What specific property of metals accounts for their unusual electrical conductivity?
To explain conductivity in metals, you need to explore "band theory". I will give a brief account (and a good reference) below.
In a solid crystal of
This creates a situation in which valence electrons occupy a portion of these orbitals, but because there were more orbitals than valence electrons, there will also be a band of empty orbitals at nearby energies.
All that remains is for a small energy application, such as a voltage applied to the crystal to cause the valence electrons to jump into one of the orbitals in the empty orbitals. These electrons will be able to move easily among the many empty orbitals that link the metal atoms together.
Viola! We have electrical conductivity.
Here is a source that I think explains this topic quite clearly. Check it out: