# Why does each element have "at least one isotope with an unstable nucleus"? **URL:** \ **Category:** Factual Questions\ **Created:** [January 19, 2013, 10:09pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748 "2013-01-19T22:09:56Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [January 19, 2013, 10:09pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/1 "2013-01-19T22:09:56Z")
Saw this statement over on wikipedia ([http://en.wikipedia.org/wiki/Atom](http://en.wikipedia.org/wiki/Atom)): “Each element has at least one isotope with an unstable nucleus”. Is there some innate feature of atoms that makes this true? or have we just found it to be true with every element we’ve discovered so far? ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [January 19, 2013, 10:20pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/2 "2013-01-19T22:20:45Z")
> [@dstarfire](#): > > Saw this statement over on wikipedia ([http://en.wikipedia.org/wiki/Atom](http://en.wikipedia.org/wiki/Atom)): “Each element has at least one isotope with an unstable nucleus”. > > Is there some innate feature of atoms that makes this true? or have we just found it to be true with every element we’ve discovered so far? One of the key indicators of stability is the neutron-proton ratio,so taking a stable isotope and adding or taking away a sufficient number of neutrons will create a an unstable isotope. ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [January 19, 2013, 10:40pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/3 "2013-01-19T22:40:52Z")
Yes, this is a fundamental characteristic of the nuclear force. Neutrons are needed in order for the attraction between protons to be stable. If you have too many neutrons or too few, the nucleus is unstable. Since an isotope can have any arbitrary number of neutrons, you can always specify an isotope that is unstable. Here is an interesting plot. Stable isotopes are shown in black, and isotopes with half-lives too short to have ever been measured are shown in white. Atomic number (Z) is on the bottom, neutron number (N) on the left. > **[File:Isotopes and half-life.svg](https://en.wikipedia.org/wiki/File:Isotopes_and_half-life.svg)** > > Original file ‎(SVG file, nominally 640 × 768 pixels, file size: 57 KB) > Esperanto > > Click on a date/time to view the file as it appeared at that time. ---
**Author:** ![dstarfire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dstarfire/32/5762_2.png) [@dstarfire](https://boards.straightdope.com/u/dstarfire)\ **Post date:** [January 19, 2013, 11:25pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/4 "2013-01-19T23:25:11Z")
I see. So the “at least one” part refers to the number of protons or neutrons that can be removed. ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [January 19, 2013, 11:31pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/5 "2013-01-19T23:31:19Z")
> [@dstarfire](#): > > I see. So the “at least one” part refers to the number of protons or neutrons that can be removed. Well, if you add or remove a proton you change which element it is. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [January 19, 2013, 11:32pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/6 "2013-01-19T23:32:22Z")
> [@dstarfire](#): > > I see. So the “at least one” part refers to the number of protons or neutrons that can be removed. In many ways it’s a very trivial observtion, because if you have an isotope with 500 neutrons in the nucleus, you know it will be incredibly unstable whatever element (though such an isotope would be for all intents and purposes impossible to create). ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [January 19, 2013, 11:51pm UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/7 "2013-01-19T23:51:36Z")
> [@Asympotically\_fat](#): > > In many ways it’s a very trivial observtion, because if you have an isotope with 500 neutrons in the nucleus, you know it will be incredibly unstable whatever element (though such an isotope would be for all intents and purposes impossible to create). Indeed it is, and it is also quite an understatement, because as you can see from the linked chart, the vast majority of isotopes are unstable. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [January 20, 2013, 12:16am UTC](https://boards.straightdope.com/t/why-does-each-element-have-at-least-one-isotope-with-an-unstable-nucleus/647748/8 "2013-01-20T00:16:03Z")
> [@Absolute](#): > > Here is an interesting plot. Stable isotopes are shown in black, and isotopes with half-lives too short to have ever been measured are shown in white. Atomic number (Z) is on the bottom, neutron number (N) on the left. > > [File:Isotopes and half-life.svg - Wikipedia](http://en.wikipedia.org/wiki/File:Isotopes_and_half-life.svg) looks really cool in poster size.