Why Is SO2 Bent? Understanding SO2’s sp2 Hybridization and Molecular Geometry
The hybridization of SO2 is a foundational concept often tested in JEE Main Chemistry. Understanding sulphur dioxide’s bonding and its resulting shape provides key insight into hybridization theories and molecular geometry, which are frequently examined in competitive scenarios. This page unpacks SO2’s sp2 hybridization, its bent shape, hybridization formula application, and key contrasts with similar molecules like SO3 — ensuring thorough and exam-ready conceptual clarity for aspirants.
Sulphur dioxide (SO2) is a colourless gas with a sharp odour, known both as an environmental pollutant and a key industrial chemical. In JEE questions, SO2 appears frequently due to its illustrative nature for analyzing molecular structure, bonding and hybridization type.
Hybridization of SO2: Electron Arrangement and Stepwise Derivation
Let’s break down how the hybridization of SO2 is determined from atomic principles:
- Valence Electron Calculation: Sulphur (S) has 6 valence electrons (group 16), each oxygen brings 6.
- Lewis Structure Formation: SO2 features two double bonds between S and O. Realistically, resonance gives S–O bond order between 1 and 2.
- Sigma Bonds & Lone Pairs: Each S=O consists of one sigma (σ) and one pi (π) bond. Sulphur also has one lone electron pair.
- Steric Number (SN) Determination: SN = number of σ bonds + number of lone pairs = 2 + 1 = 3.
- Hybridization Assignment: Steric number 3 fits the pattern: 2 (sp) → linear, 3 (sp2) → trigonal planar-derived. So, S in SO2 is sp2 hybridized.
Importantly, only sigma bonds and lone pairs count towards the steric number for hybridization — pi bonds do not. This principle is key for rapid JEE calculations.
SO2 Structure: Shape, Bond Angles, and VSEPR Theory
Although sp2 hybridization corresponds to trigonal planar electron geometry, the presence of one lone pair on sulphur distorts the shape. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, lone pairs exert more repulsion than bonding pairs, making SO2 adopt a bent or V-shaped molecular geometry instead of linear or trigonal planar.
| Property | SO2 |
|---|---|
| Central Atom | Sulphur (S) |
| Hybridization | sp2 |
| Electron geometry | Trigonal planar |
| Molecular shape | Bent (V-shaped) |
| Bond angle | ~119° (slightly less due to lone pair) |
Thus, the actual SO2 bond angle is slightly less than 120° — typical for an ideal sp2 hybridized centre — due to increased lone pair-bond pair repulsions.
SO2 vs SO3 Hybridization: Key Contrasts
Both SO2 and SO3 involve sulphur-oxygen double bonds, but their hybridizations and shapes differ due to the number of bonds and lone pairs surrounding the central sulphur atom.
| Molecule | Hybridization | Shape | Bond Angle (°) | Lone Pairs (Central Atom) |
|---|---|---|---|---|
| SO2 | sp2 | Bent | <120 | 1 |
| SO3 | sp2 | Trigonal planar | 120 | 0 |
While both display sp2 hybridization, the critical difference is SO2’s lone pair resulting in a bent shape, versus SO3’s all-bonding pairs yielding perfect trigonal planar geometry. For more examples, refer to hybridization of SO2 and hybridization of SO3.
Hybridization of SO2: Shortcuts, Formula and Exam Tricks
Quickly determine the hybridization of SO2 using this standard formula:
- Steric Number (SN) = Number of σ-bonds + Number of lone pairs on the central atom
- If SN = 2 → sp; SN = 3 → sp2; SN = 4 → sp3
- For SO2, SN = 2 (σ) + 1 (lone pair) = 3 → sp2
Remember: Count only σ bonds and lone pairs, never π bonds! This trick avoids common JEE errors, especially for molecules with resonance like SO2.
SO2 Lewis Structure, Resonance and Hybridization Diagram
A clear hybridization of SO2 diagram improves recall during descriptive and graphical JEE Main questions. The best representation combines:
- Lewis Structure: S atom centre, double bonds to two O atoms, one lone pair on S.
- Resonance Forms: Shown by shifting double bonds; actual structure is resonance hybrid.
- Orbital View: Sulphur’s sp2 orbitals overlap with O’s p-orbitals; unhybridized p orbital on S forms π bond.
Even without d-orbital involvement in standard JEE-level SO2 hybridization, you should note the possibility of expanded octet by resonance, but hybridization calculation remains based on σ bonds and lone pairs.
Practice and Application: JEE Main-Style SO2 Hybridization Questions
To convert your knowledge of hybridization of SO2 into exam success, try these question types:
- Calculate hybridization for SO2, SO3, and SO2− by steric number.
- Draw resonance structures for SO2 with full lone pair notations.
- Compare shape, bond angle and hybridization for SO2, CO2, and O3.
- Reason assertion MCQs, e.g., “SO2 is V-shaped because its hybridization is…”
For reliable practice, review Chemical Bonding and Molecular Structure Mock Test 1, and P-Block Elements Mock Test for more context.
Summary: Key Points on Hybridization of SO2
- SO2 exhibits sp2 hybridization at sulphur, due to two σ bonds + one lone pair.
- The molecular shape is bent (V-shaped), not linear, because of the lone pair.
- Bond angle ~119°, slightly less than ideal 120° due to lone-pair repulsion.
- Hybridization type is determined via steric number formula—σ bonds plus lone pairs.
- Compare carefully to SO3 (trigonal planar, no lone pairs, also sp2) in JEE questions.
For more details about hybridization in similar compounds, refer to hybridization of NO2 and see the Group 16 Elements topic. Remember, building a strong conceptual base with reliable resources like Vedantu ensures clarity and confidence in your chemistry problem solving.
FAQs on Hybridization of SO2 Explained for JEE Main Chemistry
1. What is the hybridization of SO2?
SO2 exhibits sp2 hybridization in its molecular structure.
- Sulphur atom in SO2 uses sp2 hybrid orbitals to form bonds.
- It forms two sigma bonds with oxygen atoms and retains one lone pair.
- This hybridization leads to a bent (V-shaped) geometry.
2. Is SO2 sp2 or sp3 hybridized?
SO2 is sp2 hybridized, not sp3.
- Sulphur in SO2 uses three sp2 hybrid orbitals (two for sigma bonds, one for a lone pair).
- No sp3 (tetrahedral) arrangement occurs, as there are only three domains around sulphur.
3. Why is SO2 bent instead of linear?
SO2 is bent (V-shaped) due to the presence of a lone pair on sulphur, which causes electron pair repulsion.
- sp2 hybridization gives a trigonal planar electron geometry.
- One location is occupied by a lone pair, pushing the two bonded oxygen atoms closer together, resulting in a bent shape.
- The actual bond angle is approximately 119°.
4. How is the shape of SO2 determined?
The shape of SO2 is determined using VSEPR theory and by analyzing its hybridization.
- Count the number of electron domains (bond pairs + lone pairs) around sulphur.
- SO2 has 3 domains: 2 bonding pairs and 1 lone pair.
- This results in a bent/V-shaped molecule due to electron repulsion.
5. How does SO2 hybridization differ from SO3?
SO2 and SO3 differ in their hybridization due to the number of electron domains.
- In SO2: Sulphur has 2 bonds + 1 lone pair (sp2 hybridization, bent shape).
- In SO3: Sulphur forms 3 bonds, has no lone pair (also sp2, but trigonal planar shape).
- SO2 and SO3 have similar hybridization but different molecular geometries.
6. What is the bond angle in SO2?
The bond angle in SO2 is about 119°, slightly less than ideal trigonal planar angle (120°).
- Lone pair-bond pair repulsion decreases angle compared to SO3.
- This angle and shape (bent) are often tested in entrance exams.
7. Can SO2 show resonance, and does it affect hybridization?
Yes, SO2 shows resonance, with electrons delocalized across the molecule.
- Resonance structures provide equivalent descriptions of SO2’s bonding.
- Hybridization remains sp2 despite resonance; only pi-electrons are delocalized.
- Understanding resonance is essential for drawing Lewis structures in exams.
8. Is there any d-orbital participation in SO2 hybridization?
In basic hybridization models (for JEE/NEET), SO2 is explained using sp2 orbitals only.
- No significant d-orbital participation is required to describe SO2's structure at the high school level.
- Advanced theories may discuss d-pi bonding, but it’s not needed for board or JEE exam solutions.
9. What is the formula or trick for finding SO2 hybridization?
The shortcut formula to find hybridization is:
Number of Hybrid Orbitals = (Number of sigma bonds) + (Number of lone pairs on central atom)
- For SO2: 2 sigma bonds + 1 lone pair = 3 → sp2 hybridization
- This trick helps in quickly solving hybridization questions in exams.
10. Why doesn’t SO2 have a trigonal planar shape despite sp2 hybridization?
Although SO2 is sp2 hybridized, it does not have a trigonal planar shape because of one lone pair on sulphur.
- Lone pairs occupy more space and repel bonding pairs, lowering the symmetry to a bent shape.
- This results in a V-shaped molecular geometry instead of trigonal planar, which is a common question in entrance tests.
