In metallic bonding, valence electrons are not confined to one particular pair of atoms. They occupy states that extend through many atoms, while the positively charged ion cores form the underlying solid structure.

This delocalization gives metals a distinctive combination of properties.

Electrical and thermal conduction

Because some electronic states can change their motion in response to an electric field, metals can carry electrical current. Mobile electrons also transport thermal energy efficiently, so good electrical conductors are often good thermal conductors.

Nondirectional cohesion

Unlike a strongly directional covalent bond, metallic cohesion does not require one fixed bond angle between a particular pair of neighbors. Atomic planes can therefore often shift while cohesion is retained. This helps explain why many metals can deform plastically rather than fracturing as soon as atoms move from their original positions.

Bonding strength still matters

Metallic bonding is not equally strong in every metal. Electronic structure, atomic spacing and crystal structure affect cohesive energy, elastic stiffness and melting temperature. Metallic bonding therefore explains broad trends, not every property of every alloy.

A useful conceptual picture is thus positive ion cores held together by a shared, delocalized electronic system. The later theories of energy bands and electron transport make this picture more precise.