page_title: Copper
section_title: Physical
hierarchical_section_title: Copper / Characteristics / Physical
caption_attribution_description: Deutsch: Strangguss-Kupferscheibe in der Reinheit von ≥ 99,95%, makrogeätzt zur Verdeutlichung der inneren kristallinen Strukturen ∅ ≈83 mm. Zwecks Konservierung lackiert. Man sieht deutlich die von Außen nach Innen verlaufende Kristallisation. English: Continuous casting copper disc (99.95% pure), macro etched, ∅ ≈83 mm. Français&#160;: Disque de cuivre obtenu par coulée continue (Pureté&#160;: 99,95%, diamètre&#160;: 83 mm environ), et dépoli par traitement chimique. Polski: Miedziany krążek (∅ ≈83 mm) o czystości ≥99,95% otrzymany metodą ciągłego odlewu i wytrawiony powierzchniowo dla uwidocznienia struktury wewnętrznej. Português: Disco de cobre obtido por lingotamento contínuo (pureza: 99,95%, diâmetro: 83 mm), e polido por tratamento químico. Suomi: Jatkuvavalettu kuparilevy (puhtaus 99,95&#160;%, etsattu, halkaisija: 83&#160;mm) Türkçe: Sürekli döküm yöntemiyle üretilmiş bakır disk (%99.95 safiyet), dağlanmış numune, çap yaklaşık 83 mm. ‪中文（简体）‬: 连续铸造的铜盘（纯度为99,95%，直径83毫米）
context_page_description: Copper is a chemical element with the symbol Cu 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. 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.
  In the Roman era, copper was mined principally on Cyprus, the origin of the name of the metal, from aes сyprium, later corrupted to сuprum. Coper and copper were derived from this, the later spelling first used around 1530.
context_section_description: 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. 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.
  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. 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. 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.
  Copper is one of a few metallic elements with a natural color other than gray or silver. 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.
caption: A copper disc (99.95% pure) made by continuous casting; etched to reveal crystallites
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