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Planarity of Organic Molecules (Cambridge (CIE) A Level Chemistry): Revision Note

Exam code: 9701

Philippa Platt

Last updated

Planar Molecules

  • Planar molecules have all their atoms in the same plane

    • E.g. linear, bent, trigonal planar and square planar

 Examples of planar molecules

Diagram of molecular shapes: linear, non-linear (bent), trigonal planar, and square planar, showing bond angles of 180°, 104.5°, 120°, and 90°.
The diagram shows molecules which have all their atoms in the same plane with their name and the associated bond angle

  • The presence of an sp2 hybridised carbon can force the molecule to adopt a planar configuration (trigonal planar)

  • The 3 σ bonds position themselves in a trigonal planar position so that the bonding pair of electrons are as far away from each other and therefore minimise the repulsion between them

The planarity of ethene

Diagram of ethene showing structural formula and ball-and-stick model, illustrating trigonal planar geometry of carbon atoms and hydrogen bonds.
Ethene is a planar molecule with two trigonal planar centres around the carbon atoms

The planarity of propene

Structural diagrams of propene, showing molecular geometry: tetrahedral and trigonal planar centres, with hydrogen and carbon atoms labelled.
Propene has two trigonal planar centres around the carbon-carbon double bond and one tetrahedral centre

  • The presence of an sp hybridised carbon can also force the molecule to adopt a planar configuration (linear)

  • The 2 σ bonds position themselves in a linear position to minimise the repulsion between the bonding pairs of electrons

The planarity of ethyne

 

Diagram of ethyne molecule, showing its linear structure. Includes chemical formula HC≡CH, with hydrogen and carbon atoms in blue and pink circles.
Ethyne is a planar molecule with one planar centre: the molecule is linear

The planarity of propyne 

Propane structure with a linear and tetrahedral configuration, showing carbon (C) and hydrogen (H) atoms labelled, with a red tetrahedral outline.
Propyne has one planar centre around the carbon-carbon triple bond (linear) and one tetrahedral centre

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    Philippa Platt

    Author: Philippa Platt

    Expertise: Chemistry Content Creator

    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