It is to do with the ionisation of the atom. Copper is a metal, so it will lose electrons. When reacted with a non-metal, it will form an ionic bond.
In copper (I) sulphate, the copper ions have a charge of +1, ie they have lost ONE electron each.
Copper (I) sulphate has the chemical formula Cu2SO4. Each ionic bond involves two Cu+1 ions and a sulphate ion (SO4.
In copper (II) sulphate, the copper ions have a charge of +2, ie they have lost TWO electrons each.
Copper (II) sulphate has the chemical formula CuSO4. Each ionic bond involves a single Cu+2 ion and a sulphate ion (SO4).
So, really, it’s down to the chemical structure and the ionisation of the atom. Apart from the chemistry, copper (I) sulphate a very obscure chemical. Although, after a bit of googling, I have managed to find some info and vendors, it appears that this chemical is rarely seen and doesn’t have many practical uses.
Copper (II) sulphate, on the other hand, is incredibly common. It’s in every school chemistry lab. If someone says “copper sulphate” they will be talking about this chemical, not copper (I) sulphate. In pure form, it is a boring white powder, but when hydrated, it takes on it’s better known blue colour, with blue crystals and blue solution.
Hope this helps.
