Question

Question #c40e2

Answer 1

Roman numerals are used to indicate the oxidation state of metals which have more than one possible oxidation state.

Explanation:

Here's an example. Copper can form either `Cu^+` or `Cu^(2+)` ions.

So there are actually two different compounds that have the name copper chloride. We need the roman numeral to know which is which. Remember that halogens form ions with a -1 charge. So a chloride ion is `Cl^1`.

`CuCl` has a `Cu^+` so its name is copper(I) chloride

`CuCl_2` has a `Cu^(2+)` so its name is copper(II) chloride

This video includes some more examples...

Hope this helps!