For demonstrations, see:
1.5 Conductors and Insulators
In terms of conducting the electricity, we can classify the matter into two groups, namely conductors and insulators.
Conductors are the ones that, they provide a medium such that charges can easily move around. Typical example to conductors are all metals. All metals are good conductors of electricity.
The second group is the insulators. And they’re just the opposite of the conductors. They basically do not provide a medium such that charges can easily move around. We can give a piece of wood, plastic, paper, et cetera as some examples to electrical insulators.
To be able to understand why metals are good electrical conductors, again, we have to look at the matter from the atomic point of view. In some atoms, the outermost electron is not bound to nucleus. These electrons give the necessary electrical neutrality to the medium, but they do not orbit about the nucleus of the atom. They’re free. They’re free to move under the influence of any force.
So as they move in the medium, since they’re charged particles, they carry the charge with themselves from one point to the other one in that medium. These types of electrons are called “free electrons.” Therefore a free electron is an electron which is not bound to the nucleus of the atom and it is free to move under the influence of any force.
And the metals have abundance of free electrons. It is because of this reason as these free electrons which are not bound to nuclei of the atoms in metal mediums, move around and as they move, they carry the charge with themselves. It is because of this reason, all metals are good electrical conductors.