Explain why iron sulfide has different properties from a physical mixture of the elements iron and sulfur?

Iron is a metal, while sulfur is a nonmetal. when these two are heated together, the iron atoms combine with the sulfur atoms to make a compound known as iron sulphide. ( iron sulphide is not iron or sulfur; it is a pure substance with its own sets of distinguishing physical and chemical characteristics 

They are all solids.

; lc