Final answer:
To draw resonance structures for a cation intermediate like the carbonate anion, move π-electrons or lone pairs within the same skeletal structure, ensuring each oxygen has a turn in forming a double bond with carbon. Calculate formal charges accordingly.
Step-by-step explanation:
The resonance structures of a cation intermediate can be visualized by moving π-electrons or lone pairs while keeping the positioning of atoms and the σ-electrons (sigma) unchanged. In the case of a carbonate anion (CO32-), which was mentioned earlier, there are three oxygen atoms bonded to a central carbon atom. Every oxygen atom has at least one lone pair of electrons that can participate in resonance.
To draw the resonance structures for an intermediate like this, we would:
- Keep the skeleton of the molecule the same, ensuring the central atom remains bonded to the same atoms.
- Move one of the π-bonds of the double bond to form a lone pair on an adjacent oxygen.
- Create a new double bond by converting a lone pair from a different oxygen atom into a π-bond.
- Repeat this process to identify all possible resonance structures, which in the case of the carbonate ion, involves three structures where each oxygen atom gets a turn having a double bond with carbon.
In determining formal charges for each structure, remember that the formal charge is calculated by the valence electrons on the free atom minus the number of bonds and lone pair electrons around the atom in the structure.