A gas-phase electron-diffraction experiment compares formal charge assignments for isoelectronic species. For carbon monoxide (CO), total valence electrons are . A common Lewis structure uses a triple bond between C and O with one lone pair on each atom. Based on this Lewis structure, which formal charge assignment is most consistent with the octet rule and electron counting?
- C has +1 and O has −1.
- C has −1 and O has +1. (correct answer)
- C has 0 and O has 0.
- C has +2 and O has −2.
Explanation: This question tests understanding of covalent bonding and Lewis structures, specifically formal charge calculations. Lewis structures illustrate electron distribution, and formal charge equals valence electrons minus (lone pair electrons + ½ bonding electrons). In CO with a triple bond (C≡O) and one lone pair on each atom, carbon's formal charge = 4 - (2 + 3) = -1, while oxygen's formal charge = 6 - (2 + 3) = +1. Choice B is correct because these formal charges satisfy the octet rule while accounting for the unusual electron distribution in CO, where the less electronegative carbon carries negative charge. Choice A is incorrect because it reverses the formal charges, ignoring the electron counting rules. When calculating formal charges, carefully count all electrons assigned to each atom, remembering that bonding electrons are shared equally regardless of electronegativity differences.