# Drawing Lewis Dot Structures 1 of 10 | Molecular Geometry | www.whitwellhigh.com alright folks in this video you're going to be learning how to draw Lewis structures using an Ian chart also cover molecular geometry orbital geometry hybridization and X notation let's get started you're gonna need two handouts one of a periodic table which you see here the other is this handout this handout is a molecular geometry handout that you will need it is in unit 3 handout 6a on my website so please make sure you have this before you get started so let's get started first like we're going to draw is methane okay it's the easiest one of all to draw but I'm starting with it which is ch4 I'm starting with it because it is simple and it will help you to understand how to draw the charts so in this video I'm going to show you how to draw the chart where I'm gonna name the numbers from and the other videos I'll go a little bit faster this is going to be a basically a grid sheet okay just like this now this different the elements individually okay a stands for valence electrons basically available electrons okay that's what the a is and the N is the needed you know the the need electrons what you need okay that's in now this four is what special rules need to know about the need is you're either going to use the numbers two or eight this is the way it was explained to me while I was in college and I still explain it that way to my students now as far as the need it once again is weird about the two or the eight basically it's this the rule that I'm about to explain to you for this chart only works for the chart it doesn't work if you're trying to draw them just by looking at it doing the octet rule by hand okay this rule will only apply to the chart if you're trying to use the chart now here's this is how simple is if it's one of the very first five elements it will need to that's hydrogen helium lithium beryllium and then finally boron okay basically if you look on your periodic table these first five elements hydrogen helium lithium beryllium and boron well always need to anything past that go ahead and assume that it will need eight now on old some of you chemistry professors up never be yelling up and down but trust me this concept always works for this Ian chart okay now basically now your chemistry teachers don't tell you this because it's so much easier using the end chart you get really fast at it later on – all right basically what we're going to do here is we're going to make a grocery list when we're looking at methane we've got only one carbon so we write carbon only one time here we've got hydrogen four times homo right h h h and then finally h okay now we need to know how many valence electrons does carbon have well carbon is in column 14 it needs four valence electrons hydrogen is in column number one right here it needs one it has one valence electron okay there's those numbers now we have the neat amount carbon is not one of these five elements so it will need eight hydrogen is one of those five elements so it will need two after this you're going to add these up them okay total available we have four five six seven eight we've got eight and so a is equal to eight the need amount we've got two four six eight we got eight plus 8 which is 16 so that neat amount is 16 now the next calculation that we're going to do is s s will represent the number shared s is obtained by taking the N and subtracting a so basically s equals 16 minus 8 which is 8 now that's the number of shared this is shared electron so basically we'll make a little note over here so you can keep track of what this is s represents the shared electrons okay now the next thing that maybe calculate is bonds okay to calculate the number of bonds bonds will equal the s divided by 2 so basically we have bond equals 8 divided by 2 which is what that's right you guessed it 4 so that means that we've got 4 bonds so B means bonds now when you calculate bonds that just means the number of straight lines that you draw okay now we're almost done this is the most important one that we get we got one more important number that we must get before we can draw the next calculation is NB e NB e refers to non bonding electrons okay to get that calculation I'm sorry I'm filling up so much room n be e equals K the number of nonbonding electrons equals a minus s which in this case n be e equals a minus s is what well 8 minus 8 is 0 so that's 0 so basically when we get ready to draw this okay there you get another sheet of paper I'm going to draw this like this and we'll take these two things nonbonding electrons and the number bonds and draw this notice that you only have one carbon in methane so since you only have one of it it's it's very it's you know small amount carbon is going to be your central atom we're on the middle C now carbon has four substituents that's four things around it now the easiest way to start getting used to drawing these is putting things to the to the left the right up and then down you can be picky later but when you draw them but for now we're just going to go left right up and down okay we got four things someone go 1 2 3 4 now here's the thing I have to make sure that all of these get attached so I have to draw four bonds 1 2 3 4 I've used all four of my bonds now nonbonding electrons those are dots here's a simple rule never put dots on hydrogen okay so since you're not allowed to put dots on hydrogen you won't be putting any of them at all and since you don't have any dots to put you don't put dots anywhere okay so that's how you got to do is take care of the dots that's it that's the last step so since we don't have anything we're done now we need to answer the questions as far as what is the molecular geometry that's when we use this sheet here to answer the molecular geometry we need to look at the sheet that I've supplied to you on the website now you've got four bonds and you have no lone pairs so we're looking for four zero combination four zero occurs right here notice that the molecular geometry is tetrahedral so molecular geometry equals tetrahedral okay the orbital geometry notice that it is tetrahedral okay notice that we need to next get the polarity if it's polar or nonpolar notice here that it is shade in a light gray that means it's nonpolar so this one is non-polar okay also the next thing we need to get is the hybridization notice that right here it's sp3 okay and the last thing that we need to write as the ax notation notice that the ax notation underneath tetrahedral is a X for now let me explain this to you real quick the easiest way to get hybridization is basically start counting s and P 1 P 2 and P 3 okay now you just do that by the tops of bonds ax notation since there are four bonds that's why that's four since you got four things attached if you had any lone pairs you have the e with a number but notice that we do not have any lone pairs all right guys 