Lewis Structure for SO32- | Sulfite ion | Resonance Structures

Lewis structure of sulfite ion is drawn in this tutorial step by step. Total valence electrons concept is used to draw the lewis structure. Resonance structures of SO32- are drawn after drawing the lewis structure.

Sulfite ion | sulphite ion | SO32-

Sulfite ion is one of the oxyanion of sulfur. Sulfur is at +4 oxidation state in SO32-.

Steps of drawing lewis structure of SO32-

Following steps are required to draw the SO32- lewis structure and they are explained in detail in this tutorial.

  1. Find total number of electrons of the valance shells of sulfur and oxygen atoms
  2. Total electrons pairs
  3. Center atom selection
  4. Put lone pairs on atoms
  5. Check the stability and minimize charges on atoms by converting lone pairs to bonds.

Drawing correct lewis structure is important to draw resonance structures correctly

Total number of electrons of the valance shells of SO32-

Both Sulfur and oxygen are located at VIA group in the periodic table. So, oxygen and sulfur atoms have six electrons in their valence shell.

  • Total valence electrons given by sulfur atom = 6

There are three oxygen atoms in SO32- ion, Therefore

  • Total valence electrons given by oxygen atoms = 6 *3 = 18

There are -2 charge on SO32- ion. Therefore there are two more electrons which contribute to the valence electrons.

  • Total valence electrons = 6 + 18 + 2 = 26

Total valence electrons pairs

Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells

Total electron pairs are determined by dividing the number total valence electrons by two. For, SO32- ion, Total pairs of electrons are 13.

Center atom of SO32- ion

To be the center atom, ability of having greater valance is important. Therefore sulfur has the more chance to be the center atom (See the figure) because sulfur can show valance of 6. So, now we can build a sketch of SO32- ion.

sulfite ion (SO32-) sketch structuree.jpg

Lone pairs on atoms

  • There are already three S-O bonds in the sketch structure. Therefore only ten (13-3) valence electrons pairs are remaining.
  • First, mark those ten valence electrons pairs as lone pairs in outside atoms (on oxygen atoms). One oxygen atom will take three lone pairs following the octal rule (oxygen atom cannot keep more than eight electrons in its valence shell).
  • For three oxygen atoms, nine electrons pairs are spent. Now one electron pair (10-9) is remaining. Mark remaining electron pair on sulfur atom.
mark electrons in skech of SO32- lewis structure.jpg

Charges on atoms

After, marking electron pairs on atoms, we should mark charges of each atom. Each oxygen atom will get a -1 charge and sulfur atom get a +1 charge.

charges of SO32- anion when lewis structure is drawn

Check the stability and minimize charges on atoms by converting lone pairs to bonds

  • Oxygen atoms should hold negative charges because electronegativity of oxygen is higher than sulfur. Otherwise, we can say, ability of holding negative charges is great in oxygen atoms than sulfur atoms.
  • The drawn structure is not a stable one because all atoms have a charge.
  • Now, we should try to minimize charges by converting lone pair or pairs to bonds. So convert one lone pair of one oxygen atom to make a S-O bond.
  • Now there is a double bond between sulfur atom and one oxygen atom. Now, there are two single bonds between sulfur atom and other two oxygen atoms.
mark charges on SO32- molecule

In new structure, charges of atoms are reduced than previous structure. Now there is no charge on sulfur atom. Also, only two oxygen atoms have -1 negative charges. Now you understand this structure of SO32- is more stable than previous structure. So, this structure has more chance to be the lewis structure of SO32- ion.

Lewis structure of SO32- (sulfite) ion

lewis structure of SO32-.jpg

Resonance structures of SO32- ion

Change the location of double bond and lone pairs of molecule to draw resonance structures of SO32- ion. Three stable resonance structures can be drawn of SO32- ion.

resonance structures of SO3 2-  (sulfite ion).jpg


In sulfite and carbonate ions, are there similar number of lone pairs on all oxygen atoms?

Yes. Each sulfite and carbonate ions contain three oxygen atoms. By In both Lewis structures, there are eight lone pairs on all oxygen atoms.

how many electron groups are around the central atom? so32- ion

Central atom of SO32- ion is sulfur. Around sulfur atom, there are four bonds and a single lone pair in the lewis structure of SO32- ion. Therefore, five electron groups are around the central atom of SO32- ion.

Is there are charges on sulfur atom in sulfite ion lewis structure?

There are no charges in sulfur atom. Only negative charges exists in two oxygen atoms.

Are there pi bonds in sulfite Lewis structure?

There is only one pi bond and it is located at between one pxygen atom and sulfur atom.

Is lewis structure for so32- is different from lewis structure for so42-

Yes. They are different. In SO42- lewis structure, there are four oxygen atoms around the sulfur atom. Therefore number of valence electrons pairs are different in two ions.