[Script Info]
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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.99,0:00:10.24,Default,,0000,0000,0000,,You probably know that all stuff\Nis made up of atoms
Dialogue: 0,0:00:10.27,0:00:11.42,Default,,0000,0000,0000,,and that an atom
Dialogue: 0,0:00:11.45,0:00:15.17,Default,,0000,0000,0000,,is a really, really, really,\Nreally tiny particle.
Dialogue: 0,0:00:15.19,0:00:16.60,Default,,0000,0000,0000,,Every atom has a core,
Dialogue: 0,0:00:16.63,0:00:18.15,Default,,0000,0000,0000,,which is made up of at least one
Dialogue: 0,0:00:18.18,0:00:19.52,Default,,0000,0000,0000,,positively charged particle
Dialogue: 0,0:00:19.54,0:00:21.14,Default,,0000,0000,0000,,called a proton,
Dialogue: 0,0:00:21.17,0:00:22.40,Default,,0000,0000,0000,,and in most cases,
Dialogue: 0,0:00:22.42,0:00:25.57,Default,,0000,0000,0000,,some number of neutral\Nparticles called neutrons.
Dialogue: 0,0:00:25.59,0:00:26.94,Default,,0000,0000,0000,,That core is surrounded
Dialogue: 0,0:00:26.97,0:00:30.15,Default,,0000,0000,0000,,by negatively charged\Nparticles called electrons.
Dialogue: 0,0:00:30.79,0:00:32.61,Default,,0000,0000,0000,,The identity of an atom is determined
Dialogue: 0,0:00:32.64,0:00:36.90,Default,,0000,0000,0000,,only by the number\Nof protons in its nucleus.
Dialogue: 0,0:00:36.92,0:00:39.67,Default,,0000,0000,0000,,Hydrogen is hydrogen because it\Nhas just one proton,
Dialogue: 0,0:00:39.70,0:00:41.41,Default,,0000,0000,0000,,carbon is carbon because it has six,
Dialogue: 0,0:00:41.44,0:00:43.40,Default,,0000,0000,0000,,gold is gold because it has 79,
Dialogue: 0,0:00:43.42,0:00:44.68,Default,,0000,0000,0000,,and so on.
Dialogue: 0,0:00:45.14,0:00:47.13,Default,,0000,0000,0000,,Indulge me in a momentary tangent.
Dialogue: 0,0:00:47.15,0:00:49.49,Default,,0000,0000,0000,,How do we know about atomic structure?
Dialogue: 0,0:00:49.52,0:00:52.72,Default,,0000,0000,0000,,We can't see protons,\Nneutrons, or electrons.
Dialogue: 0,0:00:53.81,0:00:55.34,Default,,0000,0000,0000,,So, we do a bunch of experiments
Dialogue: 0,0:00:55.36,0:00:58.26,Default,,0000,0000,0000,,and develop a model\Nfor what we think is there.
Dialogue: 0,0:00:58.28,0:00:59.81,Default,,0000,0000,0000,,Then we do some more experiments
Dialogue: 0,0:00:59.83,0:01:01.59,Default,,0000,0000,0000,,and see if they agree with the model.
Dialogue: 0,0:01:01.62,0:01:02.81,Default,,0000,0000,0000,,If they do, great.
Dialogue: 0,0:01:02.84,0:01:05.68,Default,,0000,0000,0000,,If they don't, it might\Nbe time for a new model.
Dialogue: 0,0:01:05.70,0:01:08.34,Default,,0000,0000,0000,,We've had lots of very\Ndifferent models for atoms
Dialogue: 0,0:01:08.37,0:01:10.49,Default,,0000,0000,0000,,since Democritus in 400 BC,
Dialogue: 0,0:01:10.51,0:01:11.99,Default,,0000,0000,0000,,and there will almost certainly
Dialogue: 0,0:01:12.01,0:01:13.58,Default,,0000,0000,0000,,be many more to come.
Dialogue: 0,0:01:13.60,0:01:15.45,Default,,0000,0000,0000,,Okay, tangent over.
Dialogue: 0,0:01:15.47,0:01:18.21,Default,,0000,0000,0000,,The cores of atoms tend to stick together,
Dialogue: 0,0:01:18.23,0:01:19.99,Default,,0000,0000,0000,,but electrons are free to move,
Dialogue: 0,0:01:20.02,0:01:22.77,Default,,0000,0000,0000,,and this is why chemists love electrons.
Dialogue: 0,0:01:22.80,0:01:24.21,Default,,0000,0000,0000,,If we could marry them,
Dialogue: 0,0:01:24.23,0:01:25.64,Default,,0000,0000,0000,,we probably would.
Dialogue: 0,0:01:25.66,0:01:26.96,Default,,0000,0000,0000,,But electrons are weird.
Dialogue: 0,0:01:26.98,0:01:29.53,Default,,0000,0000,0000,,They appear to behave either as particles,
Dialogue: 0,0:01:29.55,0:01:31.11,Default,,0000,0000,0000,,like little baseballs,
Dialogue: 0,0:01:31.13,0:01:33.30,Default,,0000,0000,0000,,or as waves, like water waves,
Dialogue: 0,0:01:33.32,0:01:36.50,Default,,0000,0000,0000,,depending on the experiment\Nthat we perform.
Dialogue: 0,0:01:36.52,0:01:38.52,Default,,0000,0000,0000,,One of the weirdest things about electrons
Dialogue: 0,0:01:38.55,0:01:40.67,Default,,0000,0000,0000,,is that we can't exactly\Nsay where they are.
Dialogue: 0,0:01:40.70,0:01:42.72,Default,,0000,0000,0000,,It's not that we don't have the equipment,
Dialogue: 0,0:01:42.74,0:01:44.12,Default,,0000,0000,0000,,it's that this uncertainty
Dialogue: 0,0:01:44.14,0:01:46.47,Default,,0000,0000,0000,,is part of our model of the electron.
Dialogue: 0,0:01:46.50,0:01:49.04,Default,,0000,0000,0000,,So, we can't pinpoint them, fine.
Dialogue: 0,0:01:49.06,0:01:51.73,Default,,0000,0000,0000,,But we can say\Nthere's a certain probability
Dialogue: 0,0:01:51.76,0:01:53.72,Default,,0000,0000,0000,,of finding an electron in a given space
Dialogue: 0,0:01:53.74,0:01:55.68,Default,,0000,0000,0000,,around the nucleus.
Dialogue: 0,0:01:55.70,0:01:58.56,Default,,0000,0000,0000,,And that means that we can\Nask the following question:
Dialogue: 0,0:01:58.58,0:02:00.40,Default,,0000,0000,0000,,If we drew a shape around the nucleus
Dialogue: 0,0:02:00.42,0:02:02.46,Default,,0000,0000,0000,,such that we would be 95% sure
Dialogue: 0,0:02:02.49,0:02:05.50,Default,,0000,0000,0000,,of finding a given electron\Nwithin that shape,
Dialogue: 0,0:02:05.52,0:02:07.07,Default,,0000,0000,0000,,what would it look like?
Dialogue: 0,0:02:08.59,0:02:10.80,Default,,0000,0000,0000,,Here are a few of these shapes.
Dialogue: 0,0:02:10.82,0:02:12.54,Default,,0000,0000,0000,,Chemists call them orbitals,
Dialogue: 0,0:02:12.57,0:02:13.90,Default,,0000,0000,0000,,and what each one looks like
Dialogue: 0,0:02:13.93,0:02:15.84,Default,,0000,0000,0000,,depends on, among other things,
Dialogue: 0,0:02:15.87,0:02:17.69,Default,,0000,0000,0000,,how much energy it has.
Dialogue: 0,0:02:17.72,0:02:19.34,Default,,0000,0000,0000,,The more energy an orbital has,
Dialogue: 0,0:02:19.36,0:02:21.02,Default,,0000,0000,0000,,the farther most of its density is
Dialogue: 0,0:02:21.04,0:02:22.27,Default,,0000,0000,0000,,from the nucleus.
Dialogue: 0,0:02:22.29,0:02:25.25,Default,,0000,0000,0000,,By they way, why did we pick 95%
Dialogue: 0,0:02:25.28,0:02:26.89,Default,,0000,0000,0000,,and not 100%?
Dialogue: 0,0:02:26.91,0:02:28.19,Default,,0000,0000,0000,,Well, that's another quirk
Dialogue: 0,0:02:28.22,0:02:29.98,Default,,0000,0000,0000,,of our model of the electron.
Dialogue: 0,0:02:30.00,0:02:32.20,Default,,0000,0000,0000,,Past a certain distance from the nucleus,
Dialogue: 0,0:02:32.23,0:02:34.05,Default,,0000,0000,0000,,the probability of finding an electron
Dialogue: 0,0:02:34.07,0:02:35.60,Default,,0000,0000,0000,,starts to decrease
Dialogue: 0,0:02:35.62,0:02:37.91,Default,,0000,0000,0000,,more or less exponentially,
Dialogue: 0,0:02:37.94,0:02:40.13,Default,,0000,0000,0000,,which means that while it\Nwill approach zero,
Dialogue: 0,0:02:40.16,0:02:42.58,Default,,0000,0000,0000,,it'll never actually hit zero.
Dialogue: 0,0:02:43.12,0:02:44.27,Default,,0000,0000,0000,,So, in every atom,
Dialogue: 0,0:02:44.30,0:02:47.41,Default,,0000,0000,0000,,there is some small,\Nbut non-zero, probability
Dialogue: 0,0:02:47.44,0:02:50.52,Default,,0000,0000,0000,,that for a very, very\Nshort period of time,
Dialogue: 0,0:02:50.55,0:02:51.71,Default,,0000,0000,0000,,one of its electrons
Dialogue: 0,0:02:51.73,0:02:54.97,Default,,0000,0000,0000,,is at the other end of the known universe.
Dialogue: 0,0:02:55.97,0:02:58.69,Default,,0000,0000,0000,,But mostly electrons stay\Nclose to their nucleus
Dialogue: 0,0:02:58.72,0:03:00.54,Default,,0000,0000,0000,,as clouds of negative charged density
Dialogue: 0,0:03:00.56,0:03:02.66,Default,,0000,0000,0000,,that shift and move with time.
Dialogue: 0,0:03:02.68,0:03:04.39,Default,,0000,0000,0000,,How electrons from one atom
Dialogue: 0,0:03:04.42,0:03:06.41,Default,,0000,0000,0000,,interact with electrons from another
Dialogue: 0,0:03:06.44,0:03:08.76,Default,,0000,0000,0000,,determines almost everything.
Dialogue: 0,0:03:08.78,0:03:10.55,Default,,0000,0000,0000,,Atoms can give up their electrons,
Dialogue: 0,0:03:10.57,0:03:12.22,Default,,0000,0000,0000,,surrendering them to other atoms,
Dialogue: 0,0:03:12.24,0:03:14.62,Default,,0000,0000,0000,,or they can share electrons.
Dialogue: 0,0:03:15.20,0:03:17.06,Default,,0000,0000,0000,,And the dynamics of this social network
Dialogue: 0,0:03:17.08,0:03:19.53,Default,,0000,0000,0000,,are what make chemistry interesting.
Dialogue: 0,0:03:19.55,0:03:20.79,Default,,0000,0000,0000,,From plain old rocks
Dialogue: 0,0:03:20.82,0:03:22.60,Default,,0000,0000,0000,,to the beautiful complexity of life,
Dialogue: 0,0:03:22.62,0:03:24.36,Default,,0000,0000,0000,,the nature of everything we see,
Dialogue: 0,0:03:24.38,0:03:25.90,Default,,0000,0000,0000,,hear,
Dialogue: 0,0:03:25.92,0:03:28.11,Default,,0000,0000,0000,,smell, taste, touch, and even feel
Dialogue: 0,0:03:28.14,0:03:30.97,Default,,0000,0000,0000,,is determined at the atomic level.