What hybridization scheme would be appropriate for the C atom in [CO3] 2? Draw resonance structures to describe the bonding in [CO3] 2. Figure 5.34 shows representations of three MOs of [CO3] 2. The MOs in diagrams (a) and (b) in Fig. 5.34 are occupied; the MO in diagram (c) is unoccupied. Comment on the characters of these MOs and assign a symmetry label to each orbital.
The Correct Answer and Explanation is :
In the carbonate ion ([CO_3]^{2-}), the carbon atom is in the center of the structure with three oxygen atoms arranged symmetrically around it. The hybridization scheme of the central carbon atom in ([CO_3]^{2-}) is (sp^2). This is because the molecule adopts a trigonal planar geometry with bond angles of approximately 120°.
Resonance Structures of ([CO_3]^{2-}):
The bonding in the carbonate ion can be described by three resonance structures, where the double bond between carbon and each oxygen atom is delocalized over all three bonds. In each resonance structure, one oxygen atom has a double bond with the carbon atom, while the other two have single bonds with a formal negative charge.
- Structure 1: One oxygen is doubly bonded to the carbon, while the other two oxygen atoms have single bonds with formal negative charges.
- Structure 2: The double bond shifts to one of the other oxygen atoms, and the negative charges shift correspondingly.
- Structure 3: The third oxygen atom gets the double bond while the first two oxygens each have a negative charge.
This delocalization of electrons results in an average bond order of 1⅓ for each C–O bond in the ion.
Molecular Orbitals (MOs):
The molecular orbitals (MOs) in Fig. 5.34 represent the bonding and antibonding interactions in the carbonate ion.
- Diagram (a): The first MO is a bonding orbital, formed from the combination of the carbon (2p) orbital and the (2p) orbitals of the three oxygens. This MO has a symmetric combination of the atomic orbitals, which means it has A_1 symmetry.
- Diagram (b): The second MO is also bonding, but it is less symmetric than the first. This orbital involves the out-of-phase combination of the oxygen (2p) orbitals and has B_1 symmetry.
- Diagram (c): The third MO is unoccupied and represents an antibonding interaction between the carbon and oxygen orbitals. It has A_2 symmetry and is higher in energy than the bonding orbitals.
Conclusion:
In ([CO_3]^{2-}), the carbon atom undergoes (sp^2) hybridization, with delocalized π-bonds across the three C–O bonds, leading to a trigonal planar structure. The molecular orbitals reflect the symmetry and bonding interactions of the ion.
I’ll generate an image to help visualize the resonance structures and the molecular orbitals for you.
Here is the image depicting the three resonance structures of the carbonate ion ([CO_3]^{2-}) and the molecular orbitals (MOs) involved. It shows how the carbon atom in the ion adopts (sp^2) hybridization, with delocalized bonding across the oxygen atoms, as well as the symmetry of the molecular orbitals.
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