this video is on electron dot notation and Le structures electron dot notation is the precursor to a leis structure this is a notation that shows only the valence electrons of an element by placing dots around the element symbol we know that we can easily find the number of valence electrons of an element by looking at the group number on the periodic table as you may remember Group 1 a has one bance electron 2 a has two valence electrons so on and so forth all the way up to group 8 a which will have eight valence electrons in order to do this there are three steps we must follow the first step you simply write the element symbol the Second Step by looking at the group number you determine how many veence electrons the element has and the third and last step is that you place dots around the symbol for corresponding to the number of valence electrons the first example here is boron so you want to locate Boron on the periodic table and you will see that the symbol for Boron is B so I will just draw a capital B Boron is in group 3A which means it will have three valence electrons I like to start at the top of the element so I put one valence electron there and then I like to go go clockwise so one would go here and then one would go there and those are your three valence electrons for Florine Florine is symbol F and is it is in group 7A which means it has seven valence electrons again I start at the top 1 2 3 four and now I can start pairing up because I ran out of room on all four sides five six 7 and that is the electron Dot Structure for Florine so moving on from the dot structures we get to leis structures and these diagrams show the bonding between the atoms of a molecule the electrons that are not involved in bonding will exist as what's called a lone pair so down in this picture here we have two Florine atoms the two electrons the two dots between the two Florine atoms they are shared electrons they are bonded electrons the electrons that I am circling in blue these are lone pairs so you can see that each Florine atom has three pairs of Lone pairs or they each have six electrons that they're not sharing another way of writing which you will see this diagram right here would be replacing the shared electrons with a dash that Dash represents a bond and in this case a single Bond and you will see that on the next slide so a single bond is when there is one pair of shared electrons single bonds are the longest Bond length if you have a double bond that is when you have two pairs of electrons shared two pairs would equal four electrons and the way to depict a double bond is to draw two hyphen lines and almost looks like an equal sign this is shorter than a single Bond Bond lengthwise but it is longer than a triple bond so it's the in between Bond length it takes more energy to break a double bond than it does a single Bond and then lastly a triple bond that is where three pairs are shared that means there would be six total electrons shared there and as you can imagine this is the shortest Bond length a triple bond would look like that nitrogen is known to triple bond certain elements have more Tendencies to bond singly doubly or triple when we are drawing leis structures there's a set of rules that we need to follow and the rules will be posted for you to follow along with but these are the rules for them something to really highlight is Step number five here these two spots here are exceptions or these are added rules so if steps 1 through 4 and then number six does not work you need to refer to number five and I wrote these rules kind of to guide you through different scenarios so we will refer to them as we do this so draw the Le structure for ch3i so the first step you want to determine how many total valence electrons the compound or the molecule has so C on the periodic table has four H has one but notice we have three H's so we have to multiply that one by three and I has seven again I'm getting those numbers just by the group number so we have to total a total of 14 valence electrons that we need to use here if you refer to your rules it says that carbon is most likely going to be present in the center I'm sorry if it is present so we are going to put a c right there and a lot of times it's nice if you just read from left to right it kind of tells you what is bonded to what so attached to this C there are going to be three H's now you want to be symmetrical when you can meaning if I put an H up top I want to put an H down low or if I put H to the left I want to put an H to the right in this case I have three of them so I can't really be too symmetrical here on a 2d plane so I'm just going to put three hes there and then the I will go over here and it says to connect all of those elements together with a bond so I want to refer back to the rules so we can look at them so step number one we did step number two notice we followed that this is very important that hydrogen will always have one bond from it so notice here why didn't I put put this I onto one of the H's why didn't I put an i there well because I knew that once hydrogen has one of those bonds it is done it cannot do anything else and that is because it's in the 1s Su and the highest electrons in the 1s suev is two electrons and by hydrogen sh comping one with carbon notice it already has two there so it cannot have any more so you need to know the hydrogen can only have one Bond coming from it so I knew that I had to go there I also know that most of the time not all of the time but most of the time carbon will have four bonds from it again it's not always there are exceptions but a lot of times that holds true and then we connected all the elements together so we did that step number three says to add unshared pairs of electrons to each non-metal except hydrogen and carbon so that each is surrounded by eight electrons this is called the octet rule so you want everything to have eight electrons again there are different exceptions to this to these rules you some elements sulfur and phosphorus are big ones they can have expanded veent shells so they can actually have more than eight or there are some smaller elements like brillium that can have less than eight aluminum can have less than eight um but these are general rules so I want to add dots to everything so they have eight electrons except hydrogen and carbon which leaves just iodine right so iodine right now it just has this Bond here which we know counts for two electrons that we could redraw this by doing this and that means the same thing so if I need iodine have eight and already has two that means I need to add six more to iodine that's what rule number three is telling me rule number four says count up the electrons and make sure that you used the number you started with make sure you used 14 so let's count these Each Bond counts as two remember so this is 2 4 6 8 10 12 14 that matches and again five is our like exception rules so we'll skip that for now six says be sure that all atoms except hydrogen have an octet meaning eight electrons notice carbon has 2 4 6 eight electrons around it and iodine also has 2 4 6 8 this is the correct low structure next one draw the low structure for ncl3 so again we need to determine valence electrons first chlorine has seven but we have three chlorine so we have a total of 26 electrons we need to use here so we have 1 n we have 3 cl's hopefully it's common sense that the N will be in the middle surrounded by the CLS I could have put this CL up here or I could have put the CLS like this it does not matter if you can be symmetrical you want to be rule number three says to add dots to everything so they have eight so this chlorine would need six this chlorine would need six this chlorine would need six and that nitrogen would just need two because it already has six electrons three bonds times two now let's count them up let's see if we got our 26 here 2 4 6 8 10 12 14 16 18 20 22 2 24 26 we do and last step step number six make sure everything has an octet they all all do have eight electrons surrounding them so here we will run into one of our exceptions with rule number five here so we have ch2o so it looks like here we have 12 electrons we're going to use if C is present again put that in the center and kind of read left to right here now step number two again it's not an always thing like the rules say but 99% of the time carbon's going to have four bonds coming from it so looking at this carbon has three bonds there and there's no other elements to bond to it like there's nothing else down here so that looks strange to me so a red flag's going off but however let's just keep going here it says to add dots to everything except carbon and hydrogen so they have eight so there oxygen now has eight let's count them up let's see if we have this 12 2 4 6 8 10 12 you may be thinking okay we're on we're we're good here step number six be sure all atoms except hydrogen have an octet our carbon does not have an octet our carbon only has six electrons around it the three bonds so that is an issue it did not satisfy the octet rule so look at step number five here it's the second part if an octet is not met move one or more lone pairs to existing bonds between non-hydrogen atoms until the outer shells of all atoms are completely filled which means we know that the hydrogens are finished hydrogen can only have one Bond so it's not even worth looking at These Guys these guys are done so what it's telling us to do is to take a lone pair from oxygen any lone pair doesn't matter which one I just picked the top one and move it to here and what that does is that is just making oxygen share those two with carbon so what's going to happen is those two that are coming down are going to form our double bond there so notice we didn't use any more or less electrons we still use 12 electrons but now forming that double bond helped us satisfy the octet rule for carbon and notice oxygen still has its octet how about for c2h2 looks like we have 10 electrons to use we have more than one carbon so they're both going to be Central and then we have two h's again be symmetrical when you can be so instead of giving one of the carbons two h's give each of them one okay right away I'm looking at my carbon we should have four bonds so something is off here we only use six electrons so we don't want to put dots on C usually you never put dots on H so something weird is going to happen here maybe you see it a double bond doesn't help us because carbon still doesn't have four bonds but a triple bond will help us so what does that do did we use all 10 2 4 6 8 10 we did does everything have an octet this carbon has an octet because there's four bonds and four * 2 is 8 this carbon has four bonds 4 * 2 is 8 we did satisfy the octet in real life leis structures of very many compounds and molecules are very long so here's one you know just a bigger more intense structure which we'll get to later in the course but you can see you know double bonds here you can actually see this is an ion separated that's a little bit different but just want to give you exposure to bigger Lew structures out there in the world this little structure you can see this is kind of in a ring or it is in a ring formation here so that's something special as well I encourage you to think of something you use in your everyday life or something you eat um like look up vanilla for example and just look up the Lis structure of different things you come across in your everyday lives look up the Louis structure on Google um I think you'll be pretty surprised with what you find