Some small pieces of copper in a tube. New copper is a pink color. The color changes to the more orange colour that many people have seen soon when new copper is left in air.
Tinned Copper Wire anaglyph

Copper is a chemical element. It is the 29th element in the periodic table and has 29 protons. Its mass number is 63.55. It is a transition metal in the middle of the periodic table. The symbol for copper is "Cu", which comes from the Latin word cuprum, which, in turn, came from the Latin word for the island of Cyprus, where copper was found.


Physical properties

copper disc, acid etched, you see the normally invisible crystalline structure

Copper is a pinkish color when it is new, but soon turns a reddish orange color after it is exposed to air.

Copper is one of the few colored metals. Most metals are gray or silver. Gold, copper, caesium and osmium are the only four colored metals. Copper is green as copper(II) carbonate and copper(II) hydroxide. It turns green because it oxidises. After a time in the air, copper forms green copper carbonate at the surface, called verdigris. That is why the copper roof of a building looks green.

Copper is very flexible and ductile. It can be stretched into wires easily. Copper is also very soft, it has a Mohs hardness of 2.5 to 3. That means that it is harder than a fingernail but softer than a steel pocketknife.

It reacts with solutions of hydrochloric acid or ammonia containing oxygen. It can also dissolve in a mixture of hydrogen peroxide and hydrochloric acid. This makes copper(II) chloride. It does not dissolve in weak acids. It can dissolve in nitric acid to make copper(II) nitrate and nitrogen dioxide or nitric oxide.


Copper forms chemical compounds. In these compounds, it has two normal oxidation states: +1 and +2. +2 is more common. Most +2 copper compounds are blue. +1 copper compounds can be white. Copper compounds are weak oxidizing agents. They corrode many metals. This corrosion takes the metal and puts it in the chemical compound, leaving the copper behind. An example would be iron and copper(II) sulfate reacting to make copper and iron(II) sulfate. +1 copper compounds are reducing agents when in air. They are normally made by reduction of +2 compounds.

Copper compounds can be black, green, reddish, white, blue, or yellow.

Copper(I) compounds

Copper(I) compounds have copper in +1 oxidation state. They are weak reducing agents. They react with air to make copper(II) compounds. They also disproportionate to copper and copper(II) compounds. Most of them do not dissolve in water.

Copper(II) compounds

Copper(II) compounds have copper in +2 oxidation state. They are weak oxidizing agents. They are greenish when hydrous (water molecules added). They are more stable in air than copper(I) compounds.


Copper as a metal in the ground
Min chalcopyrite

Copper can be found as a metal in the ground. Normally, it is green on the outside. Most copper is not as a metal but in chemical compounds. Chalcopyrite is the most common copper ore. It is a mixture of pyrite and copper sulfide. Copper is found in small amounts in living things. Some mollusks and arthropods have blue blood because they have copper in their blood. Animals such as humans and other mammals have red blood because it contains iron.


As an element

Copper may be the oldest metal in use, as very old copper tools have been found. Copper is used in electrical wiring. It can also be shaped into various parts. It can be used in a heat sink. The Statue of Liberty is made of copper. It is also used in pipes carrying water, because it does not corrode.

When people mix copper with tin, bronze is made. Bronze is an important metal because it can be shaped into useful things, but it was more important before the use of iron. When zinc is mixed with copper, brass is made. It can be alloyed with nickel to make cupronickel.

As chemical compounds

Copper is important in the human body. If a person does not get enough copper, the molecules in the body might not work. Having too much copper, though, can be a problem. Humans get most of the copper they need from food, and vitamins also contain copper to make sure we get enough. Copper compounds are also used to kill fungi and algae.


Copper is not as toxic as a metal. Copper compounds are toxic though, although small amounts are needed to live. Copper is expelled from the body easily, so it does not build up in toxic effects.


Copper is sometimes just taken out of the ground and shaped into objects. But most copper is not in a metal form in the ground. Chalcopyrite is the main copper ore. It is heated with air to separate the iron as iron(II) oxide. Some copper(I) oxide is made. Sulfur dioxide is also made. Then silicon dioxide is added, which reacts with the iron(II) oxide to make a liquid which is drained. Now only copper and sulfide are left. The copper sulfide reacts with air to make copper metal and sulfur dioxide. Some copper sulfide reacts with the copper(I) oxide to make copper and sulfur dioxide. This makes impure copper.

Copper is made pure by electrolyzing it. A thin sheet of pure copper is put on the cathode and a thick sheet of impure copper is put on the anode. The electrolyte is copper sulfate. The impure copper gets dissolved in the solution. It then coats the thin sheet of pure copper. This makes the copper pure.

Large amounts of copper are recycled because of its high value and the increasing depletion of worldwide copper reserves.

Related pages


Copper for Kids. Kiddle Encyclopedia.