CCEA A Level Chemistry
CCEA A Level Chemistry 1.6 Shapes of Molecules and Ions Exam Questions
Free CCEA A Level Chemistry revision for 1.6 Shapes of Molecules and Ions: what you need to know, common mistakes and exam-style questions with answers. Covers VSEPR theory, shapes with up to six electron pairs, bond angles, lone pair repulsion and polar molecules.
Practise 1.6 Shapes of Molecules and Ions with past papers
Once you have learnt this topic, find the 1.6 Shapes of Molecules and Ions questions in real CCEA A Level Chemistry past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
StemUp mark scheme flashcards
A-Level Chemistry Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
From £10.99View flashcards
About CCEA A Level Chemistry 1.6 Shapes of Molecules and Ions
Section 1.6 of Unit AS 1 uses electron pair repulsion theory to predict shapes of molecules and ions with up to six electron pairs. You need to name and draw linear, bent, trigonal planar, tetrahedral, pyramidal, trigonal bipyramidal, octahedral, square planar and T-shaped arrangements, give bond angles, and explain why lone pairs repel more than bonding pairs, giving 107 degrees in NH3 and 104.5 degrees in H2O. CCEA also expects you to decide whether a molecule is polar from both bond polarity and shape. This draws on bonding (1.3) and links to intermolecular forces (1.4). Questions usually ask for a sketch, the name of the shape and the bond angle.
What you need to know
- VSEPR theory Electron pairs around a central atom repel each other and arrange themselves as far apart as possible. Lone pair-lone pair repulsion is greater than lone pair-bonding pair, which is greater than bonding pair-bonding pair.
- Shapes with no lone pairs 2 pairs: linear, 180 (BeCl2). 3: trigonal planar, 120 (BF3). 4: tetrahedral, 109.5 (CH4). 5: trigonal bipyramidal, 90 and 120 (PCl5). 6: octahedral, 90 (SF6).
- Shapes with lone pairs NH3 has 3 bonding pairs and 1 lone pair: pyramidal, 107. H2O has 2 bonding and 2 lone pairs: bent, 104.5. XeF4 with 4 bonding and 2 lone pairs is square planar, 90. ClF3 with 3 bonding and 2 lone pairs is T-shaped.
- Counting electron pairs Count the central atom's outer electrons, add one for each bonded atom (for single bonds), adjust for charge, then halve to get pairs. Subtract bonding pairs to find lone pairs.
- Polar molecules A molecule with polar bonds is non-polar if the dipoles cancel by symmetry (CO2, BF3, CCl4). If they do not cancel, as in H2O, NH3 and CHCl3, the molecule is polar.
Common mistakes in 1.6 Shapes of Molecules and Ions
- Giving 109.5 degrees for ammonia. The lone pair repels more strongly, reducing the angle to 107 degrees.
- Calling water linear because it has three atoms. It has two lone pairs so it is bent.
- Forgetting to adjust for charge in ions. For NH4+ subtract one electron; for anions add electrons.
- Saying a molecule is polar just because its bonds are polar. Consider shape: symmetrical molecules have cancelling dipoles.
- Drawing 3D shapes without wedges and dashes. Use wedge and dashed bonds to show the arrangement clearly.
Try three 1.6 Shapes of Molecules and Ions exam-style questions
1. State the shape and bond angle of the ammonium ion, NH4+. (2 marks)
Show the mark scheme answer
Tetrahedral; 109.5 degrees (four bonding pairs, no lone pairs).
2. Explain why the bond angle in water is 104.5 degrees. (3 marks)
Show the mark scheme answer
Four electron pairs around oxygen: two bonding and two lone pairs; lone pairs repel more than bonding pairs; this pushes bonding pairs closer, reducing the angle from 109.5 to 104.5 degrees.
3. Explain why CO2 is non-polar although its C=O bonds are polar. (2 marks)
Show the mark scheme answer
Molecule is linear and symmetrical; the two bond dipoles are equal and opposite so they cancel.
1.6 Shapes of Molecules and Ions FAQs
What does CCEA A Level Chemistry 1.6 Shapes of Molecules and Ions cover?
It covers VSEPR theory, the shapes and bond angles of molecules and ions with up to six electron pairs, and how shape decides polarity.
Which unit is 1.6 Shapes of Molecules and Ions examined in?
It is examined in Unit AS 1: Basic Concepts in Physical and Inorganic Chemistry, a 1 hour 30 minute paper with a multiple-choice section and structured questions. Related practical skills can also be assessed in Unit AS 3.
Which shapes should I learn for CCEA?
Linear, bent, trigonal planar, tetrahedral, pyramidal, trigonal bipyramidal, octahedral, square planar and T-shaped, each with its bond angles and an example.
