[enzzz]

Hi,

I'm new to this forums and quite new to chemistry also. I have just started high school. Anyway I have a question about stability of different isotopes.
I know that as atomic number grows also the relationship between protons and neutrons grows ( to have a stable isotope ). Yet there are so many exceptions. For example Chlorine is stable with 18 and 20 neutrons. Why isn't it stable with 19 neutrons? What does it depend on whether it is stable or it isn't? It's really confusing since I didn't find any logic for it in my chemistry book neither did find the answer on the google, so I thought perhaps someone here can help me satisfy my curiousity. Sorry for my English and chemical terminology, since I'm not really native speaker, as you can probably tell

[AWK]

There is no definite theory of isotope stability. May be this link will be a good start:
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucstructcon.html

[Astrokel]

Just to add on bit..

that is a different between radioactive isotope and stable isotope. stable isotope usually have a very very very huge half-lives compare to radioactive isotope, such that they are considered relatively stable. As such stable isotopes do not decay easily, probably in your example Cl-18 & 20 is stable isotope while Cl-19 is a radioactive isotope.

[enzzz]

Ooh, okay, seems way too complicated for me, considering I can't understand half of the terminology on that theory site.
So you are saying that it is quite impossible/difficult to calculate whether an isotope is stable or not with not having a chance to test? A formula that is based on neutrons, protons or electrons? Because I can't go on to quarks before I have fully understood the electrons

[cliverlong]

What an interesting question.

I don't know the answer but I have found the following links that may be relevant

First the question is why does the nucleus hold together at all when the electrostatic or coulomb force between the protons must be forcing the nucleus apart? The answer is the (strong) nuclear force described here:

http://en.wikipedia.org/wiki/Strong_interaction

In summary there was postulated a force from the interaction of neutrons and protons that held nuclei together. Now , the force is thought to be that that hold the proton and neutron particles themselves together and the nuclear force is a by-product. So we have reached a point where we have an explanation why some nuclei are stable. The we need to think why some nuclei are stable and some unstable.

We move on to this article

http://en.wikipedia.org/wiki/Atomic_nucleus

The wikipedia article suggests in section "Shell models and other quantum models" that the nucleus has energy shells or levels roughly equivalent to electron energy levels .  That section contains the phrase

present nuclear theory does predict the "magic numbers" of filled nuclear shells for both protons and neutrons.

which I interpret to mean (I may be wrong) there is no simple model for predicting whether a particular combination of neutrons and protons results in a stable or unstable nucleus.

However the next couple of sentences are:

The closure of the stable shells predicts unusually stable configurations, analogous to the noble group of nearly-inert gases in chemistry. An example is the stability of the closed shell of 50 protons, which allows tin to have 10 stable isotopes, more than any other element.


So it seems there are empirical rules to identify very stable nuclei

Now look at the powerpoint presentation

http://www.physics.gatech.edu/frog/lectures/ModernPhysicsLectures/MP18Nuclei.ppt

Slide 13 shows the line of stability
Slide 15 and 18 suggest most stable nuclei have even-even numbers of protons and neutrons a few stable nuclei  have odd-odd numbers of protons and neutrons
Slides 20 and 21 suggest there are energy levels in the nucleus occupied by nucleons and the pairing or non-pairing of nucleons has a bearing on the nucelus stability - but I can't quite interpret that yet


Any other contributions or corrections to my interpretation?

Clive

[enzzz]

Oh, thanks for that very good reply and snacks to all of you.

I think I understood most of your text, although I probably would need to look over the formulas and other stuff, since it's I really don't know anything about quarks, gluons, fermions and other. I'm still having troubles understanding what a spin is.
I'd have to look over your text again some other day, since I've had way too much chemistry for today : ).

Although just out of curious I would like to ask how long have you (all of you who gave me those answers) dealing with chemistry (studying, teaching, experimenting, working with it, whatever : )). I just want to see how long time it takes to be skilled enough to understand all this.
For me I have been studying chemistry from 6th or 7th grade (don't remember exactly) and now am in 10th. And before 10th I really didn't study it, didn't have any motivation, but as soon as I switched to another school in 10th I've started to have extreme interest in chemistry, but I have so many missing links so it's hard to catch up, since the new school is quite elite in my country : ).
Now I feel like I just want to know more and more in chemistry since I feel like the secret of life flows behind it : )

[Astrokel]

well! since you are new why not introduce yourself?

http://www.chemicalforums.com/index.php?topic=8548.0