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What is the limit on isotopes that a element can have? what dec ides the number of neutrons for an elements isotope?

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!)

Arthur Smith

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