Question:
What is the limit on isotopes that a element can have? what dec ides
the number of neutrons for an elements isotope?
Replies:
There is no limit on the number of isotopes an element can
have, in principle. In practice however the most of these isotopes
will be unstable. There is something called the Shell model
and that can be used to find out the stable isotopes theoretically.
jasjeet s bagla
Basically there is a balance between a couple of different
effects - the nucleus is held together by the strong
nuclear force which requires those neutrons (otherwise
the positively charged protons repel one another too strongly
to be bound together in a heavy nucleus), but if you have
too many neutrons the neutron itself is not stable, and
will decay into a proton and an electron (and a neutrino). If
it were not for the charge on the protons, the shell model
Jasjeet mentions would predict the most stable configurations
would have equal numbers of neutrons and protons. Because
of the proton-proton repulsion, slightly more neutrons
are required to stabilize a nucleus that contains lots
of protons.
Actually, the shell model also predicts greatest stability
for nuclei with an even number of neutrons and an even number
of protons - nuclei with both neutron number odd and proton
number odd are hardly ever stable (check out a chart of the
nuclides some time!)
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