The questions are on the ionic bonding test. Take it under real conditions before reading the mark scheme.
Quick answer: Ionic bonding is the strong electrostatic attraction between oppositely charged ions, formed when metal atoms transfer electrons to non-metal atoms. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 9-10 test on ionic bonding, from magnesium oxide to ion arrangements, with the equivalent answers to accept.
Each model answer is followed by the marking points. Accept any correct equivalent wording, and award marks for correct charges even when the formula is written without subscripts.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-3, GCSE C2
Question 1 Magnesium oxide (3 marks)
(a) Each magnesium atom transfers its two outer electrons to an oxygen atom.
(b) Magnesium ion 2+ and oxide ion 2−.
(c) MgO
Marking: 1 mark each.
Question 2 Crystal diagram (3 marks)
(a) Each row repeats one X with two Y, so the ratio is 1 : 2.
(b) XY₂
(c) Two Y⁻ ions give 2− in total, so X must be 2+.
Marking: 1 mark each.
Question 3 Conduction (3 marks)
Sodium chloride contains ions. In the solid the ions are held in fixed positions in the lattice, so they cannot move. When molten the ions are free to move and carry charge.
Marking: 1 mark contains ions; 1 mark fixed in solid; 1 mark free to move when molten.
Question 4 Aluminium oxide (2 marks)
Lowest common multiple of 3 and 2 is 6. Two Al³⁺ give +6 and three O²⁻ give −6.
Al₂O₃
Marking: 1 mark for balancing charge; 1 mark for the formula.
Question 5 Melting points compared (3 marks)
Both have giant ionic lattices with strong attractions between ions. The ions in magnesium oxide have charges of 2+ and 2− but those in sodium chloride have 1+ and 1−. The attraction is stronger in magnesium oxide, so more energy is needed to separate the ions.
Marking: 1 mark giant lattice; 1 mark larger charges; 1 mark stronger attraction needs more energy.
Question 6 Counting ions (2 marks)
The ratio is 2 Na⁺ : 1 O²⁻. Oxide ions = 6.0 × 10²⁰ ÷ 2 = 3.0 × 10²⁰.
3.0 × 10²⁰ oxide ions
Marking: 1 mark for the ratio; 1 mark for the answer.
Question 7 Brittle crystal (2 marks)
A force moves a layer of ions along by one position, so ions with the same charge are next to each other. They repel, and the crystal splits.
Marking: 1 mark for like charges meeting; 1 mark for repulsion splits the crystal.
Question 8 Ion arrangements (2 marks)
Ca²⁺ has 18 electrons: 2,8,8. Br⁻ has 35 + 1 = 36 electrons.
Marking: 1 mark each.
