Normal atoms cannot carry electrical current through a liquid. Only moving charged ions can do this job. Ions can only migrate if they are free to travel.
This freedom happens when a solid salt is dissolved in water. It also happens if the solid salt is heated and melted into a liquid. Solid salt crystals cannot conduct electricity because the ions are locked tightly in place.
When you place two charged metal wires into a salt solution, an electric field forms. This field pushes positive cations toward the negative wire. It also pushes negative anions toward the positive wire.
This steady two-way flow of ions creates an actual electric current in the liquid. The speed of the moving ions depends on their size and their total charge. Smaller ions usually move faster because they face less drag from the water molecules.
Ions with higher charges feel a much stronger pull from the electric field. Students often confuse ionic migration with basic diffusion. Diffusion is just particles spreading out randomly from crowded areas to empty areas.
Migration requires an outside electrical force to pull the ions in one specific direction. Scientists use a value called the transport number to track this movement. This number shows exactly how much current each specific ion carries through the liquid.