Lewis Dot Structure of the sulfite ion SO3-2 - Electron Dot - #40

A simple method for writing Lewis Structures is given in a previous article entitled “Lewis Structures and the Octet Rule”.  
Several worked examples relevant to this procedure were given in previous posts please see the Sitemap - Table of Contents (Lewis Electron Dot Structures).

Let us consider the case of the sulfite ion. The chemical formula is SO₃^-2. 

What is the SO₃^-2 Lewis structure?

 Step 1: Connect the atoms with single bonds. The central atom is the sulfur atom.

Fig. 1 : Connect the atoms of the sulfite ion (SO₃^-2) with single bonds.

 Step 2:  Calculate the # of electrons in π bonds (multiple bonds) using  formula (1): 

Where n in this case is 4 since SO₃^-2 consists of four atoms.

Where V = (6 + 6 + 6 + 6 ) – (-2) = 26 , V is the number of valence electrons of the ion.

Therefore, P = 6n + 2 – V = 6 * 4 + 2 – 26  = 0    So, there are no  π electrons in SO₃^-2 

Therefore, the structure in Step 1 is a plausible Lewis structure of SO₃^-2.

Electrons are placed around each atom so that the octet rule is obeyed. Since S is a third row element can accommodate more than 8 valence electrons.

Step 3 & 4: The Lewisresonance structuresof  SO₃^-2   areas follows:

Fig. 2 : Lewis dot structures of SO₃^-2 

 Resonance Structures #1-#3 are more stable due to less charge separation - even though the S atom has more than 8 electrons - comparing to Structure #4. Structure #4 is less stable because of larger charge separation.