Valence electrons are the electrons of an atom which are situated at the highest energy level (in the Bohr model: outermost shell of the atom). If this highest energy level is not fully occupied, which is the case with noble gases, the valence electrons are available for generating molecule formations, or the free places of the highest energy level can be made available for the admission of valence electrons. Molecules are formed by atoms connecting in such a way that valence electrons are exchanged so that the highest energy level in the molecule as a whole is just fully occupied. An electron is a low-mass elementary particle. It is the carrier of the negative electric charge and the carrier of the electric current in metals. The atomic shell consists of electrons.
In the plasma, there are always free electrons separated from the atomic or molecular compound of the plasma gas.