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.


Property Molecular oxygen
Melting point – 219°C – 193°C Ozone 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)
Density About the same as air About 1.5 times that of air Ozone is a larger molecule than oxygen
Solubility in water Sparingly soluble Considerably more soluble than oxygen Ozone is slightly polar, while oxygen is non-polar
Stability Very stable Easily decomposed It is much easier for ozone’s single coordinate covalent bond to be broken than oxygen’s double covalent bond
Oxidising strength Moderately strong Very strong (Same as for stability, above)
Properties of molecular oxygen and ozone