Materials: Metals and Non-Metals

All the elements around us can be broadly divided into metals and non-metals, based on their properties. We can tell them apart first by their physical properties.

Metals (such as iron, copper, aluminium, gold) usually:

• are lustrous (shiny) when freshly cut;
• are hard and strong (except a few like sodium);
• are malleable — can be beaten into thin sheets;
• are ductile — can be drawn into thin wires;
• are good conductors of heat and electricity;
• are sonorous — make a ringing sound when struck;
• generally have high melting points and are solids at room temperature (mercury is a liquid metal).

Non-metals (such as carbon, sulphur, oxygen, iodine) usually have the opposite properties: they are dull (not shiny), soft or brittle (break easily), poor conductors of heat and electricity, not sonorous, and may be solids, liquids or gases at room temperature.

There are a few exceptions that you must remember: iodine is a non-metal but is lustrous; graphite (a form of carbon) is a non-metal but conducts electricity; and diamond (also carbon) is the hardest natural substance though it is a non-metal.

Metals and non-metals also differ in how they react with other substances — their chemical properties.

• Reaction with oxygen: Metals react with oxygen to form metal oxides, which are basic in nature. Non-metals react with oxygen to form non-metal oxides, which are acidic. For example, magnesium burns in air to form magnesium oxide (basic), while sulphur burns to form sulphur dioxide (acidic).
• Reaction with water: Some metals react with water to give a metal hydroxide and hydrogen gas. Very reactive metals like sodium react violently even with cold water, while many non-metals do not react with water at all.
• Reaction with acids: Metals react with dilute acids to give a salt and release hydrogen gas (seen as bubbles). Non-metals generally do not react with dilute acids.
• Displacement reactions: A more reactive metal can push out (displace) a less reactive metal from its salt solution. For example, iron displaces copper from copper sulphate solution, and the blue solution slowly turns greenish while a brown coating of copper forms on the iron.

The order of metals from most to least reactive is called the reactivity series. It helps us predict which metal will displace another and how vigorously a metal will react.

Because of their useful properties, metals and non-metals are used everywhere in daily life and industry.

Uses of metals:

• Iron and steel — for making machines, vehicles, tools, bridges and buildings (they are strong).
• Copper and aluminium — for electrical wires (they are good conductors); aluminium is also used in foil and cooking pots because it is light.
• Gold and silver — for jewellery (they are shiny and do not corrode easily).
• Metals are used to make cooking utensils because they conduct heat well.

Uses of non-metals:

• Oxygen — needed by all living things for breathing (respiration) and for burning fuels.
• Nitrogen — used in fertilisers to help plants grow.
• Carbon — graphite is used in pencil leads, diamond in cutting tools and jewellery.
• Chlorine — used to purify (disinfect) drinking water; iodine is used as an antiseptic on wounds.

Some metals react with air and moisture and slowly get spoilt — for example iron forms a brown layer of rust. To prevent rusting we apply paint, grease or a coating of another metal (such as zinc, in a process called galvanisation). Knowing the properties of metals and non-metals helps us choose the right material for each job and protect them from damage.