Metallic bonding

Representing a Metallic Lattice

A metallic lattice is represented in 2-D as rows of positive ions arranged in a regular pattern, surrounded by delocalised electrons.

In this type of diagram, circles represent metal ions (each labelled with a positive charge, e.g. Na⁺ or simply "+"), and small dots or a shaded region between and around the ions represent the delocalised electrons.

The ions are drawn in an orderly, repeating arrangement — typically with offset rows, so that each ion sits in the "dip" between two ions in the row above, showing a close-packed structure.

Reading convention: each circle is a metal cation [a positive ion formed when an atom loses its outer electrons]. The dots or shading filling the spaces between the circles represent the "sea" of delocalised electrons that belongs to the whole structure, not to any single ion.

MisconceptionStudents sometimes draw metallic lattice diagrams with electrons sitting inside or attached to individual ions. The delocalised electrons must be shown spread throughout the entire structure, shared among all ions, not localised on any single atom.

Exam TipAlways shade or dot the spaces between ions to show the electrons are free to move throughout the lattice.

Metallic Bonding as Electrostatic Attraction

Metallic bonding is the strong electrostatic attraction between the positive metal ions and the delocalised electrons that surround them.

When metal atoms pack together, each atom loses its outer-shell electron(s). These electrons are no longer associated with one particular atom — they become delocalised electrons [electrons free to move throughout the whole metal structure].

The atoms that have lost electrons become positively charged ions (cations). These positive ions sit in fixed positions within the lattice.

The bonding force is the electrostatic attraction between two things with opposite charges: the positively charged metal ions and the negatively charged delocalised electrons.

This attraction acts in all directions throughout the structure, which is why metallic bonding produces a giant structure — millions of ions held together by the shared electron sea. The bond is strong because the attraction operates continuously across the entire lattice, not just between pairs of atoms.

Examiner InsightEdexcel frequently requires students to name both charges involved in the bond. Simply writing "attraction between ions and electrons" may lose a mark because it does not state the charges. The full answer must reference "positive ions" and "negative delocalised electrons" (or equivalent).

Exam TipAlways state both "positive metal ions" and "delocalised electrons" when defining metallic bonding.

Physical Properties of Metals

The structure of a metallic lattice directly explains two key physical properties: electrical conductivity and malleability.

Electrical conductivity: Metals conduct electricity because the delocalised electrons are free to move through the lattice. When a potential difference (voltage) is applied, these electrons flow in one direction, carrying charge through the metal. Because the electrons are not fixed to any one ion, they can drift from one end of the metal to the other — this movement of charged particles is an electric current.

Malleability: Metals can be hammered or bent into shape without shattering because the layers of positive ions can slide over one another. When a force is applied, one layer shifts relative to the next. Crucially, the delocalised electrons move with the ions and continue to surround them, so the electrostatic attraction is maintained in the new position. The bonding does not break — it simply reforms. This is why metals deform rather than fracture.

These two properties contrast sharply with ionic compounds, which are brittle and do not conduct electricity when solid, because ionic lattices have no delocalised electrons and their rigid ion positions cannot slide without disrupting the alternating charge pattern.

MisconceptionStudents sometimes state metals conduct because "they have free electrons" without linking this to movement of charge. Conductivity requires the electrons to move through the structure when a voltage is applied, carrying charge. State that delocalised electrons are free to move, and that this movement carries charge/constitutes current.

Exam TipAlways write "delocalised electrons are free to move through the structure, carrying charge."

Examiner InsightFor malleability, examiners expect students to explain why the structure does not break: layers of ions slide, and the delocalised electrons continue to hold the ions together in the new positions. Answers that only say "layers slide" without mentioning the ongoing attraction from delocalised electrons often lose a mark.

Exam TipInclude "metallic bonding is maintained" or "delocalised electrons still attract the ions in the new position."