Question

Which of the following pair of species have different Lewis structures? (A) \( \mathrm{SO_3^{2-}, CO_3^{2-}} \)
(B) \( \mathrm{O_2^{2-}, F_2} \)
(C) \( \mathrm{CN^- , CO} \)
(D) \( \mathrm{NH_3, H_3O^+} \)
(E) \( \mathrm{MnO_4^- , CrO_4^{2-}} \)

• (A) only
• (A) & (B) only
• (A) & (E) only
• (C) & (D) only

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify pairs of species that do not share the same Lewis structure (isostructurality and isoelectronic nature).
Step 2: Detailed Explanation:
- Pair (A): \(SO_3^{2-}\) vs \(CO_3^{2-}\).
In \(SO_3^{2-}\), Sulfur has 6 valence electrons + 2 from charge = 8. It forms 3 sigma bonds and has 1 lone pair (Steric number = 4). Its geometry is tetrahedral and shape is trigonal pyramidal.
In \(CO_3^{2-}\), Carbon has 4 valence electrons + 2 from charge = 6. It forms 3 sigma bonds with no lone pair (Steric number = 3). Its geometry and shape are trigonal planar.
Since they have different steric numbers and shapes, they have different Lewis structures.
- Other Pairs:
(B) \(O_2^{2-}\) and \(F_2\) are isoelectronic (18 electrons) and both are linear single-bonded species.
(C) \(CN^-\) and \(CO\) are isoelectronic (14 electrons) and both have a triple bond.
(D) \(NH_3\) and \(H_3O^+\) are isoelectronic and both are trigonal pyramidal.
(E) \(MnO_4^-\) and \(CrO_4^{2-}\) are both tetrahedral transition metal oxoanions.
Step 3: Final Answer:
Only pair (A) consists of species with different Lewis structures.