Question

Total number of non-bonded electrons present in \( \text{NO}_2 \); ion based on Lewis theory is:

Hint:

In Lewis structures, non-bonded electrons are the valence electrons that are not shared between atoms. Count these electrons after assigning bonds to the atoms.

Answer 1

Correct Answer: 12

For the \( \text{NO}_2 \) ion, we consider the electron configuration based on the Lewis structure. The total number of electrons in \( \text{NO}_2^- \) is the sum of the electrons from nitrogen and oxygen atoms. Nitrogen has 5 valence electrons and each oxygen has 6 valence electrons. The negative charge adds an additional electron.
The total number of valence electrons is: \[ 5 \, (\text{from N}) + 6 \times 2 \, (\text{from 2 O}) + 1 \, (\text{from the negative charge}) = 18 \, \text{electrons} \]
In the Lewis structure of \( \text{NO}_2^- \), 2 electrons are involved in the bonding between nitrogen and oxygen atoms, while the remaining electrons are non-bonded.
Thus, the number of non-bonded electrons is \( \boxed{12} \).

Answer 2

Step 1: Write the molecular formula and determine total valence electrons.
The ion given is \( \text{NO}_2^- \) (nitrite ion).
- Nitrogen (N) has 5 valence electrons.
- Each oxygen (O) has 6 valence electrons → 2 × 6 = 12 electrons.
- The negative charge (–1) adds 1 extra electron.
Total valence electrons = 5 + 12 + 1 = 18 electrons.

Step 2: Construct the Lewis structure.
- Nitrogen is the central atom bonded to two oxygens.
- To satisfy the octet, one N–O bond is a double bond and the other is a single bond with a negative charge on the singly bonded oxygen.
Resonance occurs between the two equivalent structures:
\[ \text{O=N–O}^- \quad \leftrightarrow \quad \text{O–N=O}^- \] Thus, the ion has one N–O double bond and one N–O single bond (on average, bond order = 1.5).

Step 3: Count non-bonded (lone pair) electrons.
- Each oxygen atom has lone pairs.
- The double-bonded oxygen has 2 lone pairs = 4 electrons.
- The single-bonded oxygen (with –1 charge) has 3 lone pairs = 6 electrons.
- Nitrogen has 1 lone pair = 2 electrons.
\[ \text{Total non-bonded electrons} = 4 + 6 + 2 = 12 \]

Step 4: Final Answer.
The total number of non-bonded electrons present in \( \text{NO}_2^- \) ion is:
\[ \boxed{12} \]