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

Feb 22, 2020
In this video we're going to look at the

periodic

table

, we're going to classify the

elements

into groups, and as we review these terms, we're going to mark them so that the groups are the vertical columns of the

periodic

table

, etc. If I go here I can see that all 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 these elements are also in the same column on the right, so all these elements are in the same group and we also call this group.
the periodic table   classification of elements chemistry khan academy
I can continue labeling my groups, this would be group 3 4 5 6 7 8 9 10 11 12 and then I come back up here and I can see that I have another vertical. column, then the 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 1 and group two is group 2a and then ignore. Groups 3 to 12 continue their numbering systems to 1 to 2 a which would make this group 3 a group to a group 5 a group 6 to 7 a and finally ate a and the second way of numbering your groups is useful when we are thinking in valence electrons, so let's move on to the concept of periods, so a period is a horizontal row on the periodic table, so if I look at period one and just move across my periodic table, hydrogen is on 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 I can continue numbering my period, so this is period B, three, four, five and six.
the periodic table   classification of elements chemistry khan academy

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the periodic table classification of elements chemistry khan academy...

Now notice that I don't have a full period. periodic table in this video didn't have enough space and we're not really going to talk about all the elements anyway, so let's go ahead and focus on the metals next, so let's talk about the alkali metals and so when I'm talking about metals. I'm going to try to write in red here so that the alkali metals are in Group One or Group 1a, so things like lithium and sodium and potassium, here are my alkali metals. Alkali metals are soft silvery metals. which are extremely reactive and one good thing about arranging elements into groups, these elements in the same group have similar chemical properties and therefore alkali metals react similarly, for example all alkali metals will react with water and the alkali metals will turn out to be so reactive that you won't find them in their pure state in nature, you're not going to go out for a walk and find some sodium lying on the ground, that's fine, they are found in nature in combination with other elements, okay, let's talk about it. hydrogen because hydrogen is also in Group One, but hydrogen is not an alkali metal.
the periodic table   classification of elements chemistry khan academy
Hydrogen is not a metal. I'm going to go ahead and draw it in green here, so I'm going to represent the non-metals in green, so hydrogen is no exception in Next, in group one, let's talk about the alkaline earth metals so you can find those in group two or in group 2a, so right here, things like magnesium, calcium, and strontium are your alkaline earth metals. The earth metals in their line of application are reactive, not as reactive as the metals in group one, but you do not find them in their pure state, nor do you find them in combination with other elements, so, once again, alkaline earth metals They're going to react in a similar way, they have similar chemical properties and that's it again. a convenient way to organize the periodic table into groups, so for now let's go ahead and say that groups 3 through 12 are all metals here and let's talk about metals in general for a minute, so the properties of metals. metals, so metals are solids at room temperature, except for mercury, so here is mercury, which is a liquid at room temperature.
the periodic table   classification of elements chemistry khan academy
Metals are very valuable, meaning you can mold them into different shapes, they are very workable, they are not. Metals are not brittle, they are also ductile, which means you can make them into wires, you can make them into wires, for example, copper, so here's copper, so copper wires, of course, carry current in homes. , so metals are good conductors of heat and electricity and those are the properties of metals that most textbooks will talk about, so let's contrast them with nonmetals, so nonmetals, yeah you have a solid non-metal, those solids would tend to be brittle, non-malleable, like metals, non-metals.
They are poor conductors of heat and electricity, so non-metals are found in different states that matter, so let's talk now about one of the non-metals, which would be halogens, so let's look for halogens in our periodic table, you will find them in group 7. a or group 17 and things like fluorine, chlorine, bromine, so here are the halogens, so halogens are very reactive non-metals, so they are often very colorful, very, very corrosive and the name halogen actually means salt former, so we're actually We'll come back to that in the next video, when we look at some electron configurations and talk about why these things are so reactive and those are the halogens.
Next, let's look at the noble gases to find the noble gases. in group 8a or group 18, some of these are very famous like helium, neon, argon, krypton. Well, here are the noble gases, they are colorless gases and generally they are not very reactive, so once again we will talk about why in the next video when we talk about some electronic configurations, well, there are other non-metals here that I will identify in a minute first. First I want to talk about the fact that you practically find metals on the left side of the periodic table, on the right. so let me go back to the red color and you can see on the right, I have all of these metals here on the left side and then for my non-metals in green, you'll find them here on the right side of your newspaper. table and then the dividing line between them let me go ahead and draw it there, it's kind of zig zag lines, let me see if I can draw it here so that the dividing line is something like this, so Let's go through a zig zag line a along our periodic table and some of the elements that are on this zigzag line have properties between those of metals and non-metals and we call them metalloids, so let's go ahead and talk about metalloids now, so metalloids, TRUE?
Of course, it's like a metal, so it's similar to metals, but again the properties are between those of a metal and a non-metal, so some of the elements that are considered metalloids would be boron here, so than silicon germanium arsenic antimony tellurium and sometimes you will see a satin listed as such, so it depends on which textbook you are looking at so you can see that some of the elements along this zigzag line are considered metalloids and there is no official definition for what elements are considered metalloids and so you might see a little bit of discrepancy there for some of these elements, but generally those are the ones that are considered to be metalloids and silicon are probably the most famous, right, so silicon is a semiconductor, okay, it's a metalloid, it's like a metal, so it conducts electricity, but not to the same extent as a metal, wood, so these intermediate properties sometimes they're useful, so let's go ahead and mark some of the rest of these on the right so these are other metals and then here on the right would be the rest of your non-metals here, so carbon is a non-nitrogen. metal.
Nonmetallic oxygen is not metallic phosphorus, sulfur, so it's just a quick way to break down the periodic table with some simple definitions. In the next video we'll talk more about the electronic structure and get into the transition of definitions. rails

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