Draw the Lewis structure for the polyatomic amide anion(NH2-). Be sure to include all resonance structures that satisfy the octet rule.
The Correct Answer and Explanation is :
The amide anion (( \text{NH}_2^- )) is a polyatomic ion where nitrogen (N) is bonded to two hydrogen (H) atoms and carries a negative charge. To draw the Lewis structure and the resonance structures, we must consider the valence electrons and satisfy the octet rule where applicable.
Step-by-Step Lewis Structure for NH₂⁻
- Count the Valence Electrons:
- Nitrogen (N) has 5 valence electrons.
- Each hydrogen (H) has 1 valence electron, and since there are two hydrogen atoms, they contribute 2 electrons.
- The additional negative charge adds 1 more electron.
- Total: ( 5 + 2 + 1 = 8 ) valence electrons.
- Draw the Skeleton Structure:
- Place nitrogen at the center, bonded to two hydrogen atoms:
[
H – N – H
]
- Distribute Electrons:
- Start by placing two electrons (one bond) between each N and H. This uses 4 of the 8 valence electrons.
- The remaining 4 electrons will be placed as a lone pair on nitrogen. Thus, the initial structure looks like this:
[
H \, : \, N \, : \, H
]
- Indicate the Charge:
- Since the structure carries a negative charge, indicate this on the nitrogen atom:
[
H \, : \, N^{-} \, : \, H
]
Resonance Structures
The amide anion does not have significant resonance structures as it does not allow for the delocalization of electrons. The nitrogen atom already fulfills its octet by holding one lone pair and two bonding pairs, which effectively completes the octet.
Summary
In summary, the Lewis structure for the amide anion ( \text{NH}_2^- ) shows a nitrogen atom with two single bonds to hydrogen atoms and one lone pair, ensuring nitrogen has a full octet. While the amide anion does not exhibit resonance, its primary Lewis structure suffices to explain its bonding and charge distribution. The negative charge on the nitrogen indicates the ion’s overall stability, as nitrogen readily accepts electrons to achieve its octet. This structure is crucial for understanding its behavior in chemical reactions and interactions, particularly in organic and biological chemistry contexts.