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Metal lattices consist of positive metal ions, to maintain stability the electrons are free moving (delocalized) these electrons are what allow the metal to be conductive.
The way that an object can be defined into the three categories which are conductors, insulators and semiconductors is by their electric conductivity. This is then based on the energy band level which is determined by the band gap between the conduction band and the valence band. The difference between conductors insulators and semiconductors is the effect on the electricity when electricity is sent through the object. The electrical conductivity is determined by the electrons in the atom as the electros are said to occupy particular energy levels. Conductors are from the highest energy band which means that they partly fill the valence band and have empty levels which allows the electrons to move freely under the influence of an electric field. Insulators on the other hand completely fill the valence band which means the electrons cannot move freely which prevents them from conducting the electricity from the electric field. In semiconductors the gap between the conduction band and the valence band is smaller than the insulator but larger than conductors. From this you can see that it is possible to conduct electricity but not as well as the conductors this is because the electrons are closer together and have less room to move around which means they are not the best conductors for electricity.
Electrons that move in a nearly full band create what is known as a hole. This means there is one less valence electron and another electron can now move to cover this hole creating another hole and the cycle continues as the holes will not all be filled. With the electrons moving from hole to hole in this cycle it means that all the electrons are travelling in one direction with the holes travelling in the opposite direction (as they cannot travel same ways due to the fact that the electrons are covering the holes when needed).
In conductors the number of electrons that are moving between the conduction band and the valence band are is of a high number which means that there is a lot of room for the electrical current to travel through. Temperature plays an important role in the electrons as slight temperature changes can cause the electrons to travel into the conduction band making the object more conductible. For example in semiconductors if