I'm assuming you mean 2AgS vs. Ag2S (the 2 is subscript, of course). And the answer is they are not the same. Saying you cannot have AgS, it's just the way that the valence electrons for the elements work, in order to obtain the ideal octet, you must have Ag2S. 2AgS is two formula units (ionic molecule) of an impossible ionic compound. I hope this helped!
