AQA GCSE Chemistry Foundation (8462), Foundation tier · Bonding, structure and the properties of matter › Chemical bonds: ionic, covalent and metallic
Practise Ionic compounds. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
What an ionic compound is like: a giant lattice of oppositely charged ions held by strong electrostatic forces acting in all directions. You need to recognise ionic structures in diagrams, work out empirical formulae from diagrams, and give the limitations of each type of diagram.
Key facts
Ionic compound = giant lattice of oppositely charged ions
Held by strong electrostatic forces of attraction, acting in all directions
No molecules: the formula gives the ratio of the ions
Empirical formula = simplest whole-number ratio of ions
Ball and stick: shows the 3D pattern, but the gaps and sticks are not real
2D diagram: only one layer. Space-filling: can't see the ions inside
Every diagram shows only a tiny part of the lattice
Notes
Giant ionic lattices
diagram
An ionic compound is a giant structure of ions, called a giant ionic lattice. The ions are arranged in a regular, repeating pattern.
The ions are held together by strong electrostatic forces of attraction between oppositely charged ions. This is ionic bonding.
The forces act in all directions in the lattice: each ion is attracted to all the oppositely charged ions around it, not just to one partner.
In sodium chloride, each Na+ ion is surrounded by six Cl− ions, and each Cl− ion by six Na+ ions.
Ball and stick model of sodium chloride. The centre ion has six neighbours of the opposite charge.
There are no molecules in an ionic compound. A formula such as NaCl gives the ratio of the ions.
Diagrams of ionic structures and their limitations
Dot and cross diagram: shows how the ions formed (electron transfer) and their charges. It does not show how the ions are arranged in the lattice or their relative sizes.
Ball and stick model: shows the regular 3D arrangement of the ions. But the sticks are not real, there are no large gaps between ions in reality, and the forces act in all directions, not just along the sticks.
2D diagram: easy to draw and shows the alternating pattern of ions, but only one layer, not the 3D arrangement.
3D space-filling diagram: shows the ions touching and their relative sizes (a Cl− ion is bigger than an Na+ ion). But you can only see the outside ions, and the forces are not shown.
Every diagram shows only a tiny part of the lattice, which really continues in all directions.
Empirical formula from a diagram
The empirical formula is the simplest whole-number ratio of the ions (or atoms) in a compound.
Count the ions of each type in the diagram, write the ratio, and cancel it down: 12 of X and 6 of Y gives X : Y = 2 : 1, so X2Y.
If charges are shown, check that they balance: two 1+ ions and one 2− ion give zero overall.
How to answer each type of question
Describe the structure and bonding in an ionic compound
3 marksGrade 5
Say it is a giant lattice (giant ionic structure).
Name the particles: oppositely charged ions, with their formulae if you can.
Say they are held by strong electrostatic forces of attraction acting in all directions.
Example. Describe the structure and bonding in magnesium oxide.
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Magnesium oxide is a giant (ionic) lattice (1) of Mg2+ ions and O2− ions (1), held together by strong electrostatic forces of attraction between the oppositely charged ions, acting in all directions (1).
Identify an ionic structure from a diagram
1 to 2 marksGrade 5
Look for two types of particle, labelled + and − or with charges.
Check they are in a regular arrangement that continues in all directions, with no separate molecules.
Give the structure and the evidence you used.
Example. The diagram shows part of the structure of substance Z. The pattern continues in all directions.
What type of structure does Z have? Give a reason.
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Giant ionic lattice (1). It is made of oppositely charged ions in a regular pattern (1).
Don’t lose marks
Calling an ionic compound 'molecules' or mentioning intermolecular forces. It is a giant lattice of ions.
Saying the forces act only between pairs of ions or in one direction. They act in all directions.
Writing the numbers counted (e.g. M8Q16) instead of the simplest ratio.
Giving a vague limitation such as 'it is not accurate'. Say exactly what is wrong, e.g. 'the ions are not really joined by sticks'.
Writing 'strong forces' without saying they are electrostatic and between oppositely charged ions.
More tips
Memory tricks
Picture a 3D chessboard of + and − ions that keeps going in every direction.
Limitations checklist: sticks, gaps, scale, 3D, tiny part. Pick the ones that apply to the diagram in the question.
Cancel a ratio of ions like a fraction: 6 : 12 → 1 : 2.
Exam technique
Learn the key phrase word for word: 'strong electrostatic forces of attraction between oppositely charged ions'.
For advantage and disadvantage questions, make each point specific to the type of diagram named.
If the diagram labels the ions with charges, use the charges to check your empirical formula.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Describe an ionic compound as a giant structureIt is a giant structure (lattice) of ions arranged in a regular pattern.
Grade 4
Name the force holding the ions togetherStrong electrostatic forces of attraction between oppositely charged ions.
Grade 5
State that the forces act in all directionsEach ion is attracted to all the oppositely charged ions around it, throughout the lattice.
Grade 5
Recognise an ionic structure from a diagramLook for a regular lattice of two types of ion, often labelled with charges, and no separate molecules.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
This question is about ionic compounds. In which directions do these forces act?
in all directions
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
This question is about ionic compounds.
(a) Which of these substances is an ionic compound? Tick (✓) one box.[1]
Carbon dioxide
Copper
Magnesium oxide
Methane
(b) What holds the particles together in an ionic compound? Tick (✓) one box.[1]
Weak forces between molecules
Shared pairs of electrons
Strong electrostatic forces between oppositely charged ions
Delocalised electrons
(c) In which directions do these forces act?[1]
(d) What name is given to the regular arrangement of ions in an ionic compound?[1]
Show the answer and mark scheme
(a)Answer: Magnesium oxide
(b)Answer: Strong electrostatic forces between oppositely charged ions