Choose the best Lewis structure that describes the bonding in the SeO32— ion.

Question

Choose the best Lewis structure that describes the bonding in the SeO32— ion.

BlackTom AI · Accepted Answer

Question restatement: Choose the best Lewis structure that describes the bonding in the SeO3^{2−} ion.

Option-by-option analysis:

- Option (a): This structure shows Se forming three bonds to oxygen atoms with two double bonds and one single bond, or some arrangement that leaves Se without a lone pair. If Se has no lone pair in this depiction, its formal charge distribution would not properly sum to the overall 2− charge, and the octet rule would be violated for Se in a way that contradicts known chemistry for Se in the +6 oxidation state with expanded octets. The lack of a clearly placed lone pair on Se also tends to misrepresent the formal charges on the oxygen atoms.

- Option (b): In this drawing, Se appears to be bonded to three oxygens with one of the bonds being a double bond and the others singles, but the placement of lone pairs and the formal charges on the oxygens do not balance to give an overall 2− charge while keeping Se with a single lone pair. The formal charge accounting here does not align with the true resonance description of SeO3^{2−}.

- Option (c): This option shows a structure with all three bonds as single bonds (Se–O) and no clear distribution that yields the correct overall charge, or it places charges on oxygens in a way that does not satisfy the necessary resonance stabilization. The resulting formal charges would not sum to −2, and Se would lack the appropriate lone pair or expanded-octet condition.

- Option (d): Here, the arrangement may try to place a lone pair on Se but misplaces either a lone pair count or the number of double bonds, leading to an incorrect formal charge distribution across Se and the oxygens. The oxygen atoms would not achieve the proper octets or the expected −1 charges on the singly bonded oxygens.

- Option (e): This structure correctly captures the key features of SeO3^{2−}: Se has one lone pair, there is one Se=O double bond, and the other two Se–O bonds are single bonds with the corresponding negative charges localized on the singly bonded oxygens. This arrangement yields the correct formal charge accounting: Se (valence 6) with one lone pair (2 nonbonding electrons) and four bonding electron pairs (one double bond counts as two pairs and two single bonds count as two pairs) gives a formal charge of 0 on Se; the two singly bonded O atoms carry a −1 formal charge each, the doubly bonded O is neutral, giving an overall charge of −2 for the ion. Additionally, Se can expand its octet, which is consistent with third-period elements forming multiple bonds to achieve proper valence satisfaction. This mirrors the accepted resonance description where the negative charge is distributed over the singly bonded oxygens in different resonance forms, while Se retains a lone pair and a double bond in at least one resonance form.

Rationale and common conceptual checks:
- Electron count validation: SeO3^{2−} has a total of 26 valence electrons to distribute (Se 6 + 3×O 6 + 2 extra electrons for the 2− charge). The favored structure should allocate these electrons to satisfy octets where appropriate and to place the −2 charge on the oxygens rather than on Se.
- Formal charge consistency: The structure in (e) achieves the required total charge of −2 while keeping Se with a lone pair and at least one Se=O double bond, which is consistent with known chemistry of Se in oxoanions that can expand their valence shell.
- Octet vs. expanded octet: Selenium in period 4 can accommodate expanded octets; the depiction in (e) aligns with this by allowing a hypervalent arrangement around Se while satisfying overall charge considerations.

Conclusion (embedded in reasoning): Among the given options, (e) best satisfies the electron count, formal charge distribution, and the ability of Se to have an expanded octet with a lone pair, consistent with the known bonding description of SeO3^{2−}.

Choose the best Lewis structure that describes the bonding in the SeO32— ion.

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