You need to specify which iron chloride you're asking about, as there are two common ones:

* Iron(II) chloride (FeCl₂): This has 3 atoms per formula unit: 1 iron atom and 2 chlorine atoms.

* Iron(III) chloride (FeCl₃): This has 4 atoms per formula unit: 1 iron atom and 3 chlorine atoms.

Therefore, the number of atoms in iron chloride depends on the specific compound you're referring to.