0:00:00.650,0:00:03.370 In the last few videos we learned that 0:00:03.370,0:00:08.160 the configuration of electrons in an atom aren't[br] 0:00:08.160,0:00:10.540 in a simple, classical, Newtonian orbit configuration. 0:00:10.540,0:00:12.183 And that's the Bohr model of the electron. 0:00:12.183,0:00:14.320 And I'll keep reviewing it, 0:00:14.320,0:00:14.900 just because I think it's an important point. 0:00:14.900,0:00:16.900 If that's the nucleus, remember, it's just a tiny, tiny, tiny dot 0:00:16.900,0:00:20.570 if you think about the entire volume of the actual atom. 0:00:21.600,0:00:25.110 And instead of the electron being in orbits around it, 0:00:25.110,0:00:29.310 which would be how a planet orbits the sun. 0:00:29.310,0:00:32.360 Instead of being in orbits around it, it's described by orbitals, 0:00:32.360,0:00:36.680 which are these probability density functions. 0:00:36.680,0:00:41.670 So an orbital-- let's say that's the nucleus-- it would describe, 0:00:41.670,0:00:44.990 if you took any point in space around the nucleus, 0:00:44.990,0:00:48.700 the probability of finding the electron. 0:00:48.700,0:00:53.710 So actually, in any volume of space around the nucleus, 0:00:53.710,0:00:56.080 it would tell you the probability of 0:00:56.080,0:00:57.050 finding the electron within that volume. 0:00:57.050,0:00:59.850 And so if you were to just take a bunch of snapshots of electrons 0:00:59.850,0:01:02.910 -- let's say in the 1s orbital. 0:01:02.910,0:01:07.510 And that's what the 1s orbital looks like. 0:01:07.510,0:01:10.440 You can barely see it there, but it's a sphere around the nucleus, 0:01:10.440,0:01:12.850 and that's the lowest energy state that an electron can be in. 0:01:14.250,0:01:15.590 If you were to just take a number of snapshots of electrons. 0:01:17.480,0:01:21.460 Let's say you were to take a number of snapshots of helium, 0:01:21.460,0:01:22.800 which has two electrons. 0:01:22.800,0:01:25.860 Both of them are in the 1s orbital. 0:01:25.860,0:01:26.830 It would look like this. 0:01:26.830,0:01:29.140 If you took one snapshot, maybe it'll be there, 0:01:29.140,0:01:31.170 the next snapshot, maybe the electron is there. 0:01:31.170,0:01:32.520 Then the electron is there. 0:01:32.520,0:01:33.540 Then the electron is there. 0:01:33.540,0:01:34.060 Then it's there. 0:01:34.060,0:01:36.250 And if you kept doing the snapshots, 0:01:36.250,0:01:37.870 you would have a bunch of them really close. 0:01:37.870,0:01:42.150 And then it gets a little bit sparser as you get out, 0:01:42.150,0:01:45.160 as you get further and further out away from the electron. 0:01:45.160,0:01:48.498 But as you see, you're much more likely 0:01:48.498,0:01:54.580 to find the electron close to the center of the atom than further out. 0:01:54.580,0:01:56.320 Although you might have had an observation with the electron 0:01:56.320,0:01:58.620 sitting all the way out there, or sitting over here. 0:01:58.620,0:02:00.420 So it really could have been anywhere, 0:02:00.420,0:02:03.690 but if you take multiple observations, 0:02:03.690,0:02:05.070 you'll see what that probability function is describing. 0:02:05.070,0:02:07.220 It's saying look, there's a much lower probability of 0:02:07.220,0:02:11.400 finding the electron out in this little cube of volume space 0:02:11.400,0:02:14.930 than it is in this little cube of volume space. 0:02:14.930,0:02:17.610 And when you see these diagrams that draw this orbital like this. 0:02:19.110,0:02:23.565 Let's say they draw it like a shell, like a sphere. 0:02:23.565,0:02:25.510 And I'll try to make it look three-dimensional. 0:02:25.510,0:02:28.455 So let's say this is the outside of it, and the nucleus 0:02:28.455,0:02:30.200 is sitting some place on the inside. 0:02:30.200,0:02:32.830 They're just saying -- they just draw a cut-off -- 0:02:32.830,0:02:34.950 where can I find the electron 90% of the time? 0:02:34.950,0:02:36.950 So they're saying, OK, 0:02:36.950,0:02:38.940 I can find the electron 90% of the time within this circle, 0:02:38.940,0:02:40.930 if I were to do the cross-section. 0:02:40.930,0:02:43.220 But every now and then the electron can show up outside of that, right? 0:02:44.000,0:02:45.260 Because it's all probabilistic. 0:02:45.260,0:02:46.300 So this can still happen. 0:02:46.300,0:02:48.570 You can still find the electron 0:02:48.570,0:02:51.810 if this is the orbital we're talking about out here. 0:02:51.810,0:02:52.380 Right? 0:02:52.380,0:02:54.660 And then we, in the last video, we said, OK, 0:02:54.660,0:03:02.260 the electrons fill up the orbitals 0:03:02.260,0:03:06.050 from lowest energy state to high energy state. 0:03:06.050,0:03:08.050 You could imagine it. 0:03:08.050,0:03:10.720 If I'm playing Tetris-- well I don't know if Tetris is the thing 0:03:10.720,0:03:13.780 -- but if I'm stacking cubes, I lay out cubes from low energy, 0:03:13.780,0:03:16.450 if this is the floor, I put the first cube at the lowest energy state. 0:03:17.950,0:03:21.580 And let's say I could put the second cube at a low energy state here. 0:03:22.020,0:03:27.780 But I only have this much space to work with. 0:03:27.780,0:03:29.690 So I have to put the third cube at the next highest energy state. 0:03:30.800,0:03:33.280 In this case our energy would be described 0:03:33.280,0:03:33.930 as potential energy, right? 0:03:33.930,0:03:36.650 This is just a classical, Newtonian physics example. 0:03:36.650,0:03:39.460 But that's the same idea with electrons. 0:03:39.460,0:03:45.540 Once I have two electrons in this 1s orbital 0:03:45.540,0:03:50.240 -- so let's say the electron configuration of helium is 1s2-- 0:03:50.240,0:03:52.980 the third electron I can't put there anymore, 0:03:52.980,0:03:55.170 because there's only room for two electrons. 0:03:55.170,0:03:57.230 The way I think about it is these two electrons 0:03:57.230,0:03:58.970 are now going to repel the third one I want to add. 0:03:58.970,0:04:02.580 So then I have to go to the 2s orbital. 0:04:02.580,0:04:06.090 And now if I were to plot the 2s orbital on top of this one, 0:04:06.090,0:04:07.760 it would look something like this, where I have a high 0:04:07.760,0:04:13.380 where I have a high probability of finding the electrons in this shell 0:04:13.380,0:04:19.110 that's essentially around the 1s orbital, right? 0:04:19.110,0:04:22.400 So right now, if maybe I'm dealing with lithium right now. 0:04:23.300,0:04:24.820 So I only have one extra electron. 0:04:24.820,0:04:27.960 So this one extra electron, that might be 0:04:27.960,0:04:29.460 where I observed that extra electron. 0:04:29.460,0:04:31.240 But every now and then it could show up there, 0:04:31.240,0:04:33.310 it could show up there, it could show up there, 0:04:33.310,0:04:34.360 but the high probability is there. 0:04:34.360,0:04:37.100 So when you say where is it going to be 90% of the time? 0:04:37.100,0:04:39.730 It'll be like this shell that's around the center. 0:04:39.730,0:04:41.140 Remember, when it's three-dimensional 0:04:41.140,0:04:42.030 you would kind of cover it up. 0:04:42.030,0:04:43.800 So it would be this shell. 0:04:43.800,0:04:47.070 So that's what they drew here. 0:04:47.070,0:04:48.000 They do the 1s. 0:04:48.000,0:04:49.050 It's just a red shell. 0:04:49.050,0:04:51.100 And then the 2s. 0:04:51.100,0:04:53.850 The second energy shell is just this blue shell over it. 0:04:53.850,0:04:55.560 And you can see it a little bit better in, actually, 0:04:55.560,0:04:58.810 the higher energy orbits, the higher energy shells, 0:04:58.810,0:05:02.400 where the seventh‘s energy shell is this red area. 0:05:02.400,0:05:04.800 Then you have the blue area, then the red, and the blue. 0:05:04.800,0:05:06.530 And so I think you get the idea that each of those are energy shells. 0:05:07.710,0:05:10.580 So you kind of keep overlaying the s energy orbitals around each other. 0:05:12.180,0:05:14.290 But you probably see this other stuff here. 0:05:14.290,0:05:16.830 And the general principle, remember, is that 0:05:16.830,0:05:20.120 the electrons fill up the orbital 0:05:20.120,0:05:21.790 from lowest energy orbital to higher energy orbital. 0:05:21.790,0:05:25.400 So the first one that's filled up is the 1s. 0:05:25.400,0:05:26.620 This is the 1. 0:05:26.620,0:05:27.330 This is the s. 0:05:27.330,0:05:28.530 So this is the 1s. 0:05:28.530,0:05:30.460 It can fit two electrons. 0:05:30.460,0:05:32.900 Then the next one that's filled up is 2s. 0:05:32.900,0:05:35.160 It can fill two more electrons. 0:05:35.160,0:05:37.230 And then the next one, and this is where it gets interesting, 0:05:37.230,0:05:40.030 you fill up the 2p orbital. 0:05:42.950,0:05:45.180 That's this, right here. 0:05:45.180,0:05:47.220 2p orbitals. 0:05:47.220,0:05:51.260 And notice the p orbitals have something, p sub z, p sub x, p sub y. 0:05:55.040,0:05:55.620 What does that mean? 0:05:55.620,0:05:57.840 Well, if you look at the p-orbitals, they have these dumbbell shapes. 0:05:58.630,0:06:01.010 They look a little unnatural, but I think in future videos 0:06:01.010,0:06:04.600 we'll show you how they're analogous to standing waves. 0:06:04.600,0:06:06.750 But if you look at these, there's three ways that 0:06:06.750,0:06:08.040 you can configure these dumbbells. 0:06:08.040,0:06:10.120 One in the z direction, up and down. 0:06:10.120,0:06:12.280 One in the x direction, left or right. 0:06:12.280,0:06:14.760 And then one in the y direction, this way, 0:06:14.760,0:06:16.250 forward and backwards, right? 0:06:16.250,0:06:19.660 And so if you were to draw--[br] 0:06:19.660,0:06:21.410 let's say you wanted to draw the p-orbitals. 0:06:21.410,0:06:22.800 So this is what you fill next. 0:06:22.800,0:06:24.780 And actually, you fill one electron here, 0:06:24.780,0:06:26.910 another electron here, then another electron there. 0:06:26.910,0:06:29.036 Then you fill another electron, and 0:06:29.036,0:06:30.190 we'll talk about spin and things like that in the future. 0:06:30.190,0:06:32.750 But, there, there, and there. 0:06:32.750,0:06:34.590 And that's actually called Hund's rule. 0:06:34.590,0:06:36.600 Maybe I'll do a whole video on Hund's rule, 0:06:36.600,0:06:40.710 but that's not relevant to a first-year chemistry lecture. 0:06:40.710,0:06:43.310 But it fills in that order, and once again, 0:06:43.310,0:06:47.010 I want you to have the intuition of what this would look like. 0:06:47.010,0:06:47.440 Look. 0:06:47.440,0:06:50.240 I should put look in quotation marks, 0:06:50.240,0:06:52.470 because it's very abstract. 0:06:52.470,0:06:55.810 But if you wanted to visualize the p orbitals 0:06:55.810,0:06:57.810 -- let's say we're looking at the electron configuration 0:06:57.810,0:07:02.240 for, let's say, carbon. 0:07:02.240,0:07:05.890 So the electron configuration for carbon, 0:07:05.890,0:07:10.360 the first two electrons go into, so, 1s1, 1s2. 0:07:10.360,0:07:14.160 So then it fills-- sorry, you can't see everything. 0:07:14.160,0:07:17.660 So it fills the 1s2, so carbon's configuration. 0:07:21.000,0:07:24.680 It fills 1s1 then 1s2. 0:07:24.680,0:07:26.280 And this is just the configuration for helium. 0:07:26.280,0:07:30.210 And then it goes to the second shell, 0:07:30.210,0:07:30.930 which is the second period, right? 0:07:30.930,0:07:32.270 That's why it's called the periodic table. 0:07:32.270,0:07:34.960 We'll talk about periods and groups in the future. 0:07:34.960,0:07:36.070 And then you go here. 0:07:36.070,0:07:38.690 So this is filling the 2s. 0:07:38.690,0:07:40.700 We're in the second period right here. 0:07:40.700,0:07:42.120 That's the second period. 0:07:42.120,0:07:43.400 One, two. 0:07:43.400,0:07:45.820 Have to go off, so you can see everything. 0:07:45.820,0:07:47.530 So it fills these two. 0:07:47.530,0:07:50.390 So 2s2. 0:07:50.390,0:07:52.820 And then it starts filling up the p orbitals. 0:07:52.820,0:07:56.830 So then it starts filling 1p and then 2p. 0:07:56.830,0:08:02.360 And we're still on the second shell, so 2s2, 2p2. 0:08:02.360,0:08:04.420 So the question is what would this look like if 0:08:04.420,0:08:07.030 we just wanted to visualize this orbital right here, 0:08:07.030,0:08:09.420 the p orbitals? 0:08:09.420,0:08:11.600 So we have two electrons. 0:08:11.600,0:08:15.090 So one electron is going to be in a-- Let's say if this is, 0:08:15.090,0:08:17.840 I'll try to draw some axes. 0:08:17.840,0:08:20.410 That's too thin. 0:08:20.410,0:08:23.960 So if I draw a three-dimensional 0:08:23.960,0:08:25.470 volume kind of axes. 0:08:28.440,0:08:31.340 If I were to make a bunch of observations of, say, 0:08:31.340,0:08:34.770 one of the electrons in the p orbitals, 0:08:34.770,0:08:36.230 let's say in the pz dimension, 0:08:36.230,0:08:37.690 sometimes it might be here, 0:08:37.690,0:08:39.759 sometimes it might be there, sometimes it might be there. 0:08:39.759,0:08:47.070 And then if you keep taking a bunch of observations, 0:08:47.070,0:08:52.000 you're going to have something that looks like this bell shape, 0:08:52.000,0:08:54.160 this barbell shape right there. 0:08:54.160,0:08:57.510 And then for the other electron that's maybe in the x direction, 0:08:57.510,0:09:00.500 you make a bunch of observations. 0:09:00.500,0:09:01.830 Let me do it in a different, in a noticeably different, color. 0:09:03.640,0:09:04.580 It will look like this. 0:09:04.580,0:09:06.590 You take a bunch of observations, and you say, 0:09:06.590,0:09:10.360 wow, it's a lot more likely to find 0:09:10.360,0:09:12.680 that electron in kind of the dumbbell, in that dumbbell shape. 0:09:12.680,0:09:13.600 But you could find it out there. 0:09:13.600,0:09:14.460 You could find it there. 0:09:14.460,0:09:15.360 You could find it there. 0:09:15.360,0:09:17.990 This is just a much higher probability of 0:09:17.990,0:09:19.630 finding it in here than out here. 0:09:19.630,0:09:23.850 And that's the best way I can think of to visualize it. 0:09:23.850,0:09:26.840 Now what we were doing here,[br] 0:09:26.840,0:09:27.980 this is called an electron configuration. 0:09:27.980,0:09:30.610 And the way to do it-- and there's multiple ways 0:09:30.610,0:09:34.210 that are taught in chemistry class, 0:09:34.210,0:09:37.550 but the way I like to do it, is 0:09:37.550,0:09:40.890 you take the periodic table and you say, these groups, and 0:09:40.890,0:09:43.840 when I say groups I mean the columns, 0:09:43.840,0:09:48.610 these are going to fill the s subshell or the s orbitals. 0:09:51.570,0:09:53.750 You can just write s up here, just right there. 0:09:53.750,0:09:59.630 These over here are going to fill the p orbitals. 0:09:59.630,0:10:02.020 Actually, let me take helium out of the picture. 0:10:02.020,0:10:03.260 The p orbitals. 0:10:03.260,0:10:04.210 Let me just do that. 0:10:04.210,0:10:06.070 Let me take helium out of the picture. 0:10:06.070,0:10:07.670 These take the p orbitals. 0:10:07.670,0:10:10.010 And actually, for the sake of figuring out these, 0:10:10.010,0:10:12.970 you should take helium and throw it right over there. 0:10:12.970,0:10:13.230 Right? 0:10:13.230,0:10:15.810 The periodic table is just a way to organize things 0:10:15.810,0:10:18.810 so it makes sense, but in terms of trying to figure out orbitals, 0:10:18.810,0:10:19.970 you could take helium. 0:10:19.970,0:10:21.490 Let me do that. 0:10:21.490,0:10:23.690 The magic of computers. 0:10:23.690,0:10:29.050 Cut it out, and then let me paste it right over there. 0:10:29.050,0:10:29.490 Right? 0:10:29.490,0:10:32.660 And now you see that helium, you get 1s and then you get 2s, 0:10:32.660,0:10:36.140 so helium's configuration is-- 0:10:36.140,0:10:38.290 Sorry, you get 1s1, then 1s2. 0:10:38.290,0:10:41.190 We're in the first energy shell. 0:10:41.190,0:10:41.920 Right? 0:10:41.920,0:10:50.910 So the configuration of hydrogen is 1s1. 0:10:50.910,0:10:57.030 You only have one electron in the s subshell of the first energy shell. 0:10:58.172,0:11:02.590 The configuration of helium is 1s2. 0:11:02.590,0:11:06.380 And then you start filling the second energy shell. 0:11:06.380,0:11:12.240 The configuration of lithium is 1s2. 0:11:12.240,0:11:13.570 That's where the first two electrons go. 0:11:13.570,0:11:18.600 And then the third one goes into 2s1, right? 0:11:18.600,0:11:20.670 And then I think you start to see the pattern. 0:11:20.670,0:11:25.810 And then when you go to nitrogen you say, 0:11:25.810,0:11:29.600 OK, it has three in the p sub-orbital. 0:11:29.600,0:11:31.490 So you can almost start backwards, right? 0:11:31.490,0:11:36.250 So we're in period two, right? 0:11:36.250,0:11:37.500 So this is 2p3. 0:11:39.800,0:11:40.540 Let me write that down. 0:11:40.540,0:11:45.200 So I could write that down first. 2p3. 0:11:45.200,0:11:47.880 So that's where the last three electrons go into the p orbital. 0:11:49.100,0:11:54.110 Then it'll have these two that go into the 2s2 orbital. 0:11:57.860,0:12:02.240 And then the first two, or the electrons in the lowest energy state, 0:12:02.240,0:12:06.020 will be 1s2. 0:12:06.020,0:12:07.900 So this is the electron configuration, right here, of nitrogen. 0:12:12.020,0:12:15.380 And just to make sure you did your configuration right, 0:12:15.380,0:12:17.270 what you do is you count the number of electrons. 0:12:17.270,0:12:20.600 So 2 plus 2 is 4 plus 3 is 7. 0:12:20.600,0:12:22.630 And we're talking about neutral atoms, 0:12:22.630,0:12:25.240 so the electrons should equal the number of protons. 0:12:25.240,0:12:27.540 The atomic number is the number of protons. 0:12:27.540,0:12:28.580 So we're good. 0:12:28.580,0:12:29.480 Seven protons. 0:12:29.480,0:12:32.050 So this is, so far, when we're dealing just with the s's and the p's, 0:12:32.050,0:12:33.926 this is pretty straightforward. 0:12:33.926,0:12:40.070 And if I wanted to figure out the configuration of silicon, 0:12:40.070,0:12:42.130 right there, what is it? 0:12:42.130,0:12:43.970 Well, we're in the third period. 0:12:43.970,0:12:45.990 One, two, three. 0:12:45.990,0:12:48.230 That's just the third row. 0:12:48.230,0:12:50.630 And this is the p-block right here. 0:12:50.630,0:12:52.670 So this is the second row in the p-block, right? 0:12:52.670,0:12:55.830 One, two, three, four, five, six. 0:12:55.830,0:12:56.060 Right. 0:12:56.060,0:12:57.630 We're in the second row of the p-block, 0:12:57.630,0:12:59.200 so we start off with 3p2. 0:13:03.780,0:13:05.130 And then we have 3s2. 0:13:08.010,0:13:11.630 And then it filled up all of this p-block over here. 0:13:11.630,0:13:12.880 So it's 2p6. 0:13:14.900,0:13:17.340 And then here, 2s2. 0:13:17.340,0:13:19.740 And then, of course, it filled up at the first shell 0:13:19.740,0:13:20.810 before it could fill up these other shells. 0:13:20.810,0:13:22.390 So, 1s2. 0:13:22.390,0:13:27.130 So this is the electron configuration for silicon. 0:13:27.130,0:13:29.510 And we can confirm that we should have 14 electrons. 0:13:29.510,0:13:33.840 2 plus 2 is 4, plus 6 is 10. 0:13:33.840,0:13:38.020 10 plus 2 is 12 plus 2 more is 14. 0:13:38.020,0:13:40.350 So we're good with silicon. 0:13:40.350,0:13:43.120 I think I'm running low on time right now, 0:13:43.120,0:13:45.380 so in the next video we'll start addressing 0:13:45.380,0:13:48.080 what happens when you go to these elements, or the d-block. 0:13:48.080,0:13:50.120 And you can kind of already guess what happens. 0:13:50.120,0:13:54.900 We're going to start filling up these d orbitals here that 0:13:54.900,0:13:56.730 have even more bizarre shapes. 0:13:56.730,0:13:59.120 And the way I think about this, not to waste too much time, 0:13:59.120,0:14:03.310 is that as you go further and further out from the nucleus, 0:14:03.310,0:14:05.880 there's more space in between the lower energy orbitals 0:14:08.360,0:14:10.440 to fill in more of these bizarro-shaped orbitals. 0:14:10.440,0:14:13.770 But these are kind of the balance -- 0:14:13.770,0:14:15.560 I will talk about standing waves in the future--[br] 0:14:15.560,0:14:18.780 but these are kind of a balance between 0:14:18.780,0:14:20.980 trying to get close to the nucleus and the proton 0:14:20.980,0:14:22.135 and those positive charges, 0:14:22.135,0:14:23.290 because the electron charges are attracted to them, 0:14:23.290,0:14:25.940 while at the same time avoiding the other electron charges, 0:14:25.940,0:14:27.780 or at least their mass distribution functions. 0:14:27.780,0:14:29.980 Anyway, see you in the next video.