I discovered this a little while ago and have been meaning to post about it for a while. Another reason why us astrochemists are a bit atypical by the standards of virtually all other chemists…
The astronomer’s periodic table. Effectively, this is what people like me have to work with. How abundant any one element is is shown by the size of its white square. All other elements combined would probably fit inside a single pixel in this image — possibly with room to spare.
Pretty amazing, huh? Several of those wonderful elements which are essential components of us living creatures (like phosphorus, calcium and sodium) are really quite rare on the grand scale of things. So rare, in fact, that it takes a huge ball of iron and silicates (like Earth) to gravitationally scoop up enough of them for us to exist at all.
This is also why we don’t do any astrochemical searches for funkier chemicals in interstellar space. Things like phosphines, boranes and uranium oxides probably all exist in the interstellar medium. There’s no good reason why they shouldn’t. The thing is, there would be so little of them out there that we could never ever detect them!
So instead, we limit ourselves to elements we actually have a chance of finding. Incidentally, looking at that image, you can also see pretty easily why the most common molecules in the Universe are H2, CO and H2O!
Image half-inched from the McCall Research Group website.