what is the heavyest possible element? is there some sort theortical limit for the total number of protons in an atom? if I had enough energy could I make an atom the size of a basketball? (I imagin it would be short lived and very quickly radioactive). what is the limit?
While I have literally no background in particle theory, I believe that the upper limit of atom weight is increasing as the universe cools… Obviously quite slowly, though.
Aren’t neutron stars sort of a single molecule?
Atoms of elements which don’t exist here naturally can be created in an atom smasher, the heavier they get the shorter their lives, and they are all radioactive. It seems (in my own understanding) that the limit for size is really based more upon our abilities to detect the atom than for any actual law of physics relating to its size- most of the atoms created are only around for a few very small fractions of a second.
My very limited knowledge of atom thingies would put the limit on the size of an atom at whatever the range is of the strong/weak (whichever applies) force. I understand that this is not a whole lot larger than the uranium atom.
There is an ‘island of stability’ (protons vs neutons) at 114. Here the element is stable with a half-life of 30 seconds.
I think the latest that has been found is 118, ununoctium.
It was calculated in the 1970’s that 114 would be stable. There can be more theoretical islands of stability found beyond this, eg 126 should be stable according to calculations.
The elements above 100 in atomic number break down rapidly, with the most recently produced ones having half-lives in the range of a microsecond. Obviously there is a point of diminishing returns here.
There is, however, an “island of stability” significantly further up the atomic number listings where atomic-structure theory suggests that there is a good possibility of (relative) stability. However, attempts to create atoms of these superheavy elements have so far been in vain, from what I understand.
Technically, the core of a neutron star, and parts of the core of a white dwarf, might be understood to be giant atomic nuclei, but that’s quite a different subject from what can exist at STP.
‘Found’ - I mean created. The heaviest naturally occuring element ‘found’ is uranium.
I don’t think I’d call a neutron star a giant nucleus, as it’s held together by gravity, rather than the nuclear strong force.
Picky picky. It’s a big whack-o-neutrons stuck together. 
Ununoctium was a fraud. It was a major scandal last year.
The physicist involved fabricated data.
In regards to neutron stars, we don’t even know that they are completely composed of neutrons.
A recent article in (I think) New Scientist reported a new study that some neutron stars may be made up, at least in part, of quark matter.
-Oli
Element 118 was not a fraud. It was an honest mistake, and the research team recanted their claim when other researchers failed to replicate their findings. It was a misinerpretation of data, rather than a deliberate fraud. Do your research before slinging wild accusations.
I’ve heard that some tiny amounts of neptunium occurs naturally.
This page isn’t much of a reference but it says:
This somewhat more authoritative document states that:
It’s not completely clear from this quote whether they would show up in natural uranium decay, but the implication is that they would if only minimally.
Found one more:
I would assume that atoms with a half-life shorter than the Planck time can’t exist, but that is just an assumption.
I wuld draw the line a lot higher than that, ultrafilter. I would argue that if the half-life is shorter than the light travel time across the nucleus, then the atom can’t really be said to exist for any particular instant. The Planck length, if I recall correctly, is about 15 orders of magnitude smaller than a proton, and of course these heavy atoms are larger than a proton.
Well, you’re a physicist, and I’m not, so let’s go with what you think.