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Electricity is composed of moving electrons. Electrons are never really found in a free state, unless part of a plasma. The electrons must move through some medium.

Materials consist of atoms lumped together. Atoms consists of nuclei, e.g. protons and neutrons, surrounded by electrons. Materials can form when electronic charge can be shared between atoms. Not all electrons will be shared though, only those that are farthest away from the nucleus will be contenders for this and these electrons will be the ones responsible for measurable currents.