Scientists recently announced the discovery of four elements which complete the seventh row of the periodic table, leaving it without gaps for the first time in quite a while.
But is that all there is? Does the table have an eighth row or more? Having found real atoms to take the place that had been labled "ununtrium," for example, -- atomic number 113 -- are there also previously unseen atoms capable of existing in the spaces that would be marked "unbinilium?" -- atomic number 120?
Current technology doesn't provide many likely methods to produce these elements if they exist, and they all have the problem that they decay into other elements very quickly. The possibility of some more stable constructions at certain atomic numbers, which reference the number of protons in an atom's nucleus, offer the best chance to find some of these super-heavy elements. They may not decay as quickly as do some of the really unstable elements. But even a half-life -- the amount of time it would take for half of an element to decay into others -- of millions of years could mean that most of a particular element had already disappeared in a universe that is billions of years old.
There's supposed to be an upper limit to how big an atomic nucleus can get -- beyond a certain size the electrons in its surrounding energy shells would have to move faster than the speed of light to avoid collapsing into the nucleus. Which is not, as far as anyone knows, possible. As the Chemistry World article notes, famed physicist Richard Feynman believed that would happen at or near element 137, although some modern researchers think we could find elements far heavier, up into the 180s.
Of course, the really wacky could happen, and element that broke this law could be found to exist, and it would be called dilithium and power warp drive ships to the stars.