I had an exciting chat with my father yesterday about Chemistry. Chemistry is one of the most interesting topics because among other things it explores the basic building blocks of us and everything around us: Atoms.
It’s common knowledge that atoms are made of a nucleus with neutrons and protons (red and blue), and electrons (grey) swarming somewhat mysteriously around that nucleus. Weirdly, there is SO much space between the nucleus and electrons of every atom that it’s mostly made of space – not stuff. So, everything in the world, even the things that seem solid to us (a table, concrete, our own bodies), is mostly made of space.
Varying numbers of protons in the nucleus dictate the kind of element an atom is. 2 protons makes it Helium. 19 protons makes it Potassium. The numbers of electrons and neutrons can vary and cause each element to interact with other substances in different ways.
The most intriguing but dangerous types of elements are the radioactive ones. Famously, Polish physicist and chemist Marie Curie passed away as a result of prolonged exposure to radioactive substances.
Apparently the elements that have huge numbers of neutrons or tiny numbers of neutrons in their nuclei are the ones that tend to be radioactive. No one really knows why (or at least, it’s not explained in the books we’ve read) but somehow a neutron-heavy or neutron-light nucleus just can’t manage to stay intact! (Actually, it is the neutron-to-proton ratio that we care about. An atom with a neutron-to-proton ratio greater than 1.5:1 or less than 1:1 will exhibit radioactivity.) So, what happens? Well, the atom does everything it can to change the number of its neutrons – to find a more stable way of existing. There are a few options.
1) The atom can release an alpha particle. This happens to very heavy nuclei. Alpha particles consist of 2 neutrons and 2 protons. Literally, the atom ejects part of it’s own nucleus! It releases this alpha particle, which technically (if you take a look at the number of protons) is nothing but a particle of Helium without any electrons. Awesomely, as a result of releasing an alpha particle the radioactive element has changed it’s basic makeup!! It is no longer the same element.
For example, let’s start with Uranium.
It’s definitely radioactive. It starts out with lots of neutrons and has 92 protons. It releases an alpha particle with 2 of its neutrons and 2 of its protons. Now, the atom has 90 protons – which means it is no longer Uranium! It has become Thorium, a totally different element with different behavior and different properties. That’s just crazy. Radioactive elements are not just unstable because they release particles and energy that can be harmful to our bodies, but also because they can change from one basic element to an entirely different element in the process.
2) The atom can release a beta particle if there are too many neutrons and not enough protons. Beta particles, which are just electrons that are released from the atom, are created in a mind blowing way. One of the atom’s neutrons decides to sacrifice itself. It splits into a proton and an electron, and spits that electron out. Now, it has one less neutron (win! – that’s the whole goal here), but as it turns out you now also have one more proton. Again, that means that the element is no longer the same as before!
Let’s continue our example above. Our Uranium particle has already released an alpha particle and has become Thorium.
And let’s say our Thorium particle now releases a beta particle! We have one less neutron, which split into a proton and an electron. We released the electron (beta particle) so we don’t have to worry about him. But now we have one more proton in the nucleus, changing our proton count from 90 to 91! So now, the atom has changed from Thorium to Protactinium.
3) The atom can release a positron if there are too many protons and not enough neutrons. In this case, a proton in the nucleus does a funky thing. It splits into a neutron (which stays in the nucleus) and a positron (which gets released from the atom). A positron is a curious thing; it is a positively charged particle, but it is not a proton. Protons are relatively heavy particles, but positrons are super light positively charged do-hickeys. In fact, positrons weigh approximately the same as electrons. So we could choose to think of positrons as electron-like particles with positive charge that are born from protons. Bahhh – atoms be crazy!
We cannot revisit our example from before because Uranium and Thorium really needed to lose neutrons or gain protons. Releasing a positron does the opposite. But as you can guess, the release of a positron would definitely mean that the element changes from one to another, because our element would have one less proton.
4) The atom can engage in electron capture if there are too many protons and not enough neutrons. In electron capture, a proton in the nucleus literally eats one of its electrons. Yum. When you smoosh a proton (positive) and a electron (negative) together, you get a neutron (neutral). Now, we have one more neutron and one less proton in the nucleus. Goal accomplished, and element (again!) has been totally changed.
5) The atom can release gamma rays when it wants to be more stable in general. Gamma rays are electromagnetic waves (like X-rays or Microwaves, but with muuuuuuch more energy). I’m a totally mystified by gamma emission, so I can’t say much about it. Apparently, as radioactive elements release the particles we talked about in 1-4 above, they often release gamma rays. Releasing gamma rays makes the nucleus of an atom more stable because by releasing energy it kind of cools off. That’s a good way to think of it at least. (The more energy in the nucleus, the more excited it is, the more the particles bump into each other and can tear apart from each other – very unstable. The less energy in the nucleus, the less the atoms are likely to bump rudely into each other and are much less likely to change, release emission, etc.)
What really blows me away is that despite what we know, there is sooo much we don’t know still. We don’t know why atoms behave in these particular ways. When it comes down to it, we have come up with these theories as a way of modeling and predicting the behavior of the world around us, based on repeated experimentation. Who knows … 200 years from now, we might find that our current theories are insufficient and we’ll have to update them based on newer, better information.
Personally, I dislike any scientist who treats science like a religion instead of a practice. The best scientists are those who acknowledge that there are great and numerous unknowns. It’s a beautiful, exciting, and even empowering fact of modern science.