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H₂O Molecular Geometry
What Is the Molecular Geometry of H₂O? Complete Guide
Quick Answer
The molecular geometry of H₂O (water) is bent (also called angular or V-shaped) with sp³ hybridization. The central oxygen atom has four electron domains (two bonding pairs and two lone pairs), giving tetrahedral electron geometry but bent molecular geometry. Bond angles are approximately 104.5°, and the molecule is polar.
Water is the most important molecule on Earth—and one of the most frequently tested in General Chemistry. Understanding why H₂O has a bent shape (not linear) is fundamental to VSEPR theory, and this exact question appears constantly on ALEKS Chemistry, MasteringChemistry, and Cengage MindTap assignments.
This guide covers everything you need to know: how to draw the Lewis structure, determine geometry and hybridization, analyze polarity, and avoid the mistakes that cost students points.
In This Guide
Water’s bent shape is caused by two lone pairs pushing the hydrogen atoms closer together
Drawing the Lewis Structure of H₂O
The Lewis structure is your starting point for determining molecular geometry. Here’s the step-by-step process:
Count Total Valence Electrons
Oxygen (6) + Hydrogen × 2 (2) = 8 valence electrons
Identify the Central Atom
Oxygen is less electronegative than hydrogen in this context and becomes the central atom. (Hydrogen can never be central—it only forms one bond.)
Draw Single Bonds
Connect O to each H with single bonds. This uses 4 electrons (2 per bond), leaving 4 remaining.
Complete Octet on Central Atom
Place the remaining 4 electrons on oxygen as two lone pairs. Oxygen now has 8 electrons (2 bonds + 2 lone pairs) satisfying the octet rule.
💡 Key Insight
Hydrogen atoms don’t get lone pairs—they’re complete with just 2 electrons (duet rule). The two lone pairs stay on oxygen, and these lone pairs are what make water bent instead of linear.
VSEPR Theory & Geometry
VSEPR (Valence Shell Electron Pair Repulsion) theory predicts that electron domains arrange themselves to minimize repulsion. For H₂O, there’s a critical distinction:
Electron Geometry
Tetrahedral
Considers ALL electron domains
(2 bonding + 2 lone pairs = 4)
Molecular Geometry
Bent
Considers ONLY bonded atoms
(2 hydrogens visible, lone pairs “hidden”)
The four electron domains point toward the corners of a tetrahedron. But since we only “see” the two hydrogen atoms (not the lone pairs), the visible shape is bent or V-shaped.
Why H₂O Is Bent, Not Linear
This is the most common misconception about water. Many students assume that since H₂O has only two bonds, it should be linear like CO₂. Here’s why that’s wrong:
| CO₂ (Linear) | H₂O (Bent) | |
|---|---|---|
| Bonds | 2 double bonds | 2 single bonds |
| Lone pairs on central atom | 0 | 2 |
| Total electron domains | 2 | 4 |
| Electron geometry | Linear | Tetrahedral |
| Molecular geometry | Linear (180°) | Bent (104.5°) |
The bottom line: Lone pairs take up space. The two lone pairs on oxygen push the hydrogen atoms down and closer together, creating the bent shape with a 104.5° angle.
Why 104.5° and Not 109.5°?
The ideal tetrahedral angle is 109.5°. But lone pairs repel more strongly than bonding pairs (they’re only attracted to one nucleus, not two). H₂O has two lone pairs, which compress the H-O-H bond angle from 109.5° down to 104.5°.
Hybridization of H₂O
Hybridization describes how atomic orbitals combine to form new hybrid orbitals for bonding. The number of electron domains determines hybridization:
| Electron Domains | Hybridization | Example |
|---|---|---|
| 2 | sp | CO₂, BeCl₂ |
| 3 | sp² | BF₃, SO₃ |
| 4 ← H₂O | sp³ | CH₄, NH₃, H₂O |
| 5 | sp³d | PCl₅ |
| 6 | sp³d² | SF₆ |
For H₂O: Four electron domains (2 bonds + 2 lone pairs) require sp³ hybridization. Oxygen’s one 2s orbital and three 2p orbitals mix to form four equivalent sp³ hybrid orbitals—two form sigma bonds with hydrogen atoms, and two hold lone pairs.
Polarity Analysis
Water’s polarity is one of its most important properties, responsible for everything from dissolving salts to supporting life.
Bond Polarity
Each O-H bond is polar because oxygen (electronegativity 3.44) is much more electronegative than hydrogen (2.20). The electronegativity difference of 1.24 creates polar covalent bonds with partial charges: δ- on oxygen and δ+ on each hydrogen.
Molecular Polarity
H₂O is polar overall because:
- The bent shape is asymmetric
- The two O-H bond dipoles point in roughly the same direction (toward oxygen)
- The dipoles do not cancel—they add together
- Result: a net dipole moment pointing from the hydrogen atoms toward the oxygen
💡 Why Polarity Matters
Water’s polarity makes it the “universal solvent.” The partial charges allow water to dissolve ionic compounds and interact with other polar molecules. This is why oil (nonpolar) and water don’t mix.
H₂O vs. Similar Molecules
Comparing H₂O to molecules with the same electron geometry but different numbers of lone pairs shows how lone pairs affect shape:
All three have tetrahedral electron geometry but different molecular geometries
| Molecule | Lone Pairs | Molecular Geometry | Bond Angle | Polar? |
|---|---|---|---|---|
| CH₄ | 0 | Tetrahedral | 109.5° | No |
| NH₃ | 1 | Trigonal Pyramidal | 107° | Yes |
| H₂O | 2 | Bent | 104.5° | Yes |
Pattern: Each additional lone pair compresses the bond angle by about 2.5°. CH₄ (0 lone pairs) has 109.5°, NH₃ (1 lone pair) has ~107°, and H₂O (2 lone pairs) has ~104.5°.
Common Student Mistakes
❌ Mistake #1: Saying H₂O is linear
Two bonds ≠ linear geometry. You must count ALL electron domains, including lone pairs. H₂O has 4 electron domains, so the electron geometry is tetrahedral and molecular geometry is bent.
❌ Mistake #2: Using 109.5° for the bond angle
That’s the ideal tetrahedral angle. H₂O’s two lone pairs compress the angle to 104.5°. Remember: more lone pairs = smaller bond angle.
❌ Mistake #3: Saying H₂O is nonpolar
Bent geometry is asymmetric, so the bond dipoles don’t cancel. H₂O is definitely polar—that’s why it’s such a good solvent.
❌ Mistake #4: Using sp² hybridization
sp² requires 3 electron domains. H₂O has 4 electron domains (2 bonds + 2 lone pairs), so it’s sp³.
❌ Mistake #5: Forgetting the lone pairs in the Lewis structure
After drawing O-H bonds (4 electrons), you have 4 electrons left. These form 2 lone pairs on oxygen—don’t leave them out!
Assignment Due Soon?
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Platform-Specific Tips
ALEKS Chemistry
- When drawing Lewis structures, make sure both lone pairs are visible on oxygen
- For bond angle, enter 104 or 104.5 (both typically accepted)
- Scroll through geometry options carefully—”bent” and “linear” are both in the list
Pearson MasteringChemistry
- Pay attention to whether the question asks for “electron geometry” (tetrahedral) or “molecular geometry” (bent)
- Hybridization is sp³, not sp or sp²
- For polarity, answer “polar” or “yes” depending on question format
Cengage MindTap
- Spelling matters: “bent” or “angular” (check which term your textbook uses)
- 3D model questions: rotate to see the bent shape clearly
- Some questions ask for the O-H bond length (about 0.96 Å)—this is separate from geometry
Need help with these platforms? Our experts work with ALEKS Chemistry, MasteringChemistry, and Cengage MindTap daily.
Quick Reference Summary
📐 Geometry
- Electron geometry: Tetrahedral
- Molecular geometry: Bent
- Bond angle: 104.5°
🔬 Structure
- Valence electrons: 8
- Bonding pairs: 2
- Lone pairs: 2
⚗️ Properties
Hybridization: sp³ | Polarity: Polar | Shape: V-shaped / Angular
Test Your Understanding
📝 ALEKS-Style Practice Problem
For the water molecule (H₂O), determine:
- Total number of valence electrons
- Number of bonding pairs and lone pairs on the central atom
- Electron geometry
- Molecular geometry
- Hybridization of the central atom
- Whether the molecule is polar or nonpolar
Click to reveal answer
- Valence electrons: 8 (6 from O + 1 + 1 from 2 H)
- Bonding pairs: 2 | Lone pairs: 2
- Electron geometry: Tetrahedral (4 electron domains)
- Molecular geometry: Bent (only 2 atoms bonded to central atom)
- Hybridization: sp³ (4 electron domains = 4 hybrid orbitals)
- Polarity: Polar (asymmetric shape, dipoles don’t cancel)
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Frequently Asked Questions
What is the molecular geometry of H₂O?
The molecular geometry of H₂O (water) is bent, also called angular or V-shaped. The central oxygen has four electron domains (two bonding pairs and two lone pairs), giving tetrahedral electron geometry, but the molecular geometry considering only bonded atoms is bent with a 104.5° bond angle.
Why is H₂O bent and not linear?
H₂O is bent because oxygen has two lone pairs in addition to two bonding pairs. These four electron domains arrange tetrahedrally, but the two lone pairs are invisible in molecular geometry. The lone pairs push the hydrogen atoms closer together, creating a bent shape instead of linear.
What is the bond angle in H₂O?
The H-O-H bond angle in water is approximately 104.5°. This is less than the ideal tetrahedral angle of 109.5° because the two lone pairs on oxygen repel more strongly than bonding pairs, compressing the bond angle.
What is the hybridization of H₂O?
The oxygen atom in H₂O uses sp³ hybridization. Four electron domains (2 bonding pairs + 2 lone pairs) require four sp³ hybrid orbitals. Two orbitals form O-H bonds, and two hold lone pairs.
Is H₂O polar or nonpolar?
H₂O is polar. The bent shape is asymmetric, and oxygen is more electronegative than hydrogen, so the bond dipoles don’t cancel. Water has a significant dipole moment, which is why it’s an excellent solvent for ionic and polar compounds.
How many lone pairs does H₂O have?
H₂O has two lone pairs on the central oxygen atom. After forming two O-H bonds (using 4 of 8 valence electrons), the remaining 4 electrons form 2 lone pairs on oxygen.
What’s the difference between H₂O and CO₂ geometry?
CO₂ is linear (180°) while H₂O is bent (104.5°). The difference is lone pairs: CO₂ has zero lone pairs on carbon (2 electron domains → linear), while H₂O has two lone pairs on oxygen (4 electron domains → bent).
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