Question

What is the Lewis structure of `S_2O_8^(2-)`?

Answer 1

In peroxodisulfate.........?

Explanation:

A reasonable Lewis structure for `"peroxodisulfate"` or `"persulfate"` is:

`""^(-)O(O=)_2S-O-O-S(=O)_2O^(-)`, which is `S_2O_8^(2-)` as required. The terminal oxygen nuclei ARE ALL `O^(-II)`. The central oxygen linkage is a `"peroxo"` linkage; i.e. since it contains an `O-O` linkage, the oxidation state of these oxygens is `O^(-I)`

Note that by definition, the oxidation state is the charge left on the central atom when all the bonding pairs of electrons ARE BROKEN, with the charge assigned to the most electronegative atom. But since the oxygen atoms have equal electronegativities, we CONCEIVE that the electrons are SHARED, and thus:

`""^(-)O_3S-O-O-SO_3^(-) rarr 2xx""^(+)SO_3^(-)+""^(-)O-O^-`

And thus the central peroxo linkage features oxygens in the same oxidation state as `"hydrogen peroxide"`, i.e. `HO-OH`, and that is `O^(-I)`.

Confused yet?