How do positive and negative ions carry electric current through liquids and gases?

In liquids and gases, electric current is carried by the migration of ions—electrically charged atoms or molecules created through ionization.

Conduction in Liquids

In liquid electrolytes, substances dissociate into positive and negative ions. When an electrical potential difference is applied between two electrodes, these ions are set into motion:
* Positive ions (cations) migrate toward the negative electrode, or cathode.
* Negative ions (anions) migrate toward the positive electrode, or anode.

The electric current is the result of this ionic flow. Upon reaching the electrode of opposite polarity, an ion donates or receives an electric charge, converting it back into a neutral atom or group of atoms, which often results in chemical changes at the electrode surface.1

Conduction in Gases

Gases are typically insulators, but they can conduct electricity when ionized. This often occurs through ionization by collision, where electrons moving through a gas gain enough energy to knock other electrons off neutral gas molecules. This process creates ion pairs consisting of positive ions and free electrons (which may attach to other molecules to form negative ions). Once these charged particles are present, they move in response to an electric field, thereby carrying current through the gas.2