I don't understand why SO42- is considered a hard base while So32- is a soft (borderline) one
For monoatomic ionic species like Mg2+ vs K+ (or Ba2+) is say that Mg2+ is hard because has a much higher charge/ionic radius of the metal ion than Ba2+ or K+
But for polyatomic ions like SO42- or SO32- how can i say this?
what parameter I have to consider to say that SO42- is hard while SO32- is a borderline base?
The negative charge is in both case 2-
THe ionic radius ...of the entire ion I think is not so much different...