UNIT 2 CHEMISTRY · PEARSON AAQ · B1.1
Metallic Bonding and Giant Metallic Structures
FREE CHEMISTRY REVISION · TOPIC 10
A giant structure held together by a shared electron system.
Describe metallic bonding precisely and interpret original lattice models without confusing ion cores, nuclei and delocalised electrons.
Pearson BTEC Level 3 AAQ Applied Science
Unit 2: Principles and Applications of Chemistry · B1.1
What you will learn
Define metallic bonding in terms of electrostatic attraction; describe a giant metallic lattice; draw and label the positive ion cores and delocalised electrons; apply the model to sodium, magnesium and aluminium; check charge balance in a representative sample.
This lesson focuses on B1.1 bonding and representation. Detailed comparisons of melting point and electrical conductivity belong to B1.4.
1. From metal atoms to a shared electron system
An isolated sodium atom has configuration [Ne] 3s¹. In a piece of sodium metal, the outer electrons are delocalised: they are not confined to one particular atom or a single pair of atoms. The remaining positive ion cores contain the nuclei and inner electrons. These cores occupy a regular arrangement in the solid.
A positive ion core is not a bare nucleus. In the simple sodium model, it contains 11 protons and 10 bound core electrons, giving charge 1+. Magnesium is modelled as 2+ cores with two delocalised electrons per atom, and aluminium as 3+ cores with three per atom. These are useful introductory models of the bonding, not claims that the metal contains separate ionic molecules.
The delocalised electrons form a shared electron system throughout the metal. Individual electrons do not belong permanently to the nearest drawn circle. The whole piece of metal is electrically neutral because total positive and negative charges balance.
2. The metallic bond
Metallic bonding is the strong electrostatic attraction between positive metal ion cores and delocalised electrons. Opposite charges attract. This attraction acts throughout the giant structure and holds it together.
The bond is not an attraction between positive cores alone: like charges repel. It is also not a set of localised electron pairs linking isolated pairs of atoms. The electron system is spread across many atoms, so metallic bonding is described as non-directional at this level.
Positive ion cores + delocalised electrons → electrostatic attraction throughout the metal.
3. What makes the structure giant?
A giant metallic structure extends through a very large number of particles in three dimensions. The regular repeating arrangement in a crystalline solid is a lattice. A small drawing shows only a representative fragment; the edges of the drawing do not mark the edges of a metal molecule.
The cores vibrate about their lattice positions in the solid. Delocalised electrons are mobile through the structure. Avoid drawing the electron symbols attached to one core as though they were a fixed outer shell.
Metals have different crystal structures. The simple rows of circles used here are schematic, so do not infer a universal coordination number or exact packing arrangement. A real structure is three-dimensional, even when a drawing shows a flat slice.
When a metal melts, long-range crystalline order is lost, but a mobile electron system and metallic attraction remain. “No lattice order” does not mean “no bonding”.
4. Read and draw metallic models accurately
Start with a regular array of positive cores. Add clear positive-charge labels and a key. Show delocalised electrons distributed across the whole fragment rather than paired along lines. Label the electrostatic attraction and state that the drawing is a two-dimensional representation of a three-dimensional structure.
A fragment need not show the exact electron count because the electrons extend beyond its drawn boundary. If a question defines a closed representative sample for counting, however, use one delocalised electron per Na, two per Mg and three per Al, and make the total charge balance. Never count every visible e⁻ in an illustrative slice as if its border were a physical container.
In the magnesium model, each Mg core has charge 2+. This does not imply two electron pairs, or one electron permanently assigned to each neighbouring core.
5. Worked examples
Example 1 · Describe sodium metal
1. Na has one outer 3s electron per atom.
2. These outer electrons become delocalised throughout the metal.
3. The positive cores form a giant regular solid structure.
4. Attraction between the positive cores and negative delocalised electrons is metallic bonding.
Example 2 · Count charges in a magnesium model
For a representative sample containing 12 Mg cores: 12 × (+2e) = +24e. The sample contains 12 × 2 = 24 delocalised electrons, total −24e. Net charge = +24e − 24e = 0. This counts a defined neutral sample, not the arbitrary boundary of a lattice picture.
Example 3 · Label an aluminium diagram
Al has three outer electrons in the simple model. Label the cores Al³⁺ and the shared negative particles delocalised electrons. Six representative cores correspond to 6 × 3 = 18 delocalised electrons in a neutral sample. Do not put three fixed electrons on each circle: that would miss delocalisation.
Example 4 · Repair an incorrect explanation
Claim: “Metallic bonding is attraction between positive metal ions.”
Correction: positive cores repel each other. The bonding attraction is between positive ion cores and delocalised negative electrons. Include both charge carriers and name the electrostatic force.
Example 5 · Is the drawing a molecule?
A diagram shows nine cores in rows surrounded by e⁻ symbols. It is a fragment of a giant lattice, not a Na₉ molecule. The arrangement continues in three dimensions beyond the drawing. The electron symbols represent a shared system and their drawn positions are not fixed.
6. Common misconceptions and exam tips
“The circles are protons.” They represent positive ion cores containing nuclei and inner electrons.
“Electrons sit permanently between particular ions.” The electrons are delocalised throughout the metal.
“The solid is positive overall.” Positive and negative charges balance.
“All metals have this square packing.” The diagram is schematic; actual crystal arrangements differ.
“A small lattice drawing is a molecule.” It is part of an extended giant structure.
In a definition, state both particles, their charges and the attraction. In a diagram, include a key and identify the extent of the lattice. Use “delocalised electrons”, not simply “free particles”, so the model is unambiguous.
Your revision summary
Metallic bonding is electrostatic attraction between positive ion cores and delocalised electrons. Crystalline solid metals have giant repeating structures. Drawings are fragments of a three-dimensional arrangement; their circles are cores and their electron symbols represent a shared mobile system. The metal is neutral overall.
Check your understanding
Choose an answer and select Check Answer. Read the explanation, then use Try Again. Keyboard: Tab between controls, arrow keys within radio groups, Enter or Space on buttons. Answers are not saved.