FeS 同 FeS2有咩唔同

Iron(II) sulfide is a chemical compound with the formula FeS. FeS can be obtained by reacting iron and sulfur.
S8 (s) + 8Fe (s) → 8FeS(s)
　　２＋　２－
Ｆｅ　　Ｓ

Iron disulfide FeS2 on the other hand consists of (S2)2-, in association with iron in the formal 2+ oxidation state.
　　２＋　　　　　２－
Ｆｅ　　（Ｓ－Ｓ）
　　‥　‥　　２－
（：Ｓ－Ｓ：）
　　‥　‥
FeS2 is formed when iron is reacted with sulphur is in excess.

I hope this can help your understanding. =)