= Solution
\b[<Ozone> is bent, with two equivalent O–O bonds of approximate <bond order> $1.5$.] Its useful localized <orbital hybridization> description is $sp^2$ at all three oxygens. Two hybrids at the central oxygen form sigma bonds and a third contains a <lone pair>; the three perpendicular p orbitals form a <three-centre four-electron pi bond>.
The three pi orbitals are bonding, nonbonding and antibonding, filled as $\pi_{\rm b}^2\pi_{\rm nb}^2\pi_*^0$. The terminal-centred nonbonding orbital is the <Homo>, conventionally $1a_2$; the delocalized antibonding orbital is the <LUMO>, $2b_1$. The two principal <resonance structures>, $\mathrm{^-O-O^+=O}$ and $\mathrm{O=O^+-O^-}$, distribute the extra pi bond across the two links.
The 18 valence electrons comprise four sigma-bond electrons, ten in five sigma-framework lone pairs, and four in the pi system. This gives a paired ground-state model. More accurate treatments include electron correlation; the simple bond-order picture is not an exact charge-density calculation.<The Structures, Molecular Orbital Properties and Vibrational Spectra of the Homo- and Heterodimers of Sulphur Dioxide and Ozone. An Ab Initio Study by Thomas A. Ford>[2021, §2.3 and Table 9: ozone HOMO and LUMO]{ref}
Back to article page
