Copper

Copper, 29Cu
Native copper (~4 cm in size)
Copper
Appearancered-orange metallic luster
Standard atomic weight Ar, std(Cu)63.546(3)[1]
Copper in the periodic table
HydrogenHelium
LithiumBerylliumBoronCarbonNitrogenOxygenFluorineNeon
SodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon
PotassiumCalciumScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincGalliumGermaniumArsenicSeleniumBromineKrypton
RubidiumStrontiumYttriumZirconiumNiobiumMolybdenumTechnetiumRutheniumRhodiumPalladiumSilverCadmiumIndiumTinAntimonyTelluriumIodineXenon
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon
FranciumRadiumActiniumThoriumProtactiniumUraniumNeptuniumPlutoniumAmericiumCuriumBerkeliumCaliforniumEinsteiniumFermiumMendeleviumNobeliumLawrenciumRutherfordiumDubniumSeaborgiumBohriumHassiumMeitneriumDarmstadtiumRoentgeniumCoperniciumNihoniumFleroviumMoscoviumLivermoriumTennessineOganesson


Cu

Ag
nickelcopperzinc
Atomic number (Z)29
Groupgroup 11
Periodperiod 4
Blockd-block
Element category  Transition metal
Electron configuration[Ar] 3d10 4s1
Electrons per shell2, 8, 18, 1
Physical properties
Phase at STPsolid
Melting point1357.77 K ​(1084.62 °C, ​1984.32 °F)
Boiling point2835 K ​(2562 °C, ​4643 °F)
Density (near r.t.)8.96 g/cm3
when liquid (at m.p.)8.02 g/cm3
Heat of fusion13.26 kJ/mol
Heat of vaporization300.4 kJ/mol
Molar heat capacity24.440 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)150916611850208924042834
Atomic properties
Oxidation states−2, 0,[2] +1, +2, +3, +4 (a mildly basic oxide)
ElectronegativityPauling scale: 1.90
Ionization energies
  • 1st: 745.5 kJ/mol
  • 2nd: 1957.9 kJ/mol
  • 3rd: 3555 kJ/mol
  • (more)
Atomic radiusempirical: 128 pm
Covalent radius132±4 pm
Van der Waals radius140 pm
Color lines in a spectral range
Spectral lines of copper
Other properties
Natural occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for copper
Speed of sound thin rod(annealed)
3810 m/s (at r.t.)
Thermal expansion16.5 µm/(m·K) (at 25 °C)
Thermal conductivity401 W/(m·K)
Electrical resistivity16.78 nΩ·m (at 20 °C)
Magnetic orderingdiamagnetic[3]
Magnetic susceptibility−5.46·10−6 cm3/mol[4]
Young's modulus110–128 GPa
Shear modulus48 GPa
Bulk modulus140 GPa
Poisson ratio0.34
Mohs hardness3.0
Vickers hardness343–369 MPa
Brinell hardness235–878 MPa
CAS Number7440-50-8
History
Namingafter Cyprus, principal mining place in Roman era (Cyprium)
DiscoveryMiddle East (9000 BC)
Main isotopes of copper
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
63Cu69.15%stable
64Cusyn12.70 hε64Ni
β64Zn
65Cu30.85%stable
67Cusyn61.83 hβ67Zn
| references

Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.

Copper is one of the few metals that can occur in nature in a directly usable metallic form (native metals). This led to very early human use in several regions, from c. 8000 BC. Thousands of years later, it was the first metal to be smelted from sulfide ores, c. 5000 BC, the first metal to be cast into a shape in a mold, c. 4000 BC and the first metal to be purposefully alloyed with another metal, tin, to create bronze, c. 3500 BC.[5]

In the Roman era, copper was principally mined on Cyprus, the origin of the name of the metal, from aes сyprium (metal of Cyprus), later corrupted to сuprum (Latin), whence coper (Old English) and copper, first used around 1530.[6]

Commonly encountered compounds are copper(II) salts, which often impart blue or green colors to such minerals as azurite, malachite, and turquoise, and have been used widely and historically as pigments.

Copper used in buildings, usually for roofing, oxidizes to form a green verdigris (or patina). Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents, fungicides, and wood preservatives.

Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the iron-complexed hemoglobin in fish and other vertebrates. In humans, copper is found mainly in the liver, muscle, and bone.[7] The adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight.[8]

Characteristics

Physical

A copper disc (99.95% pure) made by continuous casting; etched to reveal crystallites
Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color

Copper, silver, and gold are in group 11 of the periodic table; these three metals have one s-orbital electron on top of a filled d-electron shell and are characterized by high ductility, and electrical and thermal conductivity. The filled d-shells in these elements contribute little to interatomic interactions, which are dominated by the s-electrons through metallic bonds. Unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper.[9] At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms.[10]

The softness of copper partly explains its high electrical conductivity (59.6×106 S/m) and high thermal conductivity, second highest (second only to silver) among pure metals at room temperature.[11] This is because the resistivity to electron transport in metals at room temperature originates primarily from scattering of electrons on thermal vibrations of the lattice, which are relatively weak in a soft metal.[9] The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively.[12]

Copper is one of a few metallic elements with a natural color other than gray or silver.[13] Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells corresponds to orange light.

As with other metals, if copper is put in contact with another metal, galvanic corrosion will occur.[14]

Chemical

Unoxidized copper wire (left) and oxidized copper wire (right)
The East Tower of the Royal Observatory, Edinburgh. The contrast between the refurbished copper installed in 2010 and the green color of the original 1894 copper is clearly seen.

Copper does not react with water, but it does slowly react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion (passivation). A green layer of verdigris (copper carbonate) can often be seen on old copper structures, such as the roofing of many older buildings[15] and the Statue of Liberty.[16] Copper tarnishes when exposed to some sulfur compounds, with which it reacts to form various copper sulfides.[17]

Isotopes

There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper; both have a spin of ​32.[18] The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours.[18] Seven metastable isotopes have been characterized; 68mCu is the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways.[19]

62Cu and 64Cu have significant applications. 62Cu is used in 62Cu-PTSM as a radioactive tracer for positron emission tomography.[20]

Occurrence

Native copper from the Keweenaw Peninsula, Michigan, about 2.5 inches (6.4 cm) long

Copper is produced in massive stars[21] and is present in the Earth's crust in a proportion of about 50 parts per million (ppm).[22] In nature, copper occurs in a variety of minerals, including native copper, copper sulfides such as chalcopyrite, bornite, digenite, covellite, and chalcocite, copper sulfosalts such as tetrahedite-tennantite, and enargite, copper carbonates such as azurite and malachite, and as copper(I) or copper(II) oxides such as cuprite and tenorite, respectively.[11] The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US.[22] Native copper is a polycrystal, with the largest single crystal ever described measuring 4.4×3.2×3.2 cm.[23]