectric cells, etc.
A
• Information from the WebElements site
caesium chloride structure A
type of ionic crystal structure in
which the anions are at the eight corners of a cubic unit cell with one
cation at the centre of the cell. It can
equivalently by described as cations
at the corners of the cell with an
anion at the centre. Each type of ion
has a coordination number of 8. Examples of compounds with this
structure are CsCl, CsBr, CsI, CsCN,
CuZn, and NH 4 Cl.
caesium clock An *atomic clock
that depends on the energy difference between two states of the caesium–133 nucleus when it is in a
magnetic Üeld. In one type, atoms of
caesium–133 are irradiated with
radio-frequency radiation, whose frequency is chosen to correspond to
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cacodyl An oily liquid,
(CH 3 ) 2 AsAs(CH 3 ) 2 . It has a characteristic odour of garlick and is poisonous.
Cacodyl was one of the Ürst organometallic compounds to be synthesized (by heating arsenic with
potassium acetate). The group
(CH 3 ) 2 As– is the cacodyl group.
cadmium Symbol Cd. A soft bluish
metal belonging to *group 12 (formerly IIB) of the periodic table; a.n.
48; r.a.m. 112.41; r.d. 8.65; m.p.
320.9°C; b.p. 765°C. The element’s
name is derived from the ancient
name for calamine, zinc carbonate
ZnCO 3 , and it is usually found associated with zinc ores, such as sphalerite (ZnS), but does occur as the
mineral greenockite (CdS). Cadmium
is usually produced as an associate
product when zinc, copper, and lead
ores are reduced. Cadmium is used in
low-melting-point alloys to make solders, in Ni–Cd batteries, in bearing
alloys, and in electroplating (over
50%). Cadmium compounds are used
as phosphorescent coatings in TV
tubes. Cadmium and its compounds
are extremely toxic at low concentrations; great care is essential where
solders are used or where fumes are
emitted. It has similar chemical properties to zinc but shows a greater tendency towards complex formation.
The element was discovered in 1817
by F. Stromeyer.
A
• Information from the WebElements site
cadmium cell See weston cell.
cadmium sulphide A waterinsoluble compound, CdS; r.d. 4.82.
It occurs naturally as the mineral
greenockite and is used as a pigment
and in semiconductors and Ûuorescent materials.
caesium Symbol Cs. A soft silverywhite metallic element belonging to
*group 1 (formerly IA) of the periodic
table; a.n. 55; r.a.m. 132.905; r.d.
1.88; m.p. 28.4°C; b.p. 678°C. It occurs in small amounts in a number
of minerals, the main source being
carnallite (KCl.MgCl 2 .6H 2 O). It is obtained by electrolysis of molten caesium cyanide. The natural isotope is
caesium–133. There are 15 other
radioactive isotopes. Caesium–137
(half-life 33 years) is used as a gamma
source. As the heaviest alkali metal,
caesium has the lowest ionization potential of all elements, hence its use
in photoelectric cells, etc.
A
• Information from the WebElements site
caesium chloride structure A
type of ionic crystal structure in
which the anions are at the eight corners of a cubic unit cell with one
cation at the centre of the cell. It can
equivalently by described as cations
at the corners of the cell with an
anion at the centre. Each type of ion
has a coordination number of 8. Examples of compounds with this
structure are CsCl, CsBr, CsI, CsCN,
CuZn, and NH 4 Cl.
caesium clock An *atomic clock
that depends on the energy difference between two states of the caesium–133 nucleus when it is in a
magnetic Üeld. In one type, atoms of
caesium–133 are irradiated with
radio-frequency radiation, whose frequency is chosen to correspond to
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