Chemistry 0620 · syllabus 2.4, 2.5, 2.6, 2.7
Cambridge IGCSE Chemistry 0620 — Structure and bonding topical past papers
How atoms join: ionic bonds and lattices, covalent bonds in simple molecules, the giant structures of diamond, graphite and silicon(IV) oxide, and metallic bonding.
- Questions
- 683
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 274
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What Structure and bonding covers
Atoms bond so as to reach a noble gas electronic configuration. When a metal reacts with a non-metal, the metal atoms lose electrons to become positive ions (cations) and the non-metal atoms gain them to become negative ions (anions); the ionic bond is the strong electrostatic attraction between the oppositely charged ions. Ionic compounds have high melting and boiling points and conduct electricity when molten or dissolved, when the ions can move, but not when solid. You draw dot-and-cross diagrams for Group I with Group VII at Core and for other metal–non-metal pairs on the Extended route, where you also describe the giant lattice of alternating ions and use it to explain the properties.
Between non-metal atoms, a covalent bond is a shared pair of electrons. Simple molecular substances such as H₂, Cl₂, H₂O, CH₄, NH₃ and HCl have low melting and boiling points and do not conduct. On the Extended route you add CH₃OH and molecules with double and triple bonds, O₂, CO₂, C₂H₄ and N₂, and explain the low melting and boiling points by the weak forces between molecules: these are overcome when the substance melts or boils, while the covalent bonds inside each molecule stay intact.
Some covalent substances form giant structures. In diamond each carbon atom is bonded to four others, which makes it very hard and suited to cutting tools; in graphite each carbon is bonded to three others in layers held together only weakly, so the layers slide over each other (a lubricant), and one electron from each atom is delocalised, so graphite conducts (electrodes). The Extended route adds silicon(IV) oxide, a giant structure like diamond's with similar properties, and metallic bonding: positive ions in a lattice held by a 'sea' of delocalised electrons, which explains why metals conduct and can be hammered into shape or drawn into wires.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 2.4 Ions and ionic bonds
- 2.5 Simple molecules and covalent bonds
- 2.6 Giant covalent structures
- 2.7 Metallic bonding
What you should be able to do
- Describe how atoms form positive and negative ions, and deduce an ion's charge from the element's group
- Draw dot-and-cross diagrams of ionic compounds, with the outer-shell electrons, square brackets and charges
- Draw dot-and-cross diagrams of simple molecules, including non-bonding pairs and, on the Extended route, double and triple bonds
- Explain the melting points and electrical conductivity of ionic, simple molecular and giant covalent substances from their structures
- Relate the structures of diamond and graphite to their uses, and on the Extended route compare diamond with silicon(IV) oxide
- Describe metallic bonding and use it to explain conductivity, malleability and ductility (Extended)
Key ideas
- Ionic bond: strong electrostatic attraction between oppositely charged ions, acting throughout a giant lattice
- Covalent bond: a shared pair of electrons; a double bond shares two pairs and a triple bond three
- Simple molecular substances: strong covalent bonds within molecules, weak forces between them
- Conduction needs mobile charged particles: ions in molten or aqueous ionic compounds, delocalised electrons in metals and graphite
- Diamond: each C bonded to four others; graphite: each C bonded to three others in layers; SiO₂: each Si bonded to four O and each O to two Si
How Structure and bonding has been examined
From 2022 to 2026, Structure and bonding was on Paper 4 · Theory (Extended) in 13 of 14 exam series, worth about 23% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 98 | 8% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 97 | 8% | 14 of 14 |
| Paper 3 · Theory (Core) | 36 | 15% | 11 of 14 |
| Paper 4 · Theory (Extended) | 43 | 23% | 13 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1.
Filed in Momentum under: Atoms Combining.
A worked example
Magnesium (proton number 12) reacts with nitrogen (proton number 7) to form an ionic compound. Use electronic configurations to deduce the charges on the ions and the formula of the compound, and explain why the compound conducts electricity when molten but not when solid.
- Magnesium is 2,8,2: each atom loses its two outer electrons to become Mg²⁺, with the configuration 2,8
- Nitrogen is 2,5: each atom gains three electrons to become N³⁻, also 2,8
- The charges must cancel: three Mg²⁺ give +6 and two N³⁻ give −6, so the formula is Mg₃N₂
- Check the electrons: 3 × 2 = 6 lost by magnesium atoms and 2 × 3 = 6 gained by nitrogen atoms
- In the solid the ions are held in fixed positions in the lattice; in the melt they are free to move and carry charge
Answer: Mg²⁺ and N³⁻, formula Mg₃N₂; it conducts when molten because its ions can move, but not when solid because they are fixed in the lattice
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Saying covalent bonds break when a simple molecular substance melts or boils — only the weak forces between the molecules are overcome; the molecules stay whole
- Saying solid sodium chloride does not conduct because it contains no ions — it is made of ions, but they are fixed in the lattice; they must be free to move, as in the melt or a solution
- Explaining graphite's conductivity with ions — it conducts because of delocalised electrons, one from each carbon atom, that move along the layers
- Leaving out the non-bonding pairs in a dot-and-cross diagram — nitrogen in NH₃ and oxygen in H₂O must each show eight outer electrons, lone pairs included
- Describing metallic bonding as attraction between atoms and electrons — it is between positive ions and delocalised electrons, and both terms are needed for the mark
Exam technique
- In 'explain' questions on properties, name the particles, the bond or force between them and whether it is strong or weak, then say what that means for the energy needed
- In dot-and-cross diagrams of ions, use different symbols for each atom's electrons, put square brackets round each ion and write its charge outside the bracket
- To explain conductivity, say which charged particles move and where: ions in a melt or solution, electrons in a metal or graphite
- When asked about a use of diamond or graphite, link one structural feature to the property it gives: four strong bonds per atom give hardness; weak forces between layers let them slide
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.