Conductors and insulators
The atomic structure of materials determines whether they will be electrical conductors or insulators. The difference is in the so-called valence layer.
The bodies considered electrical conductors have excess electrons in their valence shell, which is the last shell to receive electrons in an atom. The electrons present in the valence shell are called free electrons, and the force of attraction between them and the atomic nucleus is small, so they are easy to move through the material, making the substance in question a good conductor of electricity. In general, metals are excellent electrical conductors.
They are also called dielectrics . The electrons that form these materials are not easy to move, given the strong bond between them and the atomic nucleus. Styrofoam, rubber, dry wood, glass, among others, are examples of electrical insulating materials.
Materials called semiconductors have electrical properties that are intermediate between conductors and insulators. The physical conditions to which the material is subjected determine whether it will behave as a conductor or as an insulator. These materials are widely used by the electronics industry for circuit composition. Silicon and germanium are examples of materials with this characteristic.
Superconductors are materials that offer very low resistance to the flow of electric current (click here to learn more about superconductivity).
All electrical insulating materials have a maximum electric field value they can withstand. If this maximum value is exceeded, the material, even being an insulator, will start to behave as a conductor. When this occurs, we say that the dielectric strength of the material has been broken . Taking paper as an example, to break its dielectric strength, 16 kV/mm is needed, that is, for the paper’s stiffness to be broken, 16000 volts are needed for each millimeter of substance.