Question

Draw the three resonance structures for sulfur trioxide, \(\mathrm{SO}_{3}\) .

Short answer

The three resonance structures for \(\text{SO}_{3}\) involve moving the double bonds between sulfur and different oxygen atoms.

Step-by-step solution

Determine the Total Number of Valence Electrons

First, calculate the total number of valence electrons in \(\text{SO}_{3}\). Sulfur (S) has 6 valence electrons, and each oxygen (O) atom has 6 valence electrons. There are three oxygen atoms, so the total number of valence electrons is \[6 + (3 \times 6) = 24 \text{ valence electrons}\].

Draw the Skeletal Structure

Draw the skeletal structure of \(\text{SO}_{3}\) with sulfur in the center and three oxygen atoms surrounding it.

Distribute Electrons to Form Octets

Distribute the valence electrons around the oxygen atoms to satisfy the octet rule. Each oxygen atom needs 8 electrons (including bonding electrons) around it.

Check for Double Bonds and Resonance Structures

To satisfy the octet rule for sulfur while accounting for the total valence electrons, form double bonds between sulfur and oxygen. Draw the three possible resonance structures by moving the double bonds between different pairs of sulfur and oxygen atoms.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and are critical for determining how atoms interact and bond with each other. For sulfur trioxide \(\text{SO}_3\), we need to count all the valence electrons from both sulfur (S) and oxygen (O) atoms. Sulfur has 6 valence electrons. Each oxygen atom also has 6 valence electrons. With three oxygen atoms, we calculate the total number of valence electrons as follows: \[ 6 + (3 \times 6) = 24 \text{ valence electrons} \] These valence electrons are what we use to draw the Lewis structure, and they play a key role in bonding.

Octet Rule

The octet rule is a guideline in chemistry that states atoms are generally most stable when they have eight electrons in their valence shell. When drawing the Lewis structure of \(\text{SO}_3\), we need to ensure each atom satisfies this rule.

• Sulfur must have eight valence electrons around it.
• Each oxygen atom must also have eight electrons around it including bonding electrons.

To achieve this, we distribute the 24 valence electrons to form bonds and lone pairs around sulfur and oxygen atoms, following the steps outlined in the exercise.

Double Bonds

Double bonds are a type of chemical bond where two pairs of electrons are shared between two atoms. In sulfur trioxide \(\text{SO}_3\), double bonds are necessary to satisfy the octet rule for sulfur, while keeping the total count of valence electrons accurate. Here's how we incorporate double bonds into the Lewis structure:

• Draw a skeletal structure with sulfur in the center and three oxygen atoms around it.
• Distribute the valence electrons to ensure each oxygen has eight electrons (including bonding pairs).
• Since sulfur can have an expanded octet, form double bonds between sulfur and each oxygen one at a time to satisfy the octet rule.

You will find three possible resonance structures by varying the locations of the double bonds. This helps achieve the most stable electron configuration for \(\text{SO}_3\) while obeying the octet rule and proper valence electron distribution.