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Reading Selection, Lesson 23

Reactivity and Free Metals

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Copper ore

Copper is more reactive than gold. Sometimes it is found as nuggets, but most copper is obtained by smelting copper ores. During smelting, the metal is extracted from the metal ore. The exact process depends on the type of ore. For example, if the ore is copper carbonate or copper oxide, smelting is achieved by roasting the ore with carbon, usually in the form of coke. A chemical reaction takes place that produces copper metal and carbon dioxide gas.

Gold is valued for its scarcity and for its lack of reactivity. Because it does not react with other elements, such as oxygen, it can be found in its pure form as nuggets. Metals that are not combined with other substances are called free metals. Gold's lack of reactivity also means that it stays shiny and does not corrode. This makes it ideal for use in jewelry and in electrical contacts (for example, the plugs on a computer cable).

Copper is a much more common metal than gold is, and sometimes nuggets of pure copper can be found. Copper can remain shiny for a long time, and it is also used to make jewelry. However, eventually it reacts with other elements, particularly oxygen in the air, and slowly corrodes (a process called tarnishing).

Gold nugget

The low reactivity of gold explains why it can be found as metal nuggets. Most other metals exist as ores.

Iron is more reactive than copper. Because of its reactivity, iron is almost always found in Earth's crust combined with other elements. Rocks containing large amounts of iron compounds are called iron ore. Iron is extracted from these ores by a process called smelting. Chunks of natural iron are sometimes found, but these originate from outer space. Meteorites that fall to Earth are often composed mainly of iron. They can last thousands of years, but they also eventually corrode.

Iron meteorite

This giant iron meteorite is in the form of pure iron, which is rarely found on Earth. Why can iron exist in space but not for very long on the surface of Earth?



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