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Current time:0:00Total duration:12:12

Electron configurations for the second period

Video transcript

let's do electron configurations for the second period so we find the second period on the periodic table and we go across the first element we see is lithium with three electrons so three electrons to worry about for lithium let's think about the first two electrons for lithium the first two electrons for lithium are going to go into the first shell so we talked about this in the last video the first shell when n is equal to one all right the only possible value for L is zero so we're talking about an S orbital and there's only one S orbital in the first shell here so I can draw in go ahead and draw that orbital in so here's the one s orbital in the first shell so lithium has three electrons the first two electrons for lithium are going to go into this one s orbital so we pair up our spins like that so writing the electron configuration for lithium let me go ahead and we'll start it we'll start writing it right here so we have one s two so far well lithium has three electrons but the first the first shell is full right it's closed so we have to move on to the second shell to add in lithium's third electron so in the second shell n is equal to two what are the allowed values for L L could be equal to 0 or L could be equal to 1 so we talked about that again in the videos on quantum numbers so when L is equal to 0 we're talking about an S orbital so in the second shell on the second energy level we also have an S orbital and we also have one of them and we also have to think about L is equal to 1 that's talking about AP orbital the allowed values for ml would be negative 1 0 and positive 1 so 3 possible values right means 3 P orbitals here so we have 3 P orbitals in the second energy level as well let's draw those in on our orbital diagram over here so we already drew in we're already drew in this s orbital in the first shell right next let's draw in this s orbital in the second shell the second energy level it's of higher energy right so we draw it in here so this is the 2 s orbital alright and then we also have P Orbital's in the second energy level we have three of them so we draw in our P orbitals in the second energy level there of higher energy so here are here are the two P orbitals and there are three of them so one of them is it would be 2px one of them would be two py and one of them would be two PZ doesn't really matter which one is which we'll just draw them in there like that so far alright so lithium we've we've taken care of the two two of its three electrons its third electron has to go into this next this next highest orbital in terms of energy alright so that would be the two s orbitals we have energy going up this way alright so as you get higher and higher energy increases so lithium is next electron right as you build up the lithium atom must go into this orbital here alright the 2 s orbital so therefore lithium's electron configuration is 1s2 2s1 and remember what these numbers mean so this means that there is one electron and an S orbital and the second energy level so we have 1s2 2s1 for lithium's electron configuration let's do the next element so that's beryllium beryllium has four electrons to worry about so for beryllium if you look at the diagram let's see if we can just make it make a different color here for beryllium so let's make let's make William red here so one more electron so we can put beryllium fourth electron into into this orbital and pair up our spins and so let's write the electron configuration for beryllium so it'd be one s two and then we have two electrons in the 2's orbital so we'd write two s two here like that alright now we filled the 2's orbital number each orbital can hold a maximum of two electrons we filled the 2's orbital so when we move on to the next element alright which is which is a boron over here so boron has five electrons so let's let's write the electron configuration for boron well so far we have one s 2 2 s 2 but that only takes care of 4 electrons we need 5 so where does the fifth one go the fifth one goes into the next available orbital here so we're going to put the electron in the fifth electron for boron goes into a 2p orbital so we would write to p1 indicating that the fifth electron for boron went into a p orbital in the second energy level so 1s2 2s2 2p1 is the full electron configuration for boron all right let's do carbon so next we have carbon let's use let's use blue for carbon here so carbon has a total of six electrons so we have one more to think about so we know it's going to go into a p orbital a p orbital the second energy level the question is which one of these P orbitals do we put this next electron for carbon so we have to think about something called hoons rule and so I'm never going to pronounce the German properly so but hoons rule tells us that our goal is to minimize electron repulsion here so let's think about let me just go ahead and draw the P orbitals down here so we already have one electron right here alright well it doesn't make any sense it doesn't make any sense to put an electron into the same orbital here right because that puts the electrons really close together in space so if you're thinking about a p orbital remember a p orbital shaped like a dumbbell so i'm just saying we have a p orbital on this axis let's say so we we already have musa Meuse I'll just use blue here so we already have one electron in there doesn't make any sense to add an electron to that exact same p orbital right that puts them really close together in space and electrons repel so that doesn't make any sense so we need to we need to take that electron out of there all right that doesn't make any sense we need to add an electron to another p orbital so we'll take this electron out of there like that so remember there are there are other peor 'but alight on these other axes here alright so here's another p orbital and then here's another p orbital so we need to add we need to add an electron to another one of these whichever one doesn't really matter to say we're adding one here alright so we're adding an electron to a different p orbital whichever one it is px py or PZ and it turns out that it keeping the spins parallel helps to minimize the electron repulsion for for pretty complicated reasons and I think there might be still be doing research on this so and so we put the electron in a different orbital and we keep the spins parallel which helps to lower energy for the atom here and so that's where we're going to put carbons carbons 6 electron we're going to put it into a different p orbital and we're going to keep the spins parallel like that so we can go ahead and write carbons electron configuration just read off the read off everything we have on on our orbital notation here so we have 1s 2 we have 2 s 2 and we have 2 P 2 here with so two electrons in in the P orbitals in the second energy level for carbon alright so next next we have nitrogen so let's use let's use green here for nitrogen so nitrogen has 7 electrons so one more electron to think about so let's put nitrogen right here so we have so far 1 s 2 2 s 2 now let's think about nitrogen so we need to add one more electron to our diagram once again we're going to follow hoons rule here we're not going to add the electron to one of the already occupied orbitals right we're going to add this this electron for nitrogen to an unoccupied orbital and we're going to keep the spins parallel to keep everything lower in energy and so we have three electrons for nitrogen in the 2p orbitals and so we write 2 P 3 so so we have 1 2 3 so we have 1 s 2 2 s 2 2 P 3 would be the full electron configuration for nitrogen alright let's move on to oxygen so let's let's pick let's see here what color should we pick for that let's use orange here for oxygen so we have eight eight total electrons alright so for oxygen let's see let's put oxygen right here so so far we have 1 s 2 2 s 2 so how many how many more electrons do we need for oxygen oxygen is total of 8 electrons we already represented 4 so we need to represent four more oxygens eighth electron now that all of our orbitals are occupied we can start to pair our spins so we put oxygens eighth electron in there so we can start to pair up our spin so we have four electrons in the 2p orbitals for oxygen so we so we write to p4 so 1s2 2s2 2p4 notice if you add these together right 2 & 2 & 4 then you get 8 which is the total number of electrons that we had to represent for the electron configuration for oxygen alright let's move on to let's move on to fluorine so let's use let's use a different let's use a different green here four fluorines let's say fluorine right here nine total electrons alright so once again we were pairing up our spin so we add fluorines ninth electron to there and we can go ahead and write it right here so for fluorine we would write 1s2 2s2 and notice we have five electrons now so 2p five would be for fluorine and then finally let's go ahead and do neon here so neon has 10 electrons alright so we have one more electron to account for we have one more space right the the last electron for neon would go into a 2p orbital here so for neon we would write 1s2 2s2 2p6 notice we have no more we have no more places to put electrons right in the first or the second energy levels we are completely full so the second shell is now full and if you wanted to add another electron you'd have to open up a new shell you would have to go to the third energy level and so you notice a pattern here emerging on the periodic table alright so we said the hydrogen's electron configuration over here was 1s 1 alright and then we went over here to helium is 1 s 2 and then we moved on to move on to the second energy level alright so this was lithium here ended in ended in to s 1 and beryllium ended in to s 2 and we filled the s orbital and moved on to the P orbitals and notice we have over here right so Boron's last electron was 2 P 1 car our bins to pee two nitrogens to pee three oxygens to pee four fluorines to pee five and neon is 2p6 so notice we have these six boxes over here on the periodic table those represent our P orbitals and then over here on the left we have these two boxes right representing our S orbital and so that's the idea the S orbital we have one of them holds a maximum of two electrons we have these two boxes on the periodic table right over here on the right right over here on the right we had we had these six boxes right which is the maximum number of electrons that we can put into the P orbitals because we have three P orbitals each one can hold two so noticing these patterns on the periodic table helps you when you're writing electron configurations you can just sit down and look at the periodic table and write them out after you've had enough practice so make sure make sure to do all of these again and think about think about electron configurations where you're putting your electrons and think about how it relates to the structure of the periodic table