Copper is the chemical element with symbol Cu and atomic number 29. It is a reddish-gold transition metal with exceptionally high electrical and thermal conductivity, excellent ductility and strong resistance to atmospheric corrosion.
Copper quick facts
| Property | Value |
| Symbol | Cu |
| Atomic number | 29 |
| Relative atomic mass | 63.546 |
| Group | 11 |
| Period | 4 |
| Block | d-block |
| Density | 8.96 g/cm³ |
| Melting point | 1084.62°C |
| Boiling point | 2560°C |
| Electron configuration | [Ar] 3d¹⁰ 4s¹ |
| Common oxidation states | +1, +2 |
| CAS number | 7440-50-8 |
| Stable natural isotopes | ⁶³Cu, ⁶⁵Cu |
Position and electron configuration
Copper is in group 11, period 4 and the d-block. Its electron configuration is [Ar] 3d¹⁰ 4s¹. Copper commonly forms +1 and +2 compounds, with Cu²⁺ responsible for many familiar blue and green copper salts and complexes.
See the complete CleverlySmart periodic table.
Physical and electrical properties
Copper is one of the few metals with a naturally reddish colour. It can be drawn into fine wire and shaped without breaking. Among common engineering metals, copper has extremely high electrical and thermal conductivity, which is why it dominates power cables, building wiring, motors and heat-transfer equipment.
Fresh copper slowly develops oxide and carbonate layers in air. Over long periods outdoors, these reactions can produce the characteristic green patina seen on old copper roofs and statues. The patina can protect underlying metal from faster corrosion.
Important copper compounds
- Copper(II) sulfate (CuSO₄): a blue salt used in laboratories, electrochemistry, agriculture and chemical processing.
- Copper(I) oxide (Cu₂O): a red solid used in specialised coatings, pigments and semiconductor research.
- Copper(II) oxide (CuO): a black oxide used in ceramics, catalysts and materials science.
- Copper carbonates: green or blue-green compounds associated with copper mineral weathering and patinas.
Occurrence and production
Copper occasionally occurs as native metal, which helped make it one of the first metals used by humans. Most modern copper comes from ores such as chalcopyrite, bornite and other sulfide or oxide minerals. Extraction routes include concentration, smelting, leaching, solvent extraction and electrorefining.
Uses of copper
- Electrical wiring and power equipment: copper’s largest use because of high conductivity and ductility.
- Motors, generators and transformers: copper windings efficiently carry current.
- Plumbing and construction: copper tubing, roofing, heat exchangers and architectural components are durable and corrosion-resistant.
- Electronics: printed circuit boards, connectors and semiconductor interconnects use copper extensively.
- Alloys: copper with zinc forms brass; copper with tin forms bronze; many other specialised copper alloys are also important.
- Antimicrobial surfaces: copper and some copper alloys can reduce survival of many microorganisms on contact surfaces.
Biological role of copper
Copper is an essential trace nutrient. Copper-containing enzymes participate in energy metabolism, connective-tissue formation, iron handling, antioxidant defence and nervous-system function. The body tightly regulates copper because both deficiency and excess can be harmful.
Copper isotopes
Natural copper contains two stable isotopes, ⁶³Cu and ⁶⁵Cu, with copper-63 the more abundant. Radioactive copper isotopes have applications in scientific research and are also studied in nuclear medicine.
For broader isotope information, see the CleverlySmart isotope table.
Health and safety
Copper is essential in small amounts but excessive exposure can cause toxicity. Copper dusts and fumes can irritate the respiratory tract, and some soluble copper compounds are harmful if swallowed in sufficient quantities. Industrial exposure should follow appropriate occupational limits and hygiene practices.
History and name
Copper has been used for thousands of years and helped define the transition from the Stone Age to the Copper and Bronze Ages. The symbol Cu comes from the Latin cuprum, linked historically with Cyprus, an important ancient source of copper.
Frequently asked questions
Why is copper used for electrical wiring?
It combines very high electrical conductivity with ductility, corrosion resistance and practical mechanical strength.
Why does copper turn green?
Long-term exposure to air, moisture and atmospheric chemicals forms a protective mixture of copper compounds known as a patina.
Why copper is such a good conductor
Copper combines very high electrical and thermal conductivity with ductility and corrosion resistance. Its electrons move readily through the metallic lattice, which is why copper dominates household wiring, motors, transformers, power cables and many electronic connections.
Copper is also easy to form and join. Important alloys include bronze (primarily copper and tin) and brass (copper and zinc), each offering different combinations of strength, machinability and corrosion resistance.
Patina, antimicrobial action and biology
Weathered copper surfaces can develop a protective green patina containing copper carbonates and related compounds. This surface slows further corrosion and explains the characteristic appearance of old copper roofs and monuments.
Copper ions can damage microbial membranes and proteins, so copper and some copper alloys have antimicrobial properties. Copper is also an essential trace nutrient in humans because copper-containing enzymes support iron metabolism, connective tissue and antioxidant chemistry. Excessive intake, however, is harmful.
Frequently asked questions
Why does copper turn green?
Long exposure to moisture, oxygen, carbon dioxide and pollutants forms a surface patina of copper compounds rather than a single simple oxide.
Why is copper used instead of silver for most wiring?
Silver conducts slightly better, but copper offers an excellent balance of conductivity, mechanical performance, availability and cost.
