0:00:00.300,0:00:01.860 - [Instructor] Almost all[br]the matter in the universe 0:00:01.860,0:00:03.000 from the tiniest microbes 0:00:03.000,0:00:04.920 to the biggest stars in the universe, 0:00:04.920,0:00:07.920 are made from a few about[br]100 different elements, 0:00:07.920,0:00:10.920 which we arrange this[br]way in a table called 0:00:10.920,0:00:12.270 the periodic table. 0:00:12.270,0:00:14.970 But wait a second, why are[br]they arranged like this 0:00:14.970,0:00:16.710 and why do they have these colors? 0:00:16.710,0:00:18.120 And if you were to zoom into it, 0:00:18.120,0:00:19.620 you can see these different numbers. 0:00:19.620,0:00:21.300 What do they represent? 0:00:21.300,0:00:22.830 Well, let's find out. 0:00:22.830,0:00:25.200 First and foremost these[br]elements have symbols, right? 0:00:25.200,0:00:27.720 H for hydrogen, He for helium. 0:00:27.720,0:00:30.090 Well, turns out these[br]symbols are universal, 0:00:30.090,0:00:31.770 and that's pretty cool,[br]which means if you're 0:00:31.770,0:00:34.440 to look at this Chinese[br]periodic table, look, 0:00:34.440,0:00:35.760 the symbols stay the same. 0:00:35.760,0:00:38.760 It's in Latin H for[br]hydrogen, He for helium. 0:00:38.760,0:00:41.280 Similar is the case for this[br]periodic table in Hindi, one 0:00:41.280,0:00:42.690 of the Indian languages. 0:00:42.690,0:00:44.850 So of course the elements[br]have different names in Hindi 0:00:44.850,0:00:47.460 for iron we call loha. 0:00:47.460,0:00:49.440 But the the important thing is 0:00:49.440,0:00:51.630 that the symbol stays the same. 0:00:51.630,0:00:53.820 So the symbols are universal. 0:00:53.820,0:00:55.080 But the next question is, what exactly are 0:00:55.080,0:00:56.100 the numbers over here? 0:00:56.100,0:00:56.933 There are two, right? 0:00:56.933,0:00:58.440 Let's start with the number on the top. 0:00:58.440,0:01:01.530 So it starts with one for[br]hydrogen and then two for helium. 0:01:01.530,0:01:03.810 And then if you zoom[br]in, three for lithium, 0:01:03.810,0:01:06.300 four for beryllium,[br]and so on and so forth. 0:01:06.300,0:01:08.580 Well, these numbers are identification 0:01:08.580,0:01:09.870 numbers of these elements. 0:01:09.870,0:01:13.650 And we u name to it, we[br]call it the atomic number. 0:01:13.650,0:01:17.520 So for example, if I say the[br]element with atomic number 22, 0:01:17.520,0:01:19.563 well that's always going to be titanium, 0:01:20.407,0:01:22.530 element with atomic number five[br]is always going to be boron. 0:01:22.530,0:01:25.380 And so these are integers,[br]they are continuous. 0:01:25.380,0:01:28.620 And the last element has[br]the atomic number 118, 0:01:28.620,0:01:30.150 which is called Oganesson. 0:01:30.150,0:01:31.650 Fun fact elements up to uranium, 0:01:31.650,0:01:34.560 which has the atomic number[br]92 are naturally occurring, 0:01:34.560,0:01:36.870 but the elements after that[br]are pretty much synthesized in 0:01:36.870,0:01:38.190 labs as far as we know. 0:01:38.190,0:01:39.570 They do not occur in nature. 0:01:39.570,0:01:41.130 But what about the second number? 0:01:41.130,0:01:43.530 Well, that's called the atomic mass 0:01:43.530,0:01:44.490 and it tells us 0:01:44.490,0:01:48.300 how massive this element[br]is compared to hydrogen. 0:01:48.300,0:01:50.220 Again, just to give us some examples, 0:01:50.220,0:01:54.660 if you look at hydrogen's[br]atomic mass, it's 1.008 right, 0:01:54.660,0:01:56.970 now that is in some unit[br]called the atomic mass unit. 0:01:56.970,0:01:58.290 Don't worry too much about that. 0:01:58.290,0:01:59.640 But now if you look at helium, 0:01:59.640,0:02:02.520 it's atomic mass is 4.003. 0:02:02.520,0:02:06.270 This means an atom of helium[br]is about four times more 0:02:06.270,0:02:08.910 massive compared to the atom of hydrogen. 0:02:08.910,0:02:10.620 That's the meaning of atomic mass. 0:02:10.620,0:02:14.220 The atom of gold is about 1.97[br]times more massive compared 0:02:14.220,0:02:16.620 to hydrogen and so on and so forth. 0:02:16.620,0:02:18.300 Now, one technical detail is 0:02:18.300,0:02:20.730 that this number is in average value. 0:02:20.730,0:02:23.820 So this is actually an[br]average atomic mass. 0:02:23.820,0:02:26.004 And the reason for that is because these 0:02:26.004,0:02:27.382 elements can have variance. 0:02:27.382,0:02:28.860 For example, not all the[br]gold atoms will have the 0:02:28.860,0:02:30.030 exact same mass. 0:02:30.030,0:02:32.600 Some will be slightly[br]more massive science, 0:02:32.600,0:02:34.125 some will be slightly less massive. 0:02:34.125,0:02:36.570 And so this number here[br]represents the average value. 0:02:36.570,0:02:38.940 This would be true for[br]all the other elements. 0:02:38.940,0:02:40.740 They have variance. 0:02:40.740,0:02:43.230 And these variance are called isotopes. 0:02:43.230,0:02:45.090 And we'll learn more about[br]them in high school chemistry. 0:02:45.090,0:02:46.530 Don't worry too much about it right now. 0:02:46.530,0:02:47.700 All right, the next question is, 0:02:47.700,0:02:49.350 what's the deal with these colors? 0:02:49.350,0:02:51.360 Well, the colors helps us[br]categorize the elements 0:02:51.360,0:02:52.680 into three categories. 0:02:52.680,0:02:55.140 The pink ones are called metals. 0:02:55.140,0:02:57.990 The blue ones are called non-metals. 0:02:57.990,0:03:00.090 And what about these green ones over here? 0:03:00.090,0:03:02.250 Well even kind of think they're[br]someone somewhat in between. 0:03:02.250,0:03:04.710 And so we call them metalloids. 0:03:04.710,0:03:07.770 And yes, the color schemes[br]are definitely not universal. 0:03:07.770,0:03:09.990 Different periodic tables[br]might use different colors. 0:03:09.990,0:03:11.610 So better way to think about it is we, 0:03:11.610,0:03:13.830 we draw a zigzag line over here, 0:03:13.830,0:03:15.360 and all the elements to the left 0:03:15.360,0:03:17.460 of this zigzag would be metals. 0:03:17.460,0:03:20.220 And the elements to the[br]right would be non-metals. 0:03:20.220,0:03:23.190 And these elements which[br]are in between over here, 0:03:23.190,0:03:24.828 those are the metalloids. 0:03:24.828,0:03:26.400 And of course, this[br]distinction doesn't make sense 0:03:26.400,0:03:27.900 for these extremely heavy elements 0:03:27.900,0:03:29.010 that we synthesize in labs. 0:03:29.010,0:03:31.140 Okay, anyways, this brings us 0:03:31.140,0:03:32.490 to the most important thing now, 0:03:32.490,0:03:34.470 and that is the structure[br]of this periodic table. 0:03:34.470,0:03:36.210 If you count the horizontal rows, 0:03:36.210,0:03:40.740 there are 1, 2, 3, 4, 5, 6, 7 0:03:40.740,0:03:42.840 horizontal rows, right? 0:03:42.840,0:03:43.797 These horizontal rows are 0:03:43.797,0:03:47.190 what we call the periods[br]of the periodic table. 0:03:47.190,0:03:50.520 And similarly, if you're to[br]look at the vertical columns, 0:03:50.520,0:03:53.310 you'll see 1, 2, 3, 4, 5. 0:03:53.310,0:03:54.330 Okay, let's just wait. 0:03:54.330,0:03:55.537 Should wait, 18. 0:03:57.660,0:04:00.990 There are 18 vertical columns, 0:04:00.990,0:04:04.785 and these are called the[br]groups of the periodic table. 0:04:04.785,0:04:07.620 So let's look at them a[br]little bit more closely. 0:04:07.620,0:04:09.750 So this basically means that[br]if I look at this element, 0:04:09.750,0:04:13.830 say chromium, it belongs[br]to period four groups six. 0:04:13.830,0:04:16.740 If you look at carbon,[br]it belongs to period two, 0:04:16.740,0:04:18.900 group 14, and so on and so forth. 0:04:18.900,0:04:20.400 What about these elements? 0:04:20.400,0:04:23.160 Well, if you look at the atomic[br]number carefully, it starts 0:04:23.160,0:04:25.800 with 57 and you can see[br]57 to 70s over here. 0:04:25.800,0:04:28.950 So these actually belong to period six, 0:04:28.950,0:04:31.800 and this belongs to period seven. 0:04:31.800,0:04:33.630 So it's not like a new period. 0:04:33.630,0:04:34.463 Okay? 0:04:34.463,0:04:37.620 But what's interesting for[br]us is the groups elements 0:04:37.620,0:04:39.600 that belong to the same group tend 0:04:39.600,0:04:42.900 to have similar properties. 0:04:42.900,0:04:45.000 And that's why some of[br]these groups have names. 0:04:45.000,0:04:46.260 For example, elements belonging 0:04:46.260,0:04:48.540 to group one are called alkaline metals. 0:04:48.540,0:04:50.310 Elements belonging to group two are called 0:04:50.310,0:04:52.560 Alkaline Earth Metals. 0:04:52.560,0:04:55.770 Group 17 elements like fluorine, chlorine, 0:04:55.770,0:04:57.810 and all they're called halogens. 0:04:57.810,0:05:02.010 And group 18 are called the noble gases. 0:05:02.010,0:05:03.810 For example, these elements in group one, 0:05:03.810,0:05:06.840 the alkaline metals, they're[br]all soft and squishy. 0:05:06.840,0:05:07.860 I mean, look at this. 0:05:07.860,0:05:08.940 This is sodium. 0:05:08.940,0:05:10.050 You can cut it like this. 0:05:10.050,0:05:11.640 It's kind of like clay. 0:05:11.640,0:05:13.170 They also have silvery color 0:05:13.170,0:05:14.790 and they have very low melting points. 0:05:14.790,0:05:16.890 And their behaviors are[br]similar in chemical reactions. 0:05:16.890,0:05:19.380 For example, if you were[br]to put them in water, 0:05:19.380,0:05:21.420 they all react violently. 0:05:21.420,0:05:22.253 Look at that. 0:05:23.671,0:05:24.630 Another example, 0:05:24.630,0:05:28.020 group 11 elements like[br]copper, silver, and gold. 0:05:28.020,0:05:30.360 They're all metals and[br]they're all very shiny 0:05:30.360,0:05:31.920 and super hard. 0:05:31.920,0:05:34.380 They are malleable, which[br]means they can be hammered into 0:05:34.380,0:05:36.120 shapes and ductile, 0:05:36.120,0:05:39.900 which means they can also[br]be pulled into wires. 0:05:39.900,0:05:42.600 And if you look at group[br]17 elements, the halogens 0:05:42.600,0:05:43.917 like fluorine, chlorine and so on, t 0:05:43.917,0:05:45.960 hey are quite chemically reactive. 0:05:45.960,0:05:47.949 So in the natural form,[br]they can be dangerous, 0:05:47.949,0:05:51.300 but they all form salts[br]as chemical reaction. 0:05:51.300,0:05:52.350 That's why they're called halogens. 0:05:52.350,0:05:54.540 Halogens literally means salt formers. 0:05:54.540,0:05:56.580 And you might know about[br]some of these salts, 0:05:56.580,0:05:58.260 sodium chloride for example, table salt, 0:05:58.260,0:05:59.400 which we all consume. 0:05:59.400,0:06:00.233 But guess what? 0:06:00.233,0:06:02.490 Sodium iodide is also a salt. 0:06:02.490,0:06:04.890 Sodium fluoride is also a salt,[br]which is used in toothpaste 0:06:04.890,0:06:06.780 because they can help prevent decays, 0:06:06.780,0:06:08.940 but halogens can also[br]kill germs and bacteria, 0:06:08.940,0:06:10.890 and therefore they're also found in a lot 0:06:10.890,0:06:13.530 of sanitizers like bleach,[br]swimming pool chlorine, 0:06:13.530,0:06:14.910 and other stuff. 0:06:14.910,0:06:16.980 And as a final example, if[br]you look at noble gases, 0:06:16.980,0:06:18.480 the group 18 elements, well, first of all, 0:06:18.480,0:06:19.530 they're all gases, 0:06:19.530,0:06:22.200 but more importantly, they[br]pretty much resist chemical 0:06:22.200,0:06:23.400 reactions altogether, 0:06:23.400,0:06:26.520 and they're found in tiny[br]amounts in our atmosphere. 0:06:26.520,0:06:28.110 And if you put these gases in glass tubes 0:06:28.110,0:06:31.020 and passive electricity[br]through them, they will glow. 0:06:31.020,0:06:32.220 Yes, neon lights. 0:06:32.220,0:06:34.230 Well, of course not[br]everything that glows is neon. 0:06:34.230,0:06:35.880 Different elements can[br]have different colors, 0:06:35.880,0:06:37.110 but that's pretty much it. 0:06:37.110,0:06:39.960 So to summarize, elements[br]have the atomic number, 0:06:39.960,0:06:41.610 which is the ID 0:06:41.610,0:06:43.500 and the atomic mass number that tells you 0:06:43.500,0:06:46.020 how massive it is compared to hydrogen. 0:06:46.020,0:06:48.990 They're arranged in seven horizontal rows, 0:06:48.990,0:06:49.980 which are called the periods, 0:06:49.980,0:06:52.350 and the vertical columns[br]you are called, the groups 0:06:52.350,0:06:53.490 and elements that belong 0:06:53.490,0:06:56.433 to the same groups have[br]similar properties.