Question

The molecular geometry of \( \mathrm{SF_4} \) according to VSEPR theory
• Tetrahedral
• Seesaw
• Square planar
• Trigonal bipyramidal

• A. Tetrahedral
• B. Seesaw
• C. Square planar
• D. Trigonal bipyramidal

Hint:

For \( \mathrm{SF_4} \): \[ \text{Bond pairs} = 4 \] \[ \text{Lone pairs} = 1 \] Five electron domains give trigonal bipyramidal electron geometry, but due to one lone pair, the molecular shape becomes seesaw.

Answer 1

The Correct Option is B

Concept: The shape of molecules can be predicted using the VSEPR theory (Valence Shell Electron Pair Repulsion Theory). According to VSEPR theory:
• Electron pairs around the central atom repel each other.
• The electron pairs arrange themselves in such a way that repulsion becomes minimum.
• Both bond pairs and lone pairs contribute toward repulsion. The order of repulsion is: \[ \text{Lone pair - Lone pair} > \text{Lone pair - Bond pair} > \text{Bond pair - Bond pair} \] Thus, the presence of lone pairs changes the molecular geometry significantly.

Step 1: Find the valence electrons of sulfur. Sulfur belongs to Group 16. Therefore, sulfur has: \[ 6 \text{ valence electrons} \] Fluorine belongs to Group 17 and contributes one bond each. In \( \mathrm{SF_4} \):
• Sulfur forms four S--F bonds.
• Four electrons are used in bonding. Remaining electrons on sulfur: \[ 6 - 4 = 2 \] These two electrons form: \[ 1 \text{ lone pair} \]

Step 2: Determine the total electron domains. Around sulfur:
• \(4\) bond pairs
• \(1\) lone pair Total electron domains: \[ 4 + 1 = 5 \] According to VSEPR theory, five electron domains correspond to: \[ \boxed{\text{Trigonal bipyramidal electron geometry}} \]

Step 3: Understand the placement of the lone pair. In trigonal bipyramidal geometry:
• There are two axial positions.
• There are three equatorial positions. A lone pair prefers the equatorial position because:
• Equatorial position experiences fewer repulsions.
• Axial positions have three \(90^\circ\) interactions.
• Equatorial positions have only two \(90^\circ\) interactions. Thus, the lone pair occupies an equatorial position.

Step 4: Determine the molecular shape. After placing one lone pair in trigonal bipyramidal arrangement, the remaining four fluorine atoms form a distorted geometry called: \[ \boxed{\text{Seesaw shape}} \] The molecule resembles the shape of a seesaw due to unequal distribution of atoms around sulfur.

Step 5: Verify the remaining options.
• Tetrahedral: Requires four bond pairs and no lone pair. Hence incorrect.
• Square planar: Usually arises from octahedral geometry with two lone pairs. Hence incorrect.
• Trigonal bipyramidal: This is the electron pair geometry, not the molecular geometry because one position is occupied by a lone pair. Therefore, only seesaw is correct. Final Conclusion: The molecular geometry of \( \mathrm{SF_4} \) is: \[ \boxed{\text{Seesaw}} \] Hence, the correct answer is: \[ \boxed{(2)} \]