0:00:00.660,0:00:03.120 We humans have known,[br]for thousands of years, 0:00:03.120,0:00:05.341 just looking at our[br]environment around us, 0:00:05.341,0:00:06.840 that there are[br]different substances. 0:00:06.840,0:00:08.600 And these different[br]substances tend 0:00:08.600,0:00:10.120 to have different properties. 0:00:10.120,0:00:11.470 And not only do they have[br]different properties, 0:00:11.470,0:00:13.400 one might reflect[br]light in a certain way, 0:00:13.400,0:00:16.230 or not reflect light, or[br]be a certain color, or at 0:00:16.230,0:00:20.390 a certain temperature, be[br]liquid or gas, or be a solid. 0:00:20.390,0:00:22.290 But we also start[br]to observe how they 0:00:22.290,0:00:25.030 react with each other in[br]certain circumstances. 0:00:25.030,0:00:27.410 And here's pictures of[br]some of these substances. 0:00:27.410,0:00:29.070 This right here is carbon. 0:00:29.070,0:00:31.650 And this is in[br]its graphite form. 0:00:31.650,0:00:33.910 This right here is lead. 0:00:33.910,0:00:36.030 This right here is gold. 0:00:36.030,0:00:38.750 And all of the ones that I've[br]shown pictures of, here-- 0:00:38.750,0:00:41.720 and I got them all from this[br]website, right over there-- 0:00:41.720,0:00:43.460 all of these are in[br]their solid form. 0:00:43.460,0:00:45.830 But we also know that[br]it looks like there's 0:00:45.830,0:00:49.240 certain types of air, and[br]certain types of air particles. 0:00:49.240,0:00:51.090 And depending on what[br]type of air particles 0:00:51.090,0:00:55.590 you're looking at, whether it[br]is carbon or oxygen or nitrogen, 0:00:55.590,0:00:57.790 that seems to have different[br]types of properties. 0:00:57.790,0:00:59.666 Or there are other things[br]that can be liquid. 0:00:59.666,0:01:01.665 Or even if you raise the[br]temperature high enough 0:01:01.665,0:01:02.360 on these things. 0:01:02.360,0:01:04.485 You could, if you raise[br]the temperature high enough 0:01:04.485,0:01:06.440 on gold or lead, you[br]could get a liquid. 0:01:06.440,0:01:10.360 Or if you, kind of, if[br]you burn this carbon, 0:01:10.360,0:01:12.020 you can get it to[br]a gaseous state. 0:01:12.020,0:01:13.690 You can release it[br]into the atmosphere. 0:01:13.690,0:01:14.880 You can break its structure. 0:01:14.880,0:01:18.530 So these are things that we've[br]all, kind of, that humanity 0:01:18.530,0:01:21.000 has observed for[br]thousands of years. 0:01:21.000,0:01:22.530 But it leads to a[br]natural question 0:01:22.530,0:01:24.420 that used to be a[br]philosophical question. 0:01:24.420,0:01:26.790 But now we can answer[br]it a little bit better. 0:01:26.790,0:01:31.320 And that question is, if you[br]keep breaking down this carbon, 0:01:31.320,0:01:33.970 into smaller and[br]smaller chunks, is there 0:01:33.970,0:01:38.930 some smallest chunk, some[br]smallest unit, of this stuff, 0:01:38.930,0:01:43.314 of this substance, that still[br]has the properties of carbon? 0:01:43.314,0:01:44.730 And if you were[br]to, somehow, break 0:01:44.730,0:01:46.271 that even further,[br]somehow, you would 0:01:46.271,0:01:48.270 lose the properties[br]of the carbon. 0:01:48.270,0:01:50.380 And the answer is, there is. 0:01:50.380,0:01:52.030 And so just to get[br]our terminology, 0:01:52.030,0:01:54.940 we call these[br]different substances-- 0:01:54.940,0:01:58.070 these pure substances that[br]have these specific properties 0:01:58.070,0:01:59.960 at certain[br]temperatures and react 0:01:59.960,0:02:02.020 in certain ways-- we[br]call them elements. 0:02:05.210,0:02:06.470 Carbon is an element. 0:02:06.470,0:02:07.570 Lead is an element. 0:02:07.570,0:02:08.910 Gold is an element. 0:02:08.910,0:02:10.949 You might say that[br]water is an element. 0:02:10.949,0:02:13.827 And in history, people[br]have referred to water 0:02:13.827,0:02:14.410 as an element. 0:02:14.410,0:02:18.250 But now we know that water is[br]made up of more basic elements. 0:02:18.250,0:02:21.100 It's made of oxygen[br]and of hydrogen. 0:02:21.100,0:02:25.120 And all of our elements[br]are listed here 0:02:25.120,0:02:27.830 in the Periodic[br]Table of Elements. 0:02:27.830,0:02:30.450 C stands for carbon-- I'm just[br]going through the ones that 0:02:30.450,0:02:33.280 are very relevant to humanity,[br]but over time, you'll 0:02:33.280,0:02:35.710 probably familiarize[br]yourself with all of these. 0:02:35.710,0:02:36.610 This is oxygen. 0:02:36.610,0:02:38.020 This is nitrogen. 0:02:38.020,0:02:40.140 This is silicon. 0:02:40.140,0:02:42.090 Au is gold. 0:02:42.090,0:02:43.280 This is lead. 0:02:43.280,0:02:49.380 And that most basic unit, of any[br]of these elements, is the atom. 0:02:52.620,0:02:55.050 So if you were to keep[br]digging in, and keep 0:02:55.050,0:02:56.940 taking smaller and[br]smaller chunks of this, 0:02:56.940,0:02:59.739 eventually, you would[br]get to a carbon atom. 0:02:59.739,0:03:01.530 Do the same thing over[br]here, eventually you 0:03:01.530,0:03:02.616 would get to a gold atom. 0:03:02.616,0:03:04.490 You did the same thing[br]over here, eventually, 0:03:04.490,0:03:05.864 you would get[br]some-- this little, 0:03:05.864,0:03:08.000 small, for lack of a[br]better word, particle, 0:03:08.000,0:03:09.450 that you would call a lead atom. 0:03:09.450,0:03:11.241 And you wouldn't be[br]able to break that down 0:03:11.241,0:03:13.560 anymore and still[br]call that lead, 0:03:13.560,0:03:17.110 for it to still have[br]the properties of lead. 0:03:17.110,0:03:19.490 And just to give you an idea--[br]this is really something 0:03:19.490,0:03:21.600 that I have trouble[br]imagining-- is 0:03:21.600,0:03:24.690 that atoms are[br]unbelievably small, really 0:03:24.690,0:03:26.220 unimaginably small. 0:03:26.220,0:03:27.750 So for example, carbon. 0:03:27.750,0:03:29.550 My hair is also[br]made out of carbon. 0:03:29.550,0:03:33.320 In fact, most of me[br]is made out of carbon. 0:03:33.320,0:03:36.690 In fact, most of all living[br]things are made out of carbon. 0:03:36.690,0:03:40.840 And so if you took my hair--[br]and so my hair is carbon, 0:03:40.840,0:03:42.262 my hair is mostly carbon. 0:03:42.262,0:03:43.970 So if you took my[br]hair-- right over here, 0:03:43.970,0:03:46.075 my hair isn't yellow,[br]but it contrasts nicely 0:03:46.075,0:03:46.700 with the black. 0:03:46.700,0:03:48.280 My hair is black,[br]but if I did that, 0:03:48.280,0:03:50.270 you wouldn't be able to[br]see it on the screen. 0:03:50.270,0:03:51.769 But if you took my[br]hair, here, and I 0:03:51.769,0:03:55.820 were to ask you, how many[br]carbon atoms wide is my hair? 0:03:55.820,0:03:57.870 So, if you took a cross[br]section of my hair, not 0:03:57.870,0:04:00.040 the length, the[br]width of my hair, 0:04:00.040,0:04:03.384 and said, how many carbon[br]atoms wide is that? 0:04:03.384,0:04:04.800 And you might[br]guess, oh, you know, 0:04:04.800,0:04:07.540 Sal already told me[br]they're very small. 0:04:07.540,0:04:10.016 So maybe there's 1,000 carbon[br]atoms there, or 10,000, 0:04:10.016,0:04:10.780 or 100,000. 0:04:10.780,0:04:12.000 I would say, no. 0:04:12.000,0:04:14.540 There are 1 million[br]carbon atoms, 0:04:14.540,0:04:17.579 or you could string 1[br]million carbon atoms 0:04:17.579,0:04:21.314 across the width of[br]the average human hair. 0:04:21.314,0:04:22.730 That's obviously[br]an approximation. 0:04:22.730,0:04:23.970 It's not exactly 1 million. 0:04:23.970,0:04:26.860 But that gives you a sense[br]of how small an atom is. 0:04:26.860,0:04:28.620 You know, pluck a[br]hair out of your head, 0:04:28.620,0:04:31.300 and just imagine[br]putting a million things 0:04:31.300,0:04:34.440 next to each other,[br]across the hair. 0:04:34.440,0:04:37.450 Not the length of the hair,[br]the width of the hair. 0:04:37.450,0:04:39.360 It's even hard to see[br]the width of a hair, 0:04:39.360,0:04:41.110 and there would be a[br]million carbon atoms, 0:04:41.110,0:04:43.180 just going along it. 0:04:43.180,0:04:46.860 Now it would be pretty[br]cool, in and of itself, 0:04:46.860,0:04:50.840 that we do know that there[br]is this most basic building 0:04:50.840,0:04:54.220 block of carbon, this most basic[br]building block of any element. 0:04:54.220,0:04:57.130 But what's even neater is[br]that, those basic building 0:04:57.130,0:04:58.570 blocks are related[br]to each other. 0:04:58.570,0:05:02.400 That a carbon atom is made[br]up of even more fundamental 0:05:02.400,0:05:02.950 particles. 0:05:02.950,0:05:07.671 A gold atom is made up even[br]more fundamental particles. 0:05:07.671,0:05:09.170 And depending-- and[br]they're actually 0:05:09.170,0:05:12.870 defined by the arrangement of[br]those fundamental particles. 0:05:12.870,0:05:15.430 And if you were to change the[br]number of fundamental particles 0:05:15.430,0:05:18.430 you have, you could change the[br]properties of the element, how 0:05:18.430,0:05:22.810 it would react, or you could[br]even change the element itself. 0:05:22.810,0:05:25.480 And just to understand[br]it a little bit better, 0:05:25.480,0:05:28.260 let's talk about those[br]fundamental elements. 0:05:28.260,0:05:30.365 So you have the proton. 0:05:33.020,0:05:36.000 And the proton is actually[br]the defining-- the number 0:05:36.000,0:05:38.340 of protons in the[br]nucleus of an atom, 0:05:38.340,0:05:40.610 and I'll talk about the[br]nucleus in a second-- that 0:05:40.610,0:05:43.010 is what defines the element. 0:05:43.010,0:05:45.702 So this is what[br]defines an element. 0:05:45.702,0:05:47.660 When you look at the[br]periodic table right here, 0:05:47.660,0:05:50.490 they're actually written[br]in order of atomic number. 0:05:50.490,0:05:52.250 And the atomic[br]number is, literally, 0:05:52.250,0:05:55.140 just the number of[br]protons in the element. 0:05:55.140,0:05:58.950 So by definition,[br]hydrogen has one proton, 0:05:58.950,0:06:03.120 helium has two protons,[br]carbon has six protons. 0:06:03.120,0:06:05.440 You cannot have carbon[br]with seven protons. 0:06:05.440,0:06:07.150 If you did, it[br]would be nitrogen. 0:06:07.150,0:06:09.300 It would not be carbon anymore. 0:06:09.300,0:06:10.732 Oxygen has eight protons. 0:06:10.732,0:06:12.940 If, somehow, you were to[br]add another proton to there, 0:06:12.940,0:06:14.680 it wouldn't be oxygen anymore. 0:06:14.680,0:06:16.370 It would be fluorine. 0:06:16.370,0:06:17.705 So it defines the element. 0:06:20.240,0:06:22.450 And the atomic[br]number, the number 0:06:22.450,0:06:25.549 of protons-- and[br]remember, that's 0:06:25.549,0:06:27.340 the number that's[br]written right at the top, 0:06:27.340,0:06:30.260 here, for each of these[br]elements in the periodic table-- 0:06:30.260,0:06:33.010 the number of protons is[br]equal to the atomic number. 0:06:36.705,0:06:38.080 And they put that[br]number up here, 0:06:38.080,0:06:42.160 because that is the defining[br]characteristic of an element. 0:06:42.160,0:06:46.050 The other two constituents[br]of an atom-- I 0:06:46.050,0:06:47.430 guess we could[br]call it that way-- 0:06:47.430,0:06:51.780 are the electron[br]and the neutron. 0:06:55.390,0:06:57.110 And the model you[br]can start to build 0:06:57.110,0:07:01.320 in your head-- and this model,[br]as we go through chemistry, 0:07:01.320,0:07:03.690 it'll get a little bit more[br]abstract and really hard 0:07:03.690,0:07:04.976 to conceptualize. 0:07:04.976,0:07:06.350 But one way to[br]think about it is, 0:07:06.350,0:07:08.430 you have the protons[br]and the neutrons that 0:07:08.430,0:07:09.850 are at the center of the atom. 0:07:09.850,0:07:11.710 They're the nucleus of the atom. 0:07:11.710,0:07:15.060 So for example, carbon,[br]we know, has six protons. 0:07:15.060,0:07:19.660 So one, two, three,[br]four, five, six. 0:07:19.660,0:07:22.420 Carbon-12, which is[br]a version of carbon, 0:07:22.420,0:07:24.110 will also have six neutrons. 0:07:24.110,0:07:26.100 You can have versions[br]of carbon that 0:07:26.100,0:07:27.940 have a different[br]number of neutrons. 0:07:27.940,0:07:30.330 So the neutrons can change,[br]the electrons can change, 0:07:30.330,0:07:31.830 you can still have[br]the same element. 0:07:31.830,0:07:33.280 The protons can't change. 0:07:33.280,0:07:36.480 You change the protons, you've[br]got a different element. 0:07:36.480,0:07:41.300 So let me draw a carbon-12[br]nucleus, one, two, three, four, 0:07:41.300,0:07:43.300 five, six. 0:07:43.300,0:07:46.450 So this right here is[br]the nucleus of carbon-12. 0:07:46.450,0:07:48.910 And sometimes, it'll[br]be written like this. 0:07:48.910,0:07:52.720 And sometimes, they'll actually[br]write the number of protons, 0:07:52.720,0:07:53.840 as well. 0:07:53.840,0:07:56.510 And the reason why we[br]write it carbon-12-- 0:07:56.510,0:07:58.830 you know, I counted[br]out six neutrons-- 0:07:58.830,0:08:00.760 is that, this is[br]the total, you could 0:08:00.760,0:08:04.206 view this as the total number[br]of-- one way to view it. 0:08:04.206,0:08:05.580 And we'll get a[br]little bit nuance 0:08:05.580,0:08:08.370 in the future-- is that this[br]is the total number of protons 0:08:08.370,0:08:11.870 and neutrons inside[br]of its nucleus. 0:08:11.870,0:08:15.172 And this carbon, by definition,[br]has an atomic number of six, 0:08:15.172,0:08:16.630 but we can rewrite[br]it here, just so 0:08:16.630,0:08:18.870 that we can remind ourselves. 0:08:18.870,0:08:21.550 So at the center of a carbon[br]atom, we have this nucleus. 0:08:21.550,0:08:25.000 And carbon-12 will have six[br]protons and six neutrons. 0:08:25.000,0:08:26.970 Another version of[br]carbon, carbon-14, 0:08:26.970,0:08:29.040 will still have six[br]protons, but then it 0:08:29.040,0:08:31.018 would have eight neutrons. 0:08:31.018,0:08:32.559 So the number of[br]neutrons can change. 0:08:32.559,0:08:34.950 But this is carbon-12,[br]right over here. 0:08:34.950,0:08:38.990 And if carbon-12 is neutral--[br]and I'll give a little nuance 0:08:38.990,0:08:41.419 on this word in a second[br]as well-- if it is neutral, 0:08:41.419,0:08:43.890 it'll also have six electrons. 0:08:43.890,0:08:47.690 So let me draw those six[br]electrons, one, two, three, 0:08:47.690,0:08:49.910 four, five, six. 0:08:49.910,0:08:52.190 And one way-- and this is[br]maybe the first-order way 0:08:52.190,0:08:54.980 of thinking about[br]the relationship 0:08:54.980,0:08:57.380 between the electrons[br]and the nucleus-- 0:08:57.380,0:09:00.340 is that you can imagine the[br]electrons are, kind of, moving 0:09:00.340,0:09:02.930 around, buzzing[br]around this nucleus. 0:09:02.930,0:09:04.540 One model is, you[br]could, kind of, 0:09:04.540,0:09:06.790 thinking of them as[br]orbiting around the nucleus. 0:09:06.790,0:09:08.050 But that's not quite right. 0:09:08.050,0:09:10.460 They don't orbit the[br]way that a planet, say, 0:09:10.460,0:09:11.710 orbits around the sun. 0:09:11.710,0:09:13.900 But that's a good[br]starting point. 0:09:13.900,0:09:16.430 Another way is, they're kind[br]of jumping around the nucleus, 0:09:16.430,0:09:18.680 or they're buzzing[br]around the nucleus. 0:09:18.680,0:09:20.680 And that's just[br]because reality just 0:09:20.680,0:09:22.100 gets very strange at this level. 0:09:22.100,0:09:24.183 And we'll actually have[br]to go into quantum physics 0:09:24.183,0:09:26.570 to really understand what[br]the electron is doing. 0:09:26.570,0:09:29.320 But a first mental[br]model in your head 0:09:29.320,0:09:32.740 is at the center of this[br]atom, this carbon-12 atom, 0:09:32.740,0:09:37.000 you have this nucleus,[br]right over there. 0:09:37.000,0:09:40.700 And these electrons are[br]jumping around this nucleus. 0:09:40.700,0:09:43.850 And the reason why these[br]electrons don't just 0:09:43.850,0:09:45.360 go off, away from this nucleus. 0:09:45.360,0:09:47.570 Why they're kind of[br]bound to this nucleus, 0:09:47.570,0:09:49.860 and they form part[br]of this atom, is 0:09:49.860,0:09:54.570 that protons have[br]a positive charge 0:09:54.570,0:09:57.990 and electrons have[br]a negative charge. 0:09:57.990,0:10:01.874 And it's one of these properties[br]of these fundamental particles. 0:10:01.874,0:10:03.290 And when you start[br]thinking about, 0:10:03.290,0:10:04.690 well, what is a[br]charge, fundamentally, 0:10:04.690,0:10:05.481 other than a label? 0:10:05.481,0:10:07.020 And it starts to[br]get kind of deep. 0:10:07.020,0:10:08.810 But the one thing[br]that we know, when 0:10:08.810,0:10:10.670 we talk about[br]electromagnetic force, 0:10:10.670,0:10:13.280 is that unlike charges[br]attract each other. 0:10:13.280,0:10:14.890 So the best way[br]to think about it 0:10:14.890,0:10:17.100 is, protons and[br]electrons, because they 0:10:17.100,0:10:19.990 have different charges,[br]they attract each other. 0:10:19.990,0:10:21.520 Neutrons are neutral. 0:10:21.520,0:10:25.070 So they're really just sitting[br]here inside of the nucleus. 0:10:25.070,0:10:30.700 And they do affect the[br]properties, on some level, 0:10:30.700,0:10:33.330 for some atoms of[br]certain elements. 0:10:33.330,0:10:36.340 But the reason why we have the[br]electrons not just flying off 0:10:36.340,0:10:37.970 on their own is[br]because, they are 0:10:37.970,0:10:42.470 attracted towards the nucleus. 0:10:42.470,0:10:45.690 And they also have an[br]unbelievably high velocity. 0:10:45.690,0:10:48.630 It's actually hard for-- and[br]we start touching, once again, 0:10:48.630,0:10:51.260 on a very strange[br]part of physics 0:10:51.260,0:10:54.380 once we start talking about what[br]an electron actually is doing. 0:10:54.380,0:10:56.780 But it has enough, I[br]guess you could say, 0:10:56.780,0:10:59.690 it's jumping around enough that[br]it doesn't want to just fall 0:10:59.690,0:11:04.520 into the nucleus, I guess is[br]one way of thinking about it. 0:11:04.520,0:11:08.220 And so I mentioned,[br]carbon-12 right over here, 0:11:08.220,0:11:09.820 defined by the[br]number of protons. 0:11:09.820,0:11:12.710 Oxygen would be defined[br]by having eight protons. 0:11:12.710,0:11:16.420 But once again, electrons can[br]interact with other electrons. 0:11:16.420,0:11:19.140 Or they can be taken[br]away by other atoms. 0:11:19.140,0:11:23.380 And that actually forms a lot of[br]our understanding of chemistry. 0:11:23.380,0:11:26.400 It's based on how many[br]electrons an atom has, 0:11:26.400,0:11:27.860 or a certain element has. 0:11:27.860,0:11:29.580 And how those electrons[br]are configured. 0:11:29.580,0:11:33.990 And how the electrons of[br]other elements are configured. 0:11:33.990,0:11:36.490 Or maybe, other atoms[br]of that same element. 0:11:36.490,0:11:41.180 We can start to predict[br]how an atom of one element 0:11:41.180,0:11:43.360 could react with another[br]atom of that same element. 0:11:43.360,0:11:46.700 Or an atom of one element,[br]how it could react, 0:11:46.700,0:11:48.780 or how it could[br]bond, or not bond, 0:11:48.780,0:11:51.370 or be attracted, or[br]repel, another atom 0:11:51.370,0:11:52.630 of another element. 0:11:52.630,0:11:55.230 So for example-- and we'll[br]learn a lot more about this 0:11:55.230,0:12:00.110 in the future-- it is possible[br]for another atom, someplace, 0:12:00.110,0:12:03.180 to swipe away an[br]electron from a carbon, 0:12:03.180,0:12:05.840 just because, for[br]whatever reason. 0:12:05.840,0:12:09.780 And we'll talk about certain[br]elements, certain neutral atoms 0:12:09.780,0:12:12.360 of certain elements,[br]have a larger 0:12:12.360,0:12:14.010 affinity for[br]electrons than others. 0:12:14.010,0:12:17.140 So maybe one of those swipes[br]an electron away from a carbon, 0:12:17.140,0:12:19.540 and then this carbon[br]will be having 0:12:19.540,0:12:21.730 less electrons than protons. 0:12:21.730,0:12:25.370 So then it would have five[br]electrons and six protons. 0:12:25.370,0:12:28.152 And then it would have[br]a net positive charge. 0:12:28.152,0:12:30.110 So, in this carbon-12,[br]the first version I did, 0:12:30.110,0:12:33.170 I had six protons,[br]six electrons. 0:12:33.170,0:12:34.530 The charges canceled out. 0:12:34.530,0:12:37.170 If I lose an electron, then[br]I only have five of these. 0:12:37.170,0:12:39.210 And then I would have[br]a net positive charge. 0:12:39.210,0:12:41.241 And we're going to talk[br]a lot more about all 0:12:41.241,0:12:42.990 of this throughout the[br]chemistry playlist. 0:12:42.990,0:12:44.200 But hopefully, you[br]have an appreciation 0:12:44.200,0:12:46.241 that this is already[br]starting to get really cool. 0:12:46.241,0:12:48.300 Once we can already[br]get to this really, 0:12:48.300,0:12:52.937 fundamental building[br]block, called the atom. 0:12:52.937,0:12:55.520 And what's even neater is that[br]this fundamental building block 0:12:55.520,0:12:58.800 is built of even more[br]fundamental building blocks. 0:12:58.800,0:13:00.630 And these things[br]can all be swapped 0:13:00.630,0:13:03.160 around, to change the[br]properties of an atom, 0:13:03.160,0:13:05.880 or to even go from an[br]atom of one element 0:13:05.880,0:13:08.466 to an atom of another element.