In some materials, electrons move easily from atom to atom. In others, the electrons move with difficulty. And in some materials, it is almost impossible to get them to move. An electrical conductor is a substance in which the electrons are mobile.
The best conductor at room temperature is pure elemental silver. Copper and aluminum are also excellent electrical conductors. Iron, steel, and various other metals are fair to good conductors of electricity. In most electrical circuits and systems, copper or aluminum wire is used. (Silver is impractical because of its high cost.)
Some liquids are good electrical conductors. Mercury is one example. Salt water is a fair conductor. Gases or mixtures of gases, such as air, are generally poor conductors of electricity. This is because the atoms or molecules are usually too far apart to allow a free exchange of electrons. But if a gas becomes ionized, it can be a fair conductor of electricity.
Electrons in a conductor do not move in a steady stream, like molecules of water through a garden hose. Instead, they are passed from one atom to another right next to it
This happens to countless atoms all the time. As a result, literally trillions of electrons pass a given point each second in a typical electrical circuit.