Question: why are metals described as having a sea of electrons

title: Delocalized electron
text: In diamond all four outer electrons of each carbon atom are ' localized ' between the atoms in covalent bonding . The movement of electrons is restricted and diamond does not conduct an electric current . In graphite , each carbon atom uses only 3 of its 4 outer energy level electrons in covalently bonding to three other carbon atoms in a plane . Each carbon atom contributes one electron to a delocalized system of electrons that is also a part of the chemical bonding . The delocalized electrons are free to move throughout the plane . For this reason , graphite conducts electricity along the planes of carbon atoms , but does not conduct in a direction at right angles to the plane .