In the previous post we saw that chemistry is simply the movement of electrons between atoms. The sheer number of different types of atoms and ways in which they can exchange electrons is the reason chemistry is such a complex and diverse field of science.
Electrons, as you may recall, surround the nucleus (without touching it) in what is called an electron cloud. Although the exchange of electrons during chemical reactions will affect the electron clouds around the nucleus, the nucleus itself remains unaffected. In other words even the most violent of chemical reactions will have no effect on the protons and neutrons in an atom.
Let's forget everything we know about atoms for a moment and step back in time. If you've ever heard of the term "alchemy" before, you probably associate it with ancient mad scientist types trying ruthlessly to figure out a way to convert regular metals into gold. This was supposed to be possible by mixing them with a substance known as the "philosopher's stone" but was never successfully done. Towards the 18th century, the field of alchemy was surpassed and replaced by its offshoot: chemistry. Alchemy took a more philosophical/mystical approach, while chemistry was based on testing hypotheses against the results of repeatable experiments. It was this approach that led to the discovery of the elements as well as the atom and its constituents (which we discussed in the previous article).
Recall for a second the goal of alchemy: the conversion of regular metals into gold. After centuries of trial and error, why didn't anyone succeed in making the transformation? It's true that alchemy was less robust than chemistry but alchemists still managed to figure out how to extract metals from rock and mix them into alloys like bronze. Even cavemen and cavewomen were able to produce the chemical reaction known as fire without any chemistry knowledge. You would think that someone over the centuries would have accidentally had the luck of creating gold from regular metals. That is of course, assuming it's actually possible. This is where chemistry enters into the picture, let's have a look at the periodic table.
We can see that Gold (symbol Au) is an element with atomic number 79 (located near the centre of the table). The fact that it's an element is important because that means it cannot be made by mixing other substances. Gold is one of the fundamental types of atoms that make up our universe. It happens to have 79 protons and, when neutrally charged, 79 electrons as well. We saw at the beginning of the article that chemical reactions affect only the electrons around atoms. The nucleus, including all the protons and neutrons within it, remains unaffected. It is therefore impossible to create gold from any chemical reaction. No wonder nobody was ever able to do it.
The fact that the atoms themselves are not affected by chemical reactions was a powerful discovery. Early chemists like Antoine Lavoisier were able to figure this out by carefully capturing all byproducts of reactions and weighing them. They found that they always weighed the same as the initial reactants. Lavoisier through his own experiments and the careful review of others was able to show that water, long though to be an element, was in fact made up of hydrogen and oxygen. He deduced that water could be separated into hydrogen and oxygen and that they could be recombined again into water. "Nothing is created, nothing is destroyed, everything is transformed" as he put it.
So there you have it, atoms themselves do not change during a chemical reaction, they simply re-arrange themselves to form new compounds. This idea remained a cornerstone of chemistry for about 200 years. However this long-held belief was shaken in 1902 by Ernest Rutherford and Frederick Soddy while they were studying the radioactive element thorium (symbol Th, number 90 on the periodic table). The two noted that their thorium sample was spontaneously producing helium, among other substances. Conventional wisdom suggested this should not be possible. How could one element (thorium), be creating another element (helium)? They concluded that radioactivity is the result of atoms spontaneously decaying into other atoms. So much for atoms never changing!
Although the idea was ground-breaking, it is still true that in a chemical reaction the atoms themselves do not change, they simply exchange electrons and recombine. Reactions which involve atoms decaying into other atoms (also known as transmutation) are called nuclear reactions because they are the result of changes in the nucleus of an atom. These changes happen when the nucleus is unstable and can be induced artificially in the lab. Rutherford first demonstrated this in 1919 by transmutating nitrogen into oxygen.
So if nitrogen can be transmutated into oxygen, is it really possible after all to realize the alchemist's dream of creating gold out of regular metals? The answer is yes, in fact this was demonstrated by Glenn Seaborg in 1980 starting with the metal bismuth (atomic number 83 on the periodic table). However it required the use of a sophisticated particle accelerator, something no alchemist could have gotten their hands on. Alchemists were limited to using chemical reactions only and therefore had no hope of ever producing gold. Trasmutating one atom into another requires a nuclear reaction, something we will discuss further in the next article.