ment is ABCABC…. See also cubic
crystal.
A
• An interactive version of cubic closepacking
• An interactive version of hexagonal
close packing
closo-structure See borane.
club drug A drug typically used by
young people at clubs, parties, etc.
Examples are ecstasy, gammahydroxybutyric acid (GHB), and methamphetamines.
Clusius column A device for separating isotopes by thermal diffusion.
One form consists of a vertical column some 30 metres high with a
heated electric wire running along its
axis. The lighter isotopes in a gaseous
mixture of isotopes diffuse faster
than the heavier isotopes. Heated by
the axial wire, and assisted by natural convection, the lighter atoms
are carried to the top of the column,
where a fraction rich in lighter isotopes can be removed for further enrichment.
cluster compound A compound
in which groups of metal atoms are
joined together by metal–metal
bonds. The formation of such compounds is a feature of the chemistry
of certain elements, particularly
molybdenum and tungsten, but also
vanadium, tantalum, niobium, and
uranium. Isopoly compounds are
ones in which the cluster contains
atoms of the same element; heteropoly compounds contain a mixture of different elements.
CML See chemical markup language.
coacervate An aggregate of macromolecules, such as proteins, lipids,
and nucleic acids, that form a stable
*colloid unit with properties that resemble living matter. Many are
coated with a lipid membrane and
contain enzymes that are capable of
converting such substances as glucose into more complex molecules,
such as starch. Coacervate droplets
arise spontaneously under appropriate conditions and may have been
the prebiological systems from
which living organisms originated.
coagulation The process in which
colloidal particles come together irreversibly to form larger masses. Coagulation can be brought about by
adding ions to change the ionic
strength of the solution and thus
destabilize the colloid (see flocculation). Ions with a high charge are
particularly effective (e.g. alum, containing Al
3+ , is used in styptics to coagulate blood). Another example of
ionic coagulation is in the formation
of river deltas, which occurs when
colloidal silt particles in rivers are coagulated by ions in sea water. Alum
and iron (III) sulphate are also used
for coagulation in sewage treatment.
Heating is another way of coagulating certain colloids (e.g. boiling an
egg coagulates the albumin).
coal A brown or black carbonaceous
deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in
swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which
were subsequently buried (for example, by marine sediments following a
rise in sea level or subsidence of the
land). Under the increased pressure
and resulting higher temperatures
the peat was transformed into coal.
Two types of coal are recognized:
humic (or woody) coals, derived from
plant remains; and sapropelic coals,
which are derived from algae, spores,
and Ünely divided plant material.
As the processes of coaliÜcation (i.e.
the transformation resulting from
closo-structure
130
c
www.AzShimi.ir www.AzShimi.com
crystal.
A
• An interactive version of cubic closepacking
• An interactive version of hexagonal
close packing
closo-structure See borane.
club drug A drug typically used by
young people at clubs, parties, etc.
Examples are ecstasy, gammahydroxybutyric acid (GHB), and methamphetamines.
Clusius column A device for separating isotopes by thermal diffusion.
One form consists of a vertical column some 30 metres high with a
heated electric wire running along its
axis. The lighter isotopes in a gaseous
mixture of isotopes diffuse faster
than the heavier isotopes. Heated by
the axial wire, and assisted by natural convection, the lighter atoms
are carried to the top of the column,
where a fraction rich in lighter isotopes can be removed for further enrichment.
cluster compound A compound
in which groups of metal atoms are
joined together by metal–metal
bonds. The formation of such compounds is a feature of the chemistry
of certain elements, particularly
molybdenum and tungsten, but also
vanadium, tantalum, niobium, and
uranium. Isopoly compounds are
ones in which the cluster contains
atoms of the same element; heteropoly compounds contain a mixture of different elements.
CML See chemical markup language.
coacervate An aggregate of macromolecules, such as proteins, lipids,
and nucleic acids, that form a stable
*colloid unit with properties that resemble living matter. Many are
coated with a lipid membrane and
contain enzymes that are capable of
converting such substances as glucose into more complex molecules,
such as starch. Coacervate droplets
arise spontaneously under appropriate conditions and may have been
the prebiological systems from
which living organisms originated.
coagulation The process in which
colloidal particles come together irreversibly to form larger masses. Coagulation can be brought about by
adding ions to change the ionic
strength of the solution and thus
destabilize the colloid (see flocculation). Ions with a high charge are
particularly effective (e.g. alum, containing Al
3+ , is used in styptics to coagulate blood). Another example of
ionic coagulation is in the formation
of river deltas, which occurs when
colloidal silt particles in rivers are coagulated by ions in sea water. Alum
and iron (III) sulphate are also used
for coagulation in sewage treatment.
Heating is another way of coagulating certain colloids (e.g. boiling an
egg coagulates the albumin).
coal A brown or black carbonaceous
deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in
swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which
were subsequently buried (for example, by marine sediments following a
rise in sea level or subsidence of the
land). Under the increased pressure
and resulting higher temperatures
the peat was transformed into coal.
Two types of coal are recognized:
humic (or woody) coals, derived from
plant remains; and sapropelic coals,
which are derived from algae, spores,
and Ünely divided plant material.
As the processes of coaliÜcation (i.e.
the transformation resulting from
closo-structure
130
c
www.AzShimi.ir www.AzShimi.com