Question

In $ SO_2 $, $ NO_2^- $ and $ N_3^- $ the hybridizations at the central atom are respectively :

• A. \( sp^2 \), \( sp^2 \) and \( sp \)
• B. \( sp^2 \), \( sp \) and \( sp \)
• C. \( sp^2 \), \( sp^2 \) and \( sp^2 \)
• D. \( sp \), \( sp^2 \) and \( sp \)

Hint:

To determine the hybridization of the central atom, use the steric number concept: Steric Number = Number of sigma bonds + Number of lone pairs. For resonance structures, the hybridization of the central atom remains the same across all significant contributing structures.

Answer 1

The Correct Option is A

Step 1: Determine the hybridization of the central atom in \( SO_2 \).
Central atom: Sulfur (S)
Number of valence electrons of S: 6
Number of bond pairs: 2 (with two oxygen atoms)
Number of lone pairs: To complete the octet of S, we form double bonds with both O atoms. This uses 4 electrons. The remaining 2 electrons form one lone pair.
Steric number = Number of bond pairs + Number of lone pairs = 2 + 1 = 3 Hybridization: \( sp^2 \)
Step 2: Determine the hybridization of the central atom in \( NO_2^- \).
Central atom: Nitrogen (N) Number of valence electrons of N: 5
Number of surrounding atoms: 2 (two oxygen atoms)
Total electrons to accommodate (considering the negative charge): \( 5 + 2 \times 6 + 1 = 18 \) Lewis structure: \( [O=N-O^-] \) or \( [O^-N=O] \) (resonance structures). The nitrogen atom forms one double bond and one single bond with oxygen atoms. Number of bond pairs: 2
Number of lone pairs on N: To satisfy the formal charges and octet rule, nitrogen has one lone pair.
Steric number = Number of bond pairs + Number of lone pairs = 2 + 1 = 3 Hybridization: \( sp^2 \)
Step 3: Determine the hybridization of the central atom in \( N_3^- \).
Central atom: Central Nitrogen (N)
Number of valence electrons of N: 5
Total electrons to accommodate (considering the negative charge): \( 3 \times 5 + 1 = 16 \) Lewis structure: \( [:N=N=N:]^- \) or \( [:\overset{-}{N}-N \equiv N:] \) or \( [N \equiv N-\overset{-}{N}:] \) (resonance structures). The central nitrogen atom forms two double bonds or one single and one triple bond. Number of bond pairs around the central N: 2 (regardless of the type of bonds)
Number of lone pairs on the central N: To satisfy the formal charges and octet rule, the central nitrogen has zero lone pairs in the \( [:N=N=N:]^- \) resonance structure. Steric number = Number of bond pairs + Number of lone pairs = 2 + 0 = 2 Hybridization: \( sp \)
Step 4: Combine the hybridizations.
The hybridizations of the central atoms in \( SO_2 \), \( NO_2^- \), and \( N_3^- \) are \( sp^2 \), \( sp^2 \), and \( sp \) respectively.
Step 5: Match with the given options.
This matches option (1).