Alien trade

I am having an hard time figuring out which materials aliens require for trade other than Iron and Hydrogen. I often have a good supply of minerals but so far the only ones I could select were Th and Hf (Si and Pl don't seem to be an option) and they never turned out to be the ones they want. Any idea?

Then you probably don't have what they're looking for. They may want tungsten (w) or something.

From my experience, the closer you are to the start, the more likely they're going to want H, Fe, Th, and W.

Very rarely will they want Si, and I don't recall if they like Pt or not. However, they'll NEVER want elements that can be found on breathable worlds, i.e. Au, O, C, Co, Cu.