Ozone is the triatomic state of oxygen, that is, it is a molecule comprising of three oxygen atoms having the chemical symbol O3. In 1856 Thomas Andrews showed that ozone was formed only by oxygen, and in 1863 Soret established the relationship between oxygen and ozone by finding that three volumes of oxygen produce two volumes of ozone.
Ozone formation is endothermic. Ozone is thermodynamically is unstable and spontaneously reverts back into oxygen.
In the Earth’s stratosphere, the ozone generation occurs naturally (with concentrations between 5 and 10 ppm), protecting the planet and its inhabitants by absorbing ultraviolet radiation of wavelength 290-320 nm (Ullmann’s, 1991).
Resonance Structures of Ozone
Ozone (O3), or trioxygen, is a triatomic molecule consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope (O2), breaking down with a half life of about half an hour in the lower atmosphere to O2. Ozone is diamagnetic, which means that its electrons are all paired. In contrast, O2 is paramagnetic, containing two unpaired electrons.
According to experimental evidence from microwave spectroscopy, ozone is a bent molecule, with C2v symmetry (similar to the water molecule). The O – O distances are 127.2 pm (1.272 Å). The O – O – O angle is 116.78°. The central atom is sp² hybridized with one lone pair.
Ozone is a polar molecule with a dipole moment of 0.53 D. The molecule can be represented as a hybrid resonance with two contributing structures, each with a single bond on one side and double bond on the other. The arrangement possesses an overall bond order of 1.5 for both sides.