Question

Choose the INCORRECT pair of MOLECULE and its SHAPE among the following:

• A. \( SF_4 \) — Seesaw
• B. \( BrF_5 \) — Trigonal bipyramidal
• C. \( NH_3 \) — Trigonal pyramidal
• D. \( XeF_4 \) — Square planar
• E. \( ClF_3 \) — T-shape

Hint:

Count lone pairs carefully in VSEPR.

Answer 1

The Correct Option is B

Step 1: Understanding VSEPR Theory:
The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the geometry of molecules based on the number of electron pairs surrounding their central atoms. The shape is determined by minimizing the repulsion between these electron pairs.
Step 2: Analyzing Each Molecule:
(A) SF\(_4\): Central atom is Sulfur (S). Valence electrons of S = 6. Electrons from 4 F atoms = 4. Total valence electrons = 10. This corresponds to 5 electron pairs. Arrangement: 4 bond pairs and 1 lone pair. The geometry based on 5 electron pairs is trigonal bipyramidal, but the shape considering the lone pair is Seesaw. This pair is correct.
(B) BrF\(_5\): Central atom is Bromine (Br). Valence electrons of Br = 7. Electrons from 5 F atoms = 5. Total valence electrons = 12. This corresponds to 6 electron pairs. Arrangement: 5 bond pairs and 1 lone pair. The geometry based on 6 electron pairs is octahedral, but the shape considering the lone pair is Square pyramidal. The option states Trigonal bipyramidal, which is the shape for 5 bond pairs and 0 lone pairs. Therefore, this pair is INCORRECT.
(C) NH\(_3\): Central atom is Nitrogen (N). Valence electrons of N = 5. Electrons from 3 H atoms = 3. Total valence electrons = 8. This corresponds to 4 electron pairs. Arrangement: 3 bond pairs and 1 lone pair. The geometry is tetrahedral, but the shape is Trigonal pyramidal. This pair is correct.
(D) XeF\(_4\): Central atom is Xenon (Xe). Valence electrons of Xe = 8. Electrons from 4 F atoms = 4. Total valence electrons = 12. This corresponds to 6 electron pairs. Arrangement: 4 bond pairs and 2 lone pairs. The geometry is octahedral, and to minimize repulsion, the lone pairs occupy opposite positions, resulting in a Square planar shape. This pair is correct.
(E) ClF\(_3\): Central atom is Chlorine (Cl). Valence electrons of Cl = 7. Electrons from 3 F atoms = 3. Total valence electrons = 10. This corresponds to 5 electron pairs. Arrangement: 3 bond pairs and 2 lone pairs. The geometry is trigonal bipyramidal, and the lone pairs occupy equatorial positions, resulting in a T-shape. This pair is correct.
Step 3: Final Answer:
The incorrect pair is (B) BrF\(_5\) - Trigonal bipyramidal. The correct shape is Square pyramidal.