A metallic bond: ions and electrons
Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a "sea" of delocalised electrons. Two elements are needed: attraction, between positive ions AND delocalised electrons. When metal atoms pack together each loses its outer-shell electrons, which become delocalised and free to move through the structure, leaving a lattice of positive ions. This strong attraction is why most metals have high melting points.
Metals conduct: electrons free to move
Metals conduct electricity (and heat) in BOTH the solid and molten state because they have delocalised electrons that are free to move through the structure. When a voltage is applied, these electrons drift and carry the charge — this flow is the current. The mark scheme needs two ideas: electrons are delocalised, and free to move / flow. "Free electrons" alone is not enough. The positive ions stay fixed, so the metal is not chemically changed as it conducts.
Malleable: layers of ions slide
Metals are malleable and ductile because the positive ions sit in layers that can slide over one another under force. As the layers slide, the delocalised electrons move with them, so the metallic bonding is maintained and the metal changes shape instead of shattering. The mark scheme wants layers of (positive) IONS sliding, not electrons sliding. Contrast brittle ionic solids, where a shifted layer brings like charges together, which repel and split it.
Drawn from real examiner reports.
Label positive ions, not nuclei
In the 2-D metallic-lattice diagram the large circles are positive metal ions and the small dots between them are the delocalised electrons. Candidates often mislabel the circles as "nuclei", "protons", "atoms" or just the metal name; only "positive ions" scores for the circles, and "(delocalised) electrons" for the dots. The ions are drawn large, the electrons small.
June 2024 Paper 2CR Q3(a)(i): common errors were confusing nuclei, positive/negative ions and protons; some candidates could not tell the smaller dots were (delocalised) electrons — "proton", "nuclei" and just "magnesium" were frequent.
"Free electrons" alone is not enough
The conductivity answer needs BOTH parts: the electrons must be delocalised, AND free to move (or flow) to carry the charge. Writing only "free electrons", or "electrons carry a current" without saying they move, does not score full marks. The mark-scheme form is: "delocalised electrons that are free to move through the structure, carrying the charge".
June 2024 Paper 1CR Q11(c)(i): candidates lost marks for not mentioning delocalised electrons or just saying electrons were "free" — the electrons had to be free to MOVE or FLOW to gain the second marking point.
Ions slide, not electrons
Malleability is explained by layers of positive IONS sliding over one another, not by electrons sliding. The delocalised electrons move with the layers, but it is the ions that slide — "electrons slide" loses the mark. Name the layers of ions as the movers for malleability; the electrons are the movers for conductivity, a different property.
June 2024 Paper 2CR Q3(a)(ii): candidates commonly wrote about electrons sliding instead of layers of ions sliding.
A metal is a lattice, not a molecule
A metal is a giant metallic lattice, not a molecule, and it has no intermolecular forces — the bonding is strong electrostatic attraction between positive ions and delocalised electrons. Calling a metal such as magnesium a "molecule", or blaming "weak intermolecular forces", both lose marks. Reserve "intermolecular forces" for simple molecular substances.
June 2024 Paper 2CR Q3(a)(ii): some candidates wrongly called magnesium a "molecule" and incorrectly invoked weak intermolecular forces in their explanations.
Metal conduction ≠ ionic conduction
Do not confuse metallic with ionic conduction. In a metal the electrons move while the positive ions stay fixed, so the metal is unchanged. In a molten or aqueous ionic compound the ions move to carry the charge, and the compound is decomposed (electrolysis). Naming the wrong carrier — electrons for an ionic melt, or moving ions for a metal — loses the mark.
(common Edexcel chemistry error)
High mp: the electrons are attracted too
When explaining a metal's high melting point, name the full attraction: the strong electrostatic attraction between the positive ions and the delocalised electrons, which needs a large amount of energy to overcome. "Strong metallic bonds" or "strong forces between the ions" alone is vague — the delocalised electrons are part of what is attracted, so mention them.
(common Edexcel chemistry error)
Structure to property chain
These questions follow a structure-to-property chain: state the structure (positive ions with delocalised electrons), the feature for that property (electrons free to move, or layers of ions that slide), then the consequence (carries charge, or changes shape).
Name the moving particle precisely
Name the moving particle precisely — it differs by property: conductivity moves delocalised electrons; malleability moves layers of positive ions. Swapping them ("electrons slide" for malleability, or "ions move" for a conducting metal) loses the mark.
Use exact labels on the diagram
On a "draw and label the metallic lattice" question, use the exact labels: positive ions for the large circles and delocalised electrons for the small dots, with the ions drawn larger. Do not label the circles "atoms", "nuclei" or "protons".
Metallic bond — the electrostatic attraction between a lattice of positive metal ions and a "sea" of delocalised electrons. (Two-element definition: attraction + between positive ions AND delocalised electrons.)
Delocalised electrons — outer-shell electrons that are no longer held by any one atom; they are free to move throughout the whole metal structure.
Malleable — able to be hammered or bent into shape without shattering.
Ductile — able to be drawn out into a wire.
When metal atoms pack together in a giant lattice, each atom releases its outer-shell electrons. These electrons become delocalised, leaving behind a regular arrangement of positive ions (cations). The lattice is held together by the attraction between the positive ions and the negative sea of electrons. The bonding is strong and acts in all directions, so the structure is a giant metallic lattice — never a molecule.
Define a metallic bond.
In a metallic lattice, each magnesium atom releases its outer electrons to form a ion. When magnesium burns it reacts with oxygen, which forms ions.
Deduce the formula of the ionic compound magnesium oxide.
