Choose the best Lewis structure for NH4
A)
B) H-N-H
C)
D)
E)
14) Ca
The Correct Answer Explanation is:
The correct Lewis structure for NH₄⁺ (ammonium ion) is:
A)
H
|
H - N⁺ - H
|
H
This structure shows a nitrogen (N) atom in the center, forming four single covalent bonds with four hydrogen (H) atoms. The structure also carries a +1 formal charge, making it the ammonium ion (NH₄⁺).
Explanation (300+ words)
The ammonium ion (NH₄⁺) is a positively charged polyatomic ion. To construct the correct Lewis structure, we follow these steps:
1. Count the total valence electrons:
- Nitrogen (N) has 5 valence electrons.
- Each hydrogen (H) has 1 valence electron.
- Total electrons from atoms = 5 (N) + 4×1 (H) = 9 electrons.
- Since the molecule has a +1 charge, we subtract 1 electron.
- So, total electrons = 9 – 1 = 8 valence electrons to distribute.
2. Draw the skeleton structure:
- Place nitrogen (N) at the center, with four hydrogen atoms (H) around it.
H
|
H - N - H
|
H
3. Distribute electrons as bonds:
- Each N–H bond requires 2 electrons.
- 4 bonds × 2 electrons = 8 electrons used — which matches our total.
All electrons are used to form bonds, and there are no lone pairs on the nitrogen.
4. Formal charges:
Let’s calculate formal charge on nitrogen:
- Valence electrons of N = 5
- Bonding electrons shared = 8 (in 4 bonds) → 4 owned by N
- Formal charge = 5 – 4 = +1
Each hydrogen has a formal charge of 0.
So, the entire NH₄⁺ ion has a net charge of +1, which matches the ion’s charge.
Why the others are incorrect:
Option B), showing “H–N–H”, only accounts for 2 hydrogen atoms and 2 bonds, which is incomplete for NH₄⁺. Other options are either blank or incomplete and do not correctly represent the structure or charge of the ammonium ion.
Conclusion:
The correct Lewis structure for NH₄⁺ is a central nitrogen atom bonded to four hydrogen atoms, with a +1 overall charge. There are no lone pairs on nitrogen, and the octet rule is satisfied. Therefore, Option A is correct