Periodic Chemistry- Part1(Group,Period,Block)

Hinzugefügt: 2026-05-27

[00:00:05]Hello, you are welcome to my channel once again. This is chemistry with CJ. I teach chemistry for Ole student, Alevel student, GCSE student and also was a student. Now in our previous studies looked at the structure of the atom, how the atom came into being and also the various scientists who contributed in the discovery of the atom. Today our focus will be on what we called periodic chemistry.

[00:00:52]Now in simple things we want to look at the physical and chemical properties of these element. Now I always pose this question to my student that have we ever seen gold? Gold is ducked from the ground but gold appears shiny but you would have an iron a nail which is shiny and when you put it inside the ground that nail decide to rust. So now here's the question why is something which is found in the ground appears to be shiny and why it's something which is shiny that you put it inside the ground appears to rust.

[00:01:34]This brings us to the idea that the tiny tiny things in the gold. So when we take a gold the tiny tiny things here which we call the atoms here and when we take an iron the tiny tiny things which is inside an ion here. So this is an iron and these a gold.

[00:01:57]These tiny tiny things they are different and they behave what differently.

[00:02:03]So when we talk about periodic chemistry, we are now coming to study the physical and chemical properties of the various elements and as we get to know these physical and chemical properties they change as the electron configuration of the atom changes. So as the atomic number is changing these chemical and physical properties of this individual element also what change. So what or what we mean in periodic chemistry is we are now coming to study the physical and chemical properties of element which varies with what different electron configuration So what we are saying here is that the chemical properties the physical properties of these element they change and what makes it change this because their electron configuration is changing. So please as we continue revisit my video on electron configuration to get more understanding.

[00:04:03]So as element or all most of the element are having different electron configuration. Why? Because their atomic numbers are what different. And when that happens they are physical. How you are going to see them? their chemical how they are going to behave will change and that is what we are going to look at under periodic chemistry now before we start this topic there are certain fundamental terminologies there are certain fundamental word that I'll be using that you need to understand so we want to look at some terminologies that we will use here so let's look at these terminologies Now, in our junior high school or in our JSS, we learned that this is how the atom is.

[00:05:11]Okay. And we learned that these things these bullet these circles represent what the electrons. Now as you are in your senior high you want to look at the two main various types of electrons that we have. Now remember we call these shells but at this point this last shell the last shell we call that what? The valance shell.

[00:05:42]So whenever I say valent shell it means that I'm talking about what the last shell in every atom. Now this valent shell is also called what? Outermost shell.

[00:06:00]So take note when I say the word valent shell or outer shell it means I'm talking about what a large shell. Take note. So if I have a shell like this here, what is the last shell here? This is your last shell. And in this case, I'm going to call this last shell what?

[00:06:22]The valence shell. Take note. Or the outermost shell. Now if you locate the valence shell in every valence shell, there are electrons on them. And these electrons, we call them what? Valence electron. So you see these electrons these electrons on this last shell is called what? Valence electron or valence electrons. So this atom that you see is having how many valence electrons? Three valence electrons. So I want you to know what you talk about valence electrons. So when we say valence electrons we are talking about the electrons that are found in the outermost shell take note I say when I say outermost shell I'm talking about what the last shell now so the electrons in this last shell are called val shell again you see these shells we have two shells here so two shells here are what these two shells you know in JSS that the first shell is called the K shell the second shell is called the L shell the third shell is called M shell but I'm now breaking it down that we have two main types this last shell is called what a valance or outermost shell the two shells which are not the outermost shell we call them what the inner shell shells.

[00:08:05]Inner or core shells. Take note. So we have inner or what? Core shells. So when we are talking about inner shells, we are talking about the shells which are not the outermost shell. So when you look at the inner shells, they are electrons on the inner shells. And we call these electrons inner electrons or core electrons.

[00:08:37]So today what I want you to understand is that you are seeing what two main types of electrons here. We have the valence electron. So when we say the valence electron we are talking about what the outermost electron when we say about the core electrons we are talking about what the electrons between the nucleus and the outermost electron take note. So I'll be using this word valence electron and what core electrons very well. So always understand that when I say what valence electrons it means I'm talking about the outermost electrons.

[00:09:18]When I say core electrons I'm talking about the electrons between the nucleus and the what outer most electron. Okay.

[00:10:36]So when we talk about the valence what electrons we are talking about the electrons that are found in what the outermost shell. Now there is something special about these electrons. These electrons are responsible for the chemical properties the chemical reactivities of the element. So how the element will react, how the element will behave, it depends on the valence electrons. So what we are saying is that if an electron wants to form a compound the valence electrons are the electrons that it will lose. The valence electrons are the electrons that it will share.

[00:11:18]The valence electrons are the electrons that it will gain in order to form what a compound and these valence electrons are what are very very what important.

[00:11:30]So the reactivity the chemical properties which we are going to learn depends mostly on what the valence electron. So some element who are having the same valence electron will have the same chemical or similar chemical properties. So always understand the word valence electron and you must know what type of electron I'm talking about.

[00:13:27]So now I made mention of what the core electrons. What do we say? These core electrons are also at important in helping us identifying patterns.

[00:13:41]Remember I told you that some elements behave the same. some element shows similar patterns and with the help of the core electrons we are able to identify them. So when we talk about core electrons we are talking about what the electrons between what between the what the nucleus and the valence shell.

[00:14:07]So those electrons found between the nucleus and the valence shell we call them what? We call them the core electrons. Okay.

[00:14:34]So all that I want you to now understand is we have the valence electron and the core electrons. So let's assume.

[00:14:47]Okay. So now how many valence electrons are here? You come to the outermost shell here. So this is a valence electron.

[00:14:57]The valence electrons here is one.

[00:15:06]And how many core electrons are here?

[00:15:08]The core electrons here are two.

[00:15:20]So we have one valence electron and what and two valence or two core electrons.

[00:15:28]So this is what you have to understand.

[00:15:31]Now we are building up. Now when you came to SHs you've learned about what we call the orital notation. How to write electron configuration using what? Using the orital or there's four set of quantum numbers. So as you can see this element here is lithium.

[00:15:56]Now remember that in lithium lithium is written as what? 1 s2 2 s1 Now how are you able to identify the valence electron and the core electron when you are using the orital notation. So for you to identify remember that I told you that if you have this let's say 2 px2 remember we've learned that these two here represent what the principal quantum number or the main shell or these two here is principal quantum number what two make a reference to my teachings on quantum numbers like I told you chemistry is a foundation that you are building you have to have an idea of all these topics before you we can proceed. So now this P that you are seeing here is what is the subshell or L= 1 or the angular quantum number one. This X that you are seeing is the orientation of the orital.

[00:17:07]And this two here is what we called the valence electron or the electrons. Let me put that.

[00:17:20]So with this idea which we've learned under what? Under the quantum numbers we are bringing this idea here. How are we able to identify the valence electron?

[00:17:34]So for you to be able to identify the valence electron you're coming here always what locate the highest principal quantum number.

[00:17:59]So with this here you can see that we are having what quantum number one and we have what quantum number two n is equal to one here n is equal to two here. So one and two which one is the highest.

[00:18:16]We all know that two is the highest. So after locating the highest principal quantum number you also locate what the orital which in this case we call it the subshells. So when you come here after okay now if I want to know the what the valence electron I will locate the highest. So here the highest principal quantum number here is two. After that I'll come to the subshells there. Here okay these two has the s orital or the s subshell. Now after locating the s subshell then I what I would add the number of electrons on the subshells. So now here how many electrons are here? One. This tells you that this element has one valence electron. Okay, let's also take it again.

[00:19:32]So what we are trying to say is if you have 1 s2 2 s2 2 p5 how many valence electron are here? So what is the rule saying for you to know the number of valence electron what will you first do? You will first locate or identify.

[00:20:09]So here we locate the highest principal quantum number. So we are having one and we are having what? Two. So the highest here we have two. So the two there are two. After you identify the highest principal content, then you locate or you also identify here we are going to identify the number of what subshells. So we know that this two here is having how many subshells?

[00:20:50]It has the S subshell and what the P subshell.

[00:20:56]So now how will you know the valence electron? You would add the number of electrons.

[00:21:14]So we add the number of electrons here.

[00:21:16]So this one has how many electrons? Two.

[00:21:19]Plus this one has how many electrons?

[00:21:21]Five. This will give us what? Seven.

[00:21:25]So this element is having how many valence electron. So here it has seven valence electron. So now this which is not in the highest principal quantum number in this case this is a core electron. So the core electrons here are what? Two.

[00:21:45]So what we are trying to say is that under periodic chemistry you must understand these fundamental terms and how to locate them. So when we talk about valent shell you should understand what these valential are and when we talk about core electrons you should understand what these electrons are and how to identify them. So we've looked at valence electron and we also looked at what core electrons. So let's continue.

[00:22:33]Now under periodic chemistry I will be using these what these words a lot. I've told you that there are certain terminologies that you have to understand in order to appreciate the topic and we are moving to the term period. Now in chemistry when we say period a period is not a full stop as in English but period means something which I want you to look at. Now in GHS we learned this is the structure of what?

[00:23:04]Hydrogen.

[00:24:20]Okay. So let's look at the similarities here. Now let's look at hydrogen and helium. What are they having in common?

[00:24:31]Now you with a clear understanding here you can see that hydrogen and helium they are having just one shell.

[00:24:41]So they have just one shell which we call the K shell.

[00:24:45]Now let's look at from lithium to neon.

[00:24:49]Lithium to neon what are they having in common? Yes, as you can see the number of core electrons are the same but that is not our focus. From lithium to neon how many shells are they having? They have what we called what? Two shells or two main shells. So what we mean in the period here is what period is not one thing. No take note period here is a set of elements that are having what the same what number of shells.

[00:25:26]So we call hydrogen and helium period one.

[00:25:32]So when I say period one element, it means I'm talking about what? Hydrogen and what? Helium. When I say period two elements, it means period 2 mean I'm talking about what? Lithium going up to what? Neon. So when I say period 2, it means I'm talking about lithium. I'm talking about burillium.

[00:25:56]I'm talking about boron. I'm talking about carbon. So all from lithium to neon we call them what? Period 2 elements.

[00:26:08]Now remember I've told you that shells which you learn in ghs when you come to electric or you come to chemistry we call these main shells what principle quantum number take note.

[00:26:26]So when we say a period, period are set of elements with the same number of what? Shells or set of element with the same principle quantum number. Take note.

[00:28:02]So what we are saying here is that when we say period what must come into your mind is period here we are talking about what set of element that are having what the same principle quantum number and here we We are talking about what? For period, we have period one.

[00:28:24]So when I say period one, I'm talking about what? Hydrogen and what? Helium.

[00:28:34]When I say period 2, period two, I'm talking about what?

[00:28:45]Lithium going up to what? Neon. So lithium, borillium, boron, carbon, nitrogen, oxygen, neon those are period two element. Now period three, when we talk about period 3, we are talking about what we're talking about sodium going up to what?

[00:29:10]Argon.

[00:29:12]So what you are saying? So this period 3 sodium, magnesium, aluminium, silicon these are all period 3 element. Now we have period 4.

[00:29:27]So period 4 will start from what?

[00:29:29]Potassium to kryine.

[00:29:33]Why? Because they are having what? Four main shells or their principal quantum number being what? Four. or the highest principal country number being for. So this is how we talk about the period. So whenever we are talking about period we're talking about what set of element that are having what the same what mean shells or the same principle quantum number. Now let's come back to the orbital notation. How to identify a period So how do we identify a period in the orital notation? Now let's assume that you've been given 1 s2 2 s2 2 p6 3 s1 and you ask what is the period of this element for you to know the period of this element is simple look at or locate for or identify the principal quantum number which is the highest remember I've told you here we have one we have two and we have three. So this is the three here.

[00:31:42]So this three here is the highest there.

[00:31:46]So here this element here is in period three.

[00:31:53]So the highest principal quantum number always tells you about what the period.

[00:32:00]Let's also look at this.

[00:32:18]Okay. So now let's also identify the period in this example. So always the highest principle. So here is 1 2 3 and four. So the highest year is four.

[00:32:38]So this element is in period 4.

[00:32:43]So for you to identify the period always locate always look for the highest principal quantum number in the orital notation.

[00:32:57]Okay. And this is for period. Okay.

[00:33:08]There we go.

[00:33:30]Okay, we also looking at to the fourth terminology which we call what group. So remember I'll be talking about I'll be using the word valence electron. I'll be using the word core electrons. I'll be using the word period. I'll also be using the word what group. So now how should we understand a group? So let's quickly look at this illustration.

[00:34:20]Okay. So, what is the similarity between what? Lithium and sodium. Now looking at lithium and sodium here you can only see or you can see some things but our focus here is the similarity what is here and what is here. So when you look at lithium look at the electron here it is one and look at the electron also here it is one. Remember I told you that this last electron we call it what?

[00:34:51]Valence electron.

[00:34:53]So lithium and sodium are having what?

[00:34:56]One valence electron. Again let's look at burillium and magnesium.

[00:35:22]So looking at berillium and magnesium you can see their valence electrons are the same and that is what that is two here and that is what two here. So berillium and magnesium they having what two valence electron. So in chemistry any set of elements which is having the same number of valence electron we call them what group.

[00:35:51]So when we talk about group we are talking about what set of element with the same what number of what val electron set of elements with the same number of valence or what outermost electron. So now as you can see sodium and lithium how many valence electron are they having? They're having one valence electron. So we will call this group one. with a group we'll be using Roman numerals for the numbers. So this will be called what? Group two.

[00:37:16]What you are saying? So berillium and magnesium will be called group two. So quickly help me with the group name for this.

[00:37:46]Okay. So now how many valence electron has florine and chlorine? So florine has two here, two here, two here, one here.

[00:37:59]Florine is having seven valence electron. Now let's look at chlorine.

[00:38:05]two here, two here, two here and one here. Chlorine is also having what?

[00:38:12]Seven valence electron. So the name for this group we are going to call what?

[00:38:16]The group seven. So whenever we say group we are talking about set of element with the same what valence electrons.

[00:38:39]So we have group one.

[00:38:44]So when we say group one we are talking about lithium, sodium, potassium, cesium and francium. We have group two.

[00:38:57]So group two we have what?

[00:39:01]Perilium, magnesium, calcium, strutium, berium and random. We have group three.

[00:39:13]Group three that will be what? Boron, aluminium. So what do we say? Then we go to what? Gallium tellium as you go down.

[00:39:25]So when we say group we are talking about what set of element with what with the same valence or outermost electron.

[00:39:37]So now we would once look at how do we identify the group using the orital notation.

[00:40:24]So anytime you you have been given to identify the group the first step is what always locate the highest principal quantum Back two.

[00:40:56]What will you do?

[00:40:58]You would what? You would also identify After you identify the highest principal quantum number, what will you do? You also identify the subshells of this highest principal quantum number. Then three, you add the electrons of the subshells. That is how we identify the group is the same as identifying the valence electron. So now let's look at this 1 s2 2 s1 So how what is the group for this? I'm saying first identify the highest principal number here is what? Two. Then you come to the subshells here. This two has only one or only s subshells. Then now you look at the electrons here. The electrons here is one. So this element here is a group one element.

[00:42:23]Again let's look at another example. If you are saying you have the 1 s2 2 s2 2 p5 so what will you do? Always identify the highest principal quantum number.

[00:42:37]The principal quantum number here is two.

[00:42:40]Now how many subshells are these two? It is having the s and the p. So what will you do? You add the electrons of the subshells. So here we are going to have 2 + 5 that will give us what? Seven. So this will be a group seven element.

[00:43:00]So for us to identify the group is the same as identifying the number of what?

[00:43:07]Valence electrons.

[00:43:09]So we've looked at valence electron, we've looked at core electrons, we've looked at group and we've also looked at what period. The last thing that I want you to know or I want you to understand is why we called block So when we say block, block here we are talking about set of what?

[00:44:33]Elements that are having what? The same number of electrons. So here the same number of valence electrons or the same number of electrons let me put that they have the same number of electrons entering the same orital. So now when you look at this 1 s2 2 s1 when you look at this element lithium now let's also look at sodium here 1 s2 2 s22 2p6 3s1 so now our focus is the same number of electrons here and this same number of electrons here they are entering the same orital So we are talking we are looking at the orital in which the same valence electrons are entering.

[00:45:26]So here this here we call this an X block. This here is what an S block.

[00:45:36]So when you look at the block always put it like this. The orbital which the last electron enter or enters is the block.

[00:45:48]Now let's look at carbon or let's look at boron. Boron here is 1 s2 2 s2 2 p what? 1. So the last electron here is entering a p orbital. And now we call this what? A p block.

[00:46:07]Now let's look at what we called scandium.

[00:46:12]1 s2 2 s2 2 p6 3 s2 3 p6 then I say that you write your 3d you don't fill 4 s2 3d1 so here the last electron entered what the d orbital so you call it what a d block element is what you are saying so all that I want you to remember here is we group we have period and we have a block. So when we talk about a group we are talking about set of element with the same number of valence electron.

[00:46:54]When we talking about a period we talking about set of element with the same main shells. When we talking about a block, we talking about set of element in which the last electron or they having the same number of electron entering what? The same orital.

[00:47:14]So ideally it doesn't need to be same.

[00:47:17]They have electrons entering the same orital. Take note. So this is the beginning of periodic chemistry.

[00:47:29]You have to have this understanding and with this understanding or with this technologies I know you are going to master the periodic chemistry. Thank you very much for your time. Feel free to subscribe, like and share and never forget to tell a tired soul that there is God. See you in our next lesson.

[00:47:53]Bye-bye.