Draw the Lewis structure for thiosulfate (S2O3^2-) with minimized formal charges. How many TOTAL likely resonance structures exist for S2O3^2-? Hint: In this case, it is more stable (preferred) to place the negative charge on the larger atom. B) 2 E) 5 Click to view structure Tap here to pull up additional resources.
The Correct Answer and Explanation is:
The Lewis structure for thiosulfate (S2O3^2-) involves sulfur (S) and oxygen (O) atoms. Here’s how to approach drawing the structure and understanding the resonance:
- Count the valence electrons:
- Sulfur (S) is in group 16 of the periodic table and has 6 valence electrons. For two sulfur atoms, that’s 6 x 2 = 12 electrons.
- Oxygen (O) is also in group 16 and has 6 valence electrons, but there are three oxygens in this molecule. So, 6 x 3 = 18 electrons.
- The 2- charge adds 2 more electrons to the total count.
- Total valence electrons = 12 (from sulfur) + 18 (from oxygen) + 2 (from the charge) = 32 electrons.
- Determine the skeleton structure:
- One sulfur atom is bonded to the other sulfur atom and to two oxygen atoms. The third oxygen is typically single-bonded to one sulfur.
- Distribute the electrons:
- Assign electron pairs to satisfy the octet rule for oxygen atoms.
- Place extra electrons on the sulfur atoms to complete their valence shells.
- Consider resonance:
- There are two primary resonance structures, as the negative charges are more favorably placed on the oxygen atoms due to their higher electronegativity compared to sulfur.
The correct answer is B) 2, since there are 2 likely resonance structures where the negative charges are placed on the oxygen atoms in different ways.
These resonance structures involve shifting double bonds between sulfur and oxygen and alternating where the negative charges reside, minimizing formal charges across the molecule.
