AQA GCSE Combined Science (8464), Higher tier · Chemistry › Bonding, structure, and the properties of matter › Chemical bonds, ionic, covalent and metallic
Practise Ionic compounds. 12 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.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Describe an ionic compound as a giant structureIt is a giant structure (lattice) of ions arranged in a regular pattern.
4
Name the force holding the ions togetherStrong electrostatic forces of attraction between oppositely charged ions.
5
State that the forces act in all directionsEach ion is attracted to all the oppositely charged ions around it, throughout the lattice.
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.
6
Work out an empirical formula from a diagramCount the ions of each type and simplify the ratio, e.g. 8 : 16 gives XY2.
7
Give limitations of each type of diagramFor example, ball and stick models show gaps and sticks that are not really there; 2D diagrams do not show the 3D arrangement.
Notes
Giant ionic lattices
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.
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.
Cheatsheet
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
How to answer each type of question
Describe the structure and bonding in an ionic compound
3 marks5
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.
Show the model answer
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 marks5
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. A diagram of substance Z shows a regular 3D arrangement of two types of particle, labelled + and −. Each + particle is surrounded by − particles. What type of structure does Z have? Give a reason.
Show the model answer
Giant ionic lattice (1). It is made of oppositely charged ions in a regular pattern (1).
Work out the empirical formula from a diagram
1 to 2 marks6
Count the ions of each type shown.
Write the ratio and cancel to the simplest whole numbers.
If you are told one ion's charge, use the ratio to work out the other.
Example. A 2D diagram of part of an ionic lattice shows 8 ions of metal M and 16 ions of non-metal Q. (a) Give the empirical formula of the compound. (b) The ion of M has a charge of 2+. Give the charge on the ion of Q.
Show the model answer
(a) MQ2 (1) (8 : 16 = 1 : 2) (b) 1− (1) (one 2+ ion is balanced by two ions of Q)
Give an advantage and a limitation of a diagram
2 marks7
Advantage: say what the diagram shows clearly (3D arrangement, pattern, charges, relative sizes).
Limitation: say exactly what is wrong or missing for that type of diagram (sticks, gaps, not to scale, only one layer, only a tiny part).
Example. A student uses a ball and stick model to represent sodium chloride. Give one advantage and one disadvantage of using this model.
Show the model answer
Advantage: it shows the 3D arrangement of the ions / the regular repeating pattern (1). Disadvantage, any one from: the ions are not joined by sticks; there are no gaps between the ions in reality; the ions are not drawn to scale; it shows only a small part of the lattice (1).
Shortcuts and 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.
Where marks are lost
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.
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.
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
(c)Answer: in all directions
in all directions
(d)Answer: a (giant ionic) lattice
(giant ionic) lattice
Question 2Medium5 marks
{table} shows the formulae of some ions.
[object Object]
(a) Give the formula of magnesium chloride.[1]
(b) Give the formula of aluminium oxide.[1]
(c) Give the formula of sodium sulfate.[1]
(d) Give the formula of calcium hydroxide.[1]
(e) Give the formula of iron(III) nitrate.[1]
Show the answer and mark scheme
(a)Answer: MgCl2
MgCl2
(b)Answer: Al2O3
Al2O3
(c)Answer: Na2SO4
Na2SO4
(d)Answer: Ca(OH)2
Ca(OH)2
(e)Answer: Fe(NO3)3
Fe(NO3)3
Question 3Hard6 marks
The structure of sodium chloride can be represented by a dot and cross diagram, a ball and stick model or a space-filling model.
(a) Give two limitations of the ball and stick model of sodium chloride.[2]
(b) Give one advantage of a space-filling model compared with a ball and stick model.[1]
(c) Explain why a dot and cross diagram is not useful for showing the structure of sodium chloride.[1]
(d) In sodium chloride, each Na+ ion is surrounded by six Cl− ions. Explain why the formula of sodium chloride is NaCl and not NaCl6.[2]
Show the answer and mark scheme
(a)Answer: The sticks suggest bonds between particular pairs of ions (forces act in all directions); the ions are shown far apart.
the sticks suggest bonds between particular pairs of ions / the forces actually act in all directions
the ions are shown too far apart / there are no large gaps between ions in reality
the relative sizes of the ions are not shown correctly
it only shows a small part of the giant lattice
(b)Answer: It shows the relative sizes of the ions and how closely they are packed.
shows the relative sizes of the ions / shows the ions touching / closely packed
(c)Answer: It only shows electron transfer between one pair of ions, not the arrangement of ions in the lattice.
it only shows the transfer of electrons / one pair of ions, not the arrangement of ions in the (3D) lattice
(d)Answer: Each Cl− ion is also surrounded by six Na+ ions, so each ion is shared and the overall ratio is 1 : 1.
each Cl− ion is also surrounded by / shared between six Na+ ions