Everywhere in the universe, the periodic table has the same basic structure. Even if an alien civilization's table weren't plotted out in the castle-with-turrets shape we humans favor, their spiral or pyramidal or whatever-shaped periodic table would naturally pause after 118 elements.
If you had to sum up chemistry in one sentence, it might be this: Atoms need to have full shells of electrons to feel satisfied, and different elements steal, shed, or borrow different numbers of electrons to achieve a full shell.
Scientists didn't discover the noble gas helium - the second most common element in the universe - on Earth until 1895. And they thought it existed in minute quantities only, until miners found a huge underground cache in Kansas in 1903.