Metallic Bonding

Metals have several qualities that are unique, such as the ability to conduct electricity, a low ionization energy, and a low electronegativity (so they will give up electrons easily, i.e., they are cations). Their physical properties include a lustrous (shiny) appearance, and they are malleable and ductile. Metals have a crystal structure.

• Metals that are malleable can be beaten into thin sheets, for example: aluminum foil.
• Metals that are ductile can be drawn into wires, for example: copper wire.

In the 1900's, Paul Drüde came up with the sea of electrons theory by modeling metals as a mixture of atomic cores (atomic cores = positive nuclei + inner shell of electrons) and valence electrons.  In this model, the valence electrons are free, delocalized, mobile, and not associated with any particular atom. For example: metallic cations surrounded by a "sea" of electrons. This model assumes that the valence electrons do not interact with each other.  This model may account for:

• Malleability and Ductility: The sea of electrons surrounding the protons act like a cushion, and so when the metal is hammered on, for instance, the over all composition of the structure of the metal is not harmed or changed. The protons may be rearranged but the sea of electrons with adjust to the new formation of protons and keep the metal intact. 
• Heat capacity: This is explained by the ability of free electrons to move about the solid conducting heat
• Luster: The free electrons can absorb photons in the "sea," so metals are opaque-looking. Electrons on the surface can bounce back light at the same frequency that the light hits the surface, therefore the metal appears to be shiny. 
• Conductivity: Since the electrons are free, if electrons from an outside source were pushed into a metal wire at one end, the electrons would be pushed into the the wire and come out at the other end at the same rate (conductivity is the movement of charge).

Amazingly, Drude's electron sea model predates Rutherford's nuclear model of the atom and Lewis' octet rule. It is, however, a useful qualitative model of metallic bonding even to this day.  As it did for Lewis' octet rule, the quantum revolution of the 1930s told us about the underlying chemistry.  Drude's electron sea model assumed that valence electrons were free to move in metals, quantum mechanical calculations told us why this happened.