What is the name of #"FeCl"_2#?
We know it is iron chloride because there is just iron and chloride. However, we need to know the oxidation number of the iron, since iron can form more than compound with chlorine.
For this we need two rules:
- A neutral compound has an overall oxidation number of
: Chlorine being in group 7 has an oxidation number of
We represent iron's oxidation number as roman numerals after the iron.