Drawing the Lewis Structure of SO₃²⁻ (Sulfite Ion)

The sulfite ion, SO₃²⁻, is a polyatomic ion where sulfur acts as the central atom, surrounded by three oxygen atoms. It demonstrates the fascinating aspect of resonance in molecular structures. Here's a methodical approach to deducing the Lewis structure for the sulfite ion.

Step 1: Determine Total Valence Electrons:

Sulfur (S): Being a member of Group 16, sulfur contributes 6 valence electrons.
Oxygen (O): Each oxygen atom contributes 6 valence electrons. For three oxygen atoms, this totals 3 × 6 = 18 electrons.
Extra electrons due to charge: The 2− charge implies there are 2 additional electrons. Combining all, we get a total of 6 + 18 + 2 = 26 valence electrons.

Step 2: Preliminary Structure Setup:

Place the sulfur atom in the center and surround it with the three oxygen atoms.

Step 3: Assigning Bonds and Electrons:

Begin with single bonds between sulfur and each of the three oxygen atoms. These bonds account for 3 × 2 = 6 electrons.
Use 4 more electrons to create a double bond between sulfur and one of the oxygen atoms.
Distribute the remaining electrons as lone pairs on the atoms. Each oxygen atom gets 6 electrons to complete its octet. After assigning these electrons, 3×6=18 electrons will be used up.
The sulfur atom will have a lone pair.

The Lewis structure for SO₃^2- ion is:

SO_3^2- Lewis structure

Step 4: Resonance Structures:

The double bond can be placed between the sulfur atom and any of the three oxygen atoms. This leads to the creation of three possible structures simultaneously, which are termed resonance structures. In each resonance structure, a different oxygen atom forms a double bond with the sulfur atom while the other two oxygen atoms maintain single bonds and bear a negative charge.

Step 5: Represent the Resonance:

The three resonance structures can be depicted with double-headed arrows between them, indicating that the true structure of SO₃²⁻is a hybrid of these three possibilities.

SO_3^2- Resonance structures

Question

What is lewis structure for so3 -2?

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