Question

1. write lewis structures for the following. show all resonance structures where applicable. for c and d, the central atom is carbon: 4

a) no2− b) no3−
c) ocn− d) scn−

Explanation:

Step1: Calculate total valence electrons for each ion

a) $\text{NO}_2^-$: $5 + 2\times6 + 1 = 18$
b) $\text{NO}_3^-$: $5 + 3\times6 + 1 = 24$
c) $\text{OCN}^-$: $6 + 4 + 5 + 1 = 16$
d) $\text{SCN}^-$: $6 + 4 + 5 + 1 = 16$

Step2: Draw Lewis structures with resonance (if applicable)

Resonance occurs when multiple equivalent structures exist with delocalized electrons.

Answer:

a) $\text{NO}_2^-$: Two resonance structures: central N bonded to two O (one double, one single), lone pairs on O; double bond alternates between O atoms.
b) $\text{NO}_3^-$: Three resonance structures: central N bonded to three O (one double, two single), double bond alternates among O atoms.
c) $\text{OCN}^-$: Three resonance structures: linear O-C-N with double/triple bonds alternating (O=C=N⁻, ⁻O-C≡N, O≡C-N⁻).
d) $\text{SCN}^-$: Three resonance structures: linear S-C-N with double/triple bonds alternating (S=C=N⁻, ⁻S-C≡N, S≡C-N⁻).

(Structures can be represented as:
a) $[\text{O}=\text{N}-\text{O}]^-$ ↔ $[\text{O}-\text{N}=\text{O}]^-$
b) $[\text{O}=\text{N}(-\text{O})_2]^-$ (three forms with double bond on different O)
c) $\text{O}=\text{C}=\text{N}^-$ ↔ $^-\text{O}-\text{C}≡\text{N}$ ↔ $\text{O}≡\text{C}-\text{N}^-$
d) $\text{S}=\text{C}=\text{N}^-$ ↔ $^-\text{S}-\text{C}≡\text{N}$ ↔ $\text{S}≡\text{C}-\text{N}^-$)