Category Science & Technology

            Almost 80 percent of all elements are metals. They can be distinguished from other elements because when cut, they reflect light and appear shiny. Metals also conduct heat and electricity. Most metals are malleable, which means that they can be beaten or moulded into different shapes.

            Most metals react with oxygen in the air, or with other kinds of elements, to form compounds. They are rarely found in the natural metallic state. However, gold is an exception, because it does not react easily with other elements and is often found in its natural state as grains or nuggets. Mixtures of metals are called alloys.

               Mercury is the only metal that is a liquid at ordinary room temperatures. It is a bright shiny colour, and flows rapidly when poured out of a container (this is why it used to be called ‘quicksilver’). Mercury does not stick to glass, so it is used in thermometers to indicate the temperature.

               Mercury compounds are often brightly coloured and were once widely used in coloured paints. However, mercury is an extremely poisonous substance and its use is now strictly controlled. Some other uses of mercury are in the manufacture of batteries and in medicine. Dentists still use a mixture of mercury and silver, in the form of amalgam, to fill cavities in teeth.

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               Matter exists in three states: solid, liquid and gas. The molecules in all matter are in constant motion, and in a gas they are held together so loosely that they can move freely. Gas molecules move about rapidly and at random. This means that a gas will expand to fill any space it occupies. The molecules in a gas press against anything that restrains them, causing pressure. As a gas is heated, the molecules move further apart and move about more rapidly. If it is restricted in a container, the pressure will increase. If any gas is cooled sufficiently, it will condense into a liquid. This is why some of the outer planets of the solar system are composed of liquid methane and hydrogen.

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               Radioactivity can contain large amounts of energy, which causes damage to matter, including living cells. These forms of radioactivity can knock electrons out of the atoms of a substance to produce ions, which have different properties.

               Organic compounds always contain the element carbon. Carbon compounds often have a very complicated structure, and they are responsible for most of the chemical reactions that sustain life. Carbon is found in some very large molecules, such as those in proteins and plastics. It has proved relatively easy to manufacture many of these substances artificially.

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               New elements are created by bombarding other elements with radiation in an atomic reactor. Scientists have made 16 artificial elements by bombarding uranium and other radioactive elements.