The thiosulfate ion, S2O32−, is important in photographic fixing solutions. Two skeletal arrangements are considered, each obeying the overall stoichiometry and charge:
Arrangement I: central S atom bonded to three O atoms and one terminal S atom (total of four S—X bonds around the central S).
Arrangement II: central S atom bonded to two O atoms and one terminal S atom; one O atom is singly bonded to the terminal S (that is, the O atom is attached to the terminal S rather than to the central S).
For each arrangement, multiple resonance contributors are possible depending on whether S=O or S—O single/double bonds are employed.
(a) Draw (in words) two distinct resonance contributors for Arrangement I and compute the formal charge on every atom in each contributor.
(b) Draw (in words) two distinct resonance contributors for Arrangement II and compute the formal charge on every atom in each contributor.
(c) For each arrangement, identify the single resonance contributor that is most favorable with respect to formal charges.
(d) Between Arrangement I and Arrangement II, decide which skeletal arrangement better represents the actual thiosulfate ion. Provide a detailed justification that includes formal-charge analysis, the tendency to minimize charge separation, and the relative electronegativity of oxygen versus sulfur.
(a) For Arrangement I, describe two resonance contributors and calculate the formal charge on every atom in each.
(b) For Arrangement II, describe two resonance contributors and calculate the formal charge on every atom in each.
(c) For each arrangement, identify the resonance contributor with the most favorable formal-charge distribution.
(d) Decide which skeletal arrangement (I or II) is more consistent with the actual thiosulfate ion and justify your decision using the criteria outlined in the prompt.