Question

Draw the Lewis structure of ozone. Explain why the \(\mathrm{O}-\mathrm{O}\) bond \((1.28 \AA)\) is longer in ozone than in \(\mathrm{O}_{2}(1.21 \AA)\).

Short answer

The Lewis structure of ozone (O3) is: O = O - O, with three lone pairs on each oxygen atom. The difference in O-O bond lengths between ozone and O2 can be explained by the resonance structure in ozone. In O2, there are two equivalent double bonds, whereas in ozone, there is a resonance structure with a bond order intermediate between a single and a double bond. This leads to a longer bond length in ozone (1.28 Å) compared to O2 (1.21 Å), due to the inverse relationship between bond length and bond strength/order.

Step-by-step solution

Determine the number of valence electrons

Each oxygen atom has 6 valence electrons since it is in group 16 of the periodic table. Ozone (O3) has three oxygen atoms, so the total number of valence electrons is: Total valence electrons = 6 (valence electrons per oxygen) × 3 (oxygen atoms in O3) = 18 valence electrons

Assemble the Lewis structure

To draw the Lewis structure, follow these steps: 1. Choose a central atom; in this case, it will be an oxygen atom. 2. Place the other two oxygen atoms on either side of the central atom to form a chain. 3. Create single bonds between the central oxygen atom and the other oxygen atoms using 2 electrons for each bond (4 electrons in total). 4. Distribute the remaining 14 electrons as lone pairs (each pair counts as 2 electrons) on each oxygen atom, starting with the outer atoms. Each oxygen atom will have three lone pairs. 5. Check the formal charge on each atom to ensure that each oxygen atom has a stable configuration. You'll find that the central oxygen atom has a formal charge of +1, and the other two oxygen atoms have a formal charge of -1. This means that there is a resonance structure, where the electrons from the double bond can be delocalized between the two outer oxygen atoms. The Lewis structure of ozone (O3) should look like this: O = O - O (with three lone pairs on each oxygen atom)

Explain the difference in O-O bond lengths

The difference in the O-O bond lengths in ozone and O2 can be explained by the resonance structure in ozone. In O2, there are two equivalent double bonds, with each bond sharing 2 electron pairs. In ozone, there is a resonance structure, in which one of the outer oxygen atoms shares a double bond with the central oxygen and the other outer oxygen atom shares a single bond. The delocalization of electrons between the two outer oxygen atoms results in a bond order that is intermediate between a single (2 electrons) and a double bond (4 electrons). The bond length of a chemical bond is inversely proportional to its bond strength or bond order. A single bond has a bond order of 1 and is typically longer and weaker than a double bond, which has a bond order of 1.5. Since the O-O bond in ozone has a bond order that is less than 2 (due to resonance), it is expected to have a longer bond length compared to the double bond in O2. Thus, the O-O bond length in ozone is 1.28 Å, compared to 1.21 Å in O2, due to the presence of resonance.