Question

The number of lone pairs of electrons on the central atom of \( BrF_5 \), \( XeO_3 \), \( SO_3 \) respectively are:

• A. \( 1, 1, 2 \)
• B. \( 1, 2, 2 \)
• C. \( 2, 2, 1 \)
• D. \( 1, 1, 1 \)

Hint:

To determine lone pairs, use the formula: Lone pairs = \( \frac{\text{Total valence electrons} - \text{Electrons used in bonding}}{2} \).

Answer 1

The Correct Option is D

Step 1: Finding Lone Pairs on the Central Atom
Lone pairs on the central atom can be determined using the VSEPR (Valence Shell Electron Pair Repulsion) theory.
1. Bromine Pentafluoride (\( BrF_5 \))
- Bromine (\( Br \)) has 7 valence electrons.
- It forms 5 single bonds with fluorine atoms.
- Total valence electrons used in bonding: \( 5 \times 2 = 10 \).
- Remaining electrons: \( 7 - 5 = 2 \) (1 lone pair).
- Molecular geometry: Square pyramidal.
2. Xenon Trioxide (\( XeO_3 \))
- Xenon (\( Xe \)) has 8 valence electrons.
- It forms 3 double bonds with oxygen atoms.
- Total valence electrons used in bonding: \( 3 \times 2 = 6 \).
- Remaining electrons: \( 8 - 6 = 2 \) (1 lone pair).
- Molecular geometry: Trigonal pyramidal.
3. Sulfur Trioxide (\( SO_3 \))
- Sulfur (\( S \)) has 6 valence electrons.
- It forms 3 double bonds with oxygen atoms.
- Total valence electrons used in bonding: \( 3 \times 2 = 6 \).
- Remaining electrons: \( 6 - 6 = 0 \) (No lone pairs).
- Molecular geometry: Trigonal planar.
Step 2: Conclusion The number of lone pairs on the central atom for each molecule: \[ BrF_5 = 1, \quad XeO_3 = 1, \quad SO_3 = 1 \] Thus, the correct answer is \( 1, 1, 1 \), which matches option (4).