The periodic table - classification of elements | Chemistry | Khan Academy

In this video we will see the

periodic

table

. We will divide the

elements

into groups. And I'll revisit those terms as I go through them. Groups are vertical columns on the

periodic

table

. So if I go over here, I can see that all of these

elements

are in the same vertical column. That is, all these elements are in the same group. And we call it group 1. I can see that these elements are all in the same column. That is, all these elements are in the same group and we call it group 2. I can continue categorizing my groups.

This group will be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. And then I come back here and I can see that there is another vertical column, so the group 13, 14, 15, 16, 17 and finally 18. That's one way to number your groups. There is another way to number your groups and that is to say that group 1 is group 1A and group 2 is group 2 A. And then continue with your numbering system, going from groups 3 to 12. That is, 1A , 2A: this is group 3A, group 4A, the fifth group 5A, group 6A, group 7A and finally 8A. This second way of numbering your groups is useful when you think about valence electrons.

Now let's move on to the concept of periods. A period is a horizontal row on the periodic table. So if I look at period 1 and scroll down my periodic table, I'll see that hydrogen and helium are in period one. I move on to the second period, that is, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon. So I can continue numbering my cycles, which would be cycles 3, 4, 5, and 6. Now notice that the periodic table in this video is not complete. I don't have enough space and we won't talk about all these items anyway. So let's go ahead and focus on the following metals.

Let's talk about alkali metals. When I talk about metals, I'll try to write it here in red. Alkali metals are in group 1 or group 1A, so things like lithium and sodium, potassium. Here I have alkali metals. Alkali metals are soft, silvery, extremely reactive metals. An advantage of dividing elements into groups is that elements in the same group have similar chemical properties. Therefore, alkali metals react in a similar way. For example, all alkali metals will react with water. And alkali metals are so reactive that you won't find them in their pure form in nature. When you go out, you won't find any sodium in the soil.

They are found in nature along with other elements. Let's talk about hydrogen, because hydrogen is also in group 1, but hydrogen is not an alkali metal. Hydrogen is a non-metal. Let me draw it in green here. I will represent the non-metals in green. Hydrogen is an exception in group 1. Next, let's talk about alkaline earth metals. Those in group 2 or group 2A can be found here. Things like magnesium, calcium, and strontium are your alkaline earth metals. Their alkaline earth metals are reactive, not as reactive as group 1 metals, but you won't find them in their pure state either. You can find them along with other items.

And again, alkaline earth metals will react similarly. They have similar chemical properties and therefore this is a convenient way to divide the periodic table into groups. For now, let's go ahead and say: groups 3 to 12, these are all the metals here. And in general, let's talk about metals for a minute. Metals, properties of metals. Metals are solid at room temperature, except mercury. That is, there is only mercury, which is liquid at room temperature. Metals are very malleable, which means you can make different shapes with them. They are very affordable. They are not fragile. Metals are also malleable, meaning you can bend them to form wires.

You can turn them into cables. For example, like copper. Here is the copper. Copper wires, of course, carry current in homes. Therefore, metals are good conductors of heat and electricity. These are the properties of metals that are discussed in most textbooks. Let's compare it to a non-metal. Nonmetals: Although nonmetals are solids, these solids are brittle and not as malleable as metals. Nonmetals are poor conductors of heat and electricity. Therefore, nonmetals are found in various states of matter. Now let's talk about one of the non-metals and these are halogens. Let's look up the halogens in our periodic table.

You find them in group 7A or group 17, such as fluorine, chlorine, bromine. Here are your halogens. Halogens are reactive nonmetals. Therefore, they are usually colored, often corroded and the name halogen actually means formed from salt. In fact, we'll come back here and talk about why they're so reactive when we look at some of their electronic configurations in the next video. So these are halogens. Next, let's look for the noble gases. The noble gases are found in group 8A or group 18. Some of them are very famous, such as helium, neon, argon and krypton. Here are your noble gases.

They are colorless and generally non-reactive gases. Again, we'll explain why in the next video when we talk about some electronic configurations. There are some other non-metals here, which I'll define in a minute. But first I want to talk about the metals on the left side of the periodic table. So let's go back to red. You see all these metals here on the left. You will then find them on the right side of your periodic table with the color green for non-metals. The line that separates them – let me draw it there – is a zigzag line. Let's see if I can draw here.

The dividing line would look like this. We will draw a zigzag line on our periodic table. And some of the elements that you find on this zigzag line have properties between metals and nonmetals, and we call them metalloids. Now let's talk about metalloids. Metalloids: Of course, they are like metals, so they look like metals, but again, their properties are between those of metals and non-metals. Some elements that are considered metalloids include tube, here, silicon, germanium, arsenic, stibium, tellurium, and sometimes astatine. It depends on the textbook you are looking for. So you can see that some elements along this zigzag line are considered metalloids.

There is no official, uniform definition of which elements are considered metalloids, so you may see inconsistencies for some of these elements. However, they are generally considered metalloids, with silicon probably being the most popular. Silicon is a semiconductor. It's a metalloid, so it's like a metal, so it conducts electricity, but not to the extent that a metal can. Therefore, these intermediate properties are sometimes useful. Let's mention some of them. These will be some other metals. And then your nonmetals on the right will be here. Carbon is a non-metal, nitrogen is a non-metal, oxygen is a non-metal, phosphorus and sulfur.

Here's a quick way to break down the periodic table with some simple definitions. In the next video, we will talk more about the electronic structure and explain the definition of transition metals.