CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.3.11 Shapes of Molecules

VSEPR: Theory & Predictions

  • The valence shell electron pair repulsion theory (VSEPR) predicts the shape and bond angles of molecules
  • Electrons are negatively charged and will repel other electrons when close to each other
  • In a molecule, the bonding pair of electrons will repel other electrons around the central atom forcing the molecule to adopt a shape in which these repulsive forces are minimised
  • When determining the shape and bond angles of a molecule, the following VSEPR rules should be considered:
    • Valence shell electrons are those electrons that are found in the outer shell
    • Electron pairs repel each other as they have similar charges
    • Lone pair electrons repel each other more than bonded pairs
    • Repulsion between multiple and single bonds is treated the same as for repulsion between single bonds
    • Repulsion between pairs of double bonds are greater
    • The most stable shape is adopted to minimize the repulsion forces
  • Different types of electron pairs have different repulsive forces
    • Lone pairs of electrons have a more concentrated electron charge cloud than bonding pairs of electrons
    • The cloud charges are wider and closer to the central atom’s nucleus
    • The order of repulsion is therefore: lone pair – lone pair > lone pair – bond pair > bond pair – bond pair

Chemical Bonding Electron Pairs Repulsive Forces, downloadable AS & A Level Chemistry revision notes

Different types of electron pairs have different repulsive forces

  • Molecules can adapt the following shapes and bond angles:

 

Chemical Bonding Shapes of Molecules, downloadable AS & A Level Chemistry revision notes

Molecules of different shapes can adapt with their corresponding bond angles

Examples

Chemical Bonding Shapes of Molecules 2 (1), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Shapes of Molecules 2 (2), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Shapes of Molecules 2 (3), downloadable AS & A Level Chemistry revision notes

Chemical Bonding Shapes of Molecules 2 (4), downloadable AS & A Level Chemistry revision notes

Examples of molecules with different shapes and bond angles

Worked example: VSEPR & shapes of molecules

Chemical Bonding Worked Example - VSEPR Theory & Predictions, downloadable AS & A Level Chemistry revision notes

Answer 1

Chemical Bonding Worked Example Answer 1 - VSEPR for Phosphorous(V) chloride, downloadable AS & A Level Chemistry revision notes

Answer 2

Chemical Bonding Worked Example Answer 2 - VSEPR for N(CH3)_1, downloadable AS & A Level Chemistry revision notes

Answer 3

Chemical Bonding Worked Example Answer 3 - VSEPR for CCl4_1, downloadable AS & A Level Chemistry revision notes

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top