A guide to answering Chemical Bond extended questions in SPM Paper 2, what the command words define, describe, explain and compare each demand, how to plan under time pressure, and bullet skeletons for the diagram-plus-property answers this chapter is built around.
Chemical Bond is a strong source of extended questions because it combines a diagram (dot-and-cross) with reasoning (explaining a property). Paper 2 has Section A (structured), Section B (limited-response) and Section C (open-response), and this chapter usually appears in the longer parts as a limited-response or open-response item worth several marks. This guide shows how to read the command word, plan quickly, and build the answer as a skeleton, not a memorised essay, which rarely fits the exact question asked.
How the chapter appears in Paper 2
Extended Chemical Bond questions tend to take one of these shapes:
- Describe how a compound forms, with a dot-and-cross diagram and the electron arrangements, for example sodium chloride, magnesium oxide or water.
- Explain a property from bonding, why an ionic compound has a high melting point, conducts only when molten, or dissolves in water.
- Compare an ionic compound with a simple covalent compound across melting point, conductivity and solubility.
- Explain an unusual observation, for example the high boiling point of water, using hydrogen bonding.
The best answers do two things every time: they show a correct, labelled diagram, and they name the exact structure and force in the explanation.
Command words and what each demands
The command word tells you how much to write and in what form. Read it first.
- State / Give. A short, exact answer with no explanation. “State the type of bond” → “Ionic bond.”
- Define. A precise meaning. “Define a covalent bond” → “A bond formed when two atoms share one or more pairs of electrons.”
- Describe. Say what happens, step by step, with no need to justify. Used for how a compound forms.
- Explain. Give reasons, the “because” is essential. Used for properties: the marks are in the reason, not the observation.
- Compare. Bring out similarities and differences, addressing both things for each point. Use words like “whereas” and “but”.
Exam habit. Underline the command word before you start. Many marks are lost by describing when the question said explain, so the reasons never appear.
A planning approach
Before writing, spend a moment to plan so nothing is missed:
- Identify the standard. Is this ionic (5.2), covalent (5.3), dative/hydrogen (5.4) or properties (5.5)? That tells you the key words.
- List the marking points in the margin. For a “describe formation” answer: electron arrangements, transfer or sharing, ions formed, the bond named. For an “explain property” answer: structure, force, energy to overcome, therefore the property.
- Decide if a diagram is needed. If the question mentions a dot-and-cross diagram or asks “how does the bond form”, draw one, with dots, crosses, brackets, charges and lone pairs.
- Write to the marking points, in order. Keep sentences short and precise.
Model-answer skeleton 1, Formation and property
“Describe how magnesium oxide forms, and explain why it has a high melting point.” (Magnesium is 2.8.2, oxygen is 2.6.)
- Magnesium atom transfers its two outer electrons to an oxygen atom.
- Magnesium becomes Mg²⁺ (2.8); oxygen becomes O²⁻ (2.8), both have a stable noble-gas arrangement.
- The oppositely charged ions are held by strong electrostatic forces of attraction, the ionic bond, forming a giant ionic lattice.
- (Diagram: dot-and-cross with brackets and charges.)
- High melting point because a large amount of energy is needed to overcome the strong electrostatic forces between the many oppositely charged ions throughout the lattice.
Notice how each bullet is a marking point. You do not need flowing prose, you need the right points in order.
Model-answer skeleton 2, Comparing ionic and covalent
“Compare the properties of sodium chloride and naphthalene, and relate the differences to their bonding.”
- Structure: sodium chloride is a giant ionic lattice; naphthalene is a simple molecular solid.
- Melting point: sodium chloride high (strong electrostatic forces need much energy to overcome) whereas naphthalene low (only weak forces between molecules).
- Conductivity: sodium chloride conducts when molten or aqueous (ions free to move) whereas naphthalene never conducts (no free ions or electrons).
- Solubility: sodium chloride dissolves in water whereas naphthalene dissolves in an organic solvent.
- Link: every difference follows from strong forces throughout an ionic lattice versus weak forces between covalent molecules.
Model-answer skeleton 3, An unusual observation
“Explain why water has a much higher boiling point than expected for so small a molecule.”
- In water, hydrogen is bonded to the highly electronegative oxygen atom.
- Each molecule can form hydrogen bonds with neighbouring water molecules.
- These extra attractions between molecules must be overcome before the water boils.
- Therefore more energy, and a higher temperature, is needed than the small molecular size alone would suggest.
Model-answer skeleton 4, Conductivity in different states
“Explain why solid magnesium chloride does not conduct electricity, but molten magnesium chloride does.”
- Magnesium chloride is an ionic compound made of Mg²⁺ and Cl⁻ ions.
- As a solid, the ions are held in fixed positions in the lattice and cannot move.
- There are therefore no mobile charge carriers, so the solid does not conduct.
- When molten, the lattice breaks down and the ions become free to move.
- The moving ions carry charge through the liquid, so molten magnesium chloride conducts.
The same two-part shape, “fixed, so cannot conduct” versus “free to move, so conducts”, answers every conductivity question in this chapter.
Key phrases that score
Examiners look for exact wording. Rehearse these phrases so they come out automatically:
- “strong electrostatic forces of attraction between oppositely charged ions”
- “a large amount of energy is needed to overcome the forces”
- “giant ionic lattice” versus “simple molecular structure”
- “the ions are free to move and carry charge”
- “only weak forces between molecules are overcome”
- “hydrogen is bonded to a highly electronegative atom (F, O or N)”
Dropping any one of these can cost a mark even when the idea is right, so treat them as fixed expressions rather than something to paraphrase.
Turning a skeleton into full marks
Write your skeleton first, then expand each bullet into one clear sentence. Keep the diagram neat and fully labelled, because a diagram mark is often the easiest in the whole question. Always finish an “explain” answer with the word “therefore” or “so” leading to the property, that is the examiner’s cue that your reasoning is complete. A one-to-one teacher can mark a few of your extended answers against these skeletons and show you which marking point you tend to miss, which is usually the named force or the “energy to overcome” step in the SPM Chemistry papers.
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