How do you draw the Lewis structure of SO₃?

SO₃ has 24 valence electrons. Sulfur is central, bonded to three oxygens. Three single bonds use 6 electrons; 18 remain. Distribute 18 electrons: 3 lone pairs on each O (18 total). S only has 6 electrons from bonds.

Does SO₃ have resonance structures?

Yes, SO₃ has 3 resonance structures.

Lewis Structure of SO₃ (Sulfur Trioxide)

What is the Lewis structure of SO₃?

SO₃ has 24 valence electrons, 4 bonding electron pairs, and 8 lone pairs. SO₃ has 24 valence electrons and three equivalent resonance structures where the double bond rotates among the three S-O positions. Sulfur has FC = +2 and each single-bonded oxygen has FC = -1. The real structure is a hybrid with bond order 1.33.

Lewis structure of SO₃ (Sulfur Trioxide)

Formula	SO₃
Name	Sulfur Trioxide
Total Valence Electrons	24
Lone Pairs	8
Has Resonance	Yes
Resonance Structures	3
Concept	Resonance
Difficulty	Intermediate

Step 1: Count Valence Electrons

S has 6, each O has 6: 6 + 3(6) = 24 total.

Step 2: Draw the Skeleton

Sulfur is central, bonded to three oxygens. Three single bonds use 6 electrons; 18 remain.

Step 3: Distribute Lone Pairs

Distribute 18 electrons: 3 lone pairs on each O (18 total). S only has 6 electrons from bonds.

Step 4: Form Multiple Bonds

Convert 1 lone pair from one O into a double bond: S=O. S now has 8 electrons. The double bond can be on any of the 3 O atoms, giving 3 resonance structures.

Step 5: Check Formal Charges

S: FC = 6 - 0 - ½(8) = +2
O (double bond): FC = 6 - 4 - ½(4) = 0
O (single bond): FC = 6 - 6 - ½(2) = -1
Some textbooks use an expanded octet (all double bonds) to minimize formal charges.

Resonance Structures

SO₃ has 3 resonance structures. The actual electronic structure is a hybrid of all resonance contributors.

Resonance structure 2

Resonance structure 3

Interactive Lewis structure builder with guided walkthroughs and practice quizzes.

Build the SO₃ Lewis Structure Step by Step