AQA GCSE Chemistry Chemistry Paper 1 (Foundation), November 2020: Question 8
8 marks · Standard Demand difficulty · Extended Answer
Identify substances with intermolecular forces and compare the structure and bonding of carbon dioxide, magnesium oxide, and silicon dioxide.
Practise this questionQuestion
Question text
08 This question is about structure and bonding.
08.1 Which two substances have intermolecular forces between particles?
[2 marks]
Tick ( ) two boxes.
Diamond
Magnesium
Poly(ethene)
Sodium chloride
Water
08.2 Table 5 shows the structures of three compounds.
Table 5 Diagrams not to scale
Compound Structure
Carbon dioxide
Magnesium oxide
Silicon dioxide
Compare the structure and bonding of the three compounds:
• carbon dioxide
*30* • magnesium oxide
• silicon dioxide.
[6 marks]
Mark scheme
Show the mark scheme
Question 8
AO /
Question Answers Extra information Mark
Spec. Ref.
08.1 poly(ethene) 1 AO2
4.2.1.4
water 1 4.2.2.4
4.2.2.5
Question 8 continued
AO/
Question Answers Mark
Spec. Ref
08.2 Level 2: Scientifically relevant features are identified; the way(s) in 4–6 AO1
which they are similar/different is made clear and (where 4.2.1.2
appropriate) the magnitude of the similarity/difference is noted. 4.2.1.3
4.2.1.4
Level 1: Relevant features are identified and differences noted. 1–3
No relevant content 0
Indicative content
• (both) carbon dioxide and silicon dioxide are made up of atoms
• (but) magnesium oxide is made up of ions
• (both) silicon dioxide and magnesium oxide are giant structures
• (but) carbon dioxide is small molecules
• with weak intermolecular forces
• all three compounds have strong bonds
• (both) carbon dioxide and silicon dioxide are formed from two
non-metals
• (so) bonds formed are covalent
• (so) electron (pairs) are shared (between atoms)
• (but) magnesium oxide is formed from a metal and a non-metal
• (so) bonds in magnesium oxide are ionic
• (so) electrons are transferred
• from magnesium to oxygen
• two electrons are transferred
• bonds in silicon dioxide are single bonds
• (where) each silicon forms four bonds
• (and) each oxygen forms two bonds
19 • (but) in carbon dioxide the bonds are double bonds
• (where) carbon forms two double bonds
• (and) oxygen forms one double bond
ignore properties e.g. melting point, electrical conductivity
Total 8
How to answer it
Structure & Bonding: Comparing Molecular and Giant Substances
Core Revision Focus:
- Substances with Intermolecular Forces: Distinguishing between small molecules/polymers (which have intermolecular forces) and giant ionic, giant metallic, or giant covalent structures (which do not).
- Comparing Structure & Bonding: Describing and contrasting giant covalent lattices (SiO₂), small molecules (CO₂), and giant ionic lattices (MgO).
- Exam Command Discipline: Following explicit instructions to discuss only structure and bonding, avoiding unrelated topics like melting points or electrical conductivity.
Identifying Substances with Intermolecular Forces
Tick (✓) two boxes: Diamond, Magnesium, Poly(ethene), Sodium chloride, Water
✅ Correct Selections
- Poly(ethene) [1 mark]
- Water [1 mark]
💡 Key Knowledge
Intermolecular forces exist between separate molecules:
- Water (H₂O): A small, simple covalent molecule held to neighbouring molecules by intermolecular forces.
- Poly(ethene): Made of long polymer chains held together side-by-side by intermolecular forces.
❌ Common Errors & Misconceptions
- Ticking Diamond: Diamond is a giant covalent structure. It consists entirely of strong covalent bonds between carbon atoms throughout the lattice—there are no separate molecules, so there are no intermolecular forces.
- Ticking Sodium chloride or Magnesium: Sodium chloride is a giant ionic lattice (ionic bonds); Magnesium is a giant metallic lattice (metallic bonds). Neither contains molecules.
- Overlooking Poly(ethene): Students often forget that polymers are large covalent molecules that rely on intermolecular forces between the polymer chains to hold them in a solid state.
🧠 Exam Technique
- The prefix inter- means between. Ask yourself: "Does this substance consist of discrete individual molecules?"
- If it forms a giant lattice (ionic, giant covalent, metallic), it does not have intermolecular forces.
Comparing Structure and Bonding in CO₂, MgO, and SiO₂
Compare the structure and bonding of carbon dioxide, magnesium oxide, and silicon dioxide.
❌ Critical Trap: Mark Scheme Negative Instruction
"Ignore properties e.g. melting point, electrical conductivity."
Many students waste time explaining why MgO or SiO₂ have high melting points or whether they conduct electricity. The question exclusively asks for structure and bonding. Any mention of physical properties scores 0 marks.
💡 Summary Comparison Matrix
| Feature | Carbon Dioxide (CO₂) | Magnesium Oxide (MgO) | Silicon Dioxide (SiO₂) |
|---|---|---|---|
| Type of Structure | Simple molecular (small molecules) | Giant ionic lattice | Giant covalent lattice |
| Particles Present | Atoms (forming small molecules) | Ions (Mg²⁺ and O²⁻) | Atoms |
| Type of Bonding | Covalent (shared electron pairs) | Ionic (electrostatic attraction between oppositely charged ions) | Covalent (shared electron pairs) |
| Electron Interaction | Electrons are shared between non-metal atoms | 2 electrons transferred from Mg to O atom | Electrons are shared between non-metal atoms |
| Bond Specifics | Double bonds (O=C=O); each C has 2 double bonds; each O has 1 double bond; weak intermolecular forces between molecules | Strong ionic bonds throughout lattice between Mg²⁺ and O²⁻ ions | Single covalent bonds; each Si atom forms 4 bonds; each O atom forms 2 bonds |
✅ Model 6-Mark Answer Structure
1. Compare Types of Bonding & Electrons:
- Both CO₂ and SiO₂ contain covalent bonds because they are formed between non-metal atoms that share pairs of electrons.
- In contrast, MgO contains ionic bonding formed between a metal and a non-metal, where two electrons are transferred from magnesium to oxygen to form Mg²⁺ and O²⁻ ions.
2. Compare Structures:
- Both MgO and SiO₂ have giant structures (MgO is a giant ionic lattice; SiO₂ is a giant covalent lattice).
- In contrast, CO₂ consists of small/simple molecules held together by weak intermolecular forces.
3. Specific Bond Details (For Top Marks):
- All three compounds contain strong chemical bonds internally.
- In SiO₂, bonds are single covalent (each Si forms 4 bonds, each O forms 2 bonds).
- In CO₂, there are double covalent bonds (each C forms two double bonds, each O forms one double bond).
🧠 How Examiners Grade This (Level 2: 4–6 Marks)
- Level 2 (4–6 marks): Scientifically relevant features are identified; similarities and differences are made clear, with clear comparative link words ("both", "whereas", "in contrast").
- Level 1 (1–3 marks): Isolated facts listed about one or two substances without clear, systematic comparison.
• "Giant lattice" vs "Simple molecule"
• "Shared electrons" vs "Transferred electrons"
• "Atoms" vs "Ions (Mg²⁺ and O²⁻)"
• "Weak intermolecular forces" (for CO₂)
Topics
Chemistry · C2: Bonding, Structure and the Properties of Matter
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.