Writing Electron Configurations Part 1

Added: 2026-05-12

[00:00:03]all right guys so we are going to look at the quantum mechanical model which is our current model of the atom and this kind of is based off of Bohr's model with the electron cloud model um so not necessarily that the electrons are in orbits but they have certain areas around the nucleus that they can be so this model determines the allowed energies an electron can have and How likely it is to find an electron in various locations around the nucleus so we have zones around the nucleus where we are likely to find those electrons and this is based off of probability but it does not limit electrons to energy levels this is where they're likely to be but they can still be elsewhere around the nucleus um this model was developed by Erwin Schrodinger um he had mathematical equations to find these zones or areas right so with the quantum mechanical model we end up with atomic orbitals these are not the same as the orbits from Bohr's model and they're derived from those but they are not the exact same they're not Pathways that the electrons travel so an atomic orbital is a region of space in which there's a high probability of finding electrons so where electrons are most likely going to be these are three-dimensional spaces around the nucleus and these orbitals were found using Schrodinger's mathematical equations so by using probability and some calculus they figured out these three dimensional places that come in different shapes and sizes so there are four different types of orbitals we come across you do need to know these with the shapes for some of them so we have the S orbitals which are pictured on the left where it is a sphere around the nucleus so s orbitals are sphere um s orbitals are the ones with the lowest amount of energy as well then we come into the P orbitals the P orbitals look like dumbbells or some might refer to it as peanuts um where it has that small part in the nucleus and it's two lobes like a figure eight that go out from the nucleus um so there are dumbbells that they are small in the center and then balanced on each end um and these can point in different directions they can be on any of the axes then we have D orbitals um don't worry about that one at the top it's a hybrid one but D orbitals we refer to as Clover leaves or double dumbbells um so think of like a four-leaf clover it has the midpoint where all the leaves connect and those four lobes that go off the side um and yet again that can change and rotate its orientation as well and then we have F orbitals um you do not need to know the shape of f orbitals um we rarely use f orbitals simply because these are some of those largest um elements that we come across excuse me these are some of the largest um elements we come across and they have varying shapes they can have different lobes on different planes so excuse me so know that the orbitals go spdf those are going from like lowest energy to highest energy um and you need to know the shapes of SP and D so know that s is a sphere p is that dumbbell or peanut and then D is that Cloverleaf or double dumbbell so Leia said these are different from Bohr's orbits but they're derived from Boar's orbit so Bohr's energy levels those orbits in the quantum mechanical model we refer to as principal energy levels and these energy levels are what are split into the SPD and F sub levels or orbitals so that's kind of the background part to the electron oh excuse me the quantum mechanical model and what we do with this is we show where electrons are going to be found around the nucleus of an atom sorry about that so like I said we are going to use this information to show where electrons are likely to be found around the nucleus which we refer to as an electron configuration so electron configuration shows the range of electrons around the nucleus of an atom so we simply list out the location or the likely location of electrons in an element um we are going to have a list of different principal energy levels and sub levels in this pxn form so the p is going to be a number this is going to be our principal energy level the X tells us what type of sublevel what type of orbital we're in whether it's the SPD or s sublevel and then the N that exponent is going to tell us how many electrons are in that particular sublevel so it's kind of like filling in like a checklist where you have to go in one place you have to do one task before moving on to the next but we're simply listing out everywhere that those electrons are going around the atom so that P that LE that number that starts off with are energy levels um the energy levels are associated with like the row on the periodic table how far away from the nucleus those electrons are going to be um the principal energy levels are divided into the sublevels that SPD and F sub level and not every energy level has every type of sub-level so for the energy level one the first energy level has one type of sub level so it only has an s sublevel whereas the second principal energy level will have two types of sub levels so it'll have an s sublevel and a P sublevel the third energy level will have three types of sublevels so it will have an s a p and a D and then the fourth will have an SPD and F so in general the number of the principal energy level tells you the number of sub-levels in that energy level and they always go in order of spdf so like the first energy level can only have an S it cannot have a p a d or an F foreign s so these sublevels are further split into individual orbitals so the orbitals are those sub-level shapes that we looked at but there might be more than one of them in a certain energy level so an s sublevel that sphere only has one orbital there's only one sphere or one lobe that electrons can go into a p sub level has three orbitals so remember I said that that kind of dumbbell or peanut shape can kind of rotate around the different axes so there can be three different dumbbells or peanuts around that axis um where you can have one that's up and down one side to side and one going front to back so a p sub level has three different orbitals three different places that electrons can go a d sub level is going to have five different orbitals so five different places that electrons can go around an atom and then that F sub level we don't use very much can have seven orbitals so seven different locations four electrons to go around orbital or excuse me around a nucleus and each orbital can have up to two electrons so these are the maximum number of electrons that can be in any given sublevel so an S sub-level Can Only Hold up to two electrons A P sublevel Can Only Hold up to six electrons total a d sublevel can hold up to 10 electrons total and an F sublevel can hold up to 14 electrons total so these are important for when we are actually writing our electron configurations these are the maximum numbers of electrons that are allowed in each sublevel type the orbitals will come into play tomorrow when we look at orbital diagrams which is just another way of writing out electron configurations so let's get to actually writing electron configurations this is where we are going to list out the locations of electrons around the nucleus and some things to remember are that there are only two electrons per orbital so those maximums that we just went over always apply so we said s can have up to two electrons P can have up to six D can have up to 10 F can have up to 14.

[00:11:16]and electrons are going to enter the lowest energy orbitals first there is a certain order that these orbitals are filled in based off of their energy so you have to know which order to fill these in so you can write electron configurations using two different methods the first one is using a diagonal diagram this is probably the more popular way that we've had students write these in the past um it's pretty simple and straightforward to follow but you have to be able to draw a diagonal in order to be able to use it and then there's also a way that you can write electron configurations using the periodic table um this is a little harder to grasp initially but it tends to be easier in the long run because you don't have to remember how to draw a diagonal we're not going to tell you which method to use I'll show you both methods and then you decide which one you prefer over the other so we're going to talk about drawing these using the diagonal diagram first before we can use the diagonal diagram you have to be able to draw it in order to be able to use it so I want to go through the steps of how to draw this out on your own so if you're looking at the periodic table the main part of the periodic table not including the inner transition metals at the bottom there are seven rows of the periodic table so we're going to list out our rows one through seven and all of those are going to have an s sublevel that had the lowest energy so all of these are S's so that's the start that's kind of going to be the long side of our diagonal diagram we said that first energy level that first row only has one sub-level type so that 1s is all that can have that principal energy level of one the second energy level we said has two sub-levels so it has a 2s and then it also has a 2p and all of these have a p so we can list down the principal energy level with the P sublevel and there is a 7p um we don't use it because it's those newly discovered elements but it does exist so that's the second column for our diagonal diagram so our second principal energy level only had two types of sub levels it had the 2s and 2p so that third energy level is going to introduce our third sub-level type so these are D so it's 3D 45d and there is a 60. there's not a 70 we run out of elements foreign energy level only has three sub-levels three orbital types then our fourth energy level has our F sub level so there's a 4f and a 5f so this kind of looks like a sideways triangle if everything is lined up so your diagonal diagram is going to be read from top to bottom but from right to left diagonally so our first diagonal is going to go through 1s excuse me that's all that's on that diagonal so we have another diagonal that's parallel that goes through 2s our next one will go through 2p 3s then it'll go through 3p 4S 3D 4p 5S 4D 5p 6s 4f 5D 6p 7s 5 F 6 d 7p so that gives you the order of those sublevels of those orbitals according to lowest energy so this tells us the order that these need to be filled in in order to put electrons around this nucleus so like I said you need to be able to draw this from scratch in order to be able to use it all right so here is that diagonal so you can see we drew it from scratch but this tells us the order that we go in to write an electron figuration so some key tips that we're going to look at when writing these out is we want to always start with 1s so we always start at the top of our diagonal and work our way down and they always go in this order so it always goes 1s then 2s then 2p 3s 3p 4S and then 3D so there are some that seem out of order but it's based off of the energy that they have we need to make sure that we know how many electrons are in a stable atom of whatever element we're writing an electron configuration for so remember the atomic number is our number of electrons for that atom um you need to look at that previous slide to make sure you know how many total electrons can be in a different sublevel so remember s can only have up to two electrons P can have up to six D can have up to 10 and F can have up to 14.

[00:18:05]okay using all of this information you're going to write out an electron configuration so we're going to go through some examples of these together um this is one of the things that you have to practice writing out um I will tell you if you Google these Google a lot of times has these out of order um so they're not necessarily in the lowest energy order which is the proper way to write it so let's look at some examples together so first one we're going to do is sodium and I'm going to show you how to use the diagonal as we go through writing this out so sodium if you look on the periodic table is number 11 on the periodic table that means that we have 11 electrons that we need to fill in around the nucleus and I'm just gonna write I just like to write the number of electrons to kind of help me keep track of them overall so we said you always go diagonal but diagonal and fill this in so we always go through one s first so we have a 1s sublevel and that sub-level we said could hold up to two electrons we have 11 total that need a place to go so we can put two in here you want to fill each level before going on to the next one so notice this is in that p x n um format and that means that we put two electrons out of our 11 around the nucleus so we have to keep going after 1s go the next diagonal is going to be 2s we said s can hold two electrons so now we have 7 that need a place to go that finishes out that diagonal so go on to the next one so the after 2s we can go to 2p sublevel we set a p sub level can hold up to six electrons that leaves us with one that needs a place to go so after 2p keep going on that diagonal we get to 3s now 3s we said can hold up to two but we only have one electron left once you run out of electrons you're done so there's only one electron in this 3s sublevel so this just lists out all the locations that we are likely to find electrons around this nucleus of sodium so in sodium there should be two electrons in a 1s sublevel two electrons in a 2s sublevel six electrons in a 2p sublevel and one electron floating around in a three S Sub level so it's just giving us the locations of those different electrons as we go let's look at the next example we have manganese I want you to be careful there is a manganese and a magnesium make sure you're looking at the right element manganese on our periodic table is number 25 foreign so here it's a little bit bigger we have 25 electrons that need a place to go sorry about that um so we still have to go in the same order so we are going to fill in the 1s sublevel first we said 1s can hold two electrons so now we have 23 left keep going that finishes out that diagonal go the next one we have a 2s sublevel that can hold two electrons so we have 21 left that finishes out that diagonal so go to the next one we have a 2p sublevel we said P sub levels can hold six electrons so we have 15 left that need a place to go keep going the next one is 3s which we say can hold two electrons so we have 13 left keep going that finishes out that diagonal so go to the next one we then go to 3p which can hold up to six electrons so we have seven left then next is 4S which can hold two electrons so we have five left and then after 4S times 3D and Dewey said can hold up to 10 but we only have five so five are going to go here to finish out this electron configuration so you'll notice that this gets to be very repetitive four different um Parts especially those beginning elements that you're using over and over again all right so I want you to pause the video and try bromine on your own bromine is number 35 on the periodic table so pause it try this on your own and I'll go ahead and go through to write out the answer for you to check when finished so bromine is going to go through 1s with two electrons 2s 2 P6 3s2 3p6 4s2 3D 10. and that got us to 30 electrons we have five left after 3D is 4p which will hold those last five electrons so if you notice all of our exponents should add up to equal 35 and this is something that is different from one element to the next um I may go ahead and start the video here before it times out and there will be a part two to pick up with using the periodic table way um it will also have some exceptions for honors and looking at what do we do if we have an ion