Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: sooyeah on 21/09/2007 12:49:26

Title: Atoms and there size....
Post by: sooyeah on 21/09/2007 12:49:26

I was wondering what is like the largest theoretically possible stable atom?
I was told by a proff, that atoms expand slightly with energy intake.
So what is the largest stable atom possible?

Title: Atoms and there size....
Post by: syhprum on 21/09/2007 14:11:05

U238 is the largest naturally occurring atom and has a very long half life, transuranic atoms can be artificially produced but the heaviest have lives measured in milliseconds.
It is predicted that an 'island of stability' will be reached at about atomic number 118 but there is little experimental evidence for this as yet.

See http://en.wikipedia.org/wiki/Island_of_stability

For more detail 

Title: Atoms and there size....
Post by: Soul Surfer on 21/09/2007 14:46:13

The the heaviest stable atom is bismuth which is one atomic number higher than lead.  The largest atom is probably that of Cesium  (it is not the heaviest )  it has a very weakly bound electron which makes it very large  Francium (the final alkalai metal) would probably be larger but that is radioactive and therefore not stable.

Title: Atoms and there size....
Post by: syhprum on 21/09/2007 16:09:14

U238 is credited with a half life of 4.46*10^9 years, it is a bit mean not to class that as stable.

Title: Atoms and there size....
Post by: Bored chemist on 21/09/2007 20:48:40

Bismuth isn't stable. It has a very long half life.

However, if the question is about size of atoms in excited states then I'm not sure there is a maximum.
Excited states have the electrons further away from the nuceus so they are a bit bigger on average than the ground state. A very nearly ionised state of hydrogen might be bigger than a ground state uranium atom. Of course, all these excited states are not stable.
Also while things like U are heavy they are not really big. Bi is much less dense than U and it's atoms are about the same mass (209 vs 238)so the atoms must have a larger volume. From that point of view Bi is a lot bigger than U.

Title: Atoms and there size....
Post by: lyner on 26/09/2007 15:51:08

If you think of the outer (conduction) electrons in a metal (solid), they are shared, effectively, with all the surrounding atoms. You could say that each atom has an influence over many times what is normally regarded as its radius. That could be looked upon as its radius,