VSEPR Theory (Edexcel International A Level Chemistry)

Revision Note

Philippa Platt

Last updated

Shapes & Angles

  • 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 pairs 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 the same charge
    • 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

Bond length

  • The bond length is internuclear distance of two covalently bonded atoms
    • It is the distance from the nucleus of one atom to another atom which forms the covalent bond

  • The greater the forces of attraction between electrons and nuclei, the more the atoms are pulled closer to each other
  • This decreases the bond length of a molecule and increases the strength of the covalent bond
  • Triple bonds are the shortest and strongest covalent bonds due to the large electron density between the nuclei of the two atoms
  • This increase the forces of attraction between the electrons and nuclei of the atoms
  • As a result of this, the atoms are pulled closer together causing a shorter bond length
  • The increased forces of attraction also means that the covalent bond is stronger

Chemical Bonding Bond Lengths and Strengths, downloadable AS & A Level Chemistry revision notes

Triple bonds are the shortest covalent bonds and therefore the strongest ones

Bond Angle

  • Molecules can adapt the following shapes and bond angles:

Shapes of molecules, downloadable AS & A Level Chemistry revision notes

Molecules of different shapes can adapt with their corresponding bond angles

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Philippa Platt

Author: Philippa Platt

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.

Download notes on 1.7.5 VSEPR Theory