Sulfur dioxide has sulfur in the center, two oxygen atoms and one lone pair on sulfur. Its bonding is often represented with resonance, and the molecule has a bent shape rather than a linear one.
Representation depends on whether the course permits an expanded sulfur valence shell
Total valence electrons18
Central atomSulfur
Molecular geometryBent
Bond angle≈119°
SO2 Lewis structure overview
Sulfur and the two oxygen atoms each contribute six valence electrons. An O–S–O skeleton is drawn first. After completing the oxygen octets and placing the final lone pair on sulfur, multiple-bond or resonance descriptions are used to reduce formal charges and describe the equivalent S–O bonding.
Course-model note: Some classes prefer two charge-separated resonance contributors that keep an octet on sulfur. Others also show an expanded-valence O=S=O structure with one lone pair on sulfur. Follow the convention required by your instructor.
How to draw the SO2 Lewis structure
Count 18 valence electrons.
Sulfur contributes 6 and the two oxygens contribute 12.
Use an O–S–O skeleton.
Two single bonds initially use 4 electrons.
Complete oxygen octets.
Place lone pairs on both terminal oxygen atoms.
Place the remaining lone pair on sulfur.
This gives sulfur three electron domains for VSEPR purposes.
Evaluate formal charges.
Create the resonance or expanded-valence representation expected by your course and label charges where required.
Resonance and formal charges
In octet-only contributors, one S–O bond is double and one is single; the single-bonded oxygen carries -1 and sulfur carries +1. The two contributors are equivalent. An expanded-valence O=S=O drawing gives zero formal charges but places ten electrons around sulfur.
Geometry and polarity
Two bonding regions and one lone pair around sulfur produce trigonal-planar electron geometry and bent molecular geometry. Because the S–O bond dipoles do not cancel in a bent shape, SO2 is polar.
Common mistakes
Calling SO2 linear because it has two oxygen atoms.
Omitting the lone pair on sulfur.
Mixing an octet-only structure with the formal charges from an expanded-valence structure.
Presenting one resonance contributor as the only permanent bond arrangement.
Frequently asked questions
Are the two S–O bonds equivalent?
Yes. Resonance and molecular-orbital descriptions are consistent with equivalent measured S–O bonds.
How many lone pairs are on sulfur?
The common Lewis descriptions place one lone pair on the central sulfur.
Is sulfur sp² hybridized in SO2?
Introductory VSEPR treatments often label sulfur sp² because it has three electron domains, although hybridization labels are simplified models.