so2 molecular geometry describes the three-dimensional arrangement of atoms in sulfur dioxide, \(\mathrm{SO_2}\). The sulfur atom sits at the center with two oxygen atoms bonded to it, and the observed molecular shape is bent (angular) rather than linear.
Valence-electron count and Lewis framework
Sulfur (group 16) contributes 6 valence electrons, and each oxygen contributes 6 valence electrons. The total valence-electron count is
A Lewis framework places sulfur between the two oxygens, \(\mathrm{O{-}S{-}O}\). Electron placement that satisfies oxygen octets and accounts for 18 electrons leaves sulfur surrounded by three electron domains: two bonding regions (to the oxygens) and one lone pair.
Electron-domain summary at sulfur
Two S–O bonding domains + one lone-pair domain \(\rightarrow\) 3 electron domains total \(\rightarrow\) trigonal planar electron-domain arrangement.
VSEPR classification and geometry outcome
The central sulfur in \(\mathrm{SO_2}\) corresponds to the VSEPR pattern \(\mathrm{AX_2E}\): two bonded atoms (X) and one lone pair (E) around A (sulfur). Three electron domains arrange approximately 120° apart (trigonal planar electron geometry). The presence of a lone pair means the molecular geometry (positions of atoms only) is bent.
| Feature | SO₂ value | Meaning |
|---|---|---|
| Total valence electrons | 18 | Electron bookkeeping for Lewis structures |
| Electron domains at S | 3 | Two bonding regions + one lone pair |
| Electron-domain geometry | Trigonal planar | Domains spread roughly 120° apart |
| Molecular geometry | Bent (angular) | Atoms form an O–S–O angle less than 120° |
| Typical O–S–O angle | \(\approx 119^\circ\) (slightly less than \(120^\circ\)) | Lone-pair repulsion compresses the bond angle |
| Polarity | Polar | Bent shape prevents cancellation of bond dipoles |
Resonance and bond equivalence
Lewis descriptions of \(\mathrm{SO_2}\) commonly include resonance, with two equivalent contributors that place a double bond on one side and a single bond on the other (formal charges distributed as \(\mathrm{S^{+}}\) and \(\mathrm{O^{-}}\) in each contributor). Resonance explains why the two S–O bonds are equivalent in the real molecule and why each S–O bond has partial double-bond character. The molecular geometry remains bent because the electron-domain count at sulfur stays three.
Visualization of SO₂ geometry and electron domains
Common geometry pitfalls
- Linear prediction from “two atoms attached” ignores the lone pair; \(\mathrm{AX_2E}\) yields a bent molecular geometry.
- Bond type confusion (single vs double) does not change the electron-domain count; geometry follows domain count rather than bond order.
- Nonpolarity assumption fails because the bent shape prevents full cancellation of S–O bond dipoles.
Summary statement
\(\mathrm{SO_2}\) has three electron domains around sulfur, giving a trigonal planar electron-domain arrangement and a bent (angular) SO₂ molecular geometry with an O–S–O angle slightly less than \(120^\circ\); resonance accounts for equivalent S–O bonds without changing the bent shape.