In the 1900’s Paul Drde noted that the of metals are very loosely held. He visualized metals as an array of atomic cores (nuclei and inner electrons) or metal cations immersed in a sea of surrounding . In this model the valence electrons are free delocalized mobile and not associated with any particular atom.
The free electrons in the sea can absorb photons so metals are opaque. Electrons on the surface can bounce back light at the same frequency as the light that hits the surface. Therefore the metal appears to be shiny. This model accounts for the lustre of metals.
Since the electrons are free to move if electrons from an outside source are added to a metal wire at one end the electrons will move through the wire and come out at the other end at the same rate. Thus this model accounts for the electrical conductivity of metals.
Metals usually have high densities. Hence the atoms are closely packed. That makes heat transfer by conduction more efficient. Conduction is the transfer of heat energy by vibration of particles to transfer energy from one end of the metal to the other end. Metals also have the sea of electrons to help them in this conduction. Since electrons are very small compared to the metal ions they can easily pass through the spaces between the cations and help to transfer heat energy along. Thus this model accounts for the thermal conductivity of metals.
The sea of electrons surrounding the cations act like a cushion and so when the metal is hammered on the overall composition of the structure of the metal is not harmed or changed. The cations may slide past each other but the sea of electrons will adjust to the new formation of cations and keep the metal intact. Thus this model accounts for the malleability and ductility of metals.