What is the molecular geometry of S In the structure of sulfite ion acid SO3^2-? Linear. Bent. Trigonal planar. Trigonal pyramid. Tetrahedral
The Correct Answer and Explanation is:
The molecular geometry of the sulfite ion (SO₃²⁻) is trigonal planar.
To explain this, let’s first look at the bonding and structure of the sulfite ion:
- Electron Configuration and Lewis Structure: The sulfite ion has a sulfur atom (S) centrally located, surrounded by three oxygen atoms (O). The sulfur atom has an oxidation state of +4, and the three oxygen atoms are bonded to it, each with a formal charge of -1. This creates a resonance structure, meaning the double bonds are delocalized and spread equally among the three S-O bonds.
- Valence Electrons and Electron Pair Geometry: Sulfur, in its +4 oxidation state, has 4 valence electrons. Each oxygen atom contributes 6 valence electrons, but because of the negative charge on the ion, there are two additional electrons, giving a total of 24 valence electrons. The ion’s electron geometry is determined by the repulsion between the bonding pairs of electrons.
- VSEPR Theory: According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the electron pairs around the sulfur atom will arrange themselves to minimize electron-electron repulsion. With three bonding pairs and no lone pairs on the central sulfur atom, the most favorable arrangement is trigonal planar. This means the bond angles between the oxygen atoms are approximately 120°.
- Resonance and Delocalization: Since the ion exhibits resonance, where the double bond character is spread across all three S-O bonds, the bond angles remain consistent and symmetric, further confirming the trigonal planar geometry.
In summary, the sulfite ion has a trigonal planar molecular geometry, with the sulfur atom at the center and the oxygen atoms arranged symmetrically around it.
