Atoms: Why there are differnet numbers of Neutrons and Protons in stable elements.

[danchc]

According to the American Nuclear Society website: "a Nucleus that has more Neutrons than Protons is unstable, and such Nucleus will try to become stable by giving off particles or packets of energy. These emissions are called radioactivity." If this is true, why is Silver ( 47 Protons, 60 Neutrons ) not radioactive? Similarly, most elements above Atomic Number 17 have more Neutrons than Protons, yet are also not radioactive and are called stable. An atom that has a different number of Neutrons to Protons is called an isotope, which means 80% of the known elements are, in fact, isotopes.
If we assume that the number of Neutrons differing from the number of Protons does not signify radioactivity in itself, what equation denotes the number of Neutrons difference for an element to be (or not be) unstable and radioactive ( i.e. expelling Neutrons )?
Thanks you :)

[lovehearts]

eh... you got me stumped!!! Keep up the good work! ;)

[vascop]

read this:
http://www.igcar.erne...ar/atomic_nucleus.htm

[ABerrant]

Your definition of isotope is incorrect.

[R1Geezer]

Yep you've got your Isotopes mixed up.

[vascop]

Yes, an isotope has the SAME number of protons but a different number of neutrons. So deuterium and tritium are isotopes of hydrogen since they have 1 and 2 neutrons in the nucleus respectively and ONE proton. Hydrogen itself has one proton and no neutrons.
If you've been looking at this article:
http://www.aboutnucle...Structure_of_the_Atom
then it is so simplified that it becomes misleading in places. The one I gave a link to above is still quite simple, but does not tend to confuse the reader.

[jake-the-peg]

The fact is that the statement from the American Nuclear website is an over simplification.

The nucleus is kept together by the interactions between neutrons and protons - otherwise the positive charges on the protons would cause them to fly apart,
This interaction is very complex and the above statement is just a rule of thumb.

There are many complexities - note for example that nucleii with an even number of nucleons are more likely to be stable. for example Uranium 238 compared to Uranium 235

[danchc]

Thanks to all that answered. Vascop, the first link you posted was simple and answered all I was after. The second link you posted was the article I had been reading. I think that Jake-the-peg has it right, the original definition was an over simplification, or just plain misleading. As for the isotope definition, this again is an over simplification. Perhaps a better definition would be: Isotopes are different types of atoms (nuclides) of the same chemical element, each having a different number of neutrons from the stable state of that element.
Thanks again.