Why do certain elements and compounds have Roman numerals behind them i.e. copper (II) sulphate (VI)?
In: Chemistry
The numbers represent something called the *oxidation state* of the ion in question.
Because oxidation, chemically speaking, involves the loss of electrons, the *oxidation state* can be understood to answer the question “How many electrons has this ion lost?” or more generally (since oxidation states can be negative) “What is the electric charge on this ion?”
Copper(II) sulfate has the chemical formula CuSO4. The sulfate ion, -SO4, has a charge of ^-2 , so the copper ion has a charge of ^+2 to balance it. Its oxidation state is therefore +2.
EDIT: Incidentally, this scheme was adopted because copper (and a lot of other elements) can have different oxidation states. Copper(I) oxide, for example, is Cu2O, and Copper(II) oxide is CuO.
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