I was reading about cesium or something else with a c in the encyclopedia and it mentioned that it had the largest atom. However, it is only 55 or 58 in atomic number. How could it be larger than, say, uranium? Don’t the diameter of the atoms go up steadily as they have more particles in the nucleus to accommodate, so hydrogen would be the teensiest atom and trans-uranium elements would be the most huge? 2) How large is this atom of cesium or cerium or whatever is the largest atom? Say on a scale of 10 we would have cesium at 10 and then were would the smallest diameter atom be on this scale?
Probably somebody will be along shortly with a better answer, but I’ll take a WAG…Presumably by “largest”, they were referring to volume (if that concept can really be applied to atoms?). Nuclei take up a really tiny percentage of the total volume of an atom, so more neutrons and protons wouldn’t necessarily translate to a larger atom. The “electron shell” takes up the vast majority of “space” in an atom.
Yah, but don’t more electrons mean a larger electron cloud? (Esp. given that each electron energy level can only hold a certain number of electrons so that a new one goes into a higher energy shell and therefore a larger orbit.) If so, you’d expect one of those unnamed elements in the 110’s to take the top spot.
–Cliffy
Even if you assume that the electron shells define how “large” an atom is, the higher the atomic number, the more electrons, the bigger the outer shell (sorta).
The cite is a little vague, any way you can actually quote your source?
Click on the link to learn more.
I found this when I typed “largest atom” into my favorite search engine.
(kgmm)/(s*s)
Second time today I’ve been toooo sllooowww.
I can’t believe no one has mentioned Neutron Stars yet 
Spanner meet works, works this is Mr Spanner
Most reasonable definitions of “atom” would assume that the thing is held together by nuclear and electromagnetic forces, so a neutron star is out.
And the reason that the rightmost elements are smaller is more or less that the nucleus has a larger charge, so it’s pulling the electrons in tighter. Extra size mostly only comes when you have to add a new orbital, and that’s more or less when you get a new row in the table.
::Spritle dusts off his Chemistry degree, sees that the question was sufficiently addressed, decides not to mention the Shielding Effect, and quietly leaves the thread…::
The largest atom (in terms of atomic radius) is…Fr (francium).
It is the lefternmost element in the 7th period. This goes against logic - wouldn’t the element with the most electrons (and therefore highest atomic number) be the largest? No.
The periods (rows) in the periodic table represent the energy level (1-7) that the electrons of the atom are in. Going across a row, the atomic radius decreases because the increasing positive charge in the nucleus (as more protons are added) pulls the electrons in more tightly.
Going down a column (family), new energy levels are being filled. These are shielded from the effect of the nucleus by the inner energy levels.
So, atomic radius decreases left-to-right and increases top-to-bottom. Therefore, the largest element is in the bottom left.
*Note - I am 10th grade student. This is what I was just taught a few days ago (test was yesterday). If it’s wrong, it’s my teacher’s fault.
As far as I know, the atomic radii of all elements have not been measured yet. Sure, you can make some guesses based on trends, but considering that many elements exist only under extraordinary circumstances and for fractions of a second, who really knows?