Copper (, ) is a
chemical element in the
periodic table that has the symbol
Cu () and
atomic number 29.
It is a
ductile metal with excellent
electrical conductivity, and finds extensive use as an electrical conductor, heat conductor, as a building material, and as a component of various
alloys.
Copper is an essential trace nutrient to all high plants and animals. In animals, including humans, it is found primarily in the
bloodstream, as a co-factor in various
enzymes, and in copper-based
pigments. However, in sufficient amounts, copper can be poisonous and even fatal to organisms.
Copper has played a significant part in the history of mankind, which has used the easily accessible uncompounded metal for nearly 10,000years. Civilizations in places such as
Iraq,
China,
Egypt,
Greece and the
Sumerian cities all have early evidence of using copper. During the Roman Empire, copper was principally mined on
Cyprus, hence the origin of the name of the metal as Cyprium, "metal of Cyprus", later shortened to Cuprum. A number of countries, such as
Chile and the
United States, still have sizable reserves of the metal which are extracted through large open pit mines. Nevertheless, the price of copper has risen rapidly, increasing 500% from a 60-year low in 1999, largely due to increased demand. The Earth has an estimated 61 years of copper reserves remaining.
[ New Scientist. May 26, 2007.]
Notable characteristics
Color
Copper is a reddish-colored
metal, it has its characteristic color because it reflects red and orange light and absorbs other frequencies in the visible spectrum, due to its
band structure.
In its liquefied state, a pure copper surface without ambient light appears somewhat greenish, a characteristic shared with gold. When liquid copper is in bright ambient light, it retains some of its pinkish luster.
Location in the periodic table
Copper occupies the same family of the periodic table as silver and gold, since they each have one s-orbital electron on top of a filled
electron shell. This similarity in electron structure makes them similar in many characteristics. All have very high thermal and electrical conductivity, and all are malleable metals.
Corrosion properties
Pure water and air
Copper is a metal that does not react with water (H2O), but the oxygen of the air will react slowly at room temperature to form a layer of copper oxide on copper metal.
It can be seen that copper in "pure" water is more noble than hydrogen. As a result it does not corrode in oxygen free water and the corrosion rate in oxygenated water is low.
It is important to note that in contrast to the oxidation of iron by wet air that the layer formed by the reaction of air with copper has a protective effect against further corrosion. On old copper roofs a green layer of copper carbonate can often be seen.
Sulphide media
Copper metal does react with
hydrogen sulphide and
sulfide containing solutions. A series of different copper sulphides can form on the surface of the copper metal.
Note that the copper sulphide area of the plot is very complex due to the existance of many different sulphides, a close up is also provided to make the graph more clear. It is clear that the copper is now able to corrode even without the need for oxygen as the copper is now less noble than
hydrogen. This can be observed in every day life when copper metal surfaces tarnish after exposure to air which contains sulfur compounds.
Ammonia media
Copper does react with oxygen-containing ammonia solutions because the ammonia forms water-soluble copper complexes. The formation of these complexes causes the corrosion to become more thermodynamically favoured than the corrosion of copper in an identical solution that does not contain the ammonia.
Chloride media
Copper does react with a combination of oxygen and hydrochloric acid to form a series of copper chlorides. It is interesting to note that if copper(II) chloride (green/blue) is boiled with copper metal (with little or no oxygen present) then white copper(I) chloride will be formed.
Isotopes
There are two stable
isotopes,
63Cu and
65Cu, along with a couple dozen
radioisotopes. The vast majority of radioisotopes have half lives on the order of minutes or less; the longest lived,
67Cu, has a half life of 61.8 hours. See also
isotopes of copper.
Alloys
Numerous
copper alloys exist, many with important historical and contemporary uses.
Speculum metal and
bronze are alloys of copper and
tin.
Brass is an alloy of copper and
zinc.
Monel metal, also called
cupronickel, is an alloy of copper and
nickel. While the metal "bronze" usually refers to copper-tin alloys, it also is a generic term for any alloy of copper, such as
aluminium bronze, silicon bronze, and manganese bronze.
Germicidal effect
Copper is germicidal, via the
oligodynamic effect. For example, brass doorknobs disinfect themselves of many bacteria within a period of eight hours.
This effect is useful in many applications.
Applications
Copper is
malleable and
ductile, a good
conductor of heat and, when very pure, a good
conductor of electricity.
The purity of copper is expressed as 4N for 99.99% pure or 7N for 99.99999% pure. The numeral gives the number of nines after the decimal point when expressed as a decimal (e.g. 4N means 0.9999, or 99.99%).
It is used extensively, in products such as:
===
Piping ===
including, but not limited to, extreme water supply.
History
Copper, as
native copper, is one of the few metals to naturally occur as an uncompounded mineral. Copper was known to some of the oldest civilizations on record, and has a history of use that is at least 10,000 years old. A copper pendant was found in what is now northern
Iraq that dates to 8700 BC. By 5000 BC, there are signs of copper
smelting, the refining of copper from simple copper compounds such as
malachite or
azurite. Among archaeological sites in Anatolia,
Çatal Höyük (~6000 BC) features native copper artifacts and smelted lead beads, but no smelted copper. But
Can Hasan (~5000 BC) had access to smelted copper; this site has yielded the oldest known cast copper artifact, a copper
mace head.
Copper smelting appears to have been developed independently in several parts of the world. In addition to its development in Anatolia by 5000 BC, it was developed in China before 2800 BC, in the Andes around 2000 BC, in Central America around 600 AD, and in West Africa around 900 AD.
[Richard Cowen, ''Essays on Geology, History, and People'', Chapter 3: Fire and Metals: Copper .] Copper is found extensively in the
Indus Valley Civilization by the 3rd millennium BC.
[harappa.com (Web archive)] In Europe,
Ötzi the Iceman, a well-preserved male dated to
3200 BC, was found with a copper-tipped axe whose metal was 99.7% pure. High levels of
arsenic in his hair suggest he was involved in copper smelting. There are copper and
bronze artifacts from
Sumerian cities that date to 3000 BC, and
Egyptian artifacts of copper and copper-
tin alloys nearly as old. In one pyramid, a copper plumbing system was found that is 5000 years old. The Egyptians found that adding a small amount of tin made the metal easier to cast, so bronze alloys were found in Egypt almost as soon as copper was found. In the Americas production in the
Old Copper Complex, located in present day Michigan and Wisconsin, was dated back to between 6000 to 3000 BC.
The use of
bronze became so pervasive in a certain era of civilization that it has been named the
Bronze Age. The transitional period in certain regions between the preceding
Neolithic period and the Bronze Age is termed the
Chalcolithic ("copper-stone"), with some high-purity copper tools being used alongside stone tools.
Brass was known to the Greeks, but only became a significant supplement to bronze during the Roman empire.
In Greek the metal was known by the name ''chalkos'' (χαλκός). Copper was a very important resource for the Romans, Greeks and other ancient peoples. In Roman times, it became known as ''aes Cyprium'' (''aes'' being the generic Latin term for copper alloys such as
bronze and other metals, and ''Cyprium'' because so much of it was mined in
Cyprus). From this, the phrase was simplified to ''cuprum'' and then eventually Anglicized into the English ''copper''. Copper was associated with the goddess
Aphrodite/
Venus in mythology and
alchemy, owing to its lustrous beauty, its ancient use in producing mirrors, and its association with
Cyprus, which was sacred to the goddess.
Copper mining in Britain and the United States
:''See
Copper extraction for the article on copper mining techniques.''
Copper has been mined for many centuries. By 2000 BC, Europe was using copper-tin alloys or ‘bronze’. The Bronze Age is taken as 2500 BC to 600 BC.
United States
Copper mining in the United States began with marginal workings by Native Americans and some development by early Spaniards. Europeans were mining copper in
Connecticut as early as 1709. Perhaps the oldest operating large-scale copper mine was the historic Elizabeth Mine in Vermont. Dating to the 1700s, "the Liz" produced copper until it was closed in 1958. Westward movement also brought an expansion of copper exploitation with developments of significant deposits in
Michigan and
Arizona during the 1850s and then in
Montana during the 1860s.
Copper was mined extensively in
Michigan's
Keweenaw Peninsula with the heart of extraction at the productive
Quincy Mine. Arizona had many notable deposits including the Copper Queen in Bisbee and the United Verde in Jerome. The Anaconda in Butte, Montana became the nation's chief copper supplier by 1886.
Copper is mined in many other areas of the United States, including
Utah,
Nevada and
Tennessee. Copper is the
state mineral for Utah.
Biological role
Copper is essential in all plants and animals. Copper is carried mostly in the bloodstream on a
plasma protein called
ceruloplasmin. When copper is first absorbed in the gut it is transported to the
liver bound to
albumin. Copper is found in a variety of
enzymes, including the copper centers of
cytochrome c oxidase and the enzyme
superoxide dismutase (containing copper and zinc). In addition to its enzymatic roles, copper is used for biological electron transport. The blue copper proteins that participate in electron transport include
azurin and
plastocyanin. The name "blue copper" comes from their intense blue color arising from a ligand-to-metal charge transfer (LMCT) absorption band around 600 nm.
Most
molluscs and some
arthropods such as the
horseshoe crab use the copper-containing pigment
hemocyanin rather than
iron-containing
hemoglobin for oxygen transport, so their blood is blue when oxygenated rather than red.
[''Horseshoe Crab Fun Facts'' NOAA and Univ. of Delaware]
It is believed that
zinc and copper compete for absorption in the digestive tract so that a diet that is excessive in one of these minerals may result in a deficiency in the other. The
RDA for copper in normal healthy adults is 0.9
mg/day. Because of its role in facilitating iron uptake,
copper deficiency can often produce
anemia-like symptoms.
Toxicity
All copper compounds, unless otherwise known, should be treated as if they were
toxic. Thirty grams of copper sulfate is potentially lethal in humans. The suggested safe level of copper in
drinking water for humans varies depending on the source, but tends to be pegged at 1.5 to 2 mg/L. The
DRI Tolerable Upper Intake Level for adults of dietary copper from all sources is 10 mg/day. In toxicity, copper can inhibit the
enzyme dihydrophil hydratase, an enzyme involved in
haemopoiesis.
Symptoms of copper
poisoning are very similar to those produced by
arsenic. Fatal cases are generally terminated by convulsions, palsy, and insensibility.
In cases of suspected copper poisoning,
Ovalbumin is to be administered in either of its forms which can be most readily obtained, as milk or
whites of eggs. Vinegar should not be given. The inflammatory symptoms are to be treated on general principles, and so are the nervous.
A significant portion of the toxicity of copper comes from its ability to accept and donate single electrons as it changes oxidation state. This catalyzes the production of very reactive radical ions such as
hydroxyl radical in a manner similar to
fenton chemistry.
This catalytic activity of copper is used by the enzymes that it is associated with and is thus only toxic when unsequestered and unmediated. This increase in unmediated reactive radicals is generally termed
oxidative stress and is an active area of research in a variety of diseases where copper may play an important but more subtle role than in acute toxicity.
An inherited condition called
Wilson's disease causes the body to retain copper, since it is not excreted by the
liver into the
bile. This disease, if untreated, can lead to
brain and
liver damage. In addition, studies have found that people with mental illnesses such as
schizophrenia had heightened levels of copper in their systems. However it is unknown at this stage whether the copper contributes to the mental illness, whether the body attempts to store more copper in response to the illness, or whether the high levels of copper are the result of the mental illness.
Too much copper in water has also been found to damage marine life. The observed effect of these higher concentrations on fish and other creatures is damage to gills, liver, kidneys, and the nervous system. It also interferes with the sense of smell in fish, thus preventing them from choosing good mates or finding their way to mating areas.
Miscellaneous hazards
The metal, when powdered, is a
fire hazard. At concentrations higher than 1 mg/L, copper can stain clothes and items washed in water.
Occurrence
In 2005, Chile was the top mine producer of copper with at least one-third world share followed by the USA, Indonesia and Peru, reports the
British Geological Survey.
Copper can be found as
native copper in
mineral form. Minerals such as the
sulfides:
chalcopyrite (CuFeS
2),
bornite (Cu
5FeS
4),
covellite (CuS),
chalcocite (Cu
2S) are sources of copper, as are the
carbonates:
azurite (Cu
3(CO
3)
2(OH)
2) and
malachite (Cu
2CO
3(OH)
2) and the oxide:
cuprite (Cu
2O).
Most copper ore is mined or
extracted as copper sulfides from large
open pit mines in
porphyry copper deposits that contain 0.4 to 1.0 percent copper. Examples include:
Chuquicamata in
Chile and
El Chino Mine in
New Mexico. The average abundance of copper found within crustal rocks is approximately 68
ppm by mass, and 22 ppm by atoms.
The
Intergovernmental Council of Copper Exporting Countries (CIPEC), defunct since 1992, once tried to play a similar role for copper as
OPEC does for
oil, but never achieved the same influence, not least because the second-largest producer, the
United States, was never a member. Formed in 1967, its principal members were
Chile,
Peru,
Zaire, and
Zambia.
The copper price has quintupled since 1999, rising from $0.60 per
pound in June 1999 to $3.75 per pound in May 2006, where it dropped to $2.40 in February 2007 then rebounded to $3.50 in April 2007.
[Copper Trends: Live Metal Spot Prices , MetalSpotPrice.com]
Compounds
Common
oxidation states of copper include the less stable copper(I) state, Cu
+; and the more stable copper(II) state, Cu
2+, which forms blue or blue-green salts and solutions. Under unusual conditions, a 3+ state and even an extremely rare 4+ state can be obtained. Using old nomenclature for the naming of salts, copper(I) is called cuprous, and copper(II) cupric. In
oxidation copper is mildly
basic.
Copper(II) carbonate is green from which arises the unique appearance of copper-clad roofs or domes on some buildings.
Copper(II) sulfate forms a blue crystalline penta
hydrate which is perhaps the most familiar copper compound in the laboratory. It is used as a
fungicide, known as Bordeaux mixture.
There are two stable copper oxides,
copper(II) oxide (CuO) and
copper(I) oxide (Cu
2O). Copper oxides are used to make
yttrium barium copper oxide (YBa
2Cu
3O
7-δ) or
YBCO which forms the basis of many
unconventional superconductors.
Copper(I) compounds: copper(I) chloride, copper(I) bromide, copper(I) iodide, copper(I) oxide.
Copper(II) compounds: copper(II) acetate, copper(II) carbonate, copper(II) chloride, copper(II) hydroxide, copper(II) nitrate, copper(II) oxide, copper(II) sulfate, copper(II) sulfide, copper(II) tetrafluoroborate, copper(II) trifluoromethansulfonate.
Copper(III) compounds, rare: potassium hexafluorocuprate (K3CuF6)
Copper(IV) compounds, extremely rare: caesium hexafluorocuprate (Cs2CuF6)
Copper(I) and copper(II) can also be referred to by their common names cuprous and cupric.
Tests for copper(II) ion
Add aqueous
sodium hydroxide. A blue precipitate of
copper(II) hydroxide should form.
Ionic equation:
:Cu
2+(aq) + 2OH
−(aq) → Cu(OH)
2(s)
The full equation shows that the reaction is due to hydroxide ions deprotonating the hexaaquacopper (II) complex:
:
Cu(H2O)62+(aq) + 2 OH
−(aq) → Cu(H
2O)
4(OH)
2(s) + 2 H
2O (l)
Adding aqueous
ammonia causes the same precipitate to form. It then dissolves upon adding excess ammonia, to form a deep blue ammonia complex, tetraamminecopper(II).
Ionic equation:
:Cu(H
2O)
4(OH)
2(s) + 4 NH
3(aq) →
Cu(H2O)2(NH3)42+(aq) + 2H
2O(l) + 2 OH
−(aq)
A more delicate test than the ammonia is the
ferrocyanide of potassium, which gives a brown precipitate with copper salts.
References
Further reading
Current Medicinal Chemistry, Volume 12, Number 10, May 2005, pp. 1161-1208(48) Metals, Toxicity and Oxidative Stress
Material: Copper (Cu), bulk , MEMS and Nanotechnology Clearinghouse.