Syllabus Edition

First teaching 2023

First exams 2025

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Covalent Bonds in Polymers (CIE AS Biology)

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Cara Head

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Cara Head

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Covalent Bonds in Polymers

  • A covalent bond is the sharing of two or more electrons between two atoms
    • The electrons can be shared equally forming a nonpolar covalent bond or unequally (where an atom can be more electronegative δ-) to form a polar covalent bond
  • Generally each atom will form a certain number of covalent bonds due to the number of free electrons in the outer orbital e.g. H = 1 bond, C = 4 bonds
  • Covalent bonds are very stable as high energies are required to break the bonds
  • Multiple pairs of electrons can be shared forming double bonds (e.g. unsaturated fats C=C) or triple bonds

Covalent Bond Diagram

Covalent bonds, downloadable IGCSE & GCSE Biology revision notes

Different types of covalent bonds

  • When two monomers are close enough that their outer orbitals overlap this results in their electrons being shared and a covalent bond forming. If more monomers are added then polymerisation occurs (and / or a macromolecule forms)

Condensation

  • Also known as dehydration synthesis (‘to put together while losing water’)
  • A condensation reaction occurs when monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed

Condensation Reaction Diagram

Condensation reaction, downloadable IGCSE & GCSE Biology revision notes

Written and symbolic illustrations of the removal of water to form a covalent bond between two or more monomers during a condensation reaction

Hydrolysis

  • Hydrolysis means ‘lyse’ (to break) and ‘hydro’ (with water)
  • In the hydrolysis of polymers, covalent bonds are broken when water is added

Hydrolysis Reaction Diagram

Hydrolysis reaction, downloadable IGCSE & GCSE Biology revision notes

Written and symbolic illustrations of the addition of water to break down covalent bond/s during a hydrolysis reaction

Covalent bonds in organic molecules table

Organic Molecules Covalent Bonds Diagram of Covalent Bonds
Carbohydrates Glycosidic glycosidic-highlighted
Proteins Peptide peptide-highlighted
Lipids Ester ester-highlighted
Nucleic Acids Phosphodiester phosphodiester-highlighted

Examiner Tip

You must be able to recognise and identify the location of the covalent bonds in the molecules – note that these molecules may be unfamiliar to you.

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding