They are called conductors. Others conduct electricity partially and they are called semi-conductors. The concept of electric transmission is very simple to understand. The wire that conducts the electric current is made of atoms which have equal numbers of protons and electrons making the atoms electrically neutral. If this balance is disturbed by gain or loss of electrons, the atoms will become electrically charged and are called ions.
Electrons occupy energy states.
Each level requires a certain amount of energy. For an electron to move to a higher level, it will require the right amount of energy. We can then say that conduction of an electrical current is simply electrons moving from one empty slot to another in the atoms' outer shells. The problem with these conductors is the fact that they do not let all the current get through. Whenever an electric current flows, it encounters some resistance, which changes the electrical energy into heat.