1.2 Classification using the properties of matter  (Page 22/4)

Metals, semi-metals and non-metals

The elements in the Periodic Table can also be divided according to whether they are metals , semi-metals or non-metals . On the right hand side of the Periodic Table you can draw a 'zigzag' line (This line starts with Boron (B) and goes down to Polonium (Po)). This line separates all the elements that are metals from those that are non-metals. Metals are found on the left of the line, and non-metals are those on the right. Along the line you find the semi-metals. Metals, semi-metals and non-metals all have their own specific properties.

Metals

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:

• Thermal conductors Metals are good conductors of heat. This makes them useful in cooking utensils such as pots and pans.
• Electrical conductors Metals are good conductors of electricity. Metals can be used in electrical conducting wires.
• Shiny metallic lustre Metals have a characteristic shiny appearance and so are often used to make jewellery.
• Malleable This means that they can be bent into shape without breaking.
• Ductile Metals (such as copper) can be stretched into thin wires, 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.

Group work : looking at metals

1. Collect a number of metal items from your home or school. Some examples are listed below:
   • hammer
   • wire
   • cooking pots
   • jewellery
   • nails
   • coins
2. In groups of 3-4, combine your collection of metal objects.
3. What is the function of each of these objects?
4. Discuss why you think metal was used to make each object. You should consider the properties of metals when you answer this question.

Non-metals

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 sulphur (S), phosphorus (P), nitrogen (N) and oxygen (O).

Semi-metals

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. Electrical conductors are usually metals. 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.