extra credit (80 pts) Structures: Which of the following statements is TRUE? A) Draw the Lewis structure for CO32- including any valid resonance. B) The CO32- ion contains one C-O single bond and two C-O double bonds. C) The CO32- ion contains three C-O double bonds. D) The CO32- ion contains two C-O single bonds and one C-O double bond. E) None of the above are true.
The Correct Answer and Explanation is:
Correct Answer: A) Draw the Lewis structure for CO₃²⁻ including any valid resonance.
Explanation:
The carbonate ion (CO₃²⁻) consists of one carbon atom and three oxygen atoms, carrying an overall charge of negative two. To determine the correct Lewis structure, we start by calculating the total number of valence electrons:
- Carbon (C) has 4 valence electrons.
- Each oxygen (O) has 6 valence electrons, and there are 3 oxygen atoms, so 6 × 3 = 18.
- The ion has a −2 charge, meaning 2 additional electrons must be added.
Total valence electrons = 4 (C) + 18 (O) + 2 (charge) = 24 electrons
Carbon is the central atom, and each oxygen is bonded to it. Distributing the electrons, we place single bonds between carbon and each oxygen atom. This uses 6 electrons (3 bonds × 2 electrons). The remaining 18 electrons are placed to satisfy the octets of the oxygen atoms.
However, this initial structure leaves the carbon atom with only 6 electrons. To satisfy the octet rule for carbon, one of the lone pairs from an oxygen atom forms a double bond with carbon. This results in one C=O double bond and two C–O single bonds. But this arrangement can happen with any of the three oxygen atoms.
As a result, there are three equivalent resonance structures for the carbonate ion. Each structure has one double bond and two single bonds, but the position of the double bond rotates among the three oxygen atoms. The actual structure is a resonance hybrid, meaning all three bonds are equivalent and intermediate in character. They are all the same length and strength, not distinct single or double bonds.
Therefore:
- Option B is incorrect because the ion does not contain one single and two double bonds.
- Option C is incorrect because it does not contain three double bonds.
- Option D is incorrect because it does not have two single and one double bond permanently.
- Option E is incorrect because option A is true.
Thus, option A is the only correct statement.
