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Thread: Please help me understand ions and isotopes

  1. #1 Please help me understand ions and isotopes 
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    This may seem like a dumb question, but can someone tell me what causes neutral atoms to end up with more or less neutrons and electrons than they need to remain neutral? My teacher isn't helping me understand how this happens and I already feel stupid.


    I know the definitions. Ions are atoms with a different number of electrons and isotopes are atoms with a different number of neutrons. What I don't know is what happens to those atoms that make them lose or gain neutrons and electrons. Does it happen naturally or some other way? Thanks.


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    Moderator Moderator Janus's Avatar
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    Atom can pick up or lose an electron from its environment. The loss can come about by something actually knocking or pulling an electron away from the atom. Positive ions can form when the outer shell of the atom is 1 short of an electron from being full. (electrons arrange themselves in shells around the atom,, these shells are more stable when full, and in some cases, the need to fill the shell over-rides the tendency to be neutral.

    Neutrons are neutral particles themselves, so adding or losing one won't change the neutrality of the atom. They act as part of the "glue" that holds the nucleus together. (a nucleus made of just protons would just fly apart.) It takes a certain minimum number of neutrons in the nucleus to hold any given number of protons together, and in many cases, on or two more won't make any difference, so if the atom is made with an extra one, it remains stable. On the other hand, neutrons by themselves are not stable and tend to decay into a proton and electron. Being in a nucleus with protons stabilizes them. If you try to add too many neutrons to a nucleus, it loses some of that stability and you get a radioactive isotope. Eventually the excess neutron(s) can decay, adding a proton to the nucleus and ejecting an electron (called beta decay), this turns the atom into a different element. which, itself, may be unstable. If it is unstable, it will undergo a further decay. (for example, it may now have too many protons. In which case it will emit a neutron-proton pair by alpha decay) This continues, through a series of alpha and beta decays until a stable nucleus is arrived at.

    This path from radioactive to stable nucleus is called a "decay series". Radioactive isotopes of two different elements can have decay series that take them through the same elements, but different isotopes of those element. And sometime they can lead to the same stable element at the end, but just different stable isotopes of that element. For example, Uranium 235 and Thorium 232 both have decay series that end with a stable lead isotope, but U-235 ends with Lead 207 and Th-232 ends with Lead 209.


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    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  4. #3  
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    Thanks, Janus.
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