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Materials

Metals

The Statue of Liberty in New YorkThe Statue of Liberty in New York There are 86 known metals. Metals are elements (pure, naturally occurring substances) that are usually shiny and solid at room temperature. Often they can be easily moulded and are good conductors of heat and electricity. These qualities have made metals highly attractive and useful to humankind for thousands of years. The first metal to be discovered was gold, which was used for jewellery from about 5000 BC. Most metals occur inside rocks. Rock especially rich in a certain metal is called a metal ore. The metal is separated from its ore by various means. Iron is obtained from ores by heating them until they melt, a process called smelting. Aluminium ore is known as bauxite. To separate the aluminium, it is treated with chemicals and electricity is passed through it, a process called electrolysis.

Fireworks burn mixtures of powdered metalsFireworks burn mixtures of powdered metals

Properties of metals

Metals have several features that the other elements or non-metals lack. They carry heat and electricity very well compared to non-metals. They are solid at normal or room temperature. They are strong, hard and tough, and they can be polished to give a smooth, shiny surface. When they are squeezed under great pressure, they change shape or deform and become squashed, rather than splinter apart or shatter. These features are true of most metals, but not all. The metal sodium is very soft, while the metal mercury is a silvery liquid at normal temperature.



Not all metals stay hard and solid. Some can burn very brightly, especially in powdered form. Fireworks contain mixtures of powdered metals such as magnesium as well as other substances, to make them flare up with bright colours.


Train, tracks and cables made from different metalsTrain, tracks and cables made from different metals

Uses of metals

Nearly a third of planet Earth is composed of iron (32%). Other metals that are common in the Earth include magnesium (14%), nickel (1.8%), calcium (1.5%) and aluminium (1.4%).

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