To draw the Lewis structure for the sulfur trioxide (SO₃) molecule, follow these steps:
1. **Count the Total Number of Valence Electrons:**
– Sulfur (S) has 6 valence electrons.
– Each oxygen (O) atom has 6 valence electrons.
– Since there are 3 oxygen atoms, the total number of valence electrons is: 6 (S) + 3 × 6 (O) = 24 valence electrons.
2. **Determine the Central Atom:**
– Sulfur is less electronegative than oxygen, so it will be the central atom.
3. **Draw the Skeleton Structure:**
– Place the sulfur atom in the center and connect it to the three oxygen atoms with single bonds.
4. **Distribute the Remaining Electrons:**
– After forming the single bonds, you have used 6 electrons (3 bonds × 2 electrons each).
– Subtract these from the total valence electrons: 24 – 6 = 18 electrons remaining.
– Distribute these electrons to the oxygen atoms to satisfy the octet rule. Each oxygen atom needs 6 more electrons to complete its octet.
5. **Form Double Bonds to Satisfy the Octet Rule:**
– To satisfy the octet rule for sulfur, you need to form double bonds between sulfur and the oxygen atoms.
– Move one lone pair from each oxygen atom to form a double bond with sulfur. This will use up 6 more electrons (3 double bonds × 2 electrons each).
– Now, each oxygen atom has 8 electrons (including the shared electrons in the double bond), and sulfur also has 8 electrons.
6. **Draw Resonance Structures:**
– Sulfur trioxide has resonance structures because the double bonds can be formed with any of the three oxygen atoms.
– Draw three resonance structures where each oxygen atom takes turns forming a double bond with sulfur.
**Final Lewis Structure:**
– The final Lewis structure for SO₃ will show sulfur in the center with one double bond to each of the three oxygen atoms. Each oxygen atom will have two lone pairs of electrons.
**Resonance Structures:**
– The three resonance structures will show the double bond rotating among the three oxygen atoms, ensuring that each oxygen atom gets a chance to form a double bond with sulfur.
This structure satisfies the octet rule for all atoms involved and accounts for the resonance in the molecule.