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?

To determine the hybridization of ozone, let's consider the Lewis structure of O3. Ozone has two resonance structures, where the central oxygen atom forms a double bond with one terminal oxygen atom and a single bond with the other terminal oxygen atom. The two resonance structures can be represented as: O = O - O ↔ O - O = O The central oxygen atom has three electron domains (one double bond, one single bond, and one lone pair), so it adopts the sp2 hybridization, forming a trigonal planar geometry. The terminal oxygen atoms have two bonding electron domains (single or double bond), and two lone pairs, so they also adopt sp2 hybridization. Thus, the best choice of hybridization scheme for ozone is sp2 hybridization for all oxygen atoms.

Let's consider the first resonance form of ozone, where the central oxygen atom is double-bonded to the left terminal oxygen atom and single-bonded to the right terminal oxygen atom: O = O - O In this resonance form: - Central Oxygen Atom: One of the sp2 hybrid orbitals forms a sigma bond with each terminal oxygen atom, while the remaining sp2 hybrid orbital holds a lone pair of electrons. The unhybridized p orbital contains one π electron involved in the double bond. - Terminal Oxygen Atoms: The sp2 hybrid orbitals are used to form sigma bonds with the central oxygen atom, and each terminal oxygen atom has two sp2 hybrid orbitals occupied by the lone pairs of electrons.

The unhybridized p orbitals of the central oxygen atom and both terminal oxygen atoms can overlap to form delocalized π bonds in ozone. Therefore, these are the orbitals that can be used for the delocalization of π electrons.

In both resonance forms of ozone, the central oxygen atom contributes one π electron while the double bonded terminal oxygen atom contributes another π electron to the delocalized π system. As these two π electrons are shared among all three oxygen atoms, there are a total of 2 delocalized π electrons in the π system of ozone.