Untriennium

Here's an interesting bit of obscure, theoretical atomic physics trivia for you: there's a cap on the number of possible elements that can ever exist, according to our current understanding of physics, and the highest element theoretically possible is element 139, untriennium.

It seems like scientists just keep smashing stuff together at higher and higher speeds, and discovering higher and higher numbered elements. Heck, we've already observed Ununoctium (that'd be element number 118), why not just keep going forever?

It turns out that the speed of an electron orbiting an atomic nucleus is proportional to the number of other electrons orbiting the nucleus (that's a gross simplification, but bear with me, I'm an engineer... it's what we do when reality is annoyingly complicated). It also turns out that as soon as you get more than, say, 137 electrons in orbit, things start to go wonky. Bohr's classical model of the atom says that the speed required of any atom after the 137th would have to be faster than the speed of light, which a lot of fairly smart physicists are convinced is impossible. If you refine the model a bit and take the effects of relativity into account, you can actually squeeze a 138th and 139th electron in there, but no elements beyond number 139 are allowed without breaking physics.

Neat!