1 00:00:00,000 --> 00:00:00,480 2 00:00:00,480 --> 00:00:03,149 In most topics you have to get pretty advanced before you 3 00:00:03,149 --> 00:00:05,410 start addressing the philosophically interesting 4 00:00:05,410 --> 00:00:08,460 things, but in chemistry it just starts right from the 5 00:00:08,460 --> 00:00:11,490 get-go with what's arguably the most philosophically 6 00:00:11,490 --> 00:00:15,000 interesting part of the whole topic, and that's the atom. 7 00:00:15,000 --> 00:00:18,910 And the idea of the atom, as philosophers long ago, and you 8 00:00:18,910 --> 00:00:21,039 could look it up on the different philosophers who 9 00:00:21,039 --> 00:00:23,539 first philosophized about it, they said, hey, you know, if I 10 00:00:23,539 --> 00:00:28,460 started off with, I don't know, if I started off with an 11 00:00:28,460 --> 00:00:32,719 apple, and I just kept cutting the apple -- let me draw a 12 00:00:32,719 --> 00:00:34,519 nice looking apple just so it doesn't look just 13 00:00:34,520 --> 00:00:36,030 like a heart . 14 00:00:36,030 --> 00:00:36,719 There you go. 15 00:00:36,719 --> 00:00:38,710 You have a nice looking apple, And you just kept cutting it, 16 00:00:38,710 --> 00:00:40,149 smaller and smaller pieces. 17 00:00:40,149 --> 00:00:44,989 So eventually, you get a piece so small, so tiny, that you 18 00:00:44,990 --> 00:00:46,080 can't cut it anymore. 19 00:00:46,079 --> 00:00:48,189 And I'm sure some of these philosophers went out there 20 00:00:48,189 --> 00:00:50,699 with a knife and tried to do it and they just felt that, 21 00:00:50,700 --> 00:00:52,685 oh, if I could just get my knife a little bit sharper, I 22 00:00:52,685 --> 00:00:53,719 could cut it again and again. 23 00:00:53,719 --> 00:00:56,560 So it's a completely philosophical construct, which 24 00:00:56,560 --> 00:00:59,380 frankly, in a lot of ways, isn't too different to how the 25 00:00:59,380 --> 00:01:00,440 atom is today. 26 00:01:00,439 --> 00:01:04,709 It's really just a mental abstraction that allows us to 27 00:01:04,709 --> 00:01:07,500 describe a lot of observations we see in the universe. 28 00:01:07,500 --> 00:01:10,379 But anyway, these philosophers said, well, at some point we 29 00:01:10,379 --> 00:01:15,319 think that there's going to be some little part of an apple 30 00:01:15,319 --> 00:01:16,979 that they won't be able to divide anymore. 31 00:01:16,980 --> 00:01:18,000 And they called that an atom. 32 00:01:18,000 --> 00:01:19,819 And it doesn't just have to just be for an apple they said 33 00:01:19,819 --> 00:01:23,549 this is true for any substance or any element to that you 34 00:01:23,549 --> 00:01:25,149 encounter in the universe. 35 00:01:25,150 --> 00:01:29,830 And so the word atom is really Greek for uncuttable. 36 00:01:29,829 --> 00:01:31,090 Uncuttable or indivisible. 37 00:01:31,090 --> 00:01:34,100 38 00:01:34,099 --> 00:01:37,679 Now we know that it actually is cuttable and even though it 39 00:01:37,680 --> 00:01:42,970 is not a trivial thing, it's not the smallest form of 40 00:01:42,969 --> 00:01:43,730 matter we know. 41 00:01:43,730 --> 00:01:47,060 We now know that an atom is made up of other more 42 00:01:47,060 --> 00:01:48,570 fundamental particles. 43 00:01:48,569 --> 00:01:50,259 And let me write that. 44 00:01:50,260 --> 00:01:55,780 So the we have the neutron. 45 00:01:55,780 --> 00:01:59,049 And I'll draw in a second how they all fit together and the 46 00:01:59,049 --> 00:02:00,730 structure of an atom. 47 00:02:00,730 --> 00:02:02,520 We have a neutron. 48 00:02:02,519 --> 00:02:05,780 We have a proton. 49 00:02:05,780 --> 00:02:09,150 And we have electrons. 50 00:02:09,150 --> 00:02:11,099 Electrons. 51 00:02:11,099 --> 00:02:13,250 And you might already be familiar with this if you look 52 00:02:13,250 --> 00:02:18,409 at old videos about atomic projects, you'll see a drawing 53 00:02:18,409 --> 00:02:20,284 that looks something like this. 54 00:02:20,284 --> 00:02:21,939 Let me see if I can draw one. 55 00:02:21,939 --> 00:02:24,340 So you'll have something like that. 56 00:02:24,340 --> 00:02:27,300 And you'll have these things spinning around 57 00:02:27,300 --> 00:02:28,800 that look like this. 58 00:02:28,800 --> 00:02:30,430 They have orbits that look like that. 59 00:02:30,430 --> 00:02:33,840 And maybe something that looks like that. 60 00:02:33,840 --> 00:02:36,844 And the general notion behind these kind of nuclear drawings 61 00:02:36,844 --> 00:02:39,280 -- and I'm sure that they still show up at some 62 00:02:39,280 --> 00:02:41,530 government defense labs or something like that -- is that 63 00:02:41,530 --> 00:02:46,020 you have a nucleus at the center of an atom. 64 00:02:46,020 --> 00:02:48,090 You have a nucleus at the center of an atom. 65 00:02:48,090 --> 00:02:52,439 And we know that a nucleus has neutrons and protons. 66 00:02:52,439 --> 00:02:53,509 Neutrons and protons. 67 00:02:53,509 --> 00:02:56,569 And we'll talk a little bit more about which elements have 68 00:02:56,569 --> 00:02:59,150 how many neutrons and how many protons. 69 00:02:59,150 --> 00:03:02,810 And then orbiting, and I'm going to use the word orbit 70 00:03:02,810 --> 00:03:05,550 right now, although we'll learn in about two minutes 71 00:03:05,550 --> 00:03:08,150 that the word orbit is actually the incorrect or even 72 00:03:08,150 --> 00:03:10,159 the mentally incorrect way of visualizing what 73 00:03:10,159 --> 00:03:11,199 an electron is doing. 74 00:03:11,199 --> 00:03:14,189 But the old idea was that you have these electrons that are 75 00:03:14,189 --> 00:03:17,180 orbiting around the nucleus very similar to the way the 76 00:03:17,180 --> 00:03:19,849 Earth orbits around the Sun or the moon 77 00:03:19,849 --> 00:03:21,810 orbits around the Earth. 78 00:03:21,810 --> 00:03:23,890 And it's been shown that that's actually 79 00:03:23,889 --> 00:03:26,899 a very wrong way. 80 00:03:26,900 --> 00:03:30,719 And when we cover quantum mechanics we'll learn why this 81 00:03:30,719 --> 00:03:34,020 doesn't work, what are the contradictions that emerge 82 00:03:34,020 --> 00:03:38,500 when you try to model an electron like a planet going 83 00:03:38,500 --> 00:03:40,110 around the Sun. 84 00:03:40,110 --> 00:03:41,920 But this was kind of the original idea, and frankly I 85 00:03:41,919 --> 00:03:45,839 think this is kind of the idea that is the most mainstream 86 00:03:45,840 --> 00:03:50,229 way of viewing an atom. 87 00:03:50,229 --> 00:03:52,549 Now, I said an atom is philosophically interesting. 88 00:03:52,550 --> 00:03:53,910 Why is it philosophically interesting? 89 00:03:53,909 --> 00:03:58,199 Because what we now view as the accepted way of viewing an 90 00:03:58,199 --> 00:04:04,609 atom really starts to blur the line between our physical 91 00:04:04,610 --> 00:04:09,120 reality and everything in the world is just information, and 92 00:04:09,120 --> 00:04:12,180 there really isn't any such thing as true matter or true 93 00:04:12,180 --> 00:04:15,439 particles as the way we define them in our everyday life. 94 00:04:15,439 --> 00:04:16,949 You know, for me a particle, oh, it looks 95 00:04:16,949 --> 00:04:17,740 like a grain of sand. 96 00:04:17,740 --> 00:04:19,149 I can pick it up, touch it. 97 00:04:19,149 --> 00:04:21,730 While a wave, that could be like a soundwave. It could be 98 00:04:21,730 --> 00:04:23,670 just this change in energy over time. 99 00:04:23,670 --> 00:04:25,870 But we'll learn, especially when we do quantum mechanics, 100 00:04:25,870 --> 00:04:29,009 that it all gets jumbled up as we start approaching the 101 00:04:29,009 --> 00:04:31,969 scales or the size of an atom. 102 00:04:31,970 --> 00:04:34,780 Anyway, I said this was an incorrect way of doing it. 103 00:04:34,779 --> 00:04:37,589 What's the correct way? 104 00:04:37,589 --> 00:04:40,500 So it turns out-- this is a picture, not a picture really, 105 00:04:40,500 --> 00:04:42,139 this is also a depiction. 106 00:04:42,139 --> 00:04:44,849 So it's an interesting question, what I just said. 107 00:04:44,850 --> 00:04:47,360 How can you have a picture of an atom? 108 00:04:47,360 --> 00:04:49,910 Because is actually turns out that most wavelengths of 109 00:04:49,910 --> 00:04:52,800 light, especially the visible wavelengths of light, are much 110 00:04:52,800 --> 00:04:56,540 larger than the size of an atom. 111 00:04:56,540 --> 00:04:58,400 Everything else we quote-unquote, observe in 112 00:04:58,399 --> 00:05:00,349 life, it's by reflected light. 113 00:05:00,350 --> 00:05:02,900 But all of a sudden when you're dealing with an atom, 114 00:05:02,899 --> 00:05:06,479 reflected light you could almost view it as too big, or 115 00:05:06,480 --> 00:05:09,470 too blunt of an instrument with which to observe an atom. 116 00:05:09,470 --> 00:05:12,150 Anyway, this is a depiction of a helium atom. 117 00:05:12,149 --> 00:05:14,799 118 00:05:14,800 --> 00:05:18,160 A helium atom has two protons and two neutrons. 119 00:05:18,160 --> 00:05:19,850 Or at least this helium atom has two 120 00:05:19,850 --> 00:05:21,520 protons and two neutrons. 121 00:05:21,519 --> 00:05:24,579 And the way they depict it here in the nucleus, right 122 00:05:24,579 --> 00:05:26,800 there, maybe these are the two-- I'm assuming they're 123 00:05:26,800 --> 00:05:29,210 using red for proton and purple for neutron. 124 00:05:29,209 --> 00:05:32,180 125 00:05:32,180 --> 00:05:34,100 Purple seems like more of a neutral color. 126 00:05:34,100 --> 00:05:39,740 And they're sitting at the center of this atom. 127 00:05:39,740 --> 00:05:42,480 And then this whole haze around there, those are the 128 00:05:42,480 --> 00:05:45,370 two electrons that helium has, or that at least 129 00:05:45,370 --> 00:05:47,399 this helium atom has. 130 00:05:47,399 --> 00:05:49,509 Maybe you could gain or lose an electron. 131 00:05:49,509 --> 00:05:50,509 But these are the two electrons. 132 00:05:50,509 --> 00:05:55,560 And you say, hey, Sal, how can two electrons be this blur 133 00:05:55,560 --> 00:05:58,329 that's kind of smeared around this atom. 134 00:05:58,329 --> 00:06:01,519 And that's where it gets philosophically interesting. 135 00:06:01,519 --> 00:06:09,069 So you cannot describe an electron's path around a 136 00:06:09,069 --> 00:06:12,769 nucleus with the traditional orbit idea that we've 137 00:06:12,769 --> 00:06:16,699 encountered when we look at planets or if we just imagine 138 00:06:16,699 --> 00:06:18,740 things at kind of a larger scale. 139 00:06:18,740 --> 00:06:24,840 It turns out that an electron, you cannot know exactly its 140 00:06:24,839 --> 00:06:28,679 momentum and location at any given point in time. 141 00:06:28,680 --> 00:06:31,870 All you can know is a probability distribution of 142 00:06:31,870 --> 00:06:33,639 where it is likely to be. 143 00:06:33,639 --> 00:06:36,490 And the way they depicted this, black is a higher 144 00:06:36,490 --> 00:06:39,699 probability, so you're much more likely to find the 145 00:06:39,699 --> 00:06:42,579 electron here than you are here. 146 00:06:42,579 --> 00:06:43,750 But the electron really could be anywhere. 147 00:06:43,750 --> 00:06:46,689 It could even to be here, even though it's completely white 148 00:06:46,689 --> 00:06:49,670 there, with some very, very, very, very, very low 149 00:06:49,670 --> 00:06:50,660 probability. 150 00:06:50,660 --> 00:06:55,180 And so this function of where an electron is, this is called 151 00:06:55,180 --> 00:06:56,720 an orbital. 152 00:06:56,720 --> 00:06:57,430 Orbital. 153 00:06:57,430 --> 00:07:00,120 Not to be confused with orbit. 154 00:07:00,120 --> 00:07:02,600 Orbital. 155 00:07:02,600 --> 00:07:05,100 Remember, an orbit was something like this. 156 00:07:05,100 --> 00:07:08,050 It's like Venus going around the Sun. 157 00:07:08,050 --> 00:07:12,750 So it's very physically easy for us to imagine. 158 00:07:12,750 --> 00:07:16,370 While an orbital is actually a mathematical probability 159 00:07:16,370 --> 00:07:17,569 function that tells us where we're 160 00:07:17,569 --> 00:07:18,920 likely to find an electron. 161 00:07:18,920 --> 00:07:21,020 We'll deal a lot more with that when we cover quantum 162 00:07:21,019 --> 00:07:23,269 mechanics, but that's not going to be in the scope of 163 00:07:23,269 --> 00:07:26,669 this kind of introductory set of chemistry lectures. 164 00:07:26,670 --> 00:07:28,150 But it's interesting, right? 165 00:07:28,149 --> 00:07:32,799 An electron's behavior is so bizarre at that scale that you 166 00:07:32,800 --> 00:07:35,780 can't-- I mean, to call it a particle is almost misleading. 167 00:07:35,779 --> 00:07:38,179 It is called a particle, but it's not a particle in the 168 00:07:38,180 --> 00:07:40,300 sense that we're used to in our everyday life. 169 00:07:40,300 --> 00:07:45,230 It's this thing that you can't even say exactly where it is. 170 00:07:45,230 --> 00:07:47,600 It can be anywhere in this haze. 171 00:07:47,600 --> 00:07:49,629 And we'll learn later that there are different shapes of 172 00:07:49,629 --> 00:07:53,159 the hazes is as we add more and more electrons to an atom. 173 00:07:53,160 --> 00:07:57,580 But to me, it starts to address philosophical issues 174 00:07:57,579 --> 00:08:01,339 of what matter even is, or do the things we look at, how 175 00:08:01,339 --> 00:08:02,149 real are they? 176 00:08:02,149 --> 00:08:04,919 Or how real are they, at least as we've defined reality? 177 00:08:04,920 --> 00:08:07,750 Anyway I don't want to get too philosophical on you. 178 00:08:07,750 --> 00:08:12,519 But the whole notion of electrons, protons, they're 179 00:08:12,519 --> 00:08:15,089 all kind of predicated on this notion of charge. 180 00:08:15,089 --> 00:08:17,579 And we've talked about it before when we learned about 181 00:08:17,579 --> 00:08:18,889 Coulomb's law. 182 00:08:18,889 --> 00:08:22,469 You could review Coulomb's laws videos in the physics 183 00:08:22,470 --> 00:08:27,810 playlist. But the idea is that an electron 184 00:08:27,810 --> 00:08:29,240 has a negative charge. 185 00:08:29,240 --> 00:08:31,069 A proton, sometimes written like that, 186 00:08:31,069 --> 00:08:33,250 has a positive charge. 187 00:08:33,250 --> 00:08:37,298 And a neutron has no charge. 188 00:08:37,298 --> 00:08:39,829 And so that's what was tempting about the original 189 00:08:39,830 --> 00:08:42,590 model of an electron. 190 00:08:42,590 --> 00:08:45,310 If they say, OK, if this thing has positive charges, right? 191 00:08:45,309 --> 00:08:47,049 So let's say this is two neutrons and two protons. 192 00:08:47,049 --> 00:08:48,584 Let's say it's a helium atom. 193 00:08:48,585 --> 00:08:51,050 Then we'll have some positive charges here. 194 00:08:51,049 --> 00:08:54,069 We have some negative charges out here. 195 00:08:54,070 --> 00:08:56,330 Opposite charges attract. 196 00:08:56,330 --> 00:09:03,710 And so if these things had some velocity, enough 197 00:09:03,710 --> 00:09:08,350 velocity, they would orbit around this, just the way a 198 00:09:08,350 --> 00:09:10,310 planet will orbit around the Sun. 199 00:09:10,309 --> 00:09:15,199 But now we learn, even though this is partially true, that 200 00:09:15,200 --> 00:09:23,759 the further away an electron is from the nucleus, it does 201 00:09:23,759 --> 00:09:27,700 have more, it's true, potential energy. 202 00:09:27,700 --> 00:09:31,240 In that it will want to move towards the nucleus, but 203 00:09:31,240 --> 00:09:34,580 because of all the mechanics at the quantum level, it won't 204 00:09:34,580 --> 00:09:37,950 just do something simple like move in a path like that, like 205 00:09:37,950 --> 00:09:41,140 a comet would do around the Sun, it actually has this kind 206 00:09:41,139 --> 00:09:43,689 of wave-like behavior, where it just has this probability 207 00:09:43,690 --> 00:09:45,170 function that describes it. 208 00:09:45,169 --> 00:09:48,679 But the further away an orbital, it 209 00:09:48,679 --> 00:09:50,279 does have more potential. 210 00:09:50,279 --> 00:09:53,079 We're going to go a lot more into that in future videos. 211 00:09:53,080 --> 00:09:56,139 But anyway, how do you recognize what an element is? 212 00:09:56,139 --> 00:09:58,500 I've talked a lot about the philosophy and all of that, 213 00:09:58,500 --> 00:10:00,049 but how do I know that this is helium? 214 00:10:00,049 --> 00:10:03,229 Is it by the number of neutrons it has? 215 00:10:03,230 --> 00:10:05,220 Is it by the number of protons it has? 216 00:10:05,220 --> 00:10:07,070 Is it by the number of electrons? 217 00:10:07,070 --> 00:10:09,960 Well the answer is, it's by the number of protons. 218 00:10:09,960 --> 00:10:13,090 So if you know the number of protons in an element, you 219 00:10:13,090 --> 00:10:14,660 know what that element is. 220 00:10:14,659 --> 00:10:21,759 And the number of protons, this is defined 221 00:10:21,759 --> 00:10:23,009 as the atomic number. 222 00:10:23,009 --> 00:10:26,559 223 00:10:26,559 --> 00:10:30,319 Now, so let's say I said something has four protons. 224 00:10:30,320 --> 00:10:33,340 225 00:10:33,340 --> 00:10:34,519 How do we know what it is? 226 00:10:34,519 --> 00:10:37,069 Well if we haven't memorized it, we could look it up on the 227 00:10:37,070 --> 00:10:39,560 periodic table of elements, which we'll be dealing with a 228 00:10:39,559 --> 00:10:43,209 lot in this playlist. And you'd say, oh, four protons, 229 00:10:43,210 --> 00:10:45,680 that is beryllium. 230 00:10:45,679 --> 00:10:46,539 Right there. 231 00:10:46,539 --> 00:10:50,149 And the atomic number is the number that you see up there. 232 00:10:50,149 --> 00:10:52,009 And that' s literally the number of protons. 233 00:10:52,009 --> 00:10:55,220 And that is what differentiates 234 00:10:55,220 --> 00:10:56,160 one atom from another. 235 00:10:56,159 --> 00:10:59,339 If you have fifteen protons, you're dealing with 236 00:10:59,340 --> 00:11:00,315 phosphorus. 237 00:11:00,315 --> 00:11:06,340 And all of a sudden, if you have seven protons, you're 238 00:11:06,340 --> 00:11:07,149 dealing with nitrogen. 239 00:11:07,149 --> 00:11:09,059 If you have eight, you're dealing with oxygen. 240 00:11:09,059 --> 00:11:11,679 That is what defines the element. 241 00:11:11,679 --> 00:11:15,939 Now, we'll talk in the future about what happens with charge 242 00:11:15,940 --> 00:11:17,140 and all of that. 243 00:11:17,139 --> 00:11:19,009 Or what happens when you gain or lose electrons. 244 00:11:19,009 --> 00:11:21,759 But that does not change what element you're dealing with. 245 00:11:21,759 --> 00:11:26,230 And likewise, when you change the number of neutrons, that 246 00:11:26,230 --> 00:11:30,289 also does not change the element you're dealing with. 247 00:11:30,289 --> 00:11:32,980 But that leads to an obvious question of, well, how many 248 00:11:32,980 --> 00:11:35,899 neutrons and electrons do you have? 249 00:11:35,899 --> 00:11:43,370 Well, if an atom is charge-neutral, that means it 250 00:11:43,370 --> 00:11:46,100 has the same number of electrons. 251 00:11:46,100 --> 00:11:47,835 So let's say that I have carbon. 252 00:11:47,835 --> 00:11:52,030 253 00:11:52,029 --> 00:11:53,620 Its atomic number is six. 254 00:11:53,620 --> 00:12:00,240 And let's say its mass number is twelve. 255 00:12:00,240 --> 00:12:01,450 Now what does this mean? 256 00:12:01,450 --> 00:12:05,870 And let me say further that this is a neutral particle. 257 00:12:05,870 --> 00:12:07,460 This is a neutral atom. 258 00:12:07,460 --> 00:12:10,570 So the atomic number for carbon is six. 259 00:12:10,570 --> 00:12:13,860 That tells us exactly how many protons it has. 260 00:12:13,860 --> 00:12:16,279 So if I were to draw a little model here, and this is in no 261 00:12:16,279 --> 00:12:17,329 way an accurate model. 262 00:12:17,330 --> 00:12:21,000 I'll draw six-- two, three, four, five, six 263 00:12:21,000 --> 00:12:23,379 protons in the center. 264 00:12:23,379 --> 00:12:26,100 And the weight of these protons, each proton is one 265 00:12:26,100 --> 00:12:28,870 atomic mass unit, and we'll talk more about how that 266 00:12:28,870 --> 00:12:31,120 relates to kilograms. It's a very small 267 00:12:31,120 --> 00:12:32,580 fraction of a kilogram. 268 00:12:32,580 --> 00:12:36,230 Roughly I think it's 1.6 times 10 to the 269 00:12:36,230 --> 00:12:38,159 minus 27th of a kilogram. 270 00:12:38,159 --> 00:12:45,079 So let's say each of these are one atomic mass unit, and 271 00:12:45,080 --> 00:12:48,990 that's approximately equal to, I think, 1.67 times 10 to the 272 00:12:48,990 --> 00:12:53,320 minus 27 kilograms. This is a very small number. 273 00:12:53,320 --> 00:12:57,290 It's actually almost impossible to visualize. 274 00:12:57,289 --> 00:12:58,750 At least it is for me. 275 00:12:58,750 --> 00:13:03,240 This tells me the mass of the entire carbon atom, of this 276 00:13:03,240 --> 00:13:04,299 particular carbon atom. 277 00:13:04,299 --> 00:13:05,789 And this can actually change from carbon 278 00:13:05,789 --> 00:13:07,099 atom to carbon atom. 279 00:13:07,100 --> 00:13:10,720 And this is essentially the mass of all of the protons 280 00:13:10,720 --> 00:13:12,410 plus all of the neutrons. 281 00:13:12,409 --> 00:13:17,539 And each proton has an atomic mass of one, in atomic mass 282 00:13:17,539 --> 00:13:20,759 units, and each neutron has an atomic mass of 283 00:13:20,759 --> 00:13:22,529 one atomic mass unit. 284 00:13:22,529 --> 00:13:28,659 So this is really the number of protons plus 285 00:13:28,659 --> 00:13:29,909 the number of neutrons. 286 00:13:29,909 --> 00:13:33,829 287 00:13:33,830 --> 00:13:37,280 So in this case we have six protons, so we must also have 288 00:13:37,279 --> 00:13:39,110 six neutrons. 289 00:13:39,110 --> 00:13:42,919 Six neutrons plus six protons. 290 00:13:42,919 --> 00:13:44,490 Now, where are the electrons? 291 00:13:44,490 --> 00:13:49,129 Well, I said it's neutral, so the proton has an equal 292 00:13:49,129 --> 00:13:51,360 positive charge as the electron's negative charge. 293 00:13:51,360 --> 00:13:55,340 So this is a neutral atom, and it has six protons, so it also 294 00:13:55,340 --> 00:13:56,379 has six electrons. 295 00:13:56,379 --> 00:13:57,000 Let me draw that. 296 00:13:57,000 --> 00:13:59,179 So we said it has six neutrons in here. 297 00:13:59,179 --> 00:14:01,899 One, two, three, four, five, six. 298 00:14:01,899 --> 00:14:04,862 So that's the nucleus right there. 299 00:14:04,863 --> 00:14:09,300 And then if we were to draw the electons-- well, I could 300 00:14:09,299 --> 00:14:12,109 draw it as a smear, but if we want to kind of visualize it a 301 00:14:12,110 --> 00:14:13,669 little better, we could say, OK, there's going to be six 302 00:14:13,669 --> 00:14:15,289 electrons orbiting. 303 00:14:15,289 --> 00:14:18,459 One, two, three, four, five, six. 304 00:14:18,460 --> 00:14:21,280 And they're going to be moving around in this unpredictable 305 00:14:21,279 --> 00:14:22,829 way that we would have to describe with 306 00:14:22,830 --> 00:14:24,770 a probability function. 307 00:14:24,769 --> 00:14:30,169 And so the interesting thing about it is, most of the mass 308 00:14:30,169 --> 00:14:32,889 of an atom is sitting right in here. 309 00:14:32,889 --> 00:14:34,860 I mean, you might notice that when people care about the 310 00:14:34,860 --> 00:14:40,480 mass, when they care about the atomic mass number of an atom, 311 00:14:40,480 --> 00:14:41,610 they ignore the electrons. 312 00:14:41,610 --> 00:14:47,659 And that's because the mass of a proton, one proton 313 00:14:47,659 --> 00:14:52,529 mass-wise, is equal to 1,836 electons. 314 00:14:52,529 --> 00:14:58,250 So for thinking about the mass of an atom, for all basic 315 00:14:58,250 --> 00:15:01,919 purposes, you can ignore the mass of an electron. 316 00:15:01,919 --> 00:15:08,569 It's really the mass of the nucleus that counts as the 317 00:15:08,570 --> 00:15:10,200 mass of the atom. 318 00:15:10,200 --> 00:15:12,400 Now, you might see this periodic table here, and you 319 00:15:12,399 --> 00:15:15,679 say, OK, they gave us the atomic number up there. 320 00:15:15,679 --> 00:15:18,029 The atomic number of oxygen is eight. 321 00:15:18,029 --> 00:15:20,189 It means it has eight protons. 322 00:15:20,190 --> 00:15:22,470 The atomic number of silicon is 14. 323 00:15:22,470 --> 00:15:24,660 It has 14 protons. 324 00:15:24,659 --> 00:15:27,230 Now what is this right here? 325 00:15:27,230 --> 00:15:28,504 Let's see, in carbon. 326 00:15:28,504 --> 00:15:34,149 In carbon they have this 12.0107. 327 00:15:34,149 --> 00:15:36,980 That is the atomic weight of carbon. 328 00:15:36,980 --> 00:15:38,230 Let me write this. 329 00:15:38,230 --> 00:15:41,659 330 00:15:41,659 --> 00:15:47,389 Atomic weight of carbon. 331 00:15:47,389 --> 00:15:56,730 The atomic weight of carbon is 12.0107. 332 00:15:56,730 --> 00:15:57,710 Now, what does that mean? 333 00:15:57,710 --> 00:16:03,200 Does that mean that carbon has six protons and then the 334 00:16:03,200 --> 00:16:09,480 remainder, the remaining 6.0107 neutrons, it has kind 335 00:16:09,480 --> 00:16:11,710 of this fraction of a neutron? 336 00:16:11,710 --> 00:16:12,129 No. 337 00:16:12,129 --> 00:16:16,789 It means if you were to average all the different 338 00:16:16,789 --> 00:16:19,469 versions of carbon you find on the planet and you were to 339 00:16:19,470 --> 00:16:25,490 average the number of neutrons based on the quantity of the 340 00:16:25,490 --> 00:16:27,360 different types of carbon, this is the 341 00:16:27,360 --> 00:16:28,730 average you would get. 342 00:16:28,730 --> 00:16:32,980 So it turns out that carbon, the two major forms, the main 343 00:16:32,980 --> 00:16:35,129 one you'll find is carbon-12. 344 00:16:35,129 --> 00:16:36,460 So that's like this. 345 00:16:36,460 --> 00:16:39,210 So that has six protons and six neutrons. 346 00:16:39,210 --> 00:16:42,710 And then another isotope of carbon. 347 00:16:42,710 --> 00:16:45,420 Now an isotope is the same element with a different 348 00:16:45,419 --> 00:16:46,370 number of neutrons. 349 00:16:46,370 --> 00:16:50,169 Another isotope of carbon is carbon-14, which is much more 350 00:16:50,169 --> 00:16:52,240 scarce on the planet. 351 00:16:52,240 --> 00:16:55,919 We don't know how much in the universe, but on the planet. 352 00:16:55,919 --> 00:16:58,750 Now, if you were to average these, not just a straight-up 353 00:16:58,750 --> 00:17:01,480 average, then you would get carbon-13 and then the atomic 354 00:17:01,480 --> 00:17:04,130 weight would be 13, but you weight this one much higher 355 00:17:04,130 --> 00:17:07,160 because this exists in much larger quantities on Earth. 356 00:17:07,160 --> 00:17:08,589 I mean, this is pretty much all of the 357 00:17:08,588 --> 00:17:09,269 carbon that you see. 358 00:17:09,269 --> 00:17:10,618 But there's a little bit of this. 359 00:17:10,618 --> 00:17:13,529 So if you weight them appropriately, the average 360 00:17:13,529 --> 00:17:14,420 becomes this. 361 00:17:14,420 --> 00:17:17,200 So most of the carbon you'll find-- if you just found 362 00:17:17,200 --> 00:17:22,568 carbon someplace, on average its weight in atomic mass 363 00:17:22,568 --> 00:17:27,039 units is going to be 12.0107. 364 00:17:27,039 --> 00:17:29,190 But that idea of an isotope is an interesting one. 365 00:17:29,190 --> 00:17:32,180 Remember, when you change the neutrons, you're not changing 366 00:17:32,180 --> 00:17:33,820 the actual, fundamental element. 367 00:17:33,819 --> 00:17:36,210 You're just getting a different isotope, a different 368 00:17:36,210 --> 00:17:37,590 version, of the element. 369 00:17:37,589 --> 00:17:41,500 So these two versions of carbon are both isotopes. 370 00:17:41,500 --> 00:17:43,500 Now, I want to leave this video with what I think is 371 00:17:43,500 --> 00:17:46,849 kind of the neatest idea behind atoms. And it's the 372 00:17:46,849 --> 00:17:49,779 most philosophically interesting things about them. 373 00:17:49,779 --> 00:17:54,190 It's that the relative size-- so, we have these electrons, 374 00:17:54,190 --> 00:17:58,340 which represent very little of the mass of an atom. 375 00:17:58,339 --> 00:18:01,470 It's 1/2000 of the mass of an atom are the electrons. 376 00:18:01,470 --> 00:18:04,559 And even those, it's hard to even describe them as 377 00:18:04,559 --> 00:18:08,789 particles, because you can't even tell me exactly where and 378 00:18:08,789 --> 00:18:11,170 how fast one of these particles is moving. 379 00:18:11,170 --> 00:18:12,880 They just have a probability function. 380 00:18:12,880 --> 00:18:16,280 So most of the atom is sitting inside the nucleus. 381 00:18:16,279 --> 00:18:17,879 And this is the interesting thing. 382 00:18:17,880 --> 00:18:21,080 If you look at an atom on average, if you 383 00:18:21,079 --> 00:18:23,039 say this is my atom. 384 00:18:23,039 --> 00:18:26,299 Let's say I had two atoms that are bonded to each other. 385 00:18:26,299 --> 00:18:29,065 And I were to say, how much of this is actual stuff? 386 00:18:29,065 --> 00:18:32,120 And when I say stuff, that's a very abstract concept, because 387 00:18:32,119 --> 00:18:33,669 we're talking about the nucleus, right? 388 00:18:33,670 --> 00:18:34,740 Because the nucleus is where all the 389 00:18:34,740 --> 00:18:36,470 mass is, all the stuff. 390 00:18:36,470 --> 00:18:39,750 It turns out that it's actually an infinitesimally 391 00:18:39,750 --> 00:18:44,160 small fraction of the volume of the atom where-- the volume 392 00:18:44,160 --> 00:18:45,920 of the atom is hard to define, because the electron can 393 00:18:45,920 --> 00:18:48,870 pretty much be anywhere, but if you view the volume as 394 00:18:48,869 --> 00:18:52,579 where you're most likely to find the electron, or with 90% 395 00:18:52,579 --> 00:18:55,710 probability you're likely to find the electron, then the 396 00:18:55,710 --> 00:18:59,150 nucleus is, in a lot of cases and the way I think about it, 397 00:18:59,150 --> 00:19:01,740 it's about 1/10,000 of the volume. 398 00:19:01,740 --> 00:19:03,589 So if you think about it, when you look at something, if you 399 00:19:03,589 --> 00:19:06,459 look at your hand or if you look at the wall or if you 400 00:19:06,460 --> 00:19:14,829 look at your computer, 99.999% of it is free space. 401 00:19:14,829 --> 00:19:15,470 It's nothing. 402 00:19:15,470 --> 00:19:18,319 It's vacuum. 403 00:19:18,319 --> 00:19:20,599 If you had ultra-small-- I guess we could call them 404 00:19:20,599 --> 00:19:23,019 particles or something-- most of them would pass straight 405 00:19:23,019 --> 00:19:24,690 through whatever you look at. 406 00:19:24,690 --> 00:19:26,529 So it already starts to kind of 407 00:19:26,529 --> 00:19:28,210 question our hold on reality. 408 00:19:28,210 --> 00:19:32,120 What is there when, if-- and this is fact, this isn't 409 00:19:32,119 --> 00:19:35,349 theory right here-- that if you take anything down to the 410 00:19:35,349 --> 00:19:39,579 building blocks, down to the atomic level, most of the 411 00:19:39,579 --> 00:19:43,449 space of that kind of, quote-unquote object, is free 412 00:19:43,450 --> 00:19:44,470 vacuum space. 413 00:19:44,470 --> 00:19:46,490 You could go straight through it if you could get down to 414 00:19:46,490 --> 00:19:47,940 that scale. 415 00:19:47,940 --> 00:19:50,880 This image of a helium atom, they say right here this is 416 00:19:50,880 --> 00:19:52,520 one femtometer. 417 00:19:52,519 --> 00:19:52,809 Right? 418 00:19:52,809 --> 00:19:54,059 One femtometer. 419 00:19:54,059 --> 00:19:57,609 420 00:19:57,609 --> 00:20:00,179 This is the scale of the nucleus of a 421 00:20:00,180 --> 00:20:01,779 helium atom, right? 422 00:20:01,779 --> 00:20:03,089 One femtometer. 423 00:20:03,089 --> 00:20:04,309 This is one angstrom, right? 424 00:20:04,309 --> 00:20:06,819 And they say that equals 100,000 femtometers. 425 00:20:06,819 --> 00:20:10,359 And just to get a sense of scale, one angstrom is 1 times 426 00:20:10,359 --> 00:20:13,419 10 to the negative 10 meters, right? 427 00:20:13,420 --> 00:20:15,830 So the atom is roughly on the scale of an angstrom. 428 00:20:15,829 --> 00:20:17,779 In the case of helium, the nucleus is 429 00:20:17,779 --> 00:20:18,990 even a smaller fraction. 430 00:20:18,990 --> 00:20:20,930 It's 1/100,000. 431 00:20:20,930 --> 00:20:23,700 So if you had-- let's say you had liquid helium, which you'd 432 00:20:23,700 --> 00:20:25,190 have to get very cold to get. 433 00:20:25,190 --> 00:20:27,610 If you're looking at that, most of it is free space. 434 00:20:27,609 --> 00:20:30,549 If you're looking at an iron bar, the great, great, great, 435 00:20:30,549 --> 00:20:33,309 great, great, great majority of it is free space. 436 00:20:33,309 --> 00:20:35,500 And we're not even talking about, maybe there's some free 437 00:20:35,500 --> 00:20:37,240 space inside the nucleus that we could talk 438 00:20:37,240 --> 00:20:38,210 about in the future. 439 00:20:38,210 --> 00:20:41,950 But to me, that just blows my mind that most things we look 440 00:20:41,950 --> 00:20:44,870 at are not really solid. 441 00:20:44,869 --> 00:20:47,529 They're really just empty space, but they look solid 442 00:20:47,529 --> 00:20:50,359 because of the way light reflects on them or the forces 443 00:20:50,359 --> 00:20:51,129 that repel us. 444 00:20:51,130 --> 00:20:55,100 But there really isn't something to touch there. 445 00:20:55,099 --> 00:20:57,799 That most of this right here is all free space. 446 00:20:57,799 --> 00:21:00,259 I think I've said the word free space now, and I think 447 00:21:00,259 --> 00:21:02,369 I'll leave further 448 00:21:02,369 --> 00:21:05,019 mind-blowing to the next video.