4.2 AS Level

Bonding and structure

Cambridge A-Level Chemistry (9701)  · Unit 4: States of matter  · 10 flashcards

Bonding and structure is topic 4.2 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 4 — States of matter .

Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).

The deck below contains 10 flashcards — 4 definitions and 6 key concepts — covering the precise wording mark schemes reward.  Use the 4 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.

Some cards in this deck are on other syllabus topics: 5.1 Enthalpy change, ΔH, 5.2 Hess’s law, 6.1 Redox processes: electron transfer and changes in oxidation number (oxidation state) and 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium. Each card is labelled with its topic.

What the Cambridge 9701 syllabus says

2025-2027 syllabus, in our words · AS Level

What the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).

  1. Describe simply the lattice structure of crystalline solids of these types, with the required examples: (a) giant ionic: sodium chloride and magnesium oxide; (b) simple molecular: iodine, ice and buckminsterfullerene C₆₀; (c) giant molecular: diamond, graphite and silicon(IV) oxide; (d) giant metallic: copper.
  2. Describe, interpret and predict how the type of structure and bonding in a substance affects its physical properties, including solubility, electrical conductivity, and melting and boiling points.
  3. Use given information to deduce the bonding and structure type present in a substance.

Also in this deck: 5.1 Enthalpy change, ΔH

  1. Understand that enthalpy changes accompany chemical reactions, and that a change may be exothermic (ΔH negative) or endothermic (ΔH positive).
  2. Construct a reaction pathway diagram and interpret it, showing the activation energy and the enthalpy change of reaction.
  3. Define and use: (a) standard conditions, shown by the symbol ⦵ and taken in this syllabus to be 101 kPa and 298 K; (b) enthalpy change, in particular of combustion (ΔHc), formation (ΔHf), neutralisation (ΔHneut) and reaction (ΔHr).
  4. Understand that energy is transferred in chemical reactions because bonds are broken and new bonds are formed.
  5. Use bond energy values (given as positive ΔH, for bond breaking) to calculate ΔHr, the enthalpy change of a reaction.
  6. Understand that certain bond energies are exact values while others are average values.
  7. Calculate enthalpy changes from suitable experimental results, including use of ΔH = −mcΔT/n and q = mcΔT.

Also in this deck: 5.2 Hess’s law

  1. Apply Hess's law to build simple energy cycles.
  2. Perform calculations based on energy cycles and the relevant energy terms, including (a) working out enthalpy changes impossible to measure directly by experiment and (b) using bond energy data.

Also in this deck: 6.1 Redox processes: electron transfer and changes in oxidation number (oxidation state)

  1. Calculate the oxidation number of an element in a compound or an ion.
  2. Use oxidation number changes as an aid to balancing chemical equations.
  3. Explain the terms oxidation, reduction, redox and disproportionation by reference to electron transfer and oxidation number changes, and use them.
  4. Explain what reducing agents and oxidising agents are, and use these terms.
  5. Use Roman numerals to show the magnitude of an element's oxidation number.

Also in this deck: 7.1 Chemical equilibria: reversible reactions, dynamic equilibrium

  1. (a) Understand what a reversible reaction is. (b) Understand dynamic equilibrium as the state in which the forward and reverse reactions go at equal rates and the concentrations of reactants and products stay constant. (c) Understand why a closed system is needed before dynamic equilibrium can be established.
  2. Define Le Chatelier's principle: when a system in dynamic equilibrium is changed, the equilibrium position shifts so as to minimise that change.
  3. Deduce qualitatively, using Le Chatelier's principle and given information, the effect on a system at equilibrium of changing the temperature, concentration or pressure, or of adding a catalyst.
  4. Deduce the expression for Kc, the equilibrium constant expressed using concentrations.
  5. Use the terms partial pressure and mole fraction.
  6. Deduce the expression for Kp, the equilibrium constant expressed using partial pressures (relating Kp to Kc is not required).
  7. Use expressions for Kc and Kp in calculations (these never require solving a quadratic equation).
  8. Calculate how much of each substance is present at equilibrium, given suitable data.
  9. State whether a reaction's equilibrium constant changes in value when the temperature, pressure or concentration is altered, or when a catalyst is present.
  10. Describe and explain the conditions chosen for the Contact and Haber processes, as examples showing why understanding dynamic equilibrium and applying Le Chatelier's principle matter in the chemical industry.

Cambridge syllabus keywords to use in your answers

These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.

lattice structure crystalline solid giant ionic simple molecular buckminsterfullerene giant molecular giant metallic

Tips to avoid common mistakes in these topics

Key Concept Flip

Topic 4.2 · Bonding and structure

Describe the lattice structure of sodium chloride (NaCl).

Answer Flip

Sodium chloride has a giant ionic lattice structure. It consists of alternating Na+ and Cl- ions held together by strong electrostatic forces in a three-dimensional arrangement.

Key Concept Flip

Topic 4.2 · Bonding and structure

How does the type of bonding and structure affect the melting point of a substance?

Answer Flip

Stronger bonding (

Example: giant ionic, giant metallic, giant covalent) generally leads to higher melting points due to the greater energy required to overcome the strong attractive forces. Simple molecular substances have weak intermolecular forces and thus lower melting points.
Definition Flip

Topic 5.1 · Enthalpy change, ΔH

Define standard enthalpy change of formation (ΔHf⦵).

Answer Flip

The standard enthalpy change of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions (298 K and 101 kPa).

Example: ΔHf⦵ [H₂O(l)] is the enthalpy change for H₂(g) + 1/2 O₂(g) → H₂O(l).
Key Concept Flip

Topic 5.1 · Enthalpy change, ΔH

Explain, in terms of bond breaking and bond making, why a reaction is exothermic.

Answer Flip

A reaction is exothermic when the energy released from forming new bonds in the products is greater than the energy required to break the bonds in the reactants. This results in a net release of energy as heat. Therefore, ΔH is negative.

Key Concept Flip

Topic 5.1 · Enthalpy change, ΔH

What does a reaction pathway diagram show, and what information can be obtained from it?

Answer Flip

A reaction pathway diagram illustrates the energy changes that occur during a chemical reaction. It shows the enthalpy change of the reaction (ΔH) and the activation energy (Ea), which is the energy required to initiate the reaction.

Definition Flip

Topic 5.2 · Hess’s law

Define Hess's Law.

Answer Flip

Hess's Law states that the total enthalpy change for a reaction is independent of the pathway taken, provided the initial and final conditions are the same. This allows for calculation of enthalpy changes that cannot be directly measured.

Key Concept Flip

Topic 6.1 · Redox processes: electron transfer and changes in oxidation number (oxidation state)

How do you determine the oxidation number of an atom in a compound?

Answer Flip

Apply oxidation number rules: Free elements have ON of 0, oxygen is usually -2, hydrogen is usually +1. The sum of ONs in a neutral compound is 0; in an ion, it equals the ion's charge.

Example: in H₂SO₄, the ON of S is +6.
Definition Flip

Topic 6.1 · Redox processes: electron transfer and changes in oxidation number (oxidation state)

Explain the terms 'oxidation' and 'reduction' in terms of electron transfer.

Answer Flip

Oxidation is the loss of electrons (OIL - Oxidation Is Loss), resulting in an increase in oxidation number. Reduction is the gain of electrons (RIG - Reduction Is Gain), resulting in a decrease in oxidation number.

Example: Zn → Zn²⁺ + 2e⁻ (oxidation).
Definition Flip

Topic 7.1 · Chemical equilibria: reversible reactions, dynamic equilibrium

State Le Chatelier's principle.

Answer Flip

Le Chatelier's principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. These 'changes' include changes in temperature, pressure, or concentration.

Key Concept Flip

Topic 7.1 · Chemical equilibria: reversible reactions, dynamic equilibrium

Write the Kc expression for the following equilibrium: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Answer Flip

Kc = [NH₃]² / ([N₂] [H₂]³). The equilibrium constant Kc is the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to the power of its stoichiometric coefficient.

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Key terms covered in this Bonding and structure deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

Standard enthalpy change of formation (ΔHf⦵)
Hess's Law
Explain the terms 'oxidation' and 'reduction' in terms of electron transfer
Le Chatelier's principle

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