Compare crystalline solid structures
Classify the four specified crystalline structures and recognise the named examples in each lattice type.
AS Level; Cambridge International Chemistry 9701, 2025–2027 syllabus. Keep pressure, volume, amount and absolute temperature consistent in gas calculations. Written practice is self-checked
Before you begin
- Rearrange a formula and convert between common metric volume units.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which structure contains separate molecules in a solid lattice?
What you will learn
- Describe giant ionic, simple molecular, giant molecular and giant metallic lattices
- Classify all named Cambridge examples
A lattice is a repeating three-dimensional arrangement
A crystalline solid has particles arranged in a regular repeating lattice. The type of particle and bonding throughout the lattice determine its structure class.
A giant ionic lattice contains cations and anions: examples include sodium chloride and magnesium oxide. A giant metallic lattice contains positive metal ions and delocalised electrons: copper is the named example.
Distinguish molecular and giant covalent structures
A simple molecular lattice consists of separate molecules held together by intermolecular forces. The named examples are iodine, buckminsterfullerene C₆₀ and ice.
A giant molecular (giant covalent) lattice has a continuous network of covalent bonds. The syllabus examples are silicon(IV) oxide, graphite and diamond. Graphite and diamond are both giant covalent structures even though their properties differ.
Pause and explain
How is graphite classified in the syllabus?
Worked example
Classify iodine, graphite and copper by crystalline structure.
Show the worked solution
- Iodine consists of separate I₂ molecules in its solid lattice.
- Graphite has a continuous covalent network.
- Copper has a metallic lattice of positive ions and delocalised electrons.
Answer Iodine is simple molecular, graphite is giant molecular (giant covalent), and copper is giant metallic.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify NaCl, MgO and copper by lattice structure and name the particles in each.
Give me a hint
Identify whether each solid contains ions or metal ions with delocalised electrons.
Compare my reasoning
- NaCl and MgO contain oppositely charged ions in giant lattices.
- Copper contains positive metal ions and delocalised electrons.
- Assign the giant ionic or giant metallic structure.
NaCl and MgO are giant ionic; copper is giant metallic with positive ions and delocalised electrons.
Look for these in your work
- All three classified
- Ionic particles identified
- Metallic particles identified
Classify iodine, C₆₀, ice, SiO₂, diamond and graphite.
Give me a hint
Separate lattices of molecules from continuous covalent networks.
Compare my reasoning
- Iodine, C₆₀ and ice consist of discrete molecules: simple molecular.
- SiO₂, diamond and graphite have giant covalent networks.
- Do not classify by whether any covalent bond exists inside a particle.
Iodine, C₆₀ and ice are simple molecular; SiO₂, diamond and graphite are giant molecular (giant covalent).
Look for these in your work
- All six examples placed
- Molecular/giant distinction stated
- Covalent bonds within molecules not confused with lattice type
A diagram shows a repeating array of positive ions with delocalised electrons between them. Identify the structure and explain the evidence.
Give me a hint
Look for the lattice particles and mobile electron system.
Compare my reasoning
- Positive metal ions repeat in a lattice.
- Electrons are delocalised through it.
- This combination defines giant metallic structure.
It is a giant metallic lattice because positive metal ions are arranged regularly and delocalised electrons extend through the structure.
Look for these in your work
- Structure identified
- Ions identified
- Delocalised electrons linked to classification
Common mistakes
- Calling graphite a simple molecular solid
- Calling iodine giant covalent because molecules contain covalent bonds
- Forgetting that copper is a lattice, not a collection of metal molecules
- Treating all giant structures as the same type
What can you explain now?
Which structure contains separate molecules in a solid lattice?
Compare with the explanation
Simple molecular
Intermolecular forces hold distinct molecules together.
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Make it stick
What particles make up each named lattice: ionic, molecular, giant covalent or metallic?
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