Question

Provide the correct Lewis structure and ALL legitimate resonance structures for Sulfuric acid. Alo indicate which resonance structures contributes most/best to the behavior of this molecule. Justify your answer.

Answer 1

The second row of table of elements, it is not uncommon to see an "expanded valence shell," where atoms have more than 8 valence electrons. The usual explanation is that the bonding involves d-orbital electrons, and the resulting Lewis structures look like that shown below.

For example,
         

        Sulfuric Acid

Notice that sulfur atom has 12 electrons around it.

However, expanded octets are not required to draw Lewis structures for these types of molecules. For example, another Lewis structure of sulfuric acid is shown here, and does not include any expanded octets.

By the rules of drawing Lewis structures, both of these structures have undesirable features. The top structure has expanded octets, whereas the bottom structure contains separated formal charge. However, quantum mechanical electronic structure calculations find little d-orbital participation in the bonding, as would be expected for expanded octet bonding, suggesting that the formal charge separation is preferable to expanding the octets. Therefore, there is generally no reason to draw structures with expanded octets, because they usually don't contribute significantly to the overall structure of the molecule.

Resonance Structures: