Conductors and Insulators

Conductors

Materials that allow electric charges to move freely through them are called conductors.
Good conductors of electricity include metals such as copper, silver, and aluminium. These are often used in electrical wires due to their high conductivity.
In conductors, the outer electrons of the atoms can move freely. These so-called free electrons can move throughout the material under the influence of an electric field (a voltage).
An electric current is constituted by the movement of free electrons from atom to atom. This is why conductors are good at conducting electricity.

Semiconductors

Semiconductors are materials that have properties in between those of conductors and insulators.
Silicon and germanium are typical semiconductors.
At room temperature, semiconductors can conduct some electricity. When the temperature increases or certain impurities are added (a process known as doping), semiconductors can become more conductive.

Insulators

Insulators are materials that resist the flow of electric charges.
Examples of good electrical insulators include plastic, rubber, glass, and air.
In insulators, electrons are not free to move around - they are tightly bound to their atoms.
Despite their resistance to electrical current, insulators play a crucial role in electrical systems. They are often used to cover and protect electrical wires, preventing unwanted flows of electricity.

Superconductors

Superconductors are materials that can conduct electricity with zero resistance when they are cooled below a certain temperature.
Common superconducting materials include certain ceramics, metals like mercury and lead, and some alloys.
Superconducting materials hold the promise for efficient energy transmission and high-speed computing among other applications, but the need for extreme cooling is a major hurdle to widespread use.

Remember that, in the context of electricity, the ability of a material to pass on electric charges (or resist their flow) is called its conductivity (or resistivity). Understanding the properties of different types of materials - conductors, semiconductors, insulators, and superconductors - is crucial to grasp the behavior of electric circuits.