Question

How many of the following interhalogen species have 2 lone pairs of electrons on the central atom?
\( \text{ClF}_3 \), \( \text{ClF}_2^- \), \( \text{ClF}_5 \), \( \text{ICl}_2^+ \)

Hint:

To determine the number of lone pairs, count the total valence electrons on the central atom and subtract the number of electrons used in bonding.

Answer 1

Correct Answer: 2

Step 1: Analyzing the interhalogen species. 
For interhalogen compounds, the central atom typically has lone pairs depending on its oxidation state and bonding. Let's consider each species: 
- \( \text{ClF}_3 \): Chlorine in this compound has 2 lone pairs because it has a total of 7 valence electrons (one from each fluorine) and requires 3 bonds to fluorine atoms. Thus, chlorine has 2 lone pairs. 

- \( \text{ClF}_2^- \): In this species, chlorine has 3 lone pairs because it gains an extra electron due to the negative charge, making the total valence electron count for chlorine 8. 

- \( \text{ClF}_5 \): In \( \text{ClF}_5 \), chlorine forms 5 bonds with fluorine, leaving no lone pairs on the central chlorine atom. 

- \( \text{ICl}_2^+ \): In this species, iodine forms 2 bonds with chlorine atoms and thus has 3 lone pairs of electrons on the central iodine atom. 
 

Step 2: Conclusion. 
Only \( \text{ClF}_3 \) and \( \text{ClF}_2^- \) have 2 lone pairs of electrons on the central atom. Thus, the correct answer is 2.