To draw the Lewis dot structure for the sulfite ion, SO3²⁻, we first need to consider the total number of valence electrons. Sulfur (S) has 6 valence electrons and each oxygen (O) has 6 valence electrons. Since there are three oxygen atoms, we have:
- Valence electrons from S: 6
- Valence electrons from 3 O: 3 × 6 = 18
- Charge contribution from 2- charge: +2 electrons
So, the total number of valence electrons is 6 + 18 + 2 = 26.
Now, we can start drawing the Lewis structure. Place sulfur in the center and connect it to the three oxygen atoms with single bonds. This uses 6 of the 26 electrons. Then, we can complete the octets for the oxygen atoms by placing 6 more electrons around each oxygen (18 electrons used), resulting in three O atoms being fully bonded to S. However, we still have 2 electrons remaining which we can place on the sulfur atom as a lone pair, giving sulfur a total of 8 electrons around it, counting its bonds.
Next, to account for resonance, we can depict the bonds between sulfur and oxygen as either a single or double bond between one of the oxygen atoms and sulfur. This means the Lewis structure can have multiple valid forms, but for simplicity, we can denote one typical resonance form.
Now, we determine the electron geometry and the molecular shape. The arrangement of electron pairs (bonding and lone pairs) around the sulfur atom would dictate the geometry:
- We have three bonding pairs (from the S-O bonds) and one lone pair.
This gives us a total of four electron pairs, which corresponds to a tetrahedral electron geometry according to VSEPR theory.
The molecular shape, however, is determined by the positions of only the atoms (and not the lone pairs). With three bonding pairs and one lone pair, the shape becomes trigonal pyramidal.
In summary:
- Lewis Structure: SO3²⁻ with resonance of single and double bonds.
- Electron Geometry: Tetrahedral.
- Molecular Shape: Trigonal pyramidal.