Question

the correct dot formulation for nitrogen trichloride has:
a 3 n - cl bonds and 10 lone pairs of electrons.
b 1 n - cl bond, 2 n = cl bonds and 7 lone pairs of electrons.
c 3 n - cl bonds and 9 lone pairs of electrons.
d 2 n - cl bonds, 1 n = cl bond and 8 lone pairs of electrons.
e 3 n = cl bonds and 6 lone pairs of electrons.

Explanation:

Step1: Determine the valence electrons

Nitrogen (\(N\)) has \(5\) valence electrons, and chlorine (\(Cl\)) has \(7\) valence electrons. For \(NCl_3\), the total number of valence electrons is \(5+(3\times7)=26\).

Step2: Analyze the bonding and lone - pairs

In \(NCl_3\), nitrogen forms \(3\) single (\(N - Cl\)) bonds. Each \(N - Cl\) bond uses \(2\) electrons. So, \(3\times2 = 6\) electrons are used in bonding.
The remaining electrons are \(26-6=20\) electrons. These remaining electrons exist as lone - pairs. Each lone - pair has \(2\) electrons.
The number of lone - pairs is \(\frac{20}{2}=10\). Nitrogen has \(1\) lone - pair (\(2\) electrons) and each \(Cl\) atom has \(3\) lone - pairs (\(3\times3 = 9\) lone - pairs from \(Cl\) atoms). In total, \(1 + 9=10\) lone - pairs.

Answer:

A. 3 N - Cl bonds and 10 lone pairs of electrons.