- What is an atom and what is an electron? - Sure, this all came together in a few years around the turn of the last century, around the year 1900. Atoms predated then, of course, the word atom goes back to the ancient Greeks, but it was the chemists in the 1800s that really first got experimental evidence for atoms.

They realized that there were two different types of tin oxide. And in these two different types of tin oxide, there was exactly twice as much oxygen in one type as the other. And like, why is that? Why is it never 1.5 times as much, right? And so Dalton said, well, it's because there are tin atoms and oxygen atoms, and one form of tin oxide is one atom of tin and one atom of oxygen.

And the other is one atom of tin and two atoms of oxygen. And on the basis of this, so this is a speculation, a theory, right, a hypothesis. But then on the basis of that, you make other predictions. And the chemists became quickly convinced that atoms were real. The physicists took a lot longer to catch on, but eventually they did.

And I mean, Boltzmann, who believed in atoms, had a really tough time his whole life 'cause he worked in Germany where atoms were not popular. They were popular in England, but not in Germany. - And there, in general, the idea of atoms is it's the smallest building block of the universe for them.

That's the kind of how they thought about-- - It's a Greek idea, but the chemists in the 1800s jumped the gun a little bit. So these days, an atom is the smallest building block of a chemical element, right? Hydrogen, tin, oxygen, carbon, whatever. But we know that atoms can be broken up further than that.

And that's what physicists discovered in the early 1900s, Rutherford especially and his colleagues. So the atom that we think about now, the cartoon is that picture you've always seen of a little nucleus and then electrons orbiting it like a little solar system. And we now know the nucleus is made of protons and neutrons.

So the weight of the atom, the mass is almost all in its nucleus. Protons and neutrons are something like 1,800 times as heavy as electrons are. Electrons are much lighter, but because they're lighter, they give all the life to the atoms. So when atoms get together, combine chemically, when electricity flows through a system, it's all the electrons that are doing all the work.

- And where quantum mechanics steps in, as you mentioned with the position of velocity, with classical mechanics and quantum mechanics is modeling the behavior of the electron. I mean, you can model the behavior of anything, but the electron, because that's where the fun is. - The electron was the biggest challenge right from the start, yeah.

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