copper Symbol Cu. A red-brown
*transition element; a.n. 29; r.a.m.
63.546; r.d. 8.92; m.p. 1083.4°C; b.p.
2567 °C. Copper has been extracted
for thousands of years; it was known
to the Romans as cuprum, a name
linked with the island of Cyprus. The
metal is malleable and ductile and an
excellent conductor of heat and elec-
tricity. Copper-containing minerals
include cuprite (Cu 2 O) as well as
azurite (2CuCO 3 .Cu(OH) 2 ), chalco-
pyrite (CuFeS 2 ), and malachite
(CuCO 3 .Cu(OH) 2 ). Native copper ap-
pears in isolated pockets in some
parts of the world. The large mines
in the USA, Chile, Canada, Zambia,
Democratic Republic of Congo, and
Peru extract ores containing sul-
phides, oxides, and carbonates. They
are usually worked by smelting,
leaching, and electrolysis. Copper
metal is used to make electric cables
and wires. Its alloys, brass (copper–
zinc) and bronze (copper–tin), are
used extensively.
Water does not attack copper but
in moist atmospheres it slowly forms
a characteristic green surface layer
(patina). The metal will not react
with dilute sulphuric or hydrochloric
acids, but with nitric acid oxides of
nitrogen are formed. Copper com-
pounds contain the element in the
+1 and +2 oxidation states. Copper(I)
compounds are mostly white (the
oxide is red). Copper(II) salts are blue
in solution. The metal also forms a
large number of coordination com-
plexes.
A
- Information from the WebElements site
copperasSee iron(ii) sulphate.
copper(I) chloride A white solid
compound, CuCl; cubic; r.d. 4.14;
m.p. 430°C; b.p. 1490°C. It is ob-
tained by boiling a solution contain-
ing copper(II) chloride, excess copper
turnings, and hydrochloric acid. Cop-
per(I) is present as the [CuCl 2 ]–com-
plex ion. On pouring the solution
into air-free distilled water copper(I)
chloride precipitates. It must be kept
free of air and moisture since it oxi-
dizes to copper(II) chloride under
those conditions.
Copper(I) chloride is essentially co-
valent and its structure is similar to
that of diamond; i.e. each copper
atom is surrounded tetrahedrally by
four chlorine atoms and vice versa.
In the vapour phase, dimeric and
trimeric species are present.
Copper(I) chloride is used in conjunc-
tion with ammonium chloride as a
catalyst in the dimerization of
ethyne to but-1-ene-3-yne (vinyl
acetylene), which is used in the pro-
duction of synthetic rubber. In the
laboratory a mixture of copper(I)
chloride and hydrochloric acid is
used for converting benzene diazo-
nium chloride to chlorobenzene –
the Sandmeyer reaction.copper(II) chlorideA brown-
yellow powder, CuCl 2 ; r.d. 3.386;
m.p. 620°C. It exists as a blue-green
dihydrate (rhombic; r.d. 2.54; loses
H 2 O at 100°C). The anhydrous solid is
obtained by passing chlorine over
heated copper. It is predominantly
covalent and adopts a layer structure
in which each copper atom is sur-
rounded by four chlorine atoms at a
distance of 0.23 and two more at a
distance of 0.295. A concentrated
aqueous solution is dark brown in
colour due to the presence of com-
plex ions such as [CuCl 4 ]2–. On dilu-
tion the colour changes to green and
then blue because of successive re-
placement of chloride ions by water
molecules, theÜnal colour being that
of the [Cu(H 2 O) 6 ]2+ion. The dihydrate
can be obtained by crystallizing the
solution.
copper glanceA mineral form of
copper(I) sulphide, Cu 2 S.143 copper glance
c