0:00:00.137,0:00:03.002 We humans have known for thousands of years, 0:00:03.002,0:00:05.867 just looking at our environment around us, 0:00:05.867,0:00:07.207 that there're different substances. 0:00:07.207,0:00:10.333 These different substances...tend to have different properties. 0:00:10.333,0:00:11.954 Not only do they have different properties; 0:00:11.954,0:00:14.745 one might reflects light in a certain way, or not reflect light. 0:00:14.745,0:00:17.601 Or be a certain color, or be have a certain temperature; 0:00:17.601,0:00:20.457 be liquid, or gas or be a solid. 0:00:20.457,0:00:22.108 But we also start to observe 0:00:22.108,0:00:24.867 how they react with each other in certain circumstances. 0:00:24.867,0:00:27.663 and here's pictures of some of these substances. 0:00:27.663,0:00:31.477 This right here is carbon, and this is in the...in its graphite form 0:00:31.477,0:00:36.069 This right here is lead; this right here is gold 0:00:36.069,0:00:38.719 and all of the ones that I've drawn, that I've shown pictures of here, 0:00:38.719,0:00:41.369 I got them all from this website right over there 0:00:41.369,0:00:45.453 All of these are in their solid form, but we also know that we... 0:00:45.453,0:00:47.395 It looks like there's certain types of air in it, 0:00:47.395,0:00:49.338 certain types of air particles, 0:00:49.338,0:00:52.210 and depending on what type of air particles you're looking at 0:00:52.210,0:00:55.079 whether it is carbon, or oxygen, or nitrogen, 0:00:55.079,0:00:57.948 that seems to have different types of properties. 0:00:57.948,0:00:59.425 Or, there are some other things that can be liquid, 0:00:59.425,0:01:02.082 or even if you raise the temperature high enough on these things. 0:01:02.082,0:01:05.018 If you raise the temperature high enough on gold or lead, 0:01:05.018,0:01:06.503 you could get a liquid. 0:01:06.503,0:01:09.841 Or if you kind of -- if you burn this carbon, 0:01:09.841,0:01:12.076 you can get it to a gaseous state, 0:01:12.076,0:01:13.351 you can release it into the atmosphere, 0:01:13.351,0:01:14.702 you can break its structure. 0:01:14.702,0:01:17.271 So these are things that we've all kind of 0:01:17.271,0:01:20.585 that humanity has observed for thousands of years. 0:01:20.585,0:01:22.452 But that leads to a natural question 0:01:22.452,0:01:24.226 that used to be a philosophical question, 0:01:24.226,0:01:26.405 but now we can answer it a little bit better, 0:01:26.405,0:01:30.898 and that question is, if you keep breaking down this carbon 0:01:30.898,0:01:33.518 into smaller and smaller chunks, 0:01:33.518,0:01:35.554 if there's some smallest chunk, 0:01:35.554,0:01:39.867 some smallest unit of this stuff, of this substance 0:01:39.867,0:01:43.166 that still has the properties of carbon? 0:01:43.166,0:01:45.256 And if you were to somehow break that down even further, 0:01:45.256,0:01:48.390 you would lose the properties of the carbon? 0:01:48.390,0:01:50.354 And the answer is: there is. 0:01:50.354,0:01:52.200 And so just to get our terminology, 0:01:52.200,0:01:56.156 we call these different substances, that these pure substances 0:01:56.156,0:01:59.025 that have these specific properties at certain temperatures, 0:01:59.025,0:02:01.185 and react in certain ways, 0:02:01.185,0:02:05.291 we call them elements. 0:02:05.291,0:02:08.729 Carbon is an element. Lead is an element. Gold is an element. 0:02:08.729,0:02:10.400 You might say that water is an element. 0:02:10.400,0:02:14.221 And in history, people have referred to water as an element. 0:02:14.221,0:02:17.892 But now we know that water is made up of more basic elements. 0:02:17.892,0:02:20.405 It's made of oxygen and of hydrogen. 0:02:20.405,0:02:25.014 And all of our elements are listed here 0:02:25.014,0:02:27.758 in the periodic table of elements. 0:02:27.758,0:02:29.374 C stands for carbon 0:02:29.374,0:02:30.400 -- I'm just going through the ones 0:02:30.400,0:02:32.379 that are very relevant to humanity -- 0:02:32.379,0:02:35.502 but over time you'll probably familiarize yourself with all of these. 0:02:35.502,0:02:39.148 This is oxygen. This is nitrogen. This is silicon. 0:02:39.148,0:02:42.867 This is -- Au is gold. This is lead. 0:02:42.867,0:02:51.995 And that most basic unit of any of these elements is the atom. 0:02:51.995,0:02:54.559 So if you were to keep digging in 0:02:54.559,0:02:57.079 and keep taking smaller and smaller chunks of this. 0:02:57.079,0:02:59.415 Eventually you would get to a carbon atom. 0:02:59.415,0:03:00.755 Do the same thing over here, 0:03:00.755,0:03:02.536 eventually you'd get to a gold atom. 0:03:02.536,0:03:03.991 You did the same thing over here, 0:03:03.991,0:03:05.856 eventually you'd get some of this little small 0:03:05.856,0:03:07.758 -- for a lack of a better word -- particle, 0:03:07.758,0:03:09.185 that you'd call a lead atom. 0:03:09.185,0:03:11.239 And you wouldn't be able to break that down anymore 0:03:11.239,0:03:13.597 and still call that lead, 0:03:13.597,0:03:17.043 for it still have the properties of lead. 0:03:17.043,0:03:18.330 And just to give you an idea 0:03:18.330,0:03:21.193 -- this is really something that I have trouble imagining -- 0:03:21.193,0:03:24.040 is that atoms are unbelievably small. 0:03:24.040,0:03:25.901 Really, unimaginably small. 0:03:25.901,0:03:27.555 So for example, carbon. 0:03:27.555,0:03:29.379 My hair is also made out of carbon. 0:03:29.379,0:03:31.882 In fact most of me is made out of carbon. 0:03:31.882,0:03:35.912 In fact most of all living things are made out of carbon. 0:03:35.912,0:03:40.533 And so if you took my hair. And so my hair is carbon. 0:03:40.533,0:03:42.231 My hair is mostly carbon. 0:03:42.231,0:03:43.989 So if you took my hair right over here 0:03:43.989,0:03:45.565 -- my hair isn't yellow 0:03:45.565,0:03:46.766 but it contrasts nicely with the black. 0:03:46.766,0:03:47.950 My hair is black. But if I did that, 0:03:47.950,0:03:49.713 you wouldn't be able to see it on the screen. 0:03:49.713,0:03:51.970 But if you took my hair here, I would have asked you 0:03:51.970,0:03:55.200 how many carbon atoms wide is my hair? 0:03:55.200,0:03:58.467 So if you took a cross-section of my hair, not the length, 0:03:58.467,0:04:00.361 the width of my hair, and said: 0:04:00.361,0:04:03.255 how many carbon atoms wide is that? 0:04:03.255,0:04:07.049 And you might guess, oh, Sal already told me, it's very small, 0:04:07.049,0:04:09.150 so maybe there's a thousand carbon atoms there, 0:04:09.150,0:04:10.484 or ten thousand, or a hundred thousands, 0:04:10.484,0:04:11.788 and I would say, no! 0:04:11.788,0:04:14.249 There are one million carbon atoms. 0:04:14.249,0:04:17.439 Or you could string one million carbon atoms 0:04:17.439,0:04:20.933 across the width of the average human hair. 0:04:20.933,0:04:22.585 And that's obviously an approximation, 0:04:22.585,0:04:24.026 it's not exactly one million, 0:04:24.026,0:04:26.605 but that gives you a sense of how small an atom is. 0:04:26.605,0:04:28.441 You know, pluck a hair out of your head 0:04:28.441,0:04:30.991 and just imagine putting a million things 0:04:30.991,0:04:33.991 next to each other across the hair, 0:04:33.991,0:04:37.037 not the length of the hair, the width of the hair. 0:04:37.037,0:04:39.175 It's even hard to see the width of hair. 0:04:39.175,0:04:40.718 And there would be a million carbon atoms 0:04:40.718,0:04:42.979 just going along it. 0:04:42.979,0:04:48.092 Now it would be pretty cool in and of itself 0:04:48.092,0:04:49.026 -- we do know that 0:04:49.026,0:04:51.375 there is this most basic building block of carbon, 0:04:51.375,0:04:53.933 this most basic building block of any element. 0:04:53.933,0:04:55.952 But what's even neater is that 0:04:55.952,0:04:59.066 those basic building blocks are related to each other. 0:04:59.066,0:05:02.556 A carbon atom is made of even more fundamental particles. 0:05:02.556,0:05:07.469 A gold atom is made up of even more fundamental particles. 0:05:07.469,0:05:10.445 And they are actually defined by 0:05:10.445,0:05:12.759 the arrangement of those fundamental particles. 0:05:12.759,0:05:14.087 And if you were to change 0:05:14.087,0:05:15.901 the number of fundamental particles you have. 0:05:15.901,0:05:17.844 You could change the properties of that element, 0:05:17.844,0:05:18.891 how it would react, 0:05:18.891,0:05:22.769 or you could even change the element itself. 0:05:22.769,0:05:25.144 And just to understand it a little bit better. 0:05:25.144,0:05:28.010 Let's talk about those fundamental elements. 0:05:28.010,0:05:31.825 So you have the proton. 0:05:31.825,0:05:35.524 And the proton is actually the defining 0:05:35.524,0:05:38.003 -- the number of protons in the nucleus of an atom 0:05:38.003,0:05:40.096 and I'll talk about the nucleus in a second -- 0:05:40.096,0:05:42.969 that is what defines the element. 0:05:42.969,0:05:45.492 So this is what defines an element. 0:05:45.492,0:05:47.333 When you look at the periodic table right here, 0:05:47.333,0:05:50.154 they are actually written in order of atomic number, 0:05:50.154,0:05:51.575 and the atomic number is 0:05:51.575,0:05:54.667 literally just the number of protons in the element. 0:05:54.667,0:05:58.667 So by definition, hydrogen has 1 proton. 0:05:58.667,0:06:02.800 Helium has 2 protons. Carbon has 6 protons. 0:06:02.800,0:06:05.333 You cannot have carbon with 7 protons. 0:06:05.333,0:06:07.172 If you did, it would be nitrogen, 0:06:07.172,0:06:09.234 It would not be carbon anymore. 0:06:09.234,0:06:10.589 Oxygen has 8 protons. 0:06:10.589,0:06:12.673 If somehow you were to add another proton to there, 0:06:12.673,0:06:14.050 it wouldn't be oxygen anymore. 0:06:14.050,0:06:18.333 It would be fluorine. So it defines the element. 0:06:18.333,0:06:20.067 It defines the element. 0:06:20.067,0:06:22.967 And the atomic number, the number of protons, 0:06:22.967,0:06:25.447 the number of protons -- and remember, 0:06:25.447,0:06:27.674 that's the number that's written right at the top here 0:06:27.674,0:06:30.116 for each of these elements in the periodic table 0:06:30.116,0:06:31.529 -- the number of protons 0:06:31.529,0:06:34.133 is equal to the atomic number. 0:06:34.133,0:06:36.852 Is equal to the atomic number. 0:06:36.867,0:06:38.861 And they put that number up here because that is 0:06:38.861,0:06:42.221 the defining characteristic of an element. 0:06:42.221,0:06:46.133 The other two constituents of an atom 0:06:46.133,0:06:47.702 -- I guess we could call it that way -- 0:06:47.702,0:06:55.123 are the electron and the neutron. 0:06:55.123,0:06:57.541 And the model you can start to build in your head 0:06:57.541,0:07:00.420 -- and this model, as we go through chemistry we'll see, 0:07:00.420,0:07:02.833 it will get a little bit more abstract 0:07:02.833,0:07:04.821 and really hard to conceptualize -- 0:07:04.821,0:07:06.548 but one way to think about it is 0:07:06.548,0:07:08.348 you have the protons and the neutrons 0:07:08.348,0:07:09.825 that are the center of the atom. 0:07:09.825,0:07:11.600 They are the nucleus of the atom. 0:07:11.600,0:07:14.867 So for example, carbon, we know, has 6 protons. 0:07:14.867,0:07:19.067 So one, two, three, four, five, six. 0:07:19.067,0:07:22.385 Carbon 12, which is a version of carbon, 0:07:22.385,0:07:24.200 will also have 6 neutrons. 0:07:24.200,0:07:25.748 You can have versions of carbon 0:07:25.748,0:07:28.021 that have a different number of neutrons. 0:07:28.021,0:07:30.113 So the neutrons can change, the electrons can change, 0:07:30.113,0:07:31.733 you can still have the same element. 0:07:31.733,0:07:33.267 The protons can't change. 0:07:33.267,0:07:35.905 You change the protons, you got a different element. 0:07:35.905,0:07:39.200 So let me draw a carbon 12 nucleus. 0:07:39.200,0:07:43.200 So one, two, three, four, five, six. 0:07:43.200,0:07:46.487 So this right here is the nucleus of carbon 12. 0:07:46.487,0:07:48.333 And sometimes it will be written like this. 0:07:48.333,0:07:51.132 And sometimes they will actually write 0:07:51.132,0:07:53.831 the number of protons as well. 0:07:53.831,0:07:56.133 And the reason why we write it carbon 12 0:07:56.133,0:07:58.677 -- you know I counted out 6 neutrons -- 0:07:58.677,0:08:00.379 is that this is the total 0:08:00.379,0:08:03.675 you could view this as the total number of 0:08:03.675,0:08:04.741 -- one way to view it, 0:08:04.741,0:08:06.405 and we'll get a little bit of nuance in the future 0:08:06.405,0:08:07.770 -- is that this is the total number 0:08:07.770,0:08:11.844 of protons and neutrons inside of its nucleus. 0:08:11.844,0:08:15.240 And this carbon by definition has an atomic number of 6, 0:08:15.240,0:08:16.628 but we can rewrite it here 0:08:16.628,0:08:18.596 just so that we can remind ourselves. 0:08:18.596,0:08:21.342 So at the center of the carbon atom we have this nucleus. 0:08:21.342,0:08:24.863 And carbon 12 will have 6 protons and 6 neutrons. 0:08:24.863,0:08:27.495 Another version of carbon, carbon 14, will still have 0:08:27.495,0:08:30.909 6 protons, but then it would have 8 neutrons. 0:08:30.909,0:08:32.467 So the number of neutrons can change, 0:08:32.467,0:08:34.610 but this is carbon 12 right over here. 0:08:34.610,0:08:36.842 And if carbon 12 is neutral -- 0:08:36.842,0:08:40.665 and I'll give a little nuance on this word in a second as well -- 0:08:40.665,0:08:43.200 if it's neutral it will also have 6 electrons. 0:08:43.200,0:08:45.400 So let me draw those 6 electrons. 0:08:45.400,0:08:49.467 One, two, three, four, five, six. 0:08:49.467,0:08:51.836 And one way -- and this is maybe the first order way 0:08:51.836,0:08:54.634 of thinking about the relationship 0:08:54.634,0:08:56.892 between the electrons and the nucleus -- 0:08:56.892,0:08:58.846 is that you can imagine the electrons 0:08:58.846,0:09:00.835 are kind of moving around, 0:09:00.835,0:09:02.956 buzzing around this nucleus. 0:09:02.956,0:09:04.692 One model is you could kind of 0:09:04.692,0:09:06.700 thinking of them as orbiting around the nucleus, 0:09:06.700,0:09:08.000 but that's not quite right. 0:09:08.000,0:09:10.499 They don't orbit the way that a planet, say, 0:09:10.499,0:09:11.660 orbits around the Sun. 0:09:11.660,0:09:13.749 But that's a good starting point. 0:09:13.749,0:09:16.267 Another way is that they kind of jumping around the nucleus 0:09:16.267,0:09:18.691 or they are buzzing around the nucleus. 0:09:18.691,0:09:19.956 And that's just because 0:09:19.956,0:09:22.073 reality just gets very strange at this level, 0:09:22.073,0:09:23.544 and we'll actually have to get to quantum physics 0:09:23.544,0:09:26.408 to really understand what the electron is doing. 0:09:26.408,0:09:29.190 But a first mental model in your head is 0:09:29.190,0:09:32.400 at the center of this atom, of this carbon 12 atom, 0:09:32.400,0:09:34.067 you have this nucleus. 0:09:34.067,0:09:36.644 You have this nucleus right over there. 0:09:36.644,0:09:40.733 And these electrons are jumping around this nucleus. 0:09:40.733,0:09:43.009 And the reason why these electrons 0:09:43.009,0:09:45.135 don't just go off away from this nucleus, 0:09:45.135,0:09:47.200 why they are kind of bound to this nucleus, 0:09:47.200,0:09:49.308 and they form part of this atom, 0:09:49.308,0:09:54.579 is that protons have a positive charge, 0:09:54.579,0:09:57.918 and electrons have a negative charge. 0:09:57.918,0:10:02.477 And it's one of these properties of these fundamental particles. 0:10:02.477,0:10:03.620 When you start thinking about 0:10:03.620,0:10:05.467 what is a charge fundamentally other than a label, 0:10:05.467,0:10:06.867 and it starts to get kind of deep. 0:10:06.867,0:10:08.400 But the one thing that we know, 0:10:08.400,0:10:10.697 when we talk about electro-magnetic force, 0:10:10.697,0:10:13.146 is that unlike charges attract each other. 0:10:13.146,0:10:14.959 So the best way to think about it is: 0:10:14.959,0:10:16.546 protons and electrons, 0:10:16.546,0:10:18.133 because they have different charges, 0:10:18.133,0:10:20.129 they attract each other. 0:10:20.129,0:10:21.457 Neutrons are neutral, 0:10:21.457,0:10:25.088 so they're really just sitting here inside of the nucleus, 0:10:25.088,0:10:28.579 and they do affect the properties on some level, 0:10:28.579,0:10:33.154 for some atoms of certain elements. 0:10:33.154,0:10:35.005 But the reason why we have the electrons 0:10:35.005,0:10:36.818 not just flying off on their own 0:10:36.818,0:10:38.600 is because they are attracted. 0:10:38.600,0:10:42.333 They are attracted towards the nucleus. 0:10:42.333,0:10:45.067 And they also have an unbelievably high velocity 0:10:45.067,0:10:47.140 -- it's actually hard for -- 0:10:47.140,0:10:48.446 we start touching once again 0:10:48.446,0:10:51.546 on a very strange part of physics 0:10:51.546,0:10:52.570 once we start talking about 0:10:52.570,0:10:54.164 what an electron actually is doing 0:10:54.164,0:10:55.946 -- but is has enough -- 0:10:55.946,0:10:56.842 I guess you could say 0:10:56.842,0:10:57.924 it's jumping around enough 0:10:57.924,0:11:00.733 that it doesn't want to just fall into the nucleus, 0:11:00.733,0:11:02.867 I guess is one way of thinking about it. 0:11:02.867,0:11:08.123 And so, I mentioned carbon 12 right over here 0:11:08.123,0:11:09.769 defined by the number or protons. 0:11:09.769,0:11:12.403 Oxygen would be defined by having 8 protons. 0:11:12.403,0:11:16.467 But once again, electrons can interact with other electrons. 0:11:16.467,0:11:18.650 They can be taken away by other atoms. 0:11:18.650,0:11:21.025 And that actually forms 0:11:21.025,0:11:23.271 a lot of our understanding of chemistry. 0:11:23.271,0:11:25.995 It's based on how many electrons an atom has, 0:11:25.995,0:11:27.600 or a certain element has. 0:11:27.600,0:11:29.467 And how those electrons are configured, 0:11:29.467,0:11:33.867 and how the electrons of other elements are configured, 0:11:33.867,0:11:36.018 or maybe other atoms of that same element. 0:11:36.018,0:11:41.267 We can start to predict how an atom of one element 0:11:41.267,0:11:43.333 can react with another atom of that same element, 0:11:43.333,0:11:46.733 or an atom of one element -- how it could react, 0:11:46.733,0:11:49.695 or how it could bond, or not bond, or be attracted to, 0:11:49.695,0:11:52.200 or repel another atom of another element. 0:11:52.200,0:11:53.420 So for example, 0:11:53.420,0:11:56.300 and we'll learn a lot more about this in the future, 0:11:56.300,0:12:00.144 is: it is possible for another atom some place 0:12:00.144,0:12:02.723 to swipe away an electron from a carbon, 0:12:02.733,0:12:05.552 just because for whatever reason -- 0:12:05.552,0:12:10.338 and we'll talk about certain neutral atoms of certain elements 0:12:10.338,0:12:13.723 have a larger affinity for electrons than others. 0:12:13.723,0:12:15.218 So one, maybe one of those, 0:12:15.218,0:12:17.160 swipes an electron away from a carbon, 0:12:17.160,0:12:19.230 and then this carbon will be 0:12:19.230,0:12:21.831 having less electrons than protons, 0:12:21.831,0:12:25.138 so then we'll have 5 electrons and 6 protons. 0:12:25.138,0:12:27.800 And then we'd have a net positive charge. 0:12:27.800,0:12:30.039 So in this carbon 12, the first version I did, 0:12:30.039,0:12:34.267 I had 6 protons, 6 electrons, the charges canceled out. 0:12:34.267,0:12:36.553 If I lose an electron, then I only have 5 of these, 0:12:36.553,0:12:38.933 and then I would have a net positive charge. 0:12:38.933,0:12:40.785 And we're going to talk a lot more 0:12:40.785,0:12:42.867 about all of this throughout the chemistry playlist, 0:12:42.867,0:12:44.302 but hopefully you have an appreciation that 0:12:44.302,0:12:46.133 this is already starting to get really cool. 0:12:46.133,0:12:51.800 We can already get to this fundamental building block 0:12:51.800,0:12:53.118 called the atom. 0:12:53.118,0:12:54.920 And what's even neater is that 0:12:54.920,0:12:56.759 this fundamental building block is built of 0:12:56.759,0:12:58.667 even more fundamental building blocks. 0:12:58.667,0:13:00.867 And these things can all be swapped around 0:13:00.867,0:13:03.129 to change the properties of an atom, 0:13:03.129,0:13:06.044 or even go from an atom of one element 0:13:06.044,0:13:09.036 to an atom of another element.