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The periodic table - classification of elements

Definitions of groups, periods, alkali metals, alkaline earth metals, halogens, and noble gases. How metals, non-metals, and metalloids can be identified by the position on the periodic table. Created by Jay.

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Video transcript

In this video, we're going to look at the periodic table. We're going to classify the elements into groups. And so as we go through these terms, I'm going to be checking them off. The groups are the vertical columns on the periodic table. And so, if I go over here, I can see that all of these elements are in the same vertical column. So all these elements are in the same group. And we call this group 1. I can see that all of these elements are also in the same column. So all these elements are in the same group, and we call this group 2. I can continue labeling my groups. This would be group 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. And then I go back up to here, and I can see I have another vertical column, so group 13, 14, 15, 16, 17, and finally 18. So that's one way to number your groups. There is another way to number your groups, and that would be to say that group 1 is group 1A, group 2 is group 2A. And then kind of ignoring groups 3 through 12, continue on with your numbering system. So 1A, 2A-- that would make this group 3A, group 4A, group five 5A, group 6A, 7A, and finally 8A. And this second way of numbering your groups is useful when you're thinking about valence electrons. And so let's move on to the concept of periods. A period is a horizontal row on the periodic table. And so, if I look at period 1, and I just move across my periodic table, hydrogen is in the first period and so is helium. I move on to the second period, so lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. And so I can continue with numbering my periods, so this would be period 3, 4, 5, and 6. Now notice I don't have the entire periodic table on this video. I didn't have enough room, and we're not really going to talk about all of those elements anyway. So let's go ahead and focus on metals next. Let's talk about the alkali metals. When I'm talking about metals, I'm going to try to write it in red here. The alkali metals are found in group 1, or group 1A, so things like lithium, and sodium, potassium. So here are my alkali metals. The alkali metals are soft, silvery metals that are extremely reactive. And one nice thing about organizing elements into groups is elements in the same group have similar chemical properties. And so the alkali metals react in similar ways. For example, all the alkali metals will react with water. And the alkali metals turn out to be so reactive that you're not going to find them in their pure state in nature. You're not going to walk outside and find some sodium lying on the ground. They're found in nature in combination 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 nonmetal. So let me go ahead and draw that in green here. I will represent nonmetals in green. Hydrogen is the exception in group 1. Next, let's talk about the alkaline earth metals. You find those in group 2, or group 2A, so right in here. Things like magnesium and calcium and strontium are your alkaline earth metals. Your alkaline earth metals are reactive-- not quite as reactive as the metals in group 1, but you don't find these in the pure state, either. You find them in combination with other elements. And so once again, the alkaline earth metals are going to react in similar ways. They have similar chemical properties, and so that's, again, a convenient way of organizing the periodic table into groups. For right now, let's just go ahead and say-- groups 3 through 12-- these are all metals in here. And let's just talk about metals in general for a minute. Metals, the properties of metals. Metals are solids at room temperature, except for mercury. So here is mercury down here, which is a liquid at room temperature. Metals are very malleable, which means you can form them into different shapes. They're very workable. They're not brittle. Metals are also ductile, which means you can draw them into wires. You can form them into wires. For example, like copper. Here's copper right here. Copper wires, of course, carry current in homes. So metals are good conductors of heat and electricity. And so those are the properties of metals that most textbooks will talk about. Let's contrast those with nonmetals. Nonmetals-- if you have a solid nonmetal, those solids would tend to be brittle, not malleable like metals. Nonmetals are poor conductors of heat and electricity. So you find nonmetals in different states of matter. Let's talk about one of the nonmetals now, and that would be the halogens. Let's find the halogens on our periodic table. You find them in group 7A, or group 17, things like fluorine, chlorine, bromine. Here are your halogens right in here. Halogens are very reactive nonmetals. So they're often very colorful, very, very corrosive, and the name halogen actually means salt former. We're actually going to come back to that in the next video when we look at some electron configurations and we talk about why these things are so reactive. And so those are the halogens. Next, let's find the noble gases. The noble gases are found in group 8A, or group 18. Some of these are very famous, like helium, neon, argon, krypton. Here are your noble gases. They're colorless gases, and they're generally very unreactive. Once again, we'll talk about why in the next video when we talk about some electron configurations. There are some other nonmetals on here, which I will identify in a minute. But first I want to talk about the fact that you pretty much find metals on the left side of the periodic table. So let me go back to the red color. And you can see I have all these metals over here on the left side. And then for my nonmetals, in green, you're going to find those over here on the right side of your periodic table. The dividing line between those-- let me go ahead and draw it in there-- it's kind of a zigzag line. Let me see if I can sketch it in here. The dividing line would go something like this. We're going to go a zigzag line down our periodic table. And some of the elements that you find on this zigzag line have properties in between those of metals and nonmetals, and we call those metalloids. Let's go ahead and talk about metalloids now. Metalloids-- oid, of course, being like a metal, so it's similar to metals, but, again, the properties are in between those of a metal and a nonmetal. Some of the elements that are considered to be metalloids would be boron-- right in here-- silicon, germanium, arsenic, antimony, tellurium, and sometimes you'll see astatine listed as one. It depends on which textbook that you're looking in. So you can see that some of the elements along this zigzag line are considered to be metalloids. And there's no official, one definition for which elements are considered to be metalloids, and so you might see a little bit of a discrepancy there for some of these elements. But in general, those are the ones that are considered to be metalloids, silicon probably being the most famous one. Silicon is a semiconductor. It's a metalloid, so it's like a metal, so it does conduct electricity, but not to the same extent that a metal would. And so these intermediate properties are sometimes useful. Let's go ahead and mark some of the rest of these. These would be some other metals. And then over here on the right would be the rest of your nonmetals here. Carbon is nonmetal, nitrogen is nonmetal, oxygen is nonmetal, phosphorus, sulfur. So that's just a quick way to divide the periodic table up with some simple definitions. In the next video, we'll talk more about the electronic structure, and we'll get into definition of transition metals.