Metals conduct electricity because their atomic structure allows for the easy movement of charge carriers. Electrical conductivity is the ability of a material to allow electric charge to flow through it. The high conductivity in metals is a direct consequence of the unique way their atoms bond together, creating a pathway for electrons to move freely when an electrical voltage is applied. This property is why metals like copper and aluminum are used extensively in wiring and power transmission.
The Electron Sea Model
The mechanism behind a metal’s ability to conduct electricity is best described by the electron sea model. In this model, the outermost electrons, known as valence electrons, are not fixed to any single atom. Instead, they become delocalized, detaching from their parent atoms and moving throughout the entire metallic structure.
These detached valence electrons form a shared “sea” or cloud of negative charge that surrounds a lattice of positively charged metal ions. The metal ions themselves are the metal atoms that have lost their valence electrons and remain in fixed positions. This non-directional metallic bond holds the structure together, allowing the electrons to roam freely.
When a voltage is applied to a piece of metal, it creates an electric field that acts as a directional force on the electron sea. The randomly moving delocalized electrons are then compelled to drift toward the positive terminal of the voltage source. This directed movement of the shared negative charge constitutes an electric current, explaining why metals are efficient conductors. The sheer number of mobile charge carriers allows current to flow with minimal resistance.
Why Non-Metals Are Insulators
Non-metallic materials, such as plastics, wood, and ceramics, are insulators because their atomic structures do not possess a sea of mobile electrons. These materials form bonds, like covalent or ionic bonds, where the electrons are tightly held and localized.
In a covalent bond, electrons are shared between two specific atoms, fixing them in place to form a molecule. In an ionic compound, electrons are transferred to create ions that are locked into a rigid crystal lattice. In both cases, the electrons are tethered and cannot easily break free to move through the material when an electric field is present.
The energy required to liberate an electron from its fixed bond in an insulator is higher than the energy supplied by a typical voltage source. Since there are no free charge carriers available, the material cannot sustain a flow of electric current. The exception is graphite, a form of carbon, which has a layered structure that allows some electrons to become delocalized within those layers, giving it a modest degree of conductivity.
How Temperature and Purity Affect Conductivity
While the electron sea grants metals their conductive properties, the efficiency of conduction is sensitive to both temperature and purity. For pure metals, an increase in temperature leads to a decrease in electrical conductivity. This occurs because rising temperatures cause the metal ions in the fixed lattice structure to vibrate more energetically.
These increased atomic vibrations interfere with the directed flow of the delocalized electrons, causing them to scatter more frequently. This scattering increases the material’s resistance to current flow. Conversely, cooling a pure metal, such as copper, reduces this vibrational interference and increases its conductivity.
The introduction of impurities also negatively impacts conductivity through a similar scattering effect. When other elements are added to a pure metal to form an alloy, the foreign atoms distort the metal’s regular crystalline structure. These structural irregularities and differences in atomic size create obstacles that impede the electrons’ path, forcing them to scatter and reducing the efficiency of charge transfer. This is why a highly pure metal, like oxygen-free copper, conducts electricity better than a common alloy, such as stainless steel.