In metallic networks, valence electrons are the ones primarily involved in the formation of metallic bonds and are responsible for the unique properties of metals. However, it is not accurate to say that only valence electrons become delocalized in metallic networks.
In a metallic network, the valence electrons of metal atoms are loosely held and can move freely throughout the lattice. These electrons are often referred to as "delocalized electrons" because they are not associated with any specific atom but instead form a sea of mobile electrons that pervades the entire metal lattice.
While valence electrons are the most important contributors to this delocalized electron sea, other electrons, such as those from inner shells, can also participate to some extent. However, the contribution of inner-shell electrons to the delocalized electron sea is relatively minor compared to that of the valence electrons.
The delocalization of electrons in metallic networks is what gives metals their characteristic properties, such as high electrical and thermal conductivity, malleability, and ductility. The mobility of these delocalized electrons allows them to carry electric current and transfer heat easily within the metal lattice.
In summary, while valence electrons play a crucial role in the delocalization of electrons in metallic networks, other electrons can also contribute to some extent. However, the delocalization of valence electrons is the primary mechanism responsible for the unique properties exhibited by metals.