Three metallic structures of  Period 3 Elements

Sodium, magnesium and aluminum all have metallic structures. In sodium, only one electron per atom is involved in the metallic bond, the single 3s electron. In magnesium, both of its outer electrons are involved, and in aluminum all three are involved. One key difference to be aware of is the way the atoms are packed in the metal crystal. Sodium is 8-coordinated with each sodium atom interacting with only 8 other atoms. Magnesium and aluminum are each 12-coordinated, and therefore packed more efficiently, creating less empty space in the metal structures and stronger bonding in the metal.