Question

In ozone, \(\mathrm{O}_{3}\), the two oxygen atoms on the ends of the molecule are equivalent to one another. (a) What is the best choice of hybridization scheme for the atoms of ozone? (b) For one of the resonance forms of ozone, which of the orbitals are used to make bonds and which are used to hold nonbonding pairs of electrons? (c) Which of the orbitals can be used to delocalize the \(\pi\) electrons? (d) How many electrons are delocalized in the \(\pi\) system of ozone?

Short answer

The central oxygen atom in ozone (\(\mathrm{O}_{3}\)) is sp² hybridized, forming sigma bonds with the terminal oxygen atoms. The 2pz orbitals on the three oxygen atoms are used to delocalize \(\pi\) electrons in the molecule, leading to resonance. There are four electrons delocalized in the \(\pi\) system of ozone.

Step-by-step solution

(a) Hybridization scheme for ozone

Ozone has a bent V-shaped structure, and its central oxygen atom is sp² hybridized. To determine this, we need to look at the Lewis structure of the Ozone molecule, which contains one double bond and one single bond between the oxygen atoms. Therefore, the central oxygen atom has a steric number of 3 (2 bonded atoms and 1 lone pair), which leads to sp² hybridization.

(b) Orbitals used for bonding and nonbonding electrons

In one of the resonance forms of ozone, there exist three atomic oxygen orbitals (1s, 2s, and 2p). The 1s atomic orbital is used to make the single sigma bond between the central oxygen atom and one of the terminal oxygens, which is formed by the overlap of sp² hybrid orbitals. The 2px and 2py orbitals form the bonding π and nonbonding π orbitals, repectively. For the central oxygen atom (O1) with sp² hybridization, one sp² hybrid orbital is used to form a sigma bond with one terminal oxygen (O2) using its 1s orbital. Another sp² hybrid orbital is used to form a sigma bond with the other terminal oxygen atom (O3) using its 1s orbital. The remaining sp² hybrid orbital on the central oxygen atom holds a lone pair of nonbonding electrons.

(c) Orbitals used to delocalize π electrons

The 2pz orbitals on the three oxygen atoms are used to delocalize the π electrons in the ozone molecule. As these orbitals overlap, they form three molecular orbitals: one bonding π orbital (π), one nonbonding π orbital (π*), and one antibonding π orbital (π**). The π electrons are delocalized over these three orbitals, allowing resonance to occur in the molecule.

(d) Number of electrons delocalized in the π system

In the ozone molecule, there are four electrons in the π system. These four electrons are delocalized over the three molecular orbitals (π, π*, and π**). In the bonding π orbital, there are two electrons. In the nonbonding π orbital, there are also two electrons. The antibonding π orbital is vacant and has no electrons. By understanding the hybridization and molecular orbital theory of ozone, we were able to describe its bonding, electron distribution, and delocalization properties.