Metallic bonding — the three-part definition
Metallic bonding is the electrostatic attraction between the positive ions in a giant metallic lattice and a "sea" of delocalised electrons. All three elements are needed for full credit: (1) electrostatic attraction, (2) positive ions in a giant metallic lattice, (3) a sea of delocalised electrons. Each metal atom loses its outer-shell electron(s) into a shared pool, leaving it as a positive ion; those electrons belong to no single ion.
Electrical conductivity — free electrons carry the charge
Delocalised electrons are fixed to no particular ion, so they move throughout the whole giant metallic lattice. Apply a potential difference and they drift through the structure, carrying electric charge — so the metal conducts. Because it is the electrons that move and not the positive ions, a metal conducts in the solid state, unlike an ionic compound, which must be molten or aqueous before its ions can move.
Malleability — layers slide, the bond survives
Malleable means able to be hammered or pressed into shape without breaking. Under force, layers of positive ions slide over one another; the sea of delocalised electrons is fixed to no particular ion, so it rearranges and continues to surround them in their new positions and the electrostatic attraction is maintained rather than broken. The metallic bond is non-directional — it needs only positive ions bathed in delocalised electrons.
Drawn from real examiner reports.
Cambridge Ar(Cu) is 64, not 63.5
Mole work on metals must use the value on the Cambridge 0654 Periodic Table data sheet: copper is 64, not the 63.5 printed by other boards. Aluminium is 27, not 13 (that is its proton number), and copper is not 29. Then divide, do not multiply: n = m / Mr, so 6.4 g of copper is 0.10 mol.
Metallic bonding ≠ ionic bonding
Both are "an electrostatic attraction", so candidates describe an attraction between oppositely charged ions — that is ionic bonding. Metallic bonding involves only ONE type of charged particle: positive ions, plus the mobile delocalised electrons. Others give the attraction but omit the giant metallic lattice. Dropping any one of the three elements loses the mark.
Flagged Jun 2022 P41 Q8d — many gave ionic bonding or omitted the lattice
Dropping the word "delocalised"
"The electrons can move" or "there are free electrons" is not precise enough. The mark scheme wants the term delocalised electrons, the idea that they are free to move throughout the whole lattice (not vaguely "around" or "between atoms"), and the statement that this movement carries electric charge. Omitting "delocalised" is the commonest way marks go on this leaf.
Flagged in the C2.6 giant-covalent entry, where the same delocalised-electrons-free-to-move wording is required and the conduction question must be answered directly (Jun 2022 P43 Q11ei; Nov 2022 P43 Q11a; Nov 2023 P41 Q8d)
Restating the property is not explaining
Both objectives say "explain, in terms of structure and bonding". "Metals conduct because they are good conductors" or "metals are malleable because they can be bent" repeats the question instead of answering it. An explain answer must start from the structure — the giant lattice of positive ions and delocalised electrons — and give the mechanism that produces the property.
Metals conduct solid; ionic needs molten
A metal conducts as a solid because its delocalised electrons are already mobile — the positive ions stay put. A solid ionic compound does not conduct: its ions are locked in the lattice with no free electrons at all, so it conducts only when molten or dissolved in water, once the ions themselves can move. Do not offer "the ions move" as the reason a metal conducts.
Metals bend, ionic lattices shatter
Sliding a layer in a metal leaves the ions still bathed in the non-directional electron sea, so the bond is maintained and the metal deforms. Sliding a layer in a giant ionic lattice brings ions of the same charge next to each other; they repel and the lattice shatters. That is why ionic solids are brittle, not malleable — the same "layers slide" phrase gives opposite outcomes.
Delocalised ≠ a shared pair of electrons
A delocalised electron is free to move through the whole structure and belongs to no particular pair of particles. A covalent bond is a shared pair localised between two specific atoms. Describing metallic bonding as atoms "sharing electrons" imports covalent language and scores nothing — and it is why graphite, which has both, is a separate case (C2.6).
Build a structure-mechanism-property chain
Name the structural feature (delocalised electrons, or sliding layers of non-directionally bonded ions), state what it physically does, then link it with "so" or "because" to the property named in the question. Stopping after step one does not earn the explain mark.
Match describe against explain
"Describe metallic bonding" wants the three-part definition and nothing more. "Explain, in terms of structure and bonding" wants the causal mechanism. Answering the wrong one produces a scientifically true but off-question answer, which the examiners flag every sitting.
Answer the property actually asked
Conductivity and malleability have different mechanisms. Conduction: delocalised electrons drift and carry charge. Malleability: layers of ions slide while the electron sea rearranges. Listing everything you know about metallic structure does not target the mark.
Lattice diagram: charges, and no bond lines
Draw a regular repeating grid of ions, each marked with a positive charge (M+), and dots for the delocalised sea in the gaps. No lines joining pairs of ions (reads covalent); no electrons paired beside one ion (reads ionic). Label "positive ions" and "delocalised electrons".
Cambridge 0654 spec reference: Section C2 "Atoms, elements and compounds", sub-topic C2.7 "Metallic bonding". This entire leaf is Extended (Supplement) content: (1) describe metallic bonding as the electrostatic attraction between the positive ions in a giant metallic lattice and a "sea" of delocalised electrons; (2) explain, in terms of structure and bonding, the properties of metals -- good electrical conductivity and malleability. There is no Core-tier statement for C2.7.
| Term | Mark-scheme-precise meaning |
|---|---|
| Metallic bonding | The electrostatic attraction between the positive ions in a giant metallic lattice and a "sea" of delocalised electrons |
| Delocalised electron | An electron that is not fixed to any one particular ion and is free to move throughout the whole metallic structure |
| Giant metallic lattice | A large, regular, repeating three-dimensional arrangement of positive metal ions |
| Malleable | Able to be hammered or pressed into shape (e.g. rolled into a sheet) without breaking/shattering |
Where the delocalised electrons come from: each metal atom in the lattice loses its outer-shell electron(s) into the shared pool. This leaves the atom as a positive ion, and the lost electron(s) become part of the delocalised sea of electrons that surrounds the whole lattice, not attached to any single ion.
Property 1 -- good electrical conductivity:
Property 2 -- malleability:
A note on moles and metals (Extended stoichiometry link): worked examples below use the fact that the relative atomic mass () of a metallic element also serves as its relative formula mass () for an amount of the pure element, letting you calculate the number of moles of metal atoms in a given mass using , where = amount (mol), = mass (g), = relative formula mass. (This mole calculation is Extended/Supplement content -- the Core tier does not use the mole concept.)
Define metallic bonding.
Electrical wiring is made from the metal copper, because the delocalised electrons in its metallic lattice let it conduct electricity well.
Calculate the relative formula mass () of copper. (1 mark)
