I seem to recall hearing somewhere that their was a limit to how big an atom can get, because at a certain point to remain in orbit around the nucleus an electron would have to travel faster than light. I don’t remember what element it was (somewhere in the 130’s rings a bell), or where I heard this, and I can’t find it anywhere. So is their a largest element, if so what is it, and have we discovered yet or is it theoretical?
Here’s a link to Wikipedia that covers the heaviest known elements currently, and discussed the “island of stability” which is a set of theoretically stable heavier elements. Island of stability - Wikipedia
The limit on size isn’t based on electrons (not at this size, anyway), but on binding energy in the nucleus.
I thought that the idea of electrons “orbiting” the nucleus was a bit of a metaphor, and that they don’t orbit in the same way that Earth is orbiting around the Sun, i.e. they are not in general free-fall, but are fixed in specific energy levels associated with specific quanta.
Right. IANA nuclear physicist, but my understanding is that the nuclear strong force, which is what allows all those highly charged protons to clump together so incredibly tightly, has a very very short range. So as nuclei get larger, some of the outer protons and neutrons start to get too far away from the center of the nucleus to be held in by the strong force.
I forget where I read that, and I’ll happily bow to superior authority that comes along.
Even better: the placement and existence of electrons is a matter of probability!
There are a lot of more complicated details, but that’s about as good as you’re going to get for a message board explanation. Meanwhile, the electrostatic forces which are trying to push protons apart fall off more slowly with distance, so for large atoms, the pushing-apart force becomes more relevant relative to the holding-together force. This can be mitigated somewhat by adding more neutrons (which are subject to the strong force, but mostly not to the electromagnetic force), but the strong force works most efficiently with equal numbers of protons and neutrons, due to the Pauli exclusion principle, so heavier elements will tend to have more neutrons than protons, but there’s still an upper limit.
And that limit is…?
Check the Wikipedia article. The heaviest we’ve observed so far is 118 protons (total weight of 294). There are some theories that we should expect elements at 120 and 126 (total weights expected at 304 and 310), but they have not yet been observed.
And note that these heavier elements are so unstable that they spontaneously break apart over a relatively short amount of time. Thus the bonds are not that strong, right?