Allotropes of Oxygen

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Compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding

  • Allotropy: The existence of two or more alternative forms of the same element in the same physical state.
  • Two allotropes of oxygen are:
    • Molecular oxygen (O2), also known as diatomic oxygen.
    • Ozone (O3), also known as triatomic oxygen.


PropertyMolecular oxygen
Melting point– 219°C– 193°COzone has a higher molecular mass than oxygen, and thus requires more energy in order to change state
Boiling point– 183°C– 111°C(Same as for melting point, above)
DensityAbout the same as airAbout 1.5 times that of airOzone is a larger molecule than oxygen
Solubility in waterSparingly solubleConsiderably more soluble than oxygenOzone is slightly polar, while oxygen is non-polar
StabilityVery stableEasily decomposedIt is much easier for ozone’s single coordinate covalent bond to be broken than oxygen’s double covalent bond
Oxidising strengthModerately strongVery strong(Same as for stability, above)
Properties of molecular oxygen and ozone