AQA A-Level Chemistry Paper 3, 2023: Question 23
1 mark · Medium difficulty · Multiple Choice
Shapes of Ions This question assesses knowledge of the geometric shapes of ions, focusing on common coordination complexes and molecular ions, to identify an incorrect statement about their shapes.
Practise this questionQuestion
Question text
23 Which statement about the shapes of ions is not correct?
[1 mark]
A [CoCl ]2– is square planar.
B NH + is tetrahedral.
C [Co(H NCH CH NH ) ]2+ is octahedral.
22 2 2 3
D [Co(H O) ]2+ is octahedral.
Mark scheme
Show the mark scheme
23 A 1 (AO1) [CoCl ]2– is square planar.
How to answer it
Understanding the Shapes of Ions
Question
Which statement about the shapes of ions is not correct?
- A: [CoCl4]2− is square planar.
- B: NH4+ is tetrahedral.
- C: [Co(H2NCH2CH2NH2)2]2+ is octahedral.
- D: [Co(H2O)6]2+ is octahedral.
Correct Answer: A
[CoCl4]2− is not square planar; it is actually tetrahedral.
Explanation
The shape of a complex ion depends on the coordination number and the type of ligands. Here's the breakdown:
- A: [CoCl4]2− has a coordination number of 4 with chloride ions as ligands. These ligands are large and typically form a tetrahedral structure, not square planar.
- B: NH4+ is tetrahedral due to the four hydrogen atoms bonded to the central nitrogen atom.
- C: [Co(H2NCH2CH2NH2)2]2+ is octahedral because it has a coordination number of 6 (two bidentate ligands).
- D: [Co(H2O)6]2+ is octahedral because it has a coordination number of 6 with six water ligands.
Teacher Tip
For questions about shapes, always consider the coordination number and type of ligands. Small, high-charge ligands like water and ammonia favour octahedral shapes, while large ligands like chloride often lead to tetrahedral structures.
Topics
Inorganic Chemistry · 3.2.5 Transition Metals
Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.