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How do metallic bonds allow metals to conduct electricity?

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A rough, translucent yellow crystal of elemental sulfur displayed against a solid black background. — crystal A crystal form of elemental sulfur. Sulfur has an atomic weight of about 32.06 atomic mass units (amu), which means that its molar mass is 32.06 grams.

In a metallic crystal, atoms are held together by metallic bonds, which are characterized by the presence of nonlocalized valence electrons. Unlike in covalently bonded substances, these electrons are not tied to specific atoms; instead, they form a "sea" of mobile charge carriers that can wander freely throughout the entire structure.12

Metals conduct electricity because these valence electrons are highly mobile and occupy a partially filled energy band. When an electrical field is applied, these electrons are free to accelerate and move toward the positive pole, creating a net electric current. Because the energy levels within the conduction band are extremely close together, only an infinitesimal amount of energy is required to promote electrons into unoccupied levels where they can travel readily through the material.213

While electrons may scatter from crystal defects or vibrations caused by high temperatures, the fundamental ability of metals to conduct electricity is a direct result of this free-electron character.14