Question

instructions

1. draw the following resonance structures:

• $co_{32}^-$
• $o_3$
• $so_2$
• $no_3^-$
• for each molecule, state the molecular geometry.

1. write a paragraph explaining:
2. why do resonance structures occur?
3. the relationship between lewis structures and resonance structures.
4. interactions involved that create resonance structures.
5. within your explanations, make sure to site at least two of the resonance structure you created from #1.

Explanation:

Step1: Analyze \( CO_{3}^{2-} \)

• Lewis Structure: Carbon is central, bonded to 3 O. Total valence electrons: \( 4 + 3\times6 + 2 = 24 \). C forms double bond with one O, single with two (each single-bonded O has -1 charge).
• Resonance: Double bond can be with any of the 3 O, so 3 resonance structures (electron delocalization in \( \pi \)-system).
• Molecular Geometry: Trigonal planar (3 bonding groups, no lone pairs on C).

Step2: Analyze \( O_3 \)

• Lewis Structure: Central O bonded to two O. Valence electrons: \( 3\times6 = 18 \). One single, one double bond; central O has 1 lone pair, terminal O (single) has 3, (double) has 2.
• Resonance: Double bond can be with either terminal O, 2 resonance structures (delocalized \( \pi \) electrons).
• Molecular Geometry: Bent (2 bonding groups, 1 lone pair on central O, electron - pair geometry trigonal planar).

Step3: Analyze \( SO_2 \)

• Lewis Structure: S central, bonded to 2 O. Valence electrons: \( 6 + 2\times6 = 18 \). One double, one single bond; S has 1 lone pair.
• Resonance: Double bond can switch between O, 2 resonance structures (delocalized \( \pi \) electrons).
• Molecular Geometry: Bent (2 bonding groups, 1 lone pair on S, electron - pair geometry trigonal planar).

Step4: Analyze \( NO_3^- \)

• Lewis Structure: N central, bonded to 3 O. Valence electrons: \( 5 + 3\times6+1 = 24 \). Double bond with one O, single with two (single - bonded O have -1 charge).
• Resonance: Double bond can be with any O, 3 resonance structures (delocalized \( \pi \) electrons).
• Molecular Geometry: Trigonal planar (3 bonding groups, no lone pairs on N).

Step5: Explain Resonance - Related Concepts

• Why Resonance Occurs: Electrons (especially \( \pi \)-electrons or lone pairs in conjugated systems) delocalize to stabilize the molecule. E.g., in \( CO_3^{2 - } \), charge is spread over 3 O, reducing electron - electron repulsion. In \( NO_3^- \), similar charge delocalization.
• Lewis and Resonance Relationship: Lewis structures show single electron - dot arrangements, resonance structures are multiple Lewis - like structures that together represent the actual electron distribution (a hybrid). E.g., \( O_3 \)’s actual structure is a hybrid of its two resonance Lewis structures.
• Interactions for Resonance: Delocalization of \( \pi \)-electrons (in \( p \)-orbitals) or lone pairs into a conjugated \( \pi \)-system. In \( SO_2 \), \( \pi \)-electrons of the double bond delocalize, and in \( CO_3^{2 - } \), lone pairs on O and \( \pi \)-electrons of C = O delocalize.

Paragraph
Resonance structures occur because electrons (especially \( \pi \)-electrons or lone pairs in conjugated systems) delocalize to achieve a more stable electron distribution. For example, in \( CO_3^{2 - } \), the negative charge is spread over three oxygen atoms (via resonance), and in \( NO_3^- \), a similar delocalization stabilizes the ion. Lewis structures represent individual electron - dot arrangements, but resonance structures are multiple Lewis - like depictions that collectively describe the actual electron distribution (a resonance hybrid). For instance, \( O_3 \)’s true structure is a hybrid of its two resonance Lewis structures. The interactions creating resonance involve the delocalization of \( \pi \)-electrons (in overlapping \( p \)-orbitals) or lone pairs into a conjugated \( \pi \)-system. In \( SO_2 \), the \( \pi \)-electrons of the sulfur - oxygen double bond delocalize between the two oxygen atoms, and in \( CO_3^{2 - } \), lone pairs on oxygen atoms and the \( \pi \)-electrons of the carbon - oxygen double bond participate in delocalization, leading to the multiple resonance structures.

Answer:

Resonance Structures and Molecular Geometry

• \( \boldsymbol{CO_3^{2-}} \): 3 resonance structures (double bond with each O), trigonal planar.
• \( \boldsymbol{O_3} \): 2 resonance structures (double bond with either terminal O), bent.
• \( \boldsymbol{SO_2} \): 2 resonance structures (double bond with either O), bent.
• \( \boldsymbol{NO_3^-} \): 3 resonance structures (double bond with each O), trigonal planar.