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All matter consists of atoms.

Atoms contain three types of smaller particles: protons, neutrons and electrons.

• Protons are positively charged;
• Electrons are negatively charged;
• Neutrons have no charge – they are neutral.

Protons and neutrons are found inside the nucleus.

Electrons orbit the nucleus.

An atom has a neutral charge, because it contains the same number of protons and electrons.

If it loses an electron, it becomes a positively charged ion.

If it gains an electron, it becomes negatively charged ion.

Charged atoms are called ions.

An electric current is a flow of charged particles in one direction.

In solids, an electric current is the flow of free electrons in one direction.

Key points

• An electric current is a flow of charged particles in one direction.
• Metals are good conductors of electricity because they contain free electrons.
• Insulators such as plastic and rubber do not generally contain free electrons and so are poor conductors of electricity.