Metals conduct electricity because
the outer electrons of their atoms are mobile.
If a piece of metal is connected to the terminals of a battery,
electrons will flow into one end of the metal block, through the
metal, out the other end, and back to the battery.
Only the electrons move; the metal ions remain in place.
In the diagram above, click
on the switch to turn the circuit on and off, and click on the Metal
for a closer view.