O₃ Lewis Structure (Ozone)
O₃ (ozone) has 18 valence electrons and two equivalent Lewis resonance structures. Each form contains one O=O double bond, one O–O single bond, and one lone pair on the central oxygen. The central oxygen has a +1 formal charge, while the single-bonded terminal oxygen has a −1 formal charge. Ozone has a bent geometry, an O–O–O bond angle of approximately 116.8°, and is polar.
| Valence electrons | 18 |
|---|---|
| Resonance forms | 2 |
| Molecular geometry | Bent |
| Bond angle | ≈116.8° |
| VSEPR | AX₂E |
| Polarity | Polar |
| Average O–O bond order | 1.5 |
| Central O lone pairs | 1 |
How to Draw the O₃ Lewis Structure
Draw the Lewis structure of ozone step by step. Count 18 valence electrons, make an O—O—O skeleton, complete the terminal octets, place the remaining lone pair on the central oxygen, then form one double bond and its equivalent resonance contributor.
Step 1Count the valence electrons
Each oxygen contributes 6 valence electrons. O₃ is neutral, so the total is 3 × 6 = 18 electrons to place. Every valid Lewis drawing of ozone must use all 18.
Step 2Draw the O—O—O skeleton
Choose one oxygen as the central atom and connect the three atoms with two single bonds. The two O—O bonds use 4 electrons, leaving 14 electrons to place.
Step 3Complete the terminal oxygen octets
Put three lone pairs on each terminal oxygen. That uses 12 more electrons, leaving 2 electrons. Place the remaining pair on the central oxygen. The terminal oxygens have octets, but the central oxygen has only six electrons around it.
Step 4Form one O=O double bond
Move one lone pair from either terminal oxygen into its O—O bond to form a double bond. The central oxygen now has an octet. In this contributor, the central oxygen has formal charge +1, the double-bonded terminal oxygen has 0, and the single-bonded terminal oxygen has −1.
Step 5Draw the second resonance contributor
Move the double bond to the other side to make the second equivalent contributor. Both drawings use 18 electrons, give every oxygen an octet, and have formal charges that sum to 0. The resonance arrow does not mean ozone switches between two separate molecules; the real molecule is a resonance hybrid.
- 18 valence electrons placed
- One O–O single bond and one O=O double bond in each contributor
- Six lone pairs total
- Every oxygen has an octet
- Formal charges sum to 0
- Both equivalent resonance forms shown
O₃ Valence Electrons
The 3 oxygen atoms contribute 3 × 6 = 18 valence electrons. Added together, O₃ starts with 18 valence electrons to place, and as a neutral molecule there is no charge to add or remove. Of those, 6 fill the bonds and 12 sit as lone pairs (O: 2, 3).
| 3 × oxygen: 3 × 6 = 18 |
| Total: 18 = 18 |
O₃ Resonance Structures
O₃ has two equivalent resonance structures. In each drawing, the central oxygen has a +1 formal charge, the single-bonded terminal oxygen has −1, and the double-bonded terminal oxygen is neutral. Moving the double bond to the other side gives the second drawing. These are not two separate forms of ozone that take turns existing. Together they describe one resonance hybrid. In that hybrid, both O–O bonds are equivalent and each has an average bond order of 1.5.
Resonance hybrid
Average O–O bond order = (1 + 2) / 2 = 1.5
Both O–O bonds are equivalent in the real molecule. Neither one is permanently a single bond or a double bond.
O₃ Lewis Structure with Formal Charges
Formula
Formal charge = valence e⁻ − nonbonding e⁻ − ½ × bonding e⁻
| Atom | Calculation | Formal charge |
|---|---|---|
| O | 6 − 2 − ½(6) = +1 | +1 |
| O | 6 − 4 − ½(4) = 0 | 0 |
| O | 6 − 6 − ½(2) = −1 | −1 |
The formal charges sum to 0, matching the neutral molecule. Smaller formal charges mark the preferred structure.
Formal charge = valence electrons − nonbonding electrons − ½(bonding electrons).
Central O: 6 − 2 − ½(6) = +1. It has one lone pair, one single bond, and one double bond.
Double-bonded terminal O: 6 − 4 − ½(4) = 0.
Single-bonded terminal O: 6 − 6 − ½(2) = −1.
The formal charges add to 0, matching neutral O₃. In the other resonance contributor, the terminal oxygens exchange the 0 and −1 assignments. There are six lone pairs total in either complete contributor.
O₃ Molecular Geometry
| Electron geometry | Trigonal planar |
|---|---|
| Molecular geometry / shape | Bent |
| VSEPR notation | AX₂E |
| Bond angle | ≈116.8° |
On the central oxygen, count electron domains the VSEPR way: each bonded neighbor is one domain (a double or triple bond still counts as one), and each lone pair is one more. O₃ has 2 bonding domains and 1 lone pair (AX₂E), for 3 electron domains in total.
O₃ has a bent molecular geometry because the central oxygen has two bonding domains and one lone pair (AX₂E).
O₃ is AX₂E: the central oxygen is A, the two O–O bonding regions are X₂, and the central lone pair is E. Three electron domains give trigonal planar electron geometry, while the atoms alone give a bent (angular) molecular geometry. A simple AX₂E model suggests an angle near 120°, but the measured O–O–O bond angle is approximately 116.8°.
Why Is O₃ Bent?
Ozone is not linear even though all three atoms are oxygen. The central oxygen has two bonding domains and one lone pair. Those three electron domains arrange roughly trigonal planar; the lone pair occupies one position, leaving the two terminal oxygens in a bent shape. Electron geometry counts the lone pair, while molecular geometry names the arrangement of atoms only.
O₃ Bond Angle
The O–O–O bond angle in ozone is approximately 116.8°. The ideal angle for three electron domains is 120°, but the central lone pair changes the repulsions and compresses the angle slightly. Thus 120° is a useful VSEPR starting point, while ≈116.8° is the experimental bond-angle value to report for ozone.
Is O₃ Polar or Nonpolar?
O₃ is polar.
O₃ is polar even though it contains only oxygen atoms. An O–O bond does not have the usual electronegativity difference found in a bond between different elements. Instead, ozone is bent and its resonance hybrid has an uneven charge distribution: the central region is electron-poor relative to the terminal regions. Those effects leave a nonzero molecular dipole. The two O–O bonds are still equivalent in the real molecule; equal bonds do not require the molecular dipole to be zero.
O₃ Hybridization
Oxygen in O₃ is sp²-hybridized.
A common introductory description labels the central oxygen sp²-hybridized. It has two bonding domains and one lone pair, for three electron domains. In that picture, two sp² hybrids form the O–O σ bonds, one holds the lone pair, and the remaining p orbital participates in the delocalized π bonding shown by the resonance structures. The sp² label is a useful way to connect the electron-domain count to trigonal planar electron geometry.
O₃ Lewis Structure Summary
| Chemical name | Ozone |
|---|---|
| Total valence electrons | 18 |
| Central atom | Oxygen |
| Structure | O═O─O |
| O=O | Double bond |
| O–O | Single bond |
| Lone pairs on oxygen | 1 |
| Lone pairs on outer atoms | O: 2, 3 |
| Electron geometry | Trigonal planar |
| Molecular geometry | Bent |
| VSEPR | AX₂E |
| Bond angle | ≈116.8° |
| Hybridization | sp² |
| Polarity | Polar |
| Formal charge | see formal charge table |
| Resonance | Yes |
| Overall charge | 0 |
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Related Lewis Structures
Common next structures from general chemistry — each link opens that molecule so you can compare geometry, polarity, or the drawing steps.
Frequently Asked Questions
What is the Lewis structure of O3?
O₃ is drawn as two equivalent resonance structures: O=O⁺–O⁻ and ⁻O–O⁺=O. Each contributor has one O=O double bond, one O–O single bond, and one lone pair on the central oxygen. The real ozone molecule is a resonance hybrid with equivalent O–O bonds.
How many valence electrons does O3 have?
O₃ has 18 valence electrons. Each oxygen contributes 6, so 3 × 6 = 18. One single bond and one double bond contain 6 bonding electrons; six lone pairs contain the other 12 nonbonding electrons.
Does O3 have resonance structures?
Yes. O₃ has two equivalent resonance structures. The double bond and the −1 formal charge switch sides between the two drawings, while the central oxygen stays +1. Together the drawings represent one resonance hybrid with two equivalent O–O bonds of average bond order 1.5.
What are the formal charges in O3?
In either ozone resonance contributor, the central oxygen has formal charge +1, the double-bonded terminal oxygen has 0, and the single-bonded terminal oxygen has −1. These charges add to 0, the overall charge of neutral ozone.
Does O3 obey the octet rule?
Yes. In each complete O₃ resonance contributor, all three oxygen atoms have eight electrons around them. The central oxygen has one lone pair, one single bond, and one double bond; each terminal oxygen also has an octet.
What is the molecular geometry of O3?
O₃ has a bent molecular geometry. The central oxygen has two bonding domains and one lone pair (VSEPR AX₂E), giving trigonal planar electron geometry and a bent arrangement of the three oxygen atoms.
What is the bond angle of O3?
The O–O–O bond angle in ozone is approximately 116.8°. This is slightly smaller than the ideal 120° associated with three electron domains because the central lone pair affects the electron-pair repulsions.
Is O3 polar or nonpolar?
O₃ is polar. Although it contains only oxygen atoms, its bent shape and resonance-related charge distribution produce a nonzero molecular dipole. This is not explained by an electronegativity difference between the two atoms of an O–O bond.
What is the hybridization of the central oxygen in O3?
In the introductory hybridization model, the central oxygen in O₃ is described as sp²-hybridized. It has two bonding domains and one lone pair, for three electron domains with trigonal planar electron geometry.