Nomenclature. When to put Roman numerals

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Answer 1

Roxana,

Many of the metals can have more than one oxidation state. So for these metals, the actual oxidation number in a particular compound is represented by a Roman numeral. Unfortunately, there is no simple rule to be applied. You might try memorizing the most common states for the most used metals. Also, many times a particular problem will give you a clue by what a metal is bonded to. For example, iron can have an oxidation state of +1, +2, or +3. But if you are given the formula: Fe₂O₃, and we know that oxygen can only be -2, then to achieve a neutral state for the pair the iron must be +3.   2*(+3) + 3*(-2) = 0  You would then write the name Iron(III) Oxide.