Copper – facts and properties
- Symbol
- Cu
- Atomic number
- 29
- Atomic mass
- 63.546 u
- Period
- 4
- Group
- 11
- Category
- transition metal
- Electron configuration
- [Ar] 3d¹⁰ 4s¹
- Electronegativity
- 1.9
- Atomic radius
- 145 pm
- Valence electrons
- 11
- State at standard conditions
- solid
- Melting point
- 1084.62 °C
- Boiling point
- 2562 °C
- Density
- 8.933 g/cm³
- Discovered
- known since antiquity
Copper is a reddish, shiny, soft metal with atomic number 29. It was one of the first metals that people worked, and it gave a whole age its name. Today electricity flows through copper in cables, sockets and electric motors almost everywhere. With tin and zinc it forms the alloys bronze and brass, and in air it develops a green coating familiar from old church roofs.
Position in the periodic table
Occurrence and extraction
Copper is one of the few metals that also occur native, as reddish lumps and wires in rock. That is one reason why it became known so early. Most deposits are ores, though. Chalcopyrite, a brass-yellow copper iron sulfide, is the most important, together with green malachite, a copper carbonate, and blue azurite. Chile is the biggest producer, followed by the Democratic Republic of Congo, Peru and China.
People in the Middle East were working copper about ten thousand years ago. The Copper Age followed, in which people smelted metal from ore, and then the Bronze Age. The Latin name Cuprum comes from the island of Cyprus, which was an important mining area in antiquity.
Today the copper content of ores is often very low, below one percent. The rock is ground and the copper mineral is separated by flotation, in which froth bubbles carry the mineral to the surface. The concentrate is roasted and smelted to give blister copper. Finally it is refined by electrolysis: the impure copper is the anode, and pure copper deposits on the cathode. Copper can be recycled without loss of quality, and about a third of demand is met from scrap.
Properties and reactions
Copper is in period 4 and group 11. Its electron configuration is [Ar] 3d¹⁰ 4s¹. This departs from the expected pattern of two electrons in the 4s orbital, because a completely filled d shell is especially stable. Its electronegativity is 1.9. The metal has a density of 8.933 g/cm³, melts at 1084.62 °C and boils at 2562 °C. It is easy to shape and can be drawn into thin wires. Among metals, only silver conducts electricity and heat better. The reason is the freely moving electrons in the metal lattice.
Copper is less reactive than hydrogen and lies below it in the reactivity series. It therefore does not dissolve in hydrochloric acid or dilute sulfuric acid. Nitric acid and hot concentrated sulfuric acid do attack it.
In damp air, copper first turns brown and then develops the patina, a green layer of basic copper carbonates and sulfates. It protects the metal underneath, which is why copper roofs and the Statue of Liberty last for centuries.
In compounds, copper appears as copper(I) and copper(II). Copper(II) salts such as copper sulfate dissolve to give a blue solution.
Uses in everyday life and technology
More than half of all copper goes into electrical engineering: house wiring, cables, coils, transformers and generators. Because of its high thermal conductivity, pans, boilers, radiators and heat exchangers are also made of copper. Copper pipes carry drinking water because the metal resists corrosion.
The alloys are important. Bronze consists of copper and tin; it is harder than copper and was used for weapons, tools, bells and statues. Brass is an alloy of copper and zinc, golden yellow and easy to work: it is found in taps, screws and musical instruments. Copper-nickel alloys are used in coins. The one-, two- and five-cent coins are copper-plated steel; the larger cent coins are made of Nordic gold, a copper alloy with aluminium, zinc and tin.
For living things, copper is a trace element. It is part of enzymes needed for respiration in the cells and for iron metabolism. In many molluscs and crustaceans, copper even carries the oxygen: the blood of squid and many snails is blue because of haemocyanin. Humans cover their needs with nuts, wholegrain foods and offal. Larger amounts of copper salt are poisonous and cause nausea, so acidic food should not be kept in uncoated copper vessels.
Molecules containing this element
- Copper(II) oxide CuO
- Copper(I) iodide CuI
- Copper(I) oxide Cu2O
Quick question
Light metals always conduct better than heavy metals - why does that still not hold for lithium (Li) and copper (Cu)?
FAQ
Why does copper conduct electricity so well?
In metals, electrons can move freely through the lattice. Copper has one such electron per atom that shifts very easily, and the atoms hinder the flow of electrons very little. Only silver conducts better, but it is far more expensive. That is why most cables in buildings and appliances are copper, while overhead power lines are mostly made of lighter, cheaper aluminium.
Why does copper turn green?
In air, copper reacts with oxygen, water, carbon dioxide and sulfur compounds. This forms basic copper carbonates and copper sulfates. The green layer is called patina and protects the metal from further corrosion. It is harmless to touch. It should not be confused with verdigris, which forms when vinegar acts on copper and is poisonous.
What is the difference between bronze and brass?
Both are copper alloys. Bronze has tin as its main additive, brass has zinc. Bronze is usually darker and very hard, brass golden yellow and easy to work. Copper remains the main component of both.