Question

In which of the molecules is the lone pair : bond pair of electrons ratio \(2:3\)?

• A. \(NH_3\)
• B. \(H_2O\)
• C. \(XeF_4\)
• D. \(ClF_3\)

Hint:

For VSEPR questions, always count lone pairs and bond pairs on the central atom.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This question requires us to determine the Lewis structure for each given molecule to count the number of lone pairs (non-bonding electron pairs) and bond pairs. A bond pair is a pair of electrons shared between two atoms. A double bond consists of two bond pairs, and a triple bond consists of three bond pairs.
Step 2: Key Formula or Approach:
1. Draw the Lewis dot structure for each molecule. 2. Count the total number of lone pairs on all atoms in the molecule. 3. Count the total number of bond pairs connecting the atoms. 4. Calculate the ratio of lone pairs to bond pairs.
Step 3: Detailed Explanation:

(A) Cl$_2$: The Lewis structure is Cl-Cl. Each chlorine atom has 3 lone pairs.
Total Lone Pairs (LP) = 3 + 3 = 6.
Total Bond Pairs (BP) = 1 (for the single bond).
Ratio LP:BP = 6:1.

(B) O$_2$: The Lewis structure is O=O. Each oxygen atom has 2 lone pairs.
Total Lone Pairs (LP) = 2 + 2 = 4.
Total Bond Pairs (BP) = 2 (for the double bond).
Ratio LP:BP = 4:2 = 2:1.

(C) HCl: The Lewis structure is H-Cl. The hydrogen atom has 0 lone pairs, and the chlorine atom has 3 lone pairs.
Total Lone Pairs (LP) = 3.
Total Bond Pairs (BP) = 1 (for the single bond).
Ratio LP:BP = 3:1.

(D) N$_2$: The Lewis structure is N$\equiv$N. Each nitrogen atom has 1 lone pair.
Total Lone Pairs (LP) = 1 + 1 = 2.
Total Bond Pairs (BP) = 3 (for the triple bond).
Ratio LP:BP = 2:3.

Step 4: Final Answer:
The molecule with a lone pair to bond pair ratio of 2:3 is N$_2$. Therefore, option (D) is correct.