Why do metals conduct electricity?

In the last post, I discussed the difference in bonding between metals and ceramics, and how that is manifested in different properties exhibited by metals and ceramics. Now, let us try to understand why metals actually conduct electricity. The reason again ties down to bonding in metals. Like, I explained here, metals typically exhibit metallic bonding in which all the valence electrons are shared by all the atoms. There is a delocalization of electrons, unlike in covalent and ionic bonds which confine electrons only to neighboring atoms. Now, when an external electric field is applied to metals, these delocalized electrons are easy to move and thus conduct. This simple explanation is basis for Drude Model where Drude actually derives simple quantitative formula for conductivity.

This explanation and thus theory is very elementary and is not be able to give correct quantitative numbers for many other properties (heat capacity and seebeck coefficient) of metals. A more detailed theory known as "band theory" is used to describe why metals conduct electricity whereas ceramics or insulators do not. Description of band theory is not aim of this post. I just wanted to describe electrical conduction in terms of bonding so we can appreciate how bonding can affect properties.