SO2 can be drawn as a molecule which satisfies the octet rule (using one double bond and
a single bond) or as an expanded octet (using two double bonds). A measurement of the
S-O bond distance demonstrates that the two bond lengths are identical. Does this clarify
which Lewis structure is correct? Explain.
No, the true structure is a resonance hybrid of all of the possible Lewis structures that one can draw. Actually, no Lewis structure that we can draw is the correct structure.
Well that was no help at all
!
To clarify which Lewis structure is correct for SO2, we can consider the concept of formal charge.
The octet rule states that atoms tend to gain, lose, or share electrons in order to have a complete set of eight outer shell electrons. In the case of sulfur dioxide (SO2), sulfur (S) has six valence electrons, and each oxygen (O) has six valence electrons. The total number of valence electrons in SO2 is 18 (6 from sulfur + 2x6 from oxygen).
Now let's evaluate the two possible Lewis structures:
1. Structure with one double bond and a single bond:
In this structure, sulfur forms a double bond with one oxygen atom and a single bond with the other oxygen atom. This arrangement yields a formal charge of 0 on sulfur and -1 on each oxygen atom, which satisfies the octet rule for all atoms. The bond lengths in this structure will be unequal since the double bond is shorter than the single bond.
2. Structure with expanded octet:
In this structure, sulfur forms two double bonds with the oxygen atoms. This arrangement yields a formal charge of 1- on sulfur and -1 on each oxygen atom, which also satisfies the octet rule for all atoms.
To determine which structure is correct, we need to consider the experimental measurement of the S-O bond distance. If the measured bond distances are identical, it suggests that both bonds possess the same strength and energy, indicating that the two Lewis structures are equally valid.
Therefore, the measurement of the S-O bond distance clarifies that both Lewis structures are correct for SO2, and the molecule exhibits resonance. Resonance is a phenomenon where the actual electronic structure of a molecule is an average of the different resonance structures. In the case of SO2, the true structure is likely a combination or hybrid between the two Lewis structures, with partial double bond character in both S-O bonds.