Full transcript
0:00[Music]
0:16In the first video, we saw that all the
0:18things in the world are made of
0:20incredibly tiny particles called
0:23atoms and also that there are 92
0:26different kinds of them.
0:28Most things have more than one kind of
0:30atom in them. But this nugget of pure
0:33gold contains only gold
0:40atoms. So we call it an element. An
0:44element is a substance made of only one
0:47kind of atom.
0:55Zooming back out, we see that the gold
0:58atoms become a lump of gold
1:04again. If we zoomed out from silver
1:07atoms, we'd see a lump of silver
1:15instead. Because there are 92 kinds of
1:18atoms, there must be 92 elements, too.
1:22one for each kind.
1:24You probably have already heard of some
1:26of them like carbon, iron, and aluminium
1:30or aluminum if you're
1:33American, but maybe not aine or
1:37uturbium. With so many elements, there's
1:40a lot of names to remember.
1:44[Music]
1:58Fortunately, there's a list showing all
2:00the
2:01elements. It starts with the element
2:03with the lightest atoms, hydrogen, and
2:06goes to the element with the heaviest
2:08atoms,
2:10uranium. This list is called the
2:12periodic table.
2:16How about grabbing your own copy now and
2:18check it as you watch the
2:20video. The lightest element hydrogen is
2:24at the top left hand side of the table.
2:27Each element can be written with a
2:29shorthand using one or two letters
2:31called its symbol which is capital H for
2:34hydrogen. Not
2:36surprisingly, each element also has its
2:39own number showing its place in this
2:42list called its atomic
2:44number. Hydrogen is the lightest
2:47element, so its atomic number is
2:521. Zooming into helium at the top right,
2:55we can see that its symbol is H E, big
2:59H, little E to make it a bit different
3:01to
3:02hydrogens's. and its atomic number is
3:05two being the second lightest
3:08element. The third lightest element is
3:11lithium. So it has an atomic number of
3:15three. Where's
3:18lithium? It starts the next
3:22row. This row goes up to atomic number
3:2510 before another row is
3:29started. How many rows are there?
3:341 2 3 4 5 6 7. The periodic table has
3:42seven horizontal
3:45rows. What about these rows down below
3:48called the lanthnides and
3:52actonides? Well, they really belong to
3:55rows six and seven and should slot into
3:58these spaces.
4:00The lanthnides are elements 57 to 71 and
4:04the actonides are elements 89 to
4:09103. To slot them in, we have to make
4:12the periodic table
4:16wider. This full table is more accurate
4:19and some versions are printed this way.
4:26This layout also makes it easier to see
4:28how many elements are in each
4:31row. Two in the first row, eight in the
4:34second, eight in the third, 18 in the
4:38fourth, 18 also in the fifth, 32 in the
4:42sixth, 32 in the
4:457th. Altogether there are 118 elements.
4:58HC.
5:00How come? Aren't there meant to be only
5:0292 elements with uranium being the last
5:07one? Yes, but clever scientists have
5:11made artificial elements in the lab like
5:14neptunium and plutonium, the elements
5:18next door that were made in 1940.
5:22These new elements make the overall list
5:24of elements a bit
5:26longer. Let's collapse the periodic
5:29table back to its usual shape, which is
5:32more convenient for fitting onto the
5:34[Music]
5:40screen. You can see that the periodic
5:42table is also arranged in vertical
5:45columns which scientists call groups.
5:49How many groups are
5:51there? 1 2 3 4 5 6 7 8 9 10
5:5918 vertical
6:01groups. The key point about groups is
6:04that they contain elements that are
6:06similar to each other, like members of a
6:09family. For example, all of group one
6:12elements except hydrogen are soft,
6:15malleable metals that explode when you
6:17put them into water.
6:20Some groups even have family names.
6:23Group one elements are called the
6:25alkaline metals. Group two elements are
6:28the alkaline earth metals. Group 17 are
6:32the halogens. And group 18 are the noble
6:34gases.
6:37[Music]
6:46Now you're ready to read the periodic
6:50table. What is the name of the element
6:53with atomic number
6:5530? You just have to scan around and
6:58find
6:5930.
7:02Zinc. What is the atomic number of
7:05calcium? Now you've got to find calcium
7:07on the table.
7:1020. Which row is sulfur
7:14in? The third
7:16row. Choose any element in the fifth
7:20row. There are a lot of possible answers
7:22for this. Could be
7:25strontium, tin, iodine. You
7:30choose. Which group is chlorine in?
7:37Group
7:3817, choose an element in group
7:4515. Could be nitrogen or arsenic or any
7:48of the others. Your
7:51choice. But what if you were asked which
7:53element is in row five and group
7:57two. There can only be one answer,
8:01strontium. Each element has its own
8:03unique combination of row and group.
8:11Can you see the gray diagonal band that
8:14splits the periodic table into two
8:18parts? This divides the elements into
8:20metals on the left and non-metals on the
8:26right. What is a metal? Here's a few.
8:30titanium, iron, chromium, aluminium,
8:34silver, and gold with the atomic numbers
8:38above the
8:39symbols. Have you noticed that these
8:41metals are shiny and
8:43solid? They all are. Well, except for
8:47liquid mercury.
8:50Metals also conduct electricity and
8:54heat. Here, the different metals are
8:57connected to an electrical circuit. If
9:00the bulb lights up, it means that the
9:02thing is an electrical
9:04conductor. They all
9:07are. Metals are also malleable, which
9:11means that if you belt them with a
9:13hammer, they'll flatten into a thinner
9:17shape. Here you can see that aluminum
9:20has three metallic properties. It's
9:22already been flattened into a thin
9:24sheet. It's shiny. And it conducts
9:27electricity.
9:30We looked at aluminium, titanium,
9:32chromium, iron, silver, and gold, all to
9:35the left of the diagonal, and saw that
9:38they all have metallic
9:40properties. What about non-metals to the
9:43right hand side of the
9:45diagonal? They're the opposite. Most
9:48non-metal elements are liquids or gases,
9:50but there are a few solids, and these
9:53can be more easily tested. Here, sulfur
9:56and selenium are showing that they don't
9:59conduct
10:00electricity. Can you see that the bulb
10:02doesn't light
10:05up? And if you hit this carbon with a
10:08hammer, it smashes into bits. This is
10:11called being brittle. It's the opposite
10:14of being malleable.
10:18Let's use the periodic table to predict
10:21whether an element would be a metal or a
10:23non-metal.
10:25How about osmium? Atomic number
10:2976. Osmium is to the left of the
10:32diagonal gray band, so it should be a
10:36metal. How about
10:40iodine? That's to the right of the
10:43diagonal line. So, it's a
10:46non-metal. Let's try something trickier.
10:50Do you reckon yrium atomic number 39
10:54would be
10:55shiny? It's to the left of the diagonal
10:58line, so it's a
11:00metal. So, it's probably
11:03shiny. Would phosphorus, atomic number
11:0715, conduct
11:09electricity? H, it's to the right of the
11:13diagonal, so it's a
11:15non-metal. Probably not.
11:18What about the elements inside the
11:20diagonal
11:22band? Let's take a look at
11:24silicon. It looks shiny like a metal,
11:27but if you whack it with a hammer, it
11:29breaks into bits. So, it's brittle like
11:32a
11:34non-metal. And the dull glow of the bulb
11:36tells us that it conducts electricity
11:39more than a non-metal, but not as much
11:41as a
11:42metal. And this gives it the name of
11:45semiconductor.
11:49These elements are also called
11:51semimetals because they have properties
11:53that are in between metals and
11:57non-metals. Are they more metal or
11:59non-metal
12:01elements? Metals. Nearly 3/4 of the
12:05elements on the periodic table are
12:08metals. But that doesn't mean they're
12:10more abundant. Because in the Earth's
12:13crust, there are more oxygen and silicon
12:16atoms than the rest
12:19combined. And the universe as a whole is
12:23mostly
12:25[Music]
12:31hydrogen. In fact, hydrogen is special
12:34in lots of ways. It's to the left of the
12:37diagonal, but it's not a metal. Well, it
12:40can't be. It's a
12:42gas. It looks like it's in group one as
12:45a member of the alkalion metals, but it
12:48can't be because it's not a metal. The
12:51truth is hydrogen doesn't belong to any
12:54group and it's considered to be a group
12:57all by
12:59itself. Some periodic tables even put it
13:02on its own to show this. Just remember,
13:06hydrogen is special.
13:10The periodic table squeezes a lot of
13:12information into a small space. The
13:15English writer CP Snow said that the
13:17periodic table took all the jumbled
13:20facts about the elements and fitted them
13:22into a pattern and it was like turning a
13:25jungle into a garden.
13:28My view is that the periodic table is
13:31the alphabet of the universe.
13:34Whereas our ordinary alphabet is a list
13:36of letters that can make all the words
13:38in our language, the periodic table is a
13:42list of elements that can make all the
13:44substances in the universe.
13:46[Music]