Question

Describe the bonding in ${\mathit{O}}_{\mathbf{3}}$molecule and $\mathit{N}{{\mathbf{O}}_{\mathbf{2}}}^{\mathbf{-}}$ion using the LE model. How would the molecular orbital model describe pi bonding in these two species?

Short answer

Ozone has a trigonal planar center oxygen atom that is sp²hybridized. If we suppose that the terminal oxygen atoms are also sp²hybridized, we get the -bonded framework illustrated in the diagram.

Because nitrogen has a lone pair of electrons and has a bent structure, the bonding in NO^2- is comparable to the bonding in ozone. The fact that nitrite has 18 valence electrons (5 from N and 6 from each O, plus 1 for the 1 charge) supports this view. Because of the bent conformation, the nitrogen is sp²hybridized.

Step-by-step solution

Step 1- Pi bonding in O3

Three 2p atomic orbitals give us three molecular orbitals, as seen in Figure when using a molecular orbital technique to characterize the bonding. A bonding molecular orbital, which is depicted as a banana-shaped region of electron density above and below the molecular plane, is one of the molecular orbitals. There are no nodes perpendicular to the O₃ plane in this region. The highest-energy molecular orbital is a π* antibonding orbital, with two nodes that bisect the O–O bonds. The third molecular orbital is a nonbonding molecular orbital with a single node that is perpendicular to the O₃plane and goes through the center O atom.

Step 2- Bonding in ozone

Three molecular orbitals are formed by the interaction of three unhybridized 2pz atomic orbitals: one π bonding orbital at lower energy, one π* antibonding orbital at higher energy, and a nonbonding orbital in the middle.

Step 3- Bonding in NO2-

If we assume that the oxygen atoms are also sp²hybridized, we can accommodate the five lone pairs of electrons by using two sp² hybrid orbitals on each oxygen and one sp² hybrid orbital on nitrogen. The remaining sp² hybrid orbitals on each oxygen create bonds with the two sp² hybrid orbitals on nitrogen. 14 electrons are accounted for sigma bonds and lone pairs. We are left with four electrons and three unhybridized 2p orbitals, one on each atom and perpendicular to the molecule's plane. These three 2p orbitals interact to generate bonding, nonbonding, and antibonding pi molecular orbitals, just like ozone. The bonding molecular orbital is distributed between the nitrogen and oxygen atoms.

Step 4- Pi bonding in NO2-

Nitrogen requires three hybridized orbitals to accommodate two sigma bonds and one electron. As a result, sp² hybridization occurs. One electron will be present in each of the three sp² hybrid orbitals in nitrogen, as well as one electron in the p orbital. Only one sp² hybrid orbital and one p orbital will have one electron each when it creates the two sigma bonds. With the oxygen atom, the p orbital will create a pi bond.