[Music] hi my name is Bashir in this video I'll teach you chapter 8 structure of atom from class 10 under pradesh and telangana state board syllabus we'll first recall what we have learnt in 9 standard and then we'll learn what are quantum numbers will learn the shapes of orbitals we'll learn the number of sub shells that are there in each shell and how many electrons are available in each shell how many electrons are available in every sub shell we'll learn what is the electronic configuration will learn Pauli's exclusion principle of power principle we'll learn how to write down an electronic configuration will also learn about hands rule so in this video we are going to learn all of this one step at a time let us first recall what was learnt in ninth standard you must have already learnt that atoms are spherical in shape just like a football an atom is spherical in shape and atoms are mostly hollow which means they are empty from inside and towards the center of the atom we have nucleus we say that the mass of the atom is mostly due to the nucleus itself because most of the atom is M D so we say that the mass of the atom is mostly due to the nucleus a nucleus is made up of protons and neutrons protons have a positive charge neutrons do not have any charge we say that they have a they don't have any charge they are neutral these protons and neutrons together are known as nucleons because they reside inside the nucleus since protons and neutrons are inside the nucleus we call them nucleons and you must have also learned that electrons revolve around the nucleus just like how all the planets revolve around the Sun all the planets including earth how they revolve around the Sun in the same way electrons revolve around the nucleus now these electrons these electrons have a negative charge the protons neutrons and electrons together are known as sub atomic particles what do we call them we call them sub atomic particles and you must have also learned in your in nine standard that the orbit close to the nucleus has less energy compared to the orbit away from the nucleus let us first understand what is an orbit C orbit is also known as shell orbit is also known as shell electrons revolve around the nucleus in a specified path that path is nothing but a orbit so what is an orbit orbit is nothing but the path taken by the electron to revolve around the nucleus is known as an orbit or a shell and the orbit close to the nucleus has less energy compared to the orbit away from the nucleus let us say this is my first orbit let us say this is my first orbit this is my second orbit and this is my third orbit which orbit is is very close to the nucleus the first of it is very close to the nucleus so it will have less energy compared to the second orbit because the second orbit is little far from the nucleus the third orbit the energy in the third orbit will be a little more than the second orbit because the third orbits orbit is even far compared to the second orbit let us now learn about quantum numbers each electron in an atom is described by a set of three quantum numbers n L M these numbers are known as random numbers they indicate the probability of finding an electron in space around the nucleus these kind of numbers they indicate where the electrons can be found around the nucleus let us first learn about principle quantum number principle quantum number is used to denote the orbits that's my first orbit this yellow color line or the orange color line is my second orbit this is my third orbit principal quantum number is used to denote the orbits we say that principal quantum number gives the size and energy of the main shell shell is nothing but orbit why do we say that principal quantum number it is related to the size and energy obviously if the value of n increases the size and energy also increases why and how see that's my first orbit the blue one when when I write n is equal to one it pretty much means that this is the first orbit orbits are denoted by principal quantum number lowercase n when I write n is equal to 2 here it means that this is my second orbit the golden color circle this is my second orbit and again this is my third orbit so you see as the n value increases the N value is increasing from 1 to 2 from 2 to 3 as the N value increases the size also increases when n is equal to 1 the size was this much when n is equal to 2 the size is this much when n is equal to 3 the size is this much so the size of the atom is increasing as the N value increases and we say that the energy also increases right because energy of second orbit is more than the first orbit energy of third orbit is more than the second orbit what is the radius in general the radius is the distance from the center of the circle to a point on the circle right in the same way what is the atomic radius here I don't mean radius is the distance from the center of the nucleus to the outermost orbit that is known as atomic radius so as the value of n increases as the principal quantum number increases the atomic radius also increases if the atomic radius increases it obviously means that the atomic size is also increasing right as the atomic size increases the energy obviously increases because electrons will move further away from the nucleus so they'll have more energy and these shells here these shells here shell is nothing but a hobbit so these shells here are denoted by the letters K L M so on n is equal to 1 means the first orbit denoted by K n is equal to 2 the second orbit denoted by L n is equal to 3 the third orbit denoted by M so on you can see that in this table also and 1 2 3 4 k l m n the first orbit denoted by case they can all be denoted by L so on right and now we'll learn about angular momentum quantum number angular momentum quantum number is denoted by lowercase L and it takes values from 0 to n minus 1 each l value represents a subshell each value of L is related to the shape of a particular sub shell in space around the nucleus if L value is 0 name of the sub shell is s L is equal to 1 means P sub shell L is equal to 2 means d subshell L it is equal to 3 means f subshell let us say the value of n is 1 when the value of n is 1 L can have how many values and can have only 0 because L takes values from 0 to n minus 1 1 n itself is 1 1 minus 1 is 0 so L value would only be 0 here when n is equal to 1 there is only one sub shell when n is equal to 1 there is only 1 sub shell L is equal to s and we denote it by 1 s see this is pretty simple so why do we denote it like this orbitals are denoted like this and this n is our principal quantum number this L right here is the angular momentum quantum number the value of n is 1 so in place of n I am going to write 1 and what is the value of L here L is 0 0 means it is s subshell so I will write s 1 s so this is designated as 1 s orbital in the same way when n is equal to 2 when n is equal to 2 what are the values of L L we know that it takes values from 0 to n minus 1 so 0 to n minus 1 what is n - 2 minus 1 is what 1 so L takes values from 0 to 1 which means L takes these two values how do we represent it in this form here simple n value is 2 so here in place of n I am going to write 2 next L L this 0 0 means it is s orbital so I'm going to write s here so when n is equal to 2 n is equal to du means the second orbit the second orbit or the second shell second shell has two sub shells second shell has two sub shells 2s and 2p again see your n is equal to 2 so and I'm writing to here L value is 1 1 means p orbital so I'm going to write P and a 2p right so when n is equal to one we have one sub shell we had one sub shell when n is equal to two we had two sub shells 2s and 2p these are two sub shells let us consider n is equal to 4 what are the possible values of L now L takes values from 0 to n minus 1 right what is n here 4 4 minus 1 should be 4 minus 1 should be 3 so L value should be 0 1 2 3 up to 3 0 1 2 3 how do we write it for first I'm going to write n value write n value is 4 so 4 I have written and then I have to write n L here L value is 0 0 means it is s orbital so 4s in the same way for 1 means P for P for 2 means D for D 3 3 means F 4 F so in the fourth orbit orbit is also known as shell so in the for the shell we have four sub shells this stuff is pretty easy for if in in first shell you have one sub shell in second shell you have two sub shells likewise in third shell you will have three sub shells in for the shell you have four sub shells what is magnetic quantum number magnetic quantum number is denoted by M subscript L so M subscript L is magnetic random number and magnetic quantum number it gives us it talks about the number of orbitals each sub shell has it talks about the number of orbitals each sub shell will have now I told you that sub shells are denoted by s P D F and what are the L values for these sub shells let's just write down 0 1 2 3 so on L value is 0 means it is s subshell if L value is 1 it is P sub shell if L value is 2 it is d subshell if L value is 3 it is f sub shell now let us let us substitute L as 0 well as 0 0 means it is exceptional right so let me substitute L as 0 2 I am writing as it is in place of L am substituting 0 2 into 0 is 0 0 plus 1 is how much 1 so how many orbitals s subshell has it has 1 orbital so L so s here s has 1 orbital in the same way let us substitute the value of L as 1 1 means it is p subshell right let us substitute the value of L as 1 2 one's a 2 2 plus 1 is 3 so how many orbitals are they in p subshell there are a set of three orbitals in p subshell how many orbitals will be there in d subshell obviously the L value of D is two so in place of L I am going to substitute 2 2 into 2 is 4 4 plus 1 is how much 5 which means D will have how many orbitals D will have 5 orbitals the value of L is 3 here let us substitute the value of L as 3 2 into 3 is 6 6 plus 1 is how much 7 so f has how many orbitals f has seven orbitals and you can see the shapes here S has only one orbital and the shape of S orbital is spherical in shape e has 3 orbitals px py PZ 3 orbitals D D it has 5 orbitals one c a d d why is it d XZ d XY DX square minus y square d z square these are 5 orbitals that you have in d subshell so d subshell has 5 orbitals 1 2 3 4 5 p subshell has 3 orbitals px py PZ s you know s has only one orbital so magnetic quantum number talks about the number of orbitals that are available in each sub shell and what are the values that magnetic quantum number takes magnetic quantum number takes values from minus L to plus L magnetic random numbers takes values from minus L to plus L 4 s orbital the value of L is 0 so watch what are the values that M should take M should take values from minus 0 to plus 0 there is no such thing 0 does not take any negative sign positive sign so the value of M here is 0 if the value of L is P the value of L is P then what are the values of M M can take values from minus 1 to plus 1 right so M will have how many values three values so p-orbitals p subshell it's split into three orbitals in the same way if l value is two what are the values here of m m can take values from minus 2 to plus 2 right and will take values from minus 2 to plus 2 how many values 1 2 3 4 5 so d subshell it splits into 5 orbitals and what are the names of d orbitals d wise it D exit DX Y DX square minus y square DZ square let us now try to understand this table right here n is equal to 1 and represents the orbit or the shell the first orbit it will have only one sub shell right n represents the orbit orbit is also known as shell right so the first shell will have only one sub shell one sub shell the second shell will have two sub shells the third shell will have three sub shells one two three three sub shells the fourth shell will have four sub shells right and what are the possible M values M takes values from minus L to plus L right M takes values from minus L to plus L so L value is 0 which means M will take values from minus zero to plus zero there is no such thing zero will not have a sign so only number that is the only value for M is zero here when the value of L is zero M value will be zero and the when the value of L is one obviously M value would be minus one to plus one right again when the value of M is when the value of L is 2 m value will be from minus 2 to plus two when the value of L is three M will take values from minus 3 to plus 3 now n is equal to one here this is this row let us only read this row the very first row let us only read the very first row which is white in color n is equal to one here L is zero so what is a subshell notation subshell notation will be one s why come on subshell notation will be one s because we denote the subshell by this NL this n is our principal quantum number this L is our angular momentum quantum number which is used to denote the sub shell the value of n is 1 so in place of n I am going to write 1 the value of L is 0 0 means it is s subshell right so this will be 1 s if you forgot already write it once again spdf value of L for s is 0 the value of L for P is 1 B is 2 FS 3 just write it down like this L 0 1 2 3 in the same way n value is 2 so in place of n I'll be writing to here L L value is 0 0 means it is s subshell so 2 s 2 s when the value of n is 2 and the value of L is 0 what is the sub shell notation that we have and and when the value of M is 0 the sufficient notation is 2 s n value is 2 L value is 1 here what would be the notation simple n value is 2 L value L value is 1 1 means p subshell so the notation would be to be and how many orbitals are there in p subshell there are 3 orbitals we have already seen p is p subshell is divided into 3 orbitals px py PZ so P has how many orbitals here p subshell has 3 orbitals s subshell will have only one orbital right as subshell has only one orbit or P P splits into three orbitals pxpypz so P has how many orbitals three orbitals D D is splitting into one two three four five five orbitals so D is splitting into how many orbitals five orbitals f likewise F splitting into seven orbitals we have seen this already F has how many orbitals here seven orbitals so f has seven orbitals and what are the maximum number of electrons in each sub shell C S has one orbital remember the number of electrons that each orbital can occupy the maximum number of electrons that each orbital can occupy is two how many electrons can each orbital occupy it can occupy a maximum of two electrons so it s orbital it has only one s subshell has only one orbital so this one orbital can have a maximum of two electrons p subshell can have a maximum of p subshell has three orbitals right three orbitals px py PZ so this orbital will have two electrons this orbital can have maximum of two electrons this orbital can have a maximum of two electrons so altogether how many electrons will be there six electrons please sub shell it has five orbitals D XY dy Z D XZ D X square minus y square DZ square and each orbital will have a maximum of two electrons each orbital will have a maximum of two electrons 2 plus 2 is 4 4 plus 2 is 6 6 plus 2 is 8 8 plus 2 is 10 so D will have a maximum of 10 electrons f it is splitting into seven orbitals each orbital will have two electrons so 2 into 7 is 14 so this will have 14 electron spot and this is very important this you have to know it if you don't know this thing it is almost impossible for you to write down the electronic configuration what has spin quantum number C electrons can have can can have a spin a clockwise spin and electrons can have an anti clockwise spin if the electrons spin clockwise we say that the spin is plus half and when the electrons spin anti-clockwise we say that the electrons have minus half spin and remember in each orbital in each orbital in each orbital if one of the electron has a positive spin the other electron will have a negative spin so there can be a maximum of two electrons only then a orbital this will be a little more clear when we write down the electronic configuration what's this electronic configuration the distribution of electrons in shells sub shells and orbital in an atom is known as electronic configuration you already know what is a shell right shell is nothing but our orbit orbit sub shell we know that sub shells are denoted by s P D F right and what is the orbital B has three orbitals px py PZ so these are nothing but orbitals let me be a little more clear with the shells sub shells and the orbital I believe I can explain it to you this way see the an orbit is also known as a main shell orbit is also known as a main shell and we have seen how many sub shells can can each shell has the first shell can have only one sub shell the second shell can have two sub shells the third shell can have three sub shells the fourth shell can have four sub shells we have already seen this earlier right let me go back and see you the fourth shell can have how many sub shells four sub shells the second shell can have two sub shells we have already seen this right and in turn these sub shells are splitting into orbitals like p sub shell is splitting into three orbitals so these Orbital's so I hope you now know the difference between shell sub shell and orbital right and each orbital can have a maximum of how many electrons two electrons can you tell me how many electrons will be there in every shell let me ask you how many electrons are there in second shell how many electrons are there in second shell to find out the number of electrons we have a pretty simple formula 2 n square so in place of n substitute 2 here 2 square is how much 4 - 4 z 8 which means the second shell will have 8 electrons when I say shell I am referring to the orbit orbit is nothing but the path taken by the electrons to revolve around the nucleus right so the second orbit or the second shell has a maximum of you know will have 8 electrons before we start writing the electronic configuration let us go through the Polly's exclusion principle Pauli's exclusion principle states that no two electrons will have all the four quantum numbers same to understand this let us consider helium atom the atomic number of helium is 2 atomic number is 2 it means it has 2 electrons it has 2 electrons and both of Bhogi electrons are there in the first orbit both the electrons are in the first orbit why because the first orbit can have a maximum of 2 electrons right let's say in place of n I substitute 1 here in place of n I am substituting 1 here what does it mean 1 square is 1 2 ones or 2 so the first orbit can have can have 2 electrons right so both of the electrons here will occupy the first orbit because the first orbit can have can have 2 electrons so both the electrons will enter into first orbit and what is the L value the lkl can take values from 0 to n minus 1 right 0 2 what is the value of any 1 0 - 1 minus 1 1 minus 1 is 0 so when in the first shell you have only 1 sub shell in the first shell you have only 1 sub shell so both electrons will have the same in value both the electrons will have the same L value and what about magnetic quantum number what about magnetic quantum number magnetic quantum number takes values from minus L to plus L right magnetic quantum numbers takes values from minus L to plus L what is Elia zero so minus 0 2 plus 0 is nothing but 0 so both the electrons have the same n value have the same L value they have the same magnetic quantum number value but what about the spin we know that what if if the first electron has a spin of plus 1/2 the second electron will have obviously a spin off minus 1/2 because they will have opposite spins so Pauli's exclusion principle says that no two electrons will have all the four quantum numbers same for an example helium atom in helium atom we see that there are two electrons both of them have the same principle kind of number you know the same value of principle quantum number same value of a single random number same value of magnetic quantum number but the spin quantum number it changes they don't have the same spin quantum number value so Pauli's exclusion principle here is a is a bit straightforward his it says that no two electrons will have all the four kind M numbers same no two electrons can have all the four kinds of numbers sing what is a power principle of our principle says that the electrons are assigned two orbitals in order of increasing menu of n plus L don't get confused here increasing value of n plus L how to find out the value of n plus L this is pretty easy let us say I want to find out the n plus L value of 2 P 2 P Co this 2 means the value of n is 2 the van let us find out the n plus L value for 2 P what is the N value n value is 2 plus what is the L value go up and see here the value of L is 1 so n plus L value is 3 for 2 P the n plus L by us three and let us consider two s here 4 2 s 4 2 s what is the N + L value n value is 2 s what is the S value s value is 0 2 Plus 0 is 2 so which has a lower n plus L value 2 s or 2p the n plus L value of 2 s is 2 n plus L value of 2 P is 3 2 is lesser or 3 is lesser obviously 2 is less than 3 which means 2 s has a lesser n plus L value so electron will first occupied 2 s because it has a lesser in present value and then it will occupy the electrons will occupy orbitals which have a less n plus L value at times what really happens as n + n values values become equal n + L value becomes equal during those cases electron will occupy the the orbital which has lower M values let us say I have 4 p + 3 d i have 4 p + 3 d i want to find out the N + L value of 3 D + 4 p finding out n + L value is not at all difficult this 3 that you see here this is the N value because we see that the orbitals are denoted like this right n L X this thing right here is nothing but the N value this thing is nothing but the N value so n value is 3 n value is 3 plus what is the L value what is the L value we have D here we know that D value should be 2 so value of L value for D is 2 3 plus 2 is 5 let us do the same thing for this also n value is 4 here and value is 4 P l value for peas 1 so 4 plus 1 is 5 L value for P this one the 4 plus 1 is 5 both of them in this case they have the same n plus L value both of them have the same n plus L value but which has a lower end value 3d has a lower end value that is the reason the or the electron will first occupy 3d orbital and then it will occupy for p orbital so this Aufbau principle is pretty easy it says that the electrons will occupy the orbital which has a lower n plus L value in case both the n plus L value are equal then it will occupy the orbital which has less of n value as simple as that this colorful diagram that you see out here is known as Mueller's diagram boilers diagram helps us in writing down the electronic configuration it helps us in writing down the electronic configuration let me draw this boilers diagram for you it is pretty simple what do you have to do is first write down one one time write down to 2 times 3 3 times 4 4 times 5 4 times and then keep decreasing 6 3 times 7 2 times 8 one time so what I am doing here one I am writing one time two times three times four times four times and then decreasing it three times two times one time 1s s P sub shells are denoted by s P D F right so write down here SP s P D s P D F s P D F s P D s P s that's it so drawing a mohinder's diagram is simple electrons do you see the direction here the pointer it is here and then the pointer is here then the pointer is here this is showing in what sequence the electrons will enter the orbitals the sequence is simple for electrons will enter into 1s orbital after 1s orbital is completely occupied it goes in the electrons will go into 2's orbital once 2's is completely filled they go into 2p orbital if two piece failed if they go into 3s orbital when 3s is filled they go into 3p orbitals then 4s then 3d then 4p and so on using the spoilers diagram let us write down the electronic configuration the electronic configuration is pretty simple let us say I have magnesium the atomic number of magnesium is 12 which means that it has 12 electrons the first two electrons will go into 1s orbital we know that s can have a maximum of 2 electrons because s has only one orbital of each orbital can have a maximum of 2 electrons p p subshell we know that p splits into 3 right 3 orbitals px py PZ and each orbital can have a maximum of 2 electrons so 2 2 2 6 electrons P can have a maximum of 6 electrons and we know that D have has a maximum of 10 electrons why because D splits into 5 orbitals right D has a total of 5 orbitals DX Y D Y Z D X DX square minus y squared DZ square and in each orbital each orbital can have a maximum of 2 electrons 2 4 6 8 10 so D can have a maximum of 10 electrons remember this thing writing down the electronic configuration will be a cakewalk for you so magnesium atomic number of magnesium is 12 which means it has 12 electrons the first two electrons will go into 1s orbital after that two more electrons will go into 2's orbital because s can have a maximum of two electrons right so so two electrons will enter into 2's orbital then to be how many electrons can can be there in P orbitals six so six electrons will go into 2p orbital after 2p they are going into 3 s orbital s can have a maximum of two electrons right so 2 plus 2 is 4 4 plus 6 is 10 10 plus 2 is 12 so although all the 12 electrons got occupied so this is the electronic configuration for magnesium 1s2 2s2 2p6 3s2 that's the electronic configuration for magnesium let me write down the electronic configuration for chromium chromium has a atomic number 24 what should be the electronic configuration the first two electrons should go into 1s after 1s is completely filled the rest of the electrons they go into 2's after 2's electrons will go into 2p how many electrons can you're the p subshell occupying 6 so 2 P 6 after 2p they are going in the rest of the electrons will go into 3s s can occupy a maximum of 2 electrons so in 3s you will have 2 electrons after 3s you have 3 P P again can have a maximum of 6 electrons so 3p will have 6 electrons after 3p you have 4 s 4 s s can have a maximum of 2 electrons so 4 s will have 2 electrons after 4s electrons go into 3 D orbital D can have a maximum of 10 electrons but how many electrons are remaining now 2 + 2 4 4 + 6 10 10 plus 2 12 12 + 6 18 18 plus 2 2020 orbitals 20 electrons are already occupied so only four electrons are remaining so four electrons will go into 3d orbital let me now write down the electronic configuration for zinc the elect the atomic number for zinc is 29 1s s can have 2 electrons after 1 s it goes into du s s can have 2 electrons after 2 s it goes into 2 P P can have 6 electrons after 2 P it goes into 3s s can have 2 electrons after 3 as it goes into 3p we can have 6 electrons after 3 Pete goes into 4s s can have 4 electrons after 4 as it goes into really they can have ten electrons but let us first found out counter how many electrons are left out 2+2 4 4 plus 6 10 10 plus 2 12 12 plus 6 is 18 18 plus 2 is 20 so 20 electrons have already occupied the orbitals 20 29 minus 20 is 9 so 9 electrons are remaining so the rest of the 9 electrons will enter 3d orbital so this is how you write down the electronic configuration chromium and zinc you have reading the electronic configuration which is well and good but the electronic configuration on off chromium and zinc is a little different bandhas why why because just to gain stability just to gain stability the orbital will take one electron from 4s orbital the 3d orbital will take one electron from 4s orbital and it becomes 4 wave become 5 this 2 becomes 1 this 4 will become 5 and in order to gain stability again 3d orbital takes one electron from 4s and this 9 will become 10 completely filled orbitals and half filled orbitals are more stable Dee can have a maximum of 10 electrons so if Dee has 10 electrons it is completely filled half of 10 is what 5 so if Dee has half filled electrons it is stable or if Dee has completely filled electrons they it is stable that's the reason there is a little change in the electronic configuration of chromium and zinc lastly we will go through Huntsville hunts rule is not at all difficult see I let us consider carbon atomic number of carbon is 6 which means it has 6 electrons the first two electrons will go into 1s orbital after that 2 electrons will go into 2's orbital after 2s the rest of the electrons will go into 2p orbital right so the first two electrons go into 1 is a second - the next 2 electrons goes into 2s the rest of the 2 electrons remaining 2 electrons they will go into 2p orbital let me write this down in a box form 1s it has 2 electrons one - it has 2 electrons - s it also has two electrons one to two electrons P we know that P splits into three orbitals 2px 2py 2pz p subshell it splits into three orbitals 2px 2py 2pz right how many electrons aren't there in p subshell two electrons the first electron can go into any one of these orbitals let us say the first electron goes into two bx orbital the second electron cannot pair cannot get paid here it goes into 2 py or 2 PZ why why because these are known as degenerate orbitals orbitals which have same energy orbitals which have same energy almost same energy orbitals which have almost same energy are known as degenerate orbitals so in degenerate orbitals what really happens is electron pairing will not take place until and unless all the region all the regional orbitals are occupied by one electron each so so Hans rule states that electron paring takes place only after all degenerate orbitals are occupied by one electron each so if in case I have one more electron that electron will not get paid here because these are degenerate orbitals pairing cannot happen until and unless all the orbitals have one electron each so that so if I have another electron it will go here into PZ but it will not get paid with 2px or 2 py if now I have one more electron then only it will get paid so in degenerate orbitals pairing will take place only after all degenerate orbitals are occupied by one electron each I hope you understood and in case you have any questions any doubts whatsoever feel free to interact with me by logging on to our website and you know using the chart too long on our website thank you so much for watching I'll see you all in the next video have a very nice day goodbye [Music]