Sean Carroll: What is an Atom?
Chapters
0:01:59 Where is most of the mass found in an atom?
00:00:00.000 | - What is an atom and what is an electron?
00:00:04.560 | - Sure, this all came together in a few years
00:00:07.320 | around the turn of the last century,
00:00:08.920 | around the year 1900.
00:00:10.240 | Atoms predated then, of course,
00:00:14.180 | the word atom goes back to the ancient Greeks,
00:00:16.180 | but it was the chemists in the 1800s
00:00:18.680 | that really first got experimental evidence for atoms.
00:00:22.480 | They realized that there were two different types
00:00:26.080 | of tin oxide.
00:00:27.860 | And in these two different types of tin oxide,
00:00:30.160 | there was exactly twice as much oxygen
00:00:32.480 | in one type as the other.
00:00:34.320 | And like, why is that?
00:00:35.560 | Why is it never 1.5 times as much, right?
00:00:38.840 | And so Dalton said, well, it's because there are tin atoms
00:00:43.600 | and oxygen atoms, and one form of tin oxide
00:00:46.440 | is one atom of tin and one atom of oxygen.
00:00:48.960 | And the other is one atom of tin and two atoms of oxygen.
00:00:51.800 | And on the basis of this, so this is a speculation,
00:00:54.800 | a theory, right, a hypothesis.
00:00:56.200 | But then on the basis of that, you make other predictions.
00:00:58.060 | And the chemists became quickly convinced
00:01:00.220 | that atoms were real.
00:01:01.740 | The physicists took a lot longer to catch on,
00:01:04.340 | but eventually they did.
00:01:05.940 | And I mean, Boltzmann, who believed in atoms,
00:01:08.380 | had a really tough time his whole life
00:01:11.340 | 'cause he worked in Germany where atoms were not popular.
00:01:14.440 | They were popular in England, but not in Germany.
00:01:16.900 | - And there, in general, the idea of atoms
00:01:19.460 | is it's the smallest building block
00:01:22.540 | of the universe for them.
00:01:24.140 | That's the kind of how they thought about--
00:01:25.740 | - It's a Greek idea, but the chemists in the 1800s
00:01:28.440 | jumped the gun a little bit.
00:01:29.920 | So these days, an atom is the smallest building block
00:01:33.360 | of a chemical element, right?
00:01:35.140 | Hydrogen, tin, oxygen, carbon, whatever.
00:01:38.120 | But we know that atoms can be broken up further than that.
00:01:40.840 | And that's what physicists discovered in the early 1900s,
00:01:44.960 | Rutherford especially and his colleagues.
00:01:47.760 | So the atom that we think about now,
00:01:50.280 | the cartoon is that picture you've always seen
00:01:53.080 | of a little nucleus and then electrons orbiting it
00:01:56.100 | like a little solar system.
00:01:57.460 | And we now know the nucleus is made of protons and neutrons.
00:02:00.300 | So the weight of the atom,
00:02:02.800 | the mass is almost all in its nucleus.
00:02:05.460 | Protons and neutrons are something like 1,800 times
00:02:08.060 | as heavy as electrons are.
00:02:10.500 | Electrons are much lighter, but because they're lighter,
00:02:13.820 | they give all the life to the atoms.
00:02:16.180 | So when atoms get together, combine chemically,
00:02:18.780 | when electricity flows through a system,
00:02:20.800 | it's all the electrons that are doing all the work.
00:02:23.660 | - And where quantum mechanics steps in,
00:02:26.120 | as you mentioned with the position of velocity,
00:02:28.460 | with classical mechanics and quantum mechanics
00:02:30.920 | is modeling the behavior of the electron.
00:02:34.760 | I mean, you can model the behavior of anything,
00:02:36.420 | but the electron, because that's where the fun is.
00:02:39.100 | - The electron was the biggest challenge
00:02:40.740 | right from the start, yeah.
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