2.3 The metallic model

Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and delocalized electrons.

Delocalized electrons can move through the structure and carry charge and thermal energy. Non-directional attraction allows layers of cations to slide while the bonding remains.

When a potential difference is applied, delocalized electrons drift through the fixed cation lattice and carry charge; the positive ions do not travel through the metal. When layers shift under force, non-directional attraction to the electron sea persists, explaining malleability rather than brittle fracture.

Property-to-use link: copper is used for electrical wiring because its delocalized electrons carry charge through the solid; aluminium can be rolled into foil because ion layers can shift while non-directional metallic attraction is maintained. A use must be justified by the relevant property, not merely by stating that the substance is a metal.

Metallic-bond strength depends on the attraction between metal ions and delocalized electrons. Ion charge, ion radius, and the number of delocalized electrons affect charge density and attraction.

A larger ion radius generally lowers attraction; greater charge or more delocalized electrons can strengthen metallic bonding. Use the stated comparison rather than a memorized trend alone.

Compare Na and Mg using the model: Mg supplies more delocalized electrons and forms smaller, more highly charged ions, giving stronger attraction and a higher melting point. State all relevant factors before predicting; across broader sets, lattice structure can prevent a perfectly smooth trend.

Transition elements have delocalized d electrons as well as s electrons in their metallic structure. These mobile electrons are attracted to a lattice of positive metal ions.

More delocalized electrons can strengthen the electrostatic attraction, so substantial energy is often needed to disrupt the lattice, helping to explain high melting points. The same mobile electrons carry charge through the solid, explaining electrical conductivity.

Use this as a causal model, not a universal ranking: electron contribution, ion radius and crystal structure vary across the transition series, so melting points need not form a perfectly smooth trend. The chemical reactions of transition elements belong to Reactivity 3.4, not this card.