Sorry about that!
>Describe the pattern of nuclear stability as mass number >increases. Which atoms are most stable?
Another point is that as the number of protons in a nucleus increases, the ratio of neutrons to pro tons increases. For example, the most common isotope (and thus generally the most stable) of uranium is 238U. It has 146 neutrons and 92 protons. However, the most stable and abundant version of Carbon, 12C, has 6 neutrons and 6 protons. So, 12C's neu tron/proton ratio is 1. 238U's, however, is much higher, around 1.5 So, as we increase in atomic number (number of protons), the number of neutrons in the most stable isotope increases more rapidly. To put it another way: As the number of protons in the nucleus increases, more and more neutrons are needed to keep it stable.
>Describe the pattern of nuclear stability as mass number increases. Which atoms are most stable?
Hmm, I guess I glossed over this a bit in the binding energy text. I don't have a deep understandin g of why the following is true (I assume you probably need some knowledge of quantum mechanics to explain those details), but the following is how I see it as of now:
Actually, before I go further, this stability I am talking about refers to the stability of the nucleus, as opposed to the chemical stability dealing with valence electrons. I may not have made this that clear in the text, but I think it is a pretty important difference. For example, the chemical stability found in the noble gases because they have 8 valence electrons is siginificantly different from the stability of its nucleus, as seen in the measurement of the nucleus' binding energy per nucleon. Iron, on the other hand does react with other elements chemically, and yet has one of the most stable nuclei of the elements. This nuclear stability is important in the explanation of fission and fusion energy.
Anyway, the general pattern is that the very light atoms with very small atomic masses have very little binding energy per nucleon that compose them. This value (the binding energy per nucleon) rises fairly sharply as the atomic mass of the nucleus increases, and then begins to taper off, reaching a max at around at a nucleus with an atomic mass of 56. This indicates that the nuclei of atoms with an atomic mass = 56 amu are the most stable. After this point, the binding energy per nucleon decreases somewhat slowly as the atomic mass continues rising.
If you were to calculate the binding energy per nucleon for each of the atomic masses, you would get a graph very similar to the general graph seen in the binding energy page at http: //hyperion.advanced.org/17940/texts/binding_energy/binding_energy.html . If I am mistaken on any of this, please correct me! :) Also, if anyone else could answer why the binding energies happen to turn out so, that would be great!
