Electric Current

Materials conduct electricity because they contain charged particles that can move around in them.
In solids these charged particles are called ELECTRONS.
Electrons are tiny negatively charged particles.
In some materials the electrons can wander about between the atoms, these electrons are called FREE ELECTRONS. The more free electrons there are in a solid the better it will conduct electricity.

If we now think of the metal as a wire as shown in the diagram then the tiny electrons show no particular direction of movement (Figure 1(a)).
But if we now connect a battery to the two ends of the wire the electrons drift down the wire in one direction (Figure 1(b)).

schoolphysics: Electric current animation

To see an animation of the movement of free electrons in an electric current click on the animation link.

Materials that will conduct electricity are called electrical CONDUCTORS. those that won't are called INSULATORS.


CONDUCTORS
Solids that will conduct electricity (by using batteries alone):
all metals (they contain a lot of free electrons)
carbon

INSULATORS
Solids that will not conduct electricity (by using batteries alone):
dry wood rubber plastic polythene
(they don't contain any, or many free electrons).

Ions come in two types:
POSITIVE IONS. - atoms that have lost one or more negative electrons
NEGATIVE IONS. - atoms that have gained one or more negative electrons
The more concentrated a liquid is the more ions there are in it and the better it will conduct electricity.
Negative ions will flow towards the positive electrode in a liquid and positive ions will flow towards the negative electrode.

Some liquids that will conduct electricity:
water (not distilled) copper sulphate all acids
(they contain a lot of ions)

Some liquids that will not conduct electricity:
paraffin meths distilled water
(they don't contain many or any ions)