Episode 2: How to Turn Lead into Gold
Atoms are made of protons, neutrons, and electrons, with the protons and neutrons in the nucleus and the electrons in orbitals, as shown in the diagram below:
This sort of diagram is quite common, but is actually somewhat misleading. For one thing, the electrons don't orbit the nucleus like a planet orbiting the star. Instead, they form sort of a cloud around the nucleus that we call "orbitals," but these are not the same as a simple orbit. Additionally, the diagram above shows the electrons being rather close to the nucleus, when this is not the case at all. They are extremely far. The following diagram is somewhat more accurate:
The above is a helium atom. The tiny dot in the middle is the nucleus. The black cloud surrounding that dot is the space occupied by helium's two electrons. Their distance from the nucleus varies, but on average the electrons are something like 10,000 times further from the nucleus than the nucleus is wide.
We often refer to the outermost orbital of an atom as an "electron cloud." Typically, when atoms bump into each other, it is the electron clouds that actually interact, and the nuclei do not even come close to touching. That is why when Ernest Rutherford shot helium nuclei at gold foil, most of the nuclei just passed right through without even noticing the foil- from the perspective of helium, the gold foil was mostly empty space.
When we show a molecule like the following one, all the "marbles" that you see are the electron clouds, not the nuclei. In chemistry, nuclei never come into contact.
Chemical changes are essentially all about moving electrons around, so chemistry never changes the identity of an atom. If it's carbon (black marbles) before the reaction, it will still be carbon after the reaction. It may be bonded to different atoms than it was before- maybe a bond to oxygen (a red marble) breaks, but the carbon is still carbon and the oxygen is still oxygen.
However, if you get the atoms going fast enough (like what happens in the extremely high temperatures at the core of the sun), you can get nuclei to bash into each other. Depending on the circumstances, this can cause nuclei to stick together (fusion) or split apart (fission).
Fusion: hydrogen atoms crash into each other and, through a series of collisions, become helium
Each of these actions changes the nucleus. And since the identity of an atom is determined by the number of protons in the nucleus, this almost always changes the identity of the atom. Which brings us to how we can make gold.
Any atom that has exactly 79 protons is gold. However, to be stable, the gold nucleus must also have 118 neutrons, making it gold-197 (79 + 118 = 197). If the gold has any number of neutrons other than 118, it will be an unstable isotope (remember, an isotope is just an element with a particular number of neutrons) and will undergo radioactive decay. It'll spit out little particles from its nucleus, becoming something other than gold.
Above, an americium atom undergoes alpha decay- it spits out a helium nucleus and becomes neptunium. Radioactive isotopes of gold can also spit out helium nuclei to become iridium, for example.
In this episode, I talked about how in 1941, scientists bashed neutrons into mercury to create gold. In the 1980's, scientists bashed carbon and neon into bismuth to create gold. And in about 2015, still more scientists sent lead ions whizzing past each other at nearly the speed of light. Some of these lead atoms turned into gold.
However, in all of these cases, the amount of gold produced was TINY. It was also almost all, if not entirely, isotopes other than gold-197. Meaning it was radioactive and did something like the above, to become "not gold."
However, there is one method to create gold-197 from mercury-196. Unfortunately, it costs at least 5 million dollars to create one ounce of gold using this method, which is over 1000 times greater than the cost of gold today. So not really worth it.
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