What is the IUPAC name for the compound #"FeS"#?
The first thing to recognize here is that you're dealing with an ionic compound made up of iron,
Right from the start, you should know that the metal will form a positively charged ion, i.e. a cation, and the nonmetal will form a negatively charged ion, i.e. an anion.
In this case, sulfur has
Keep in mind that anions are always named using the -ide suffix. In this case, the sulfur ion is called the sulfide anion,
If you take
#"FeS" = ["Fe"^(color(red)(x+))]_ color(blue)(2)["S"^(color(blue)(2-))]_ color(red)(x)#
Since the chemical formula contains
Therefore, you have
#color(red)(x+) = 2+#
This is important because iron is a transition metal, which means that it can form multiple cations. To distinguish between the possible charges on the iron cation, you must use Roman numerals.
In this case, the iron cation has a
#color(green)(|bar(ul(color(white)(a/a)color(black)("FeS " -> " iron(II) sulfide")color(white)(a/a)|)))#
It's worth mentioning that this compound is commonly called ferrous sulfide.