Using the VSEPR model, the molecular geometry of the central atom in H2S is
A) trigonal pyramid
B) trigonal planar
C) tetrahedral
D) linear
E) bent
The correct answer and explanation is :
The correct answer is:
E) Bent
Explanation:
To determine the molecular geometry of H₂S (hydrogen sulfide) using the Valence Shell Electron Pair Repulsion (VSEPR) model, follow these steps:
- Determine the Lewis Structure:
- Sulfur (S) is the central atom and has 6 valence electrons (Group 16).
- Each hydrogen (H) contributes 1 valence electron (total of 2 electrons from two H atoms).
- The total valence electrons in H₂S = 6 (S) + 2(1) = 8 electrons.
- Sulfur forms single bonds with each hydrogen, using 4 electrons (or 2 pairs), leaving 4 nonbonding electrons (or 2 lone pairs) on sulfur.
- Predict the Electron Geometry:
- The steric number (number of bonding pairs + lone pairs) around sulfur is 4 (2 bonds + 2 lone pairs).
- According to the VSEPR model, a steric number of 4 corresponds to a tetrahedral electron geometry.
- Determine the Molecular Geometry:
- The molecular geometry is determined by the positions of atoms, not lone pairs.
- Since sulfur has two lone pairs, they repel the bonding pairs, pushing the H-S-H bonds closer together.
- This distortion results in a bent molecular shape (not tetrahedral, because lone pairs are not counted in molecular geometry).
- Bond Angle Consideration:
- In a perfect tetrahedral arrangement, bond angles are 109.5°.
- However, lone pairs exert greater repulsion than bonding pairs, reducing the H-S-H bond angle to approximately 104-105°, similar to water (H₂O).
Conclusion:
The molecular geometry of H₂S is bent, making option E) Bent the correct answer.