Metals, Semi-metals and Non-metals
In the Periodic Table, elements can also be divided into metals, semi-metals or non-metals. Metals are found on the left of the line, and non-metals are those on the right. Metals, semi-metals and non-metals all have their own unique properties.
Examples of metals include copper (Cu), zinc (Zn), gold (Au) and silver (Ag). On the Periodic Table, the metals are on the left of the zig-zag line. There are a large number of elements that are metals. The following are some of the properties of metals:
Properties of metals
Thermal conductors Metals are good conductors of heat and are therefore used in cooking utensils such as pots and pans.
Electrical conductors Metals are good conductors of electricity, and are therefore used in electrical conducting wires.
Shiny metallic lustre Metals have a characteristic shiny appearance and are often used to make jewellery.
Malleable This means that they can be bent into shape without breaking.
Ductile Metals can stretched into thin wires such as copper, which can then be used to conduct electricity.
Melting point Metals usually have a high melting point and can therefore be used to make cooking pots and other equipment that needs to become very hot, without being damaged.
You can see how the properties of metals make them very useful in certain applications.
In contrast to metals, non-metals are poor thermal conductors, good electrical insulators (meaning that they do not conduct electrical charge) and are neither malleable nor ductile. The non-metals are found on the right hand side of the Periodic Table, and include elements such as sulfur (S), phosphorus (P), nitrogen (N) and oxygen (O).
Semi-metals have mostly non-metallic properties. One of their distinguishing characteristics is that their conductivity increases as their temperature increases. This is the opposite of what happens in metals. The semi-metals include elements such as silicon (Si) and germanium (Ge). Notice where these elements are positioned in the Periodic Table.
Electrical conductors, semi-conductors and insulators
An electrical conductor is a substance that allows an electrical current to pass through it. Many electrical conductors are metals, but non-metals can also be good conductors.
Copper is one of the best electrical conductors, and this is why it is used to make conducting wire. In reality, silver actually has an even higher electrical conductivity than copper, but because silver is so expensive, it is not practical to use it for electrical wiring because such large amounts are needed. In the overhead power lines that we see above us, aluminium is used. The aluminium usually surrounds a steel core which adds tensile strength to the metal so that it doesn’t break when it is stretched across distances.
Occasionally gold is used to make wire, not because it is a particularly good conductor, but because it is very resistant to surface corrosion. Corrosion is when a material starts to deteriorate at the surface because of its reactions with the surroundings, for example oxygen and water in the air.
An insulator is a non-conducting material that does not carry any charge. Examples of insulators would be plastic and wood. Do you understand now why electrical wires are normally covered with plastic insulation? Semi-conductors behave like insulators when they are cold, and like conductors when they are hot. The elements silicon and germanium are examples of semiconductors.
Magnetic and Non-magnetic Materials
We have now looked at a number of ways in which matter can be grouped, such as into metals, semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and insulators. However they can also be divided into magnetic and non-magnetic
Magnetism is a phenomena by which materials exert attractive or repulsive forces on other materials.
A metal is said to be ferromagnetic if it can be magnetised (i.e. made into a magnet). If you hold a magnet very close to a metal object, it may happen that its own electrical ﬁeld will be induced and the object becomes magnetic. Some metals keep their magnetism for longer than others. Look at iron and steel for example. Iron loses its magnetism quite quickly if it is taken away from the magnet. Steel on the other hand will stay magnetic for a longer time. Steel is often used to make permanent magnets that can be used for a variety of purposes.
Magnets are used to sort the metals in a scrap yard, in compasses to ﬁnd direction, in the magnetic strips of video tapes and ATM cards where information must be stored, in computers and TV’s, as well as in generators and electric motors.