QUANTUM NUMBER (L-1) BY BIPLAB BISWAKALYAN OJHA AT:ST.JOSEPH'S GROUP OF INSTITUTION NALIPUR, JAJPUR

Added: 2026-05-11

[00:00:02]Good morning all. I am Biplo faculty member of St. Joseph group of institution.

[00:00:12]Today I am going to discuss the very very important topic and the topic is quantum number and this topic is belong to atomic structure.

[00:00:23]This topic is very very important in 9th, 10th, 11th and 12th especially the most important topic for me and J.

[00:00:37]Okay, let's start.

[00:00:52]Quantum number. What does it mean? That first of all quantum number consist of four numbers. One is principal quantum number. Second one is assumal quantum number. Third one is magnetic quantum number and last one is spin quantum number. First of all why quantum number introduced in atomic structure because quantum number gives proper address of an electron. Address means for example someone wants to admit in St. Joseph group of institution when he want to take admission in St. Joseph group of institution first of all he or she know about the address of St. Joseph group of institution for example we know that there are different kind of countries for example Australia, India, England and etc. First of all, he has to choose which country he or she belongs to. First of all, he identified he belongs to country India and we know that in India there are different kind of state and then he has to select which state he has belonged. For example, he has select Odisa. Second, in Odisa there are different kind of district. Then he has to select which district he is belong. That's why quantum number quantum number gives idea about or gives address or complete information about an You look prone.

[00:03:28]Address means position and their energy and which orbital he occupy.

[00:03:49]There are different kind of datas which can give by the term quantum number.

[00:03:57]First of all we have to there are four quantum number. First one is principal quantum number which are represented by small n. And second one is athal quantum number which is represented by small L. And third one is magnetic quantum number which also represented by small m. And last one is spin quantum number which is represented by small s. Now we have discussed one by one these four set of quantum number gives completely address of an electron. First of all we starts from principal quantum number.

[00:05:15]Let's start.

[00:05:37]First principal quantum number is represented by small n and second one is principal quantum number gives idea about cell gives idea about cell. Let's see.

[00:05:53]Principal quantum number is represented by small n.

[00:06:06]And second one is principal quantum number gives idea about cell. Now question arises in our mind what do you mean by cell? We know that suppose and one more thing we introduce principal quantum number. I want to show complete structure of atom. Now see we know that in an atom suppose let's say we imagine a circle and this is the center of circle.

[00:06:51]Imagine an atom. We know that the smallest individual particle of an element is known as atom. And at the center of atom nucleus is present. And inside the nucleus proton and neutron are present and around the nucleus elocron revolves or otherwise we can say thatron revolves around the nucleus and this path is known as cell or orbit.

[00:07:18]Okay. Now see in the structure for example suppose this is a nucleus and inside the nucleus proton and neutron are present. I represent P for proton and N for neutron and around the nucleus electron revolves. Let's see this is the path where electron revolves. Second one is this is the path where electron devolves. Okay, this is the diagram or structure of atom and in cell or orbit electrons are present.

[00:08:02]Okay, let's come to the previous page.

[00:08:07]Principal quantum number gives idea about cell. What does it mean that where cell electron the revolves around the nucleus.

[00:08:30]Now question arises suppose we say n = 1 or n = 2. And when I say n = 1, n = 1 means the first cell or the cell closest to the nucleus. For example, suppose say this is the nucleus of an atom. This is the first cell or closest cell to the nucleus. After first cell, next cell comes and this is the second cell. And we know that this is called K cell.

[00:09:10]And this is is called L cell. Okay. Next come to the cell. This cell is known as M cell. And we know that.

[00:09:26]Next for K cell the value of N is equal to 1.

[00:09:40]And similarly for L cell the value of n is equal to 2 and for m cell the value of n is = 3. When I say n = 1, this is called first cell and this is your second cell and after second cell, third cell counts. That means n represents cell or n gives idea about cell. That means when I say n= 1, this is first cell. n = 2 second cell n = 3 this is your third cell and so on. Okay. Next principal quantum number which is represented by n gives idea about gives idea about size and energy of the cell.

[00:11:00]Next come to the second point.

[00:11:05]This is most important point. Please focus. Point number five. The statement as the value of n increases the energy also increases. Which is the statements belongs to principal quantum number.

[00:11:18]Let's I write as the value of n increases energy also increases. Now we discuss this point completely.

[00:11:47]My question is how or when the value of n increases energy also increases. Let's please explain it or explain now.

[00:11:59]Suppose this is your nucleus and inside the nucleus proton and neutron are present. This is your first cell. This is your second cell. This is your third cell. And we know that for first cell or we know that for first cell n = 1.

[00:12:26]For second cell n = 2 and third cell n = 3. My point is when the value of n increases energy also increases. Let's see suppose we go from towards right.

[00:12:41]Suppose the value of n is = 1. When the value of n increases that means n = 2 and n = 3 that means n = 1, n = 2 and n = 3. Students you know that when I say n= 1 it means first cell n = 2 second cell and n= 3 third cell. That means K cell after K cell L cell comes and after L cell M cell comes. Okay. My question is N the this is the order of energy.

[00:13:27]Now we understand this statement completely.

[00:13:34]Before we understand this concept, we have to know another concept. That concept completely interlin with this concept. And the concept is attraction and repulsion. And how energy is directly linked with attraction and repulsion. Now we clarify them. Let's see students.

[00:14:02]This is your attraction and another point is repulsion and very small thing we know that opposite charges are attracts each other and same charges or like charges reflects each other. Okay. Now I write same point opposite charges attracts each other. Now one question is when I say opposite charges that means positive negative or negative positive and we know that there are only two type of charge. One is positive charge another is negative charge and neutral. Proton have positive charge, electron have negative charge and neutron becomes neutral. When I say neutral, neutrals means when equal number of positive charge is equals to equal number of negative charge or number of positive charge is equal to number of negative charge. This state we call neutral state. Okay. Positive charge means we comes to atom. Inside the atom proton and electron are present. Proton have positive charge.

[00:15:29]Electron have negative charge. When I say equal number of positive charge and equal number of negative charge that means the number of positive charge becomes equal to the number of negative charges. Okay let's say that means opposite charge means either positive sits or negative charge or positive charge.

[00:15:50]Okay. Let's come to first point of repulsion. Repulsion means we know that like charges or otherwise we can say that same charges repels each other.

[00:16:09]Repels each other. Same charge means when negative charge can contact contact with negative charge or positive charge gets contact with positive charge that means when same charge close to each other it repels each other. Okay. Come to the next point.

[00:16:32]Now we now we come to the how energy is linked with or what is the relationship between energy attraction and repulsion. Energy means for example we know that when attraction occurs when attraction occurs energy releases energy releases and we know that suppose this is a system when the body losses its energy that means the total energy of the system decreases.

[00:17:16]Okay, that means when attraction occurs, energy releases and the whole energy of the system gets decreases. And when repulsion occurs, energy increases.

[00:17:40]That means energy increases. Okay. When I say the relationship between suppose energy energy is directly relation to directly proportional to repulsion and inversely proportional to attraction. That means when repulsion occurs the system of the body increases.

[00:18:15]When attraction occurs the whole energy of the system decreases. And the most important point the relationship between stability and energy.

[00:18:27]Let's I write this is the relationship between energy and stability. All the chemistry students must know about everybody or every reaction wants to stay in stable form.

[00:18:50]That means this is the inverse relationship between energy and stability. That means we say that or I say that when energy increases. That means inversely proportional. When the energy increases the stability becomes decreases. When the energy increases or energy decreases the stability becomes decre increases. That means everybody wants to stay in stable form. Okay. That means let's come to the structure of atom.

[00:19:25]We know that this is the first cell.

[00:19:28]This is the second cell and this one is third cell. Here electron is present.

[00:19:34]Also in second cell electron is present and in and in third cell electron also present. We know that positive charge that means proton and electrons are present in an atom and proton have positive charge. Electron have negative charge and we know that all the positive charge are concentrated at nucleus or inside the nucleus.

[00:20:16]and all the positive charge or all the protons are concentrated inside the nucleus. Suppose here electron is present and electron is also present in second cell and electron is also present in third cell. My question is which electron feels more attraction and which electron feels less attraction because we know that this is the electrostatic force of attraction between positive charge and negative charge and this is the electrostatic force of attraction is it directly proportional to linked with the distance. That means when distance decreases attraction increases. When distance sorry when distance decreases attraction increases. When distance increases attraction decreases. And we know that when attraction occurs energy of the system decreases. And when the energy of the system decreases the system or stable stability increases.

[00:21:17]Okay. Suppose one electron is belongs to first cell and one electron belong to third cell. That means the electron which is present in first cell feels more attraction as compared to electron present in third cell. That means when distance increases attraction decreases.

[00:21:39]When attraction decreases that means repulsion increases. And we know that when repulsion increases energy of the system increases. When the energy of the system increases the stability of the system decreases. This is the negative point of that. Okay.

[00:21:57]This is the complete understand of as the value of n increases energy also increases. And last point is the maximum number of electron the maximum number of electrons present in a cell present in a cell is given by 2 n² is given by 2 n². For suppose in first cell and we know that first cell the value of n is equal to n. Suppose my question is how many maximum electrons are present in first cell or how many maximum electrons are present in second cell or how many maximum number of electron present in third cell. Let's discuss it.

[00:23:12]When I say first cell that means the value of n is equal to 1 and the formula is 2 n². In first cell 2 into 1 square that means 2 electrons. That means in first cell two electrons can only present not more than two electrons. The formula is 2 n². Suppose in second cell n is equal to 2. When this value we put or I put into 2n² that is 2 into 2² that means 8 kiloprons.

[00:23:58]And last one is suppose in third cell n is = 3 that means 2 into² 18 electrons. That means I confirm that in first cell two electrons is present and in second cell 8 electrons is present and third cell 18 electrons is present. Okay, that means simply I remember that or we need remember that n = first cell n = 2 second cell that means when I say n = 3 that means the electron is present in third cell suppose I write n = 4 that means the electron present in fourth cell suppose I write n = 5 that means the electron present in fifth cell Now come to the second quantum number and second quantum number is assumethal quantum number.

[00:25:10]Principal quantum number gives idea about cell or orbit and assumethal quantum number gives idea about subell.

[00:25:18]That means number of subells is within present within the cell. That means question arises how many subells are present in a cell. For example, suppose I say first cell that mean in first cell how many sub cells can present in first cell how many subell are present in second cell and how many subell are present in third cell and so on and let's come to the second quantum number and second quantum number is assume third quantum number and assume third quantum number is represented by small n assume quantum number is represented by small n. When principal quantum number gives idea about cell. Similarly, athal quantum number gives idea about subset. That means first of all it is represented by small l.

[00:26:18]It is represented by small l. And it gives idea about gives idea about gives idea about subset gives idea about subsells. Now my question is how many number of subsells are present in a cell? Let's come to the point.

[00:27:08]This is the important point for each value of L.

[00:27:17]For each value of L there exist a subset and the value of L and the value of L lies between 0 to n -1 one please focus this point for each value of L there exist a subsell and the value of L lies between 0 to n minus one next repeat the value of L lies between 0 to n minus one and n represents principal quantum number and and also I know that or we know that n represents cell number that means when I say n= 1 cell n= to second cell and n= 3 third cell. Now we discuss the subell is present within the subell.

[00:28:25]Suppose this is your nucleus.

[00:28:30]Proton and neutron present inside the nucleus.

[00:28:34]Suppose this is your first cell and for first cell the value of n is equal to 1 and second cell the value of n is equal to two and we discussed before or before we discuss for each value of l there exist a sub and the value of l li lies between 0 to n minus one. Now discuss for first cell and we know that for first cell the value of n is equal to 1 and the value of l lies between 0 to n -1 and we know that for first cell the value of n is equal to 1. When I put this value into this that means 1 - 1 0 0 to 0 is zero.

[00:29:26]That means the value comes from one value that is L =0. When I say L=0 that means only one value comes. Since one value comes that means one subell is present in first cell and this subell is S subsell.

[00:29:45]This subell is S subsell. This subell is S subsell.

[00:29:52]Let's come to the let's come to the second cell. And we know that for second cell the value of n is equal to 2. And the I know that the value is lies between 0 to n minus one. When put this value that means 0 to 2 - one 0 to 2 - 1 is 1. That is the value is 0 and another one is l = 1 or another value is l= 1.

[00:30:24]Since two value comes that means two subsells are present in second cell.

[00:30:29]When I say L is equal to0 that means S subsell or alternatively we can say that for S of cell the value of L is equal to zero.

[00:30:41]L is equal to 1 that means P subell or alternatively we can say that or I can say that for P subell the value of L is equal to 1. That means in first cell only one subell is present that this is or that is a subsell.

[00:31:01]In second cell two subell is present that is l=0 and l= 1 that means s subell and second one is p subell. Let's come to the third cell.

[00:31:20]For third cell we know that the value of n is equal to three and and we know that the value is lies between 0 to n -1 when I put this value that means 0 to 3 -1 3 - 1 is 2 that means l =0 l = 1 l = 2 that means there are three value comes for third cell. Since three value comes that means three subsells are present in third cell and we know that when I say L=0 that means A subell is present. When I say L= 1 that means P subell is present. When I say L=2 that means B subshell is present. That means in third cell there are three subell are present. one is a subell and second one is p subell and third one is d subshell.

[00:32:25]Always remember that alternately that for a subell the value of l is equal to zero. For p subshell the value of l is equal to 1 and for d subell the value of l is equal to 2. That means in first cell one subell is present that is S subell and in second cell two subshell is present that is S subell and P subshell and in third cell there are three subell is present one is S subell P subell and D subshell and also remember that for S subshell the value of L is equal to zero for P subell the value of L is equal to 1 for D subell the value of L is equal to 2 and last cell that is n = 4 that is your fourth cell and again repeat that the value of l lies between 0 to n minus one again I repeat this point for each value of l there exist a subsell and the value of l lies between 0 to n minus one suppose when we put this value that means 0 to 4 - 1 that is 0 1 2 3 that means there are four values comes one is L =0 L = 1 L = 2 and another one is L = 3 and we know that L =0 which of cell A subell L = 1 which of cell L = 2 which subell D subsell and L= 3. Which subsell?

[00:34:14]F subsell. Again we repeat that for A subell the value of L is equal to zero.

[00:34:21]For P subell the value of L is equal to 1. For D subell the value of L is equal to 2 and for F subell the value of L is = 3. That means suppose let's all the things are kept in one phase. Suppose this is your cell and this is your soft cell.

[00:34:51]Okay.

[00:34:54]For first cell there are one values of L that is L =0. L=0 means which subell is subell.

[00:35:05]When I write N= 2, N= 2, N means principal quantum number and principal quantum number gives idea about cell.

[00:35:13]When I say N= 2, that means second cell.

[00:35:16]That means in second cell there are two sub cell is present. One is S and another one is three. That means there are two values form L = 1 or L=0 and L =0 A subset L = 1 P subset and N = 3. There are three values L =0, L = 1, L = 2. That means in first cell only one soft cell is present. This is your A subsell. In second cell two subell is present. A sub cell and P subell. And in third cell P subell is present. S P and B. Last one is N = 4, N= 4 means L =0, L = 1, L = 2 and L= 3.

[00:36:17]When I say L =0 that means S subell L = 1 means P subell. L= 2 means D subell. L = 3 means F sub. That means there are four subsets are present in forces. One is S, second one is P, third one is D and last one is F subset. And the last point is quantum number which is represented by L. L gives idea about this is very very important point. L gives idea about the safe of the subell the safe of the subell and generally we know that there are four kind of subell. One is S.

[00:37:11]Another one is P. Third one is D and last one is F. That means S subsell.

[00:37:23]Second one is P subsell.

[00:37:29]Third one is D subset. And last one is F subset and the shape of the A subsell is spirical. That means the shape of the A subell is spherical and the shape of the P subell is dumbbell and the shape of D subell is double dumbbell and the shape of F subell is complex.

[00:38:25]Okay, this is completely information about assumethal quantum number. After assumal quantum number only there are two quantum numbers left magnetic quantum number and pin quantum number.

[00:38:39]And we'll discuss this quantum number in next class. Thank you.