I have a basic understanding of it. But mostly just from what I learned in high school. Also some from watching Periodic Videos on YouTube. Eli5: But why are there radioactive and other dangerous elements?
In: Chemistry
In the beginning, there was nothing. Then, that nothing decided to explode, and thus there became many things. Now, don’t ask why that happened, cos we’re still trying to work it out. That explosion was a whole fuck ton of energy. Some of this energy decided that it wanted to become matter instead. And it can do that, because matter is really just a reorganised version of energy. The energy became a bunch of subatomic particles, which eventually became a whole ton of hydrogen atoms.
These hydrogen atoms were so numerous that they began to group together. By grouping together, it created a large mass in one place, which warped the fabric of space-time, exerting a strong gravitational force and drawing in more hydrogen atoms. The more hydrogen atoms that came, the bigger the party got, making it easier for more hydrogen atoms to be drawn in. Now, when a bunch of molecules decide to have a party, it generates quite a lot of temperature and quite a lot of pressure. Eventually so many hydrogen atoms were joining in that the ones at the center were under a huge amount of temperature and pressure – enough that they spontaneously fused together to make helium. This generated even more heat, which caused even more fusion reactions and so on, until the entire ball of hydrogen became a huge fusion reactor – a star.
And there wasn’t just one star, there were many stars. Stars keep burning until all the hydrogen is gone, and there’s no more to fuse together. When that happens, the star explodes, becoming a supernova. When a supernova happens, the helium and any remaining hydrogen fuse together in random combinations, creating all the other elements. Elements like oxygen, and iron, and carbon, and a bunch of degenerate unstable atoms that chose to split up and become two separate particles instead.
These supernova then scattered throughout the universe, until they met more hydrogen, becoming great clouds of space dust called nebula. And out of these nebulae, new stars were born from the corpses of old stars. This time, the gravity of these stars caused them to create accretion disks of stardust – heavier elements that are drawn in by the star and orbit it at great speeds – similar to the rings of Saturn. Over time, these accretion disks clumped together under their own gravity, first forming rocks, then asteroids and finally planets. That’s right, you and everything else on earth are made of the dust-like remnants of long-dead stars.
But how does fusion work, you ask? Well, as you probably know, an element is defined by three subatomic particles: Protons, neutrons and electrons. These particles are under the effects of attractive forces, which feel quite similar to magnetic forces: protons stick to neutrons and electrons orbit around the big clump of protons and neutrons. Some arrangements of protons and neutrons are strong and stable. Every element on the periodic table is reasonably stable, and can exist in nature. Radioactive elements are elements that are not very stable – the repulsive forces of the protons is stronger than the attractive forces that hold the nucleus of the atom together. Very unstable elements split into smaller more stable elements almost immediately, but some radioactive elements are only a *little* bit unstable. These can exist for ages. The radioactive elements we consider true elements are unstable, but they’re not *very* unstable – they hold themselves together reasonably well, and decay spontaneously only quite slowly. However, you can cause them to decay earlier if you bombard them with energy, and this is how nuclear bombs work.
As for “dangerous elements” – there’s no such thing as a dangerous element. Life is just a very fragile thing, and some chemicals can break the mechanisms of life: Radioactive decay causes DNA to mutate, and arsenic sticks to important proteins and prevents them doing their job. The fact these things happen is kind of just coincidence. Hypothetically speaking, it would be entirely possible for life to evolve in a direction where arsenic *wasn’t* poisonous, but say, iron was.
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