Why are the larger elements more unstable and radioactive the closer to the bottom and right of the periodic table you go?

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Why are the larger elements more unstable and radioactive the closer to the bottom and right of the periodic table you go?

In: Chemistry
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It gets progressively more difficult to smoosh that many protons together without them flying apart. You know how opposites attract? Protons aren’t opposites of each other, and they’re not really hyped about hanging out. They tolerate it to a certain extent but eventually it’s just too much and they can’t stand each other anymore

We have observed that larger elements break up into smaller elements and in the process release energy. This is because the smaller nuclei are more stable (or rather, iron nucleus is the most stable and stability decreases as you move away from it) and the energy released is the result of achieving this higher stability. Moving to the right and bottom means a heavier nucleus which is further and further away from iron and hence has a lot more “paths” by which it can become more stable through fission (more nucleons, more jiggling, more “paths”). More “paths” means higher likelihood that the nucleus will decay at any time- and so it is more unstable.

As you go down, and to a lesser extent from left to right, you’re going to elements with larger atomic weights. For radioactivity, you’d do better to look at all the isotopes. For instance, here:

https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html

As you can see there’s a thin line of stable isotopes, from hydrogen-1 to lead-208. On either side, there are radioactive ones, of shorter half-life as you move out.