[Feoggou]

Hi there!

can anyone please explain to me the term "stability" for atoms. What is stability when talking about radioactivity, and has this to do with how the atom reacts with other atoms (like H + O + H => water). How is it called when an atomic element is rather to combine with other atomic element and form a molecule (is it less stable?)?

And I read that an isotope of Iron is one of the most stable elements. What does this mean? (I know what is an isotope, but my question is what does 'stable' means here?)

And one more question I have: in what circumstances can an atomic element transform into another atomic element? Can it be transformed into one with more protons, or only decade into a lower one (like Cl into S)? And in nature, is this happening? if yes, then how?

please excuse my lack of knowledge on chemistry  And please answer. And if you can, please give me a link to a site that deals with/more with this subject.

[Borek]

Probably good starting point will be http://en.wikipedia.org/wiki/Radioactive_decay and articles linked from there.

I am not sure if stability is a precisely defined term, perhaps Mitch will be able to add something. In general we say that isotope is stable when it doesn't undergo spontaneous fission. However, some isotopes that were considered stable on further scrutiny were discovered to be decaying, just very slowly. Not sure how they are treated.

Iron isotope is stable because it has the highest binding energy per nucleon - http://en.wikipedia.org/wiki/Binding_energy

Nucleus stability has nothing to do with chemical reactions.

[Astrokel]

check this out: http://www.chemicalforums.com/index.php?topic=29135.msg110496#msg110496

[Feoggou]

ok thanks for these info, they were helpful

but still I have some questions if you don't mind answering. I read some things that I do not understand, so can you please explain?

"Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter"). This is a random process on the atomic level, in that it is impossible to predict when a given atom will decay, but given a large number of similar atoms, the decay rate, on average, is predictable." (http://en.wikipedia.org/wiki/Radioactive_decay)

how is it possible that one atom just turns into a greater one (like C into N)? And why can't it be predicted? Is this happening also in nature or only by artificial ways?

And one more question,
"Thus, light elements undergoing nuclear fusion and heavy elements undergoing nuclear fission release energy as their nucleons bind more tightly, and the resulting nuclei approach the minimum total energy per nucleon, which occurs at iron-56. As the universe ages, more of the matter is converted into extremely tightly bound nuclei, such as iron-56. This progression of matter toward iron and nickel is one of the phenomena responsible for the heat death of the universe."(http://en.wikipedia.org/wiki/Iron-56)
how is that possible that every elements would turn into Iron and Nickel?

Can you please explain these?

[Arkcon]

how is it possible that one atom just turns into a greater one (like C into N)? And why can't it be predicted? Is this happening also in nature or only by artificial ways?

You may be misunderstanding terms here.  It's known for example, that C-14 has an unstable nucleus.  It will decay, losing one beta particle, into nitrogen-14, which is stable.  For a given population of C-14 atoms, in 5,730±40 years, half of them will undergo this decay.  But which ones, can't be predicted. 

If you sat, and watched one atom of C-14 (which is barely theoretically possible), it might decay tomorrow, it might have decayed after 5,000 years, it might still be around for 6.000 or 10,000, but that doesn't change, the paragraph I wrote above.

This is a common problem, for people just learning statistical outcomes.  Every so often, someone with extraordinary patience, will flip a coin, 1000, or 10,000 times, and get greater than 50% heads or tails, and will be convinced they've rewritten statistics.  And they're just wrong.  Try to see the above discussion in that light.

[Astrokel]

Just to add on the equation from what Arkcon has already mentioned

¹⁴₆C  ----> ¹⁴₇N + ⁰_-1e (Conservation of mass number)

Can you please explain these?

The stability of nuclei is measure in terms of binding energy per nucleon. And that Iron-56 has the highest binding energy per nucleon, all other elements which is lower in atomic mass than Fe-56 will prefer to undergo fusion to 'combine' to achieve higher binding energy per nucleon, while those higher in atomic mass than Fe-56 would prefer to undergo fission to 'separate' to also achieve higher binding energy per nucleon(greater stability). While there is a graph explaining this, you have to see it to understand what i am talking about.

Check this out: http://en.wikipedia.org/wiki/Image:Binding_energy_curve_-_common_isotopes.svg

[Feoggou]

all other elements which is lower in atomic mass than Fe-56 will prefer to undergo fusion to 'combine' to achieve higher binding energy per nucleon, while those higher in atomic mass than Fe-56 would prefer to undergo fission to 'separate' to also achieve higher binding energy per nucleon(greater stability)

ok, and what is this preference? It just happens or it has a cause? And what would this mean, that after millions of years, everything would be converted into Fe-56, or nickel? (if yes, then which of them?)

It's known for example, that C-14 has an unstable nucleus.  It will decay, losing one beta particle, into nitrogen-14, which is stable.

what does this "stable" mean? does it mean that nitrogen-14 would prefer to achieve higher binding energy per nucleon (and continuing with this would be finally turned into iron-56 or nickel-62) or that would remain nitrogen-14?

also about manganase-55, what will happen with this, would he always remain manganase-55?
http://en.wikipedia.org/wiki/Isotopes_of_manganese
-here above it is stated its half-life (I might not understand well the term)

I know that some isotopes that were thought stable were actually decaying in time. But I guess not all have the same fate, right?

thanks in advance...

[Arkcon]

what does this "stable" mean? does it mean that nitrogen-14 would prefer to achieve higher binding energy per nucleon (and continuing with this would be finally turned into iron-56 or nickel-62) or that would remain nitrogen-14?

By most standard classical models of nuclear decay, N-14, C-12, O-16 and Ba-130 will not spontaneously decay.  They can be fused, with lighter nucleons, or other atoms, say in a supernova explosion, into much heavier element, which will very likely spontaneously decay, but by themselves, they don't ...

...except, well, now we're leaving behind the sort of physics I studied,  By some contemporary theories, barium has a half life on the order of 10⁴⁰ years.  And even the neutron itself has a lifespan of that long.  Therefore, logically, all matter could theoretically cease to exist at some point.  This span of time is not trivial, 10⁴⁰ years is longer than the projected lifespan of the universe, but it still rewrites reality a little bit.  Sorry, but I can't find a recent reference for this, it's what I was taught in college chemistry.

As I heard it, we tried to study a huge tank of water containing ammonia, deep in an underground mine, to shield it from extraneous radiation, tying to catch a tell tale decay of a single atom that couldn't be explained any other way except the spontaneous decay of a single neutron.  That was not detected.

[Astrokel]

well, as Arkcon has already said, fusion required high temperature. it is usually happened in the stars or galaxies(i don't know the proper term). And as i had checked up your link, it mentioned something like heat death of universe when every element approaches Fe-56, but well it needs 10¹⁰⁰ more years to go...

Stable isotopes in an isotope which has a extremely long long long half life, even more than the age of earth.

[Borek]

And even the neutron itself has a lifespan of that long.

Free neutron (that is one, that is not bounded in the nucleus)  has a half life of about 15 minutes. I suppose you meant proton.

[Feoggou]

Therefore, logically, all matter could theoretically cease to exist at some point.

And as i had checked up your link, it mentioned something like heat death of universe when every element approaches Fe-56, but well it needs 10¹⁰⁰ more years to go...

so finally all matter would cease to exist at some point or transform into Fe-56/Ni-62 according to modern theories? Or there are different modern theories that sustain different things?

So, I understand that "stable" nuclei are actually decaying in time... ok...  And by the way, don't worry, I'm not affraid of dying because of nuclear decaying

As I heard it, we tried to study a huge tank of water containing ammonia, deep in an underground mine, to shield it from extraneous radiation, tying to catch a tell tale decay of a single atom that couldn't be explained any other way except the spontaneous decay of a single neutron.  That was not detected.

sorry, but I don't understand it... what could have been the reason that at least one atom to decay?

And one more question (that was not yet answered, to re-mention it): The theory by which all chemical elements will eventually transform specify:
- "As the universe ages, more of the matter is converted into extremely tightly bound nuclei, such as iron-56."
which are these nuclei, other than iron-56?
- "This progression of matter toward iron and nickel is one of the phenomena responsible for the heat death of the universe."
this is interesting: why would eventually (if the theory is correct) all transform into more than one chemical element, and not into one which would have the most tightly boud nucleus?
quotes are from http://en.wikipedia.org/wiki/Iron-56

and by the way, I might not understand well, if you want to look upon this, does it state that in present the "heat death" theory is nowadays understood as wrong: at the "Current status" of http://en.wikipedia.org/wiki/Heat_death_of_the_universe ? (and as I understand, the "heat death" theory is based upon physics, and the fault would not be the permanent decaying of the elements)

[Dan1195]

If you look at the stability of nuclei against decay, you will find that for many so called "stable" nuclei heavier than Sn (and heavier than Nd in particular), they are energetically unstable against alpha or heavier cluster decay. e.g. all "stable" isotopes of Pt have a Qa>0.  However, the time scales for these decay processes are too long to be observed. A nucleus such as ²⁰⁹Bi with its 10¹⁹ year half-life is near the limit of what can be observed.

As for nuclei such as ¹²C possibly decay paths on long time scales are only theoretical, such as decay of the bound proton within the nucleus. (there has been some debate whether the lifetime of a bound proton is longer than that of a single proton, obviously until we actually detect such decays this cannot be answered.)

[Arkcon]

Feoggou: here's a tip.  Get a college level physics textbook, and browse it.  Wikipedia is great for a start, but it doesn't really flow, from topic to topic, in a logical or useful manner.  You're routinely switching, from nuclear decay, to atomic stability, to fission, to fusion -- expecting nuclear decay, to progress to stellar fusion, to extreme gravitational phenomena associated with astrophysics, then switch back seamlessly, to nuclear stability.  You wouldn't make these errors, if you were reading a paper book.

Don't let the physics calculations at the beginning of such a text daunt you.  Just read the back on nuclear physics, where the phenomena are explained, progressing from one related fact to another.

Back in the day, the easiest texts to understand was the nonfiction writings of Issac Asimov (I always enjoyed his fiction too, as an aside.)    When you read a text written by him, you see how, logically, science progresses from one fact to the next.  His book The Collapsing Universe (1977), can spend dozens of pages, just to introduce the concept of gravity adequately, so you can understand collapsed stars.  Even if the astrophysics facts in this book are now outdated, you see how to learn.  Which is important.  Then you can clear up the outdated facts with more current books.  Recently, I've kinda enjoyed some books by Michio Kaku, he seems pretty good at summarizing obscure physics.