Slade, you're missing the point. Who says that the physical laws that govern Earth are the same elsewhere? Molecular structure could be totally different! Maybe they don't have molecules at all! The thing I was saying aobut the elements is that before we discovered elements, such as, say, oxygen, it never entered our minds that we breathed anything but "air." Humans have a difficult time comprehending anything outside of what they already know. I've used this example before: try thinking of a color you've never seen before. We know they're there, but we can't see them because our eyeballs can't see beyond the ROYGBIV color spectrum. Because we've never seen any other colors, we can't create a new one in our heads. But they are there!!! Just like there could be some completely different way of defining "life" on other worlds. Just because we hadn't discovered "hydrogen" didn't mean it wasn't there. There could be other elements, even other "building-blocks of matter" that we don't know about, because they're not on Earth for us to discover.
I have to agree with Slade here. Hydrogen is a molocule with one proton attatched to it, add another proton and you get helium, add another and you get a new element so on and so forth. There is little room inbetween for new discoveries.
Now the way these elements react and bond together might be a bit differant due to the myriad of differant conditions that other planets may present, but the basic bricks of matter will remain the same. Much like Legos, you can build forts, spaceships, sculptures and the like, but they will all be made out of the same basic interconnectable blocks.