To understand the electroplating it is necessary to recall the general principles of electrolysis and the nature of the simpler chemical compounds and of their aqueous solutions. Metals are chemical element (alloys are mixtures of elemental metals). Metals are distinctive among the elements because the atoms of which they are composed have one or two (occasionally three) outer electrons which are rather loosely attached to the rest of the atom. In the solid metal these outer electrons are shared by all the atoms present, and are very mobile. Their mobility is the cause of the distinctively high electrical and thermal conductivity of metals.