Draw the Lewis structure for a dinitride(2-) ion N2^2-.
The Correct Answer and Explanation is:
Correct Lewis Structure for Dinitride Ion (N₂²⁻):
The dinitride ion (N₂²⁻) consists of two nitrogen atoms (N) and carries a 2− charge. The correct Lewis structure is:
mathematicaCopyEdit:⁻N≡N⁻:
Structure Explanation:
- A triple bond connects the two nitrogen atoms.
- Each nitrogen has one lone pair.
- The extra 2− charge is distributed as one negative charge per nitrogen atom, often shown as one lone pair with a negative formal charge on each N.
Explanation:
The Lewis structure of a molecule or ion shows how valence electrons are arranged among the atoms. For the dinitride ion, N₂²⁻, we begin by calculating the total number of valence electrons.
- Each nitrogen atom contributes 5 valence electrons, and the ion has an extra 2 electrons due to the 2− charge.
- Total electrons:
5 (from N) + 5 (from N) + 2 (extra) = 12 valence electrons.
Now we determine how to arrange these electrons between the two nitrogen atoms.
To satisfy the octet rule, each nitrogen atom should ideally have 8 electrons around it (bonding + non-bonding). The most stable structure for N₂²⁻ is one with a triple bond between the nitrogen atoms:
- Three shared pairs (6 electrons) form the triple bond.
- The remaining 6 electrons are distributed as 3 lone pairs: one on each nitrogen atom (2 electrons each), and one more on each nitrogen to reflect the negative charges (for a total of 4 non-bonded electrons per N).
This configuration ensures:
- Each N has a full octet: 3 bonds (6 electrons) + 1 lone pair (2 electrons) = 8 electrons.
- The formal charge on each N is −1, resulting in a total charge of −2 for the ion.
Thus, the Lewis structure is :⁻N≡N⁻:, with one lone pair and a −1 formal charge on each nitrogen, and a triple bond between them. This structure reflects correct bonding, full octets, and the appropriate total charge.
