Michael faraday hypothesized that electric current was carried through molten compounds or solution by charged atoms which he called ions. One type of the ion called anion bears the negative charge and travels towards the positive terminal of electrode called the anode. The other called the cation bears the positive charge and travels towards the negative terminal of the electrode called the cathode. He concluded that compounds that are capable of conducting electricity in the molten state or in solution are electrolytes while those that are unable do so are non-electrolytes.

In trying to explain the phenomenon observed by faraday in electrolysis, Arrhenius proposed the ionic theory. The theory proposed that: when an electrolyte is melted or dissolved in water, some if not all the molecules of the substance dissociate into freely moving charged particles.

This process is known as ionization or dissociation. For example sodium chloride will ionize to give Na⁺ and Cl^- ions

The Na⁺  ions and the Cl^- ions move randomly in solution in the absence of an electric current. But when an electric current is introduced,  the positive charges move towards the cathode while the negative charges move towards the anode.