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Current time:0:00Total duration:13:08

Electron configurations for the third and fourth periods

Video transcript

we ended the previous video with the electron configuration for neon so 1s2 2s2 2p6 now shows you how you can look at the periodic table and kind of run through these electron configurations for example this would be 1 s 1 1 s 2 and then 2 s 2 would be here and then we had 6 so 2p 6 brings you all the way over to neon and so for for an electron configuration for an element in the third period right so this would be the first period second period 3rd period so let's do sodium so sodium has 11 electrons so one more than neon but the second shell is full right so the second shell is completely full so four sodium's eleventh electron we need to go into the third shell to the third energy level and so n is equal to 3 for the third shell possible values of L include 0 1 & 2 so in the third shell we're talking about an S orbital right one of them P orbitals right three P orbitals and when L is equal to two we're talking about a D orbital right and if you if you do your magnetic quantum number you get five values for that so we're talking about five D orbitals in the third shell and the third energy level and so if we if we plot those orbitals alright so let's go ahead and plot those in terms of increasing energy so this side will put o put increasing energy going this way and the 3s orbital is here and so that's what we're talking about we're talking about the third shell we're talking about the S orbital in the third shell and there's one of them alright next we we have three P orbitals right in the third shell so let's go ahead and draw in those P orbitals right so there's three of them so one two and three so those are our three P orbitals and then finally we have we have some D orbitals we have five of them and the third and the third shell so five D orbitals let me go ahead and draw those in so those are our higher energy so one two three four and five so here the d orbital's like that alright so let's uh let's do sodium's let's go back to sodium down here eleven electrons alright so we need a so sodium has 11 electrons and so the first 10 we could put the first 10 electrons in just like neon 1s2 2s2 2p6 and remember your superscripts tell you the total number of electrons that's 2 4 and then 10 so that takes care of 10 electrons we have one more one more to account for and so the xi electron for sodium is going to go into the third shell right and the lowest lowest energy here will be the 3 s orbital so we go ahead and put the xi electron for sodium into the 3 s orbital so we can complete the electron configuration for sodium and we have to add on 3 s 1 because we have 1 electron in an S orbital in the third shell so the complete electron configuration for sodium becomes 1s2 2s2 2p6 + 3 s 1 notice that all of this 1s2 2s2 2p6 this is the same electron configuration as neon and so we could represent all of that right we could represent all of this right here we put neon in brackets and then we could write 3 s 1 and this is another way to write an electron configuration for sodium so we can call this noble gas notation because we're using the noble gas that precedes sodium so if you just work backwards on the periodic table or if you go backwards from sodium the first noble gas that you hit here is neon and so we do neons electron configurations the same as neons and then we have to add on 3 s 1 so neon 3 s 1 is our noble gas notation for sodium alright let's do let's just do another element in the 3rd period let's just go all the way over here to aluminum alright so 13 electrons for aluminum we can use noble gas notation to save us some time so we're saying the electron configuration is the same as neon and that puts us that puts this right here let me use a different color all right so that puts us right here and then we have sodium right sodium would be 3 s 1/9 ZM would be 3s 2 and then we let's go ahead and put those in so so magnesium would be 3 s 2 so we fill that in here and then we need one more electron for aluminum right so we need one more electron and of course that electron goes into one of these P orbitals here and so let's go ahead and write the write the write the electron configuration just look at what we have on our orbital notation here so we have two electrons in the 3s orbital so 3 s 2 and 1 electron in one of the 3 P orbitals so we write 3 P 1 so brackets neon 3 s 2 3 P 1 is the electron configuration for aluminum let's go ahead and do let's jump all the way over to argon here so let's go all the way over to argon so let's write the electron configuration for argon using noble gas notation the noble gas before argon is neon alright so we put neon in brackets and then once again we think we can think this is 3 s 1 we could think this is 3 s 2 right so we have 3 s 2 we go over here this is 3 P 1 3 P 2 3 P 3 3 P 4 3 P 5 and 3 P 6 alright so we can go ahead and write 3s2 3p6 here for argon and if we wanted to put in those electrons right and how they fill right we could put in those electrons right following hoons rule and we talked about in the last video all right and then and then we put in all of those electrons and we can see that we've now filled the 3p orbitals like that so that's argon next up is potassium so now we're at the fourth period on the periodic table right so if we go one more one more one more element here we hit the fourth period of the periodic table and we get 2 potassium all right so you might think all right so one more electron than argon so you might think potassium electron would go into would go into a D orbital right because that makes that make sense we have this D orbital here but that's not what happens so let's go ahead and take that electron out of that D orbital we we are now right where in the fourth period and we can actually we can actually open up a new shell here so we can go to n is equal to four we can go to n is equal to four I'm going go and write this down and in the fourth shell right I won't draw I won't write in all of the values for L right but we we definitely have an S orbital so there's an S orbital in the fourth energy level right one of them and it turns out the energy for that for s orbital is a tiny bit lower than the 3d orbitals so we can let me draw that in with a different color here so the four S orbital turns out to be a little bit lower in energy let me use a different blue so we don't confuse it here so this is representing this is representing our four s orbital so for potassium potassium this actually the four S orbital is a little bit lower in energy so the next electron that we add for potassium is going to go into this four S orbital so we can go ahead and write the electron configuration for potassium if we're using noble gas notation we go backwards so what's the noble gas that precedes potassium right so just go backwards in the periodic table and that is of course argon that's our gone right here so we could say that the electron configuration for potassium is the same as argon and then we have one more electron to worry about here that extra electron that that nineteenth electron for potassium is going to go into this 4 s orbital here so we write we write the same electron configuration as argon and we write for s and one electron in that 4s orbital so we write for s one for potassium right one more electron so we can go ahead and write sorry for calcium I should say so for calcium one more electron to worry about so the noble gas that precedes calcium is once again argon so we say it's the same electron configuration as argon one more electron and we know that there's space in our 4s orbital here so we can add another electron pair our spins up and so we can say for s2 here for the electron configuration for calcium once again right we notice this pattern on the periodic table all right so this right here I mean we use a blue here so we could say this is for s1 we could say this is for s2 and so all of these over here on the Left we have called we've just state but thought about them as being S orbitals anyway so this is the s block on the periodic table alright that takes care of that takes care of calcium and the next the next ones that you're going to hit right are all of these elements in here so all these elements and we know we know that in the third energy level right there are D orbitals all right so let's go back up to here let me go ahead and mark this so we can see we know there are five D orbitals in the third energy level all right each D orbital can hold a maximum of two electrons so five times two is 10 so how many spots do we have here one two three four five six seven eight nine ten so we have these we have these ten spots here right and I'm actually going to do a whole separate video on the D orbitals so I'm not going to worry about them in great detail right now but we have ten spots all right this is the third shell and and we have ten spots for electrons so 3d10 would fill these D orbitals so 3d10 fills these D orbitals here and this is why the the periodic table is shown the way it is here it just helps you to think about writing your electron configurations for example let's just go ahead to gallium here let's write a let's write a electron configuration for gallium so if we're using noble gas notation the noble gas that precedes gallium if you work backwards would be argon so we can go ahead and write that in here that takes us to this area so that would be 4s1 4s2 so we write for s2 right here and then we have all of our DS so we can just we can just go ahead and put the DS in there 3d10 so we put in three D 10 here and this takes us to this is this takes us to the we're still we're in the fourth shell here and is equal to four so L is equal to one is another possibility and so those are the P orbitals so once again we have three P orbitals in the fourth shell and of course right here this is where we hit the P orbitals we start to fill the P orbitals so we can go ahead and say this is a p orbital in the fourth energy level right so a p orbital in the fourth shell and we have one electron so we can write for P one and so this is one way to represent the electron configuration for gallium so not using noble gas notation so argon 4s2 3d10 for P one sometimes you might see the 3d 10 and the 4s switched in terms of their order so you might see 3d 10 for s 2 for P 1 and it doesn't really matter how you do it you'll see you'll see both ways done alright finally let's do let's do a Krypton here so let's do let's do Krypton and so our last electron configuration here so the preceding noble gas would be argon and let me use a color that we can see here so our GaN would take us to here and then we have for s 2 so we fill for s 2 and then we have all of our D orbitals here so 3 D 10 so 3 D 10 takes us to here now we're in the fourth shell and the p orbitals so 1 2 3 4 5 and then 6 so 4s2 3d10 for p6 would be one way to represent the electron configuration for Krypton and once again you could you could switch the 3 D 10 and the 4 s 2 if you wanted to get say 4 Krypton the electron configuration the noble gas notation would be argon 3 D 10 for s2 for p6 so just to just do whichever way your your professor wants you to do it so that's that's covering the third in the fourth period but we've ignored the the D orbitals again that'll be that'll be a whole separate video because there it gets a little bit complicated when you get into D orbital D orbitals