When is it appropriate to use Roman Numerals in naming compounds?

Help please :)?





and also if you know this


what does a numerical subscript following any element in a chemical formula mean?





but if you know the answer to either one please let me know!

When is it appropriate to use Roman Numerals in naming compounds?
It is appropriate to name Compounds with roman numerals when a transition metal say iron has more than one ion ie; FeO is written Iron(II)Oxide because oxygen has a 2- charge and iron therefore has a 2+ charge making it Iron(II) ion. A subscript in any formula stands for the number of atoms/ions the preceding symbol has in the formula so H2O has 2 hydrogen atoms therefore the 2 subscript is after H.
Reply:When there are two or more oxidation states for the cation.





A numerical subscript means there are that many of that element in the compound.





For example, Iron(II) chloride, FeCl2 means the cation (plus charge), iron has an oxidation state of 2. The 2 below chlorine indicates two chlorines for every iron.

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