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From Models to Materials · Paper 2 — Free Chemistry SL Practice Questions

What this topic covers

Every property question IB throws at you — why does this melt higher, why does that conduct here but not there — traces back to one of three bonding models: ionic, covalent, or metallic. This topic asks you to build each model from its electrostatic basics, then use it to predict and explain real behaviour: melting point, conductivity in different states, shape, solubility, malleability. The exam almost never tests the model in isolation — it tests whether you can name the right structural detail (coordination number, electron domain count, number of delocalized electrons) and explain why that detail produces the observed property. Vocabulary without mechanism gets you nowhere on the mark scheme.

Read the full Structure: Models of Bonding and Structure lesson notes →

1ChallengeSAQ-LSolids, liquids, and gases: Structural differences10 marksPaper 2~15 min

A student investigates the properties of three different solid substances at room temperature (

298\,\text{K}

) and standard pressure. - Substance X: Diamond — a giant covalent network solid - Substance Y: Solid iodine (

\text{I}_2

) — a simple molecular solid - Substance Z: Sodium chloride (NaCl) — an ionic lattice The student measures the electrical conductivity of each substance in the solid state and again after melting. Results are shown below. Substance — Conductivity (solid) — Conductivity (liquid) Diamond — Does not conduct Iodine — Does not conduct Sodium chloride — Does not conduct — Conducts

(a)

State the type of particle (atoms, ions, or molecules) present in each substance in the liquid state. [3 marks]

(b)

Explain how the bonding and structure of each substance accounts for its electrical conductivity, or lack thereof, in the liquid state. [3 marks]

(c)

Evaluate the following statement, using all three substances as evidence: "The boiling point of a substance is always higher than its melting point because intermolecular forces are stronger in the liquid state than in the solid state." [4 marks]

Solutions

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