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