Spark image
In solids electric current is a flow of electrons but in liquids and gases the electric current is a flow of electrons and ions.

An ion is a charged atom and these can be either positive or negative. The picture is a diagrammatic view of what the two types of ion are like.

A positive ion is an atom that has one or more electrons taken away from it
A negative ion is one which has had one or more electrons added to it

In the electrolysis of copper sulphate the liquid is ionised to give positive copper ions and negative sulphate ions. Two electrons are torn from the copper atoms and added to the sulphate ions. The positive copper ions are then attracted to the negative electrode while the negative sulphate ions are pulled towards the positive electrode.

© Keith Gibbs 2009