Draw Three Resonant Lewis Structures for Sulfite (SO₂³⁻) with sp³ Hybridization

To draw the resonant Lewis structures for sulfite (SO₃²⁻), we need to consider the valence electrons and the possible arrangements of the atoms. Sulfite has a sulfur atom in the center surrounded by three oxygen atoms. Here’s a step-by-step explanation of the three possible structures:

1. Count the valence electrons: Sulfur has 6 valence electrons, and each oxygen has 6. Since there are three oxygens, that totals to 18 valence electrons from oxygen. Additionally, sulfite carries a -2 charge, which adds 2 more electrons. Therefore, the total number of valence electrons is 6 (S) + 18 (O) + 2 (charge) = 26 electrons.
2. Draw the basic skeleton: Place sulfur at the center and attach three oxygen atoms around it. Each sulfur-oxygen bond will consist of one pair of electrons (2 electrons).
3. Bond and lone pairs: Start by forming single bonds between sulfur and each oxygen. This uses 6 of the 26 valence electrons (3 bonds x 2 electrons). Now you have 20 electrons remaining. Distribute these remaining electrons as lone pairs on the oxygen atoms to fulfill their octet. Each oxygen needs 8 electrons total including bonds.
4. Forming multiple bonds: Since oxygen may have lone pairs after forming single bonds, we can create double bonds in the structures. By moving lone pairs from one oxygen to form a double bond with sulfur, you create a new resonance structure. Repeat this process for the other oxygen atoms to create three unique resonance structures.

Here are the three predominant resonance structures:

• Structure 1: One sulfur-oxygen double bond and two single bonds. The double bonded oxygen has no lone pairs, while the other two oxygens each have three lone pairs.
• Structure 2: Another variation where sulfur is double bonded to the second oxygen, with the first and third oxygens held by single bonds, still maintaining the lone pairs appropriately.
• Structure 3: In this structure, the sulfur atom is double bonded to the third oxygen instead, with the others as single bonds. Again, the lone pairs on oxygens should total to satisfy their octets.

In each structure, the sulfur exhibits sp³ hybridization because it involves the arrangement of three sigma bonds and a lone pair (non-bonding pair) around it, resulting in a tetrahedral electron geometry, although the actual molecular geometry is trigonal pyramidal due to the presence of lone pairs. The resonance indicates that the true structure is an average of these representations.