Edexcel IGCSE Chemistry Ionic bonding questions

Revise the key specification points for Ionic bonding, then try focused exam-style questions with worked explanations.

Edexcel IGCSE Chemistry Subtopic 1.f

What You Need To Know

Ionic bonding questions can test recall, explanation, calculations, practical method, or data handling. For this subtopic, you should be able to:

  • 1.37 understand how ions are formed by electron loss or gain
  • 1.38 know the charges of these ions: metals in Groups 1, 2 and 3 non-metals in Groups 5, 6 and 7 Ag+, Cu2+, Fe2+, Fe3+, Pb2+, Zn2+ hydrogen (H+), hydroxide (OH–), ammonium (NH4+), carbonate (CO32–), nitrate (NO3-), sulfate (SO42–).
  • 1.39 write formulae for compounds formed between the ions listed above
  • 1.40 draw dot-and-cross diagrams to show the formation of ionic compounds by electron transfer, limited to combinations of elements from Groups 1, 2, 3 and 5, 6, 7 only outer electrons need be shown
  • 1.41 understand ionic bonding in terms of electrostatic attractions
  • 1.42 understand why compounds with giant ionic lattices have high melting and boiling points
  • 1.43 know that ionic compounds do not conduct electricity when solid, but do conduct electricity when molten and in aqueous solution

How To Answer Ionic bonding Questions

  1. Start by identifying exactly which specification point the question is testing.
  2. Use the command word carefully: state and identify need a direct answer, while describe and explain need linked detail.
  3. For tables, graphs, diagrams, and practical questions, quote the relevant observation or reading before drawing a conclusion.
  4. When a question asks for a calculation, show the key substitution and include units where they are needed.

Example Questions With Worked Explanations

Example 1: Core Knowledge

Question 1

This question is about ionic compounds. The diagram shows the electronic configuration of a potassium atom and an oxygen atom.
Electron configuration diagram (shell model): potassium atom with four shells (2,8,8,1) and oxygen atom with two shells (2,6). Question asks to draw the potassium ion and oxide ion with charges.

Potassium oxide (K2O) is an ionic compound.
Draw the electronic configuration of a potassium ion and an oxide ion.
Show the charge on each ion.

oxide ion

Final answer

See diagram.

K+ potassium ion O2- oxide ion

K+ has electron arrangement 2,8,8 and O2− has 2,8.

Mark scheme points

  1. M1 Potassium ion drawn correctly with electron arrangement 2,8,8.
  2. M2 Oxide ion drawn correctly with electron arrangement 2,8.
  3. M3 Correct charges shown: K+ and O2−.

Explanation

  • For the potassium ion, start from potassium atom 2,8,8,1. It loses 1 electron, so the ion is 2,8,8.
  • For the oxide ion, start from oxygen atom 2,6. It gains 2 electrons, so the ion is 2,8 with a full outer shell.
  • Add the charges clearly: potassium becomes K+ and oxygen becomes O2−.
  • Any sensible use of dots and crosses is acceptable, but for full marks you should show all the electron shells, not just the outer shell.

Common mistakes

  • Examiners reported that many candidates got the electron arrangements right but lost the charge mark. They also reminded students that if electron configuration is asked for, electrons in each shell should be shown.
  • Leaving potassium as 2,8,8,1 instead of removing one electron for K+.
  • Drawing oxide ion as 2,6 instead of showing the gained electrons to make 2,8.
  • Writing the charges wrongly, such as K2+ or O−.
  • Showing only the outer shell electrons; this can limit the answer to a maximum of 2 marks.

Example 2: Using Data and Practical Skills

Question 2

This question is about the insoluble salt, lead(II) bromide.
Lead(II) bromide can be made by a precipitation reaction.
This is the equation for the reaction.
Pb(NO3)2(aq) + 2KBr(aq) → PbBr2(s) + 2KNO3(aq)
Blank graph grid for plotting electrical conductivity against total volume of lead(II) nitrate added.
A student investigates the change in electrical conductivity as dilute lead(II) nitrate solution is added to dilute potassium bromide solution.
This is the student’s method.
Step 1 add 50cm3 of potassium bromide solution to a beaker
Step 2 measure the electrical conductivity of the solution
Step 3 add 10cm3 of lead(II) nitrate solution to the beaker
Step 4 stir the mixture
Step 5 measure the electrical conductivity of the mixture
Repeat steps 3, 4 and 5 until a total of 50cm3 of lead(II) nitrate solution has been added.
The table shows the student’s results.
Total volume of lead(II) nitrate solution added in cm3 Electrical conductivity in arbitrary units
010.00
109.80
209.77
309.40
409.20
509.00
Explain the shape of the graph.



Final answer

The electrical conductivity decreases as more lead(II) nitrate solution is added. This is because ions are removed from the solution when insoluble PbBr2 forms, so there are fewer mobile ions to carry charge.

Mark scheme points

  1. M1 The conductivity decreases as the volume of lead(II) nitrate added increases.
  2. M2 There are fewer ions in the mixture / ions are removed from solution as PbBr2 is formed.

Explanation

To get full marks, make both ideas clear:

  • State the trend: the graph goes down, so conductivity decreases as more lead(II) nitrate is added.
  • Explain why: lead(II) ions react with bromide ions to make solid lead(II) bromide, PbBr2.
  • Because PbBr2 is a precipitate, those ions are no longer free in solution.
  • With fewer mobile ions in the solution, less charge is carried, so the conductivity falls.

A concise full-mark answer is: “The conductivity decreases because PbBr2 precipitates, so ions are removed from the solution and there are fewer ions to conduct electricity.”

Common mistakes

  • Only describing the graph shape without explaining why loses a mark.
  • Saying “the solution has fewer particles” is too vague; you need to say fewer ions.
  • Do not say the variables are “directly proportional” — that is incorrect here.
  • Examiners reported that most candidates said conductivity would just keep decreasing or gave no change. The scoring idea was to link the change to ions being removed from solution as PbBr2 forms.

Practise This Subtopic

Build a focused practice set on ionic bonding, with questions selected from this part of the Edexcel IGCSE Chemistry specification.

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