Structures of Thiosulfate, Dithionate & Tetrathionate Ions
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Thiosulfate $\ce{[S2O3]^{-2}}$



There ia a negative charge on the apical sulfur and another negative charge distributed across the 3 oxygens by resonance

Dithionate $\ce{[S2O6]^{-2}}$



There is one negative charge distributed by resonance over each group of 3 oxygens.

Dithionite $\ce{[S2O4]^{-2}}$



There is one negative charge distributed by resonance over each group of 2 oxygens.

Tetrathionate $\ce{[S4O6]^{-2}}$



There is one negative charge distributed by resonance over each group of 3 oxygens.