Electron Geometry, Molecular Geometry & Polarity

hello hello everyone welcome to another Sunday tutoring session with me Melissa Maribel so happy to see that everyone is joining in and we're focusing on a new topic today and every single Sunday we'll be getting into more and more detail with different concepts of chemistry just to really guarantee that you will not only pass but succeed if you want to get an A or a B or if you do decide to get a C so be it but I'm always trying to to get all my students to get at least a B or an A and I also wanted to talk about why I'm doing this why every single Sunday I am committed to being here within this hour in this timeframe to really just give you my knowledge and share my knowledge of chemistry and what I've learned throughout the years and all my you know my little trip tricks and tips on chemistry in general so the reason why I'm doing this is as a thank you for subscribing and really appreciate that you guys are such great subscribers you're viewing and commenting on everything and I love that participation so as I thank you I'm doing these Sunday sessions also something really cool is if you guys help me get to 10,000 subscribers so if you share with any classmates or if you know anyone that can really benefit from these tutoring sessions or really just my channel in general please share my my videos to get us to 10,000 subscribers and if that is the case if we get to 10,000 subscribers I will do an eight-hour live tutoring session yes you heard correctly eight hours live where you can ask your questions and let's just really really get down to all the other questions that you have and to really prepare you for your finals so you can succeed again because I know the chaos of finals I live it every single semester with my students and I have dealt with it myself before as a student previously so really helped me to get there guys and let's let's jump right into today's topic of different geometries so we're going to have several different types so we're going to have geometry molecular geometry and also something known as Vesper theory so we'll go over all of this as well as polarity so what we'll be doing at towards the end so make sure to stick stick around towards the end we're gonna be focusing on polarity and a really cool trick as to how to know if something's polar versus non polar it's a really awesome visual that incorporates like just bodybuilding so tune in for that okay so let's dive right in and we'll focus on C we'll focus on just the differences of our typical Lewis structure that we've seen before as you can tell here so last week we were doing just your regular lewis structures and how to draw them and how they're bonding to other elements to form the structure or compound as a whole now today we're gonna focus on something known as Vesper theory and what Vesper theory indicates or stands for is our valence shell electron pair repulsion okay I know it's a mouthful so our Vesper Theory here is really just showing you how the structure or the molecule actually wants to be drawn so when it's talking about electron pair repulsion note that electrons are negative and electrons as they come together they want to repel against each other that's why it's called repulsion so in our case we wouldn't necessarily have this sort of structure we would actually have hydrogen all spaced out or all the bonds properly spaced out so they can repel each other so once again best birthday as a whole is really just a valence shell electron pair repulsion where our electrons are repelling away from each other all right so there are several different types which we'll get to you probably are starting to see different types of charts like this in class or if you haven't just yet you will get there this is specifically the different types of Vesper theory and you'll see that everything on this table is something that you will have to know just is pretty much the proper way to raw different Lewis structures in Vesper theory and we'll get to that the next portion of this is really diving into different types of geometries and what in the world they are alright so we're gonna have two different types of geometries electron and molecular now electron geometry is really just based on the total number of electrons or electron groups and molecular geometry is the description of the overall shape so like let's say electron geometry could be something known as tetrahedral while molecular geometry is known as something like bent so tetrahedral is telling you that there are four tetra meaning four electron groups and bent is really just describing the shape of that structure but we'll dive into that so to figure out how many electron groups in total you have I have a formula here and our electron groups are our bonds plus our lone pairs and it's not the individual lone pairs it is the pair itself so we'll get into that and we're actually gonna get really really into detail of every single type you're ready all right so our first type is linear and I have an example of a linear structure so far now I'm going to first start off with identifying the group the overall electron groups so I'm going to show this as electron groups and we said that electron groups are our bonds plus our lone pairs now specifically this is going to be on your central atom so in our case beryllium or B E is our central atom for this Lewis structure now we'll have our lone pairs so specifically there are only two bonds and there are no lone pairs on your central atom so I'm gonna say plus zero and that's where I get this value to number of this is also saying electron dense areas I want you to think electron groups alright so when it says electron dense areas or electron pairs or electron groups there all really just referring to how many electrons are surrounding that a central atom so this is just a simple little structure or representation of a linear electron geometry all right so that's our first part and then also it's going to be the same exact thing for our molecular geometry so we don't start till like whenever we start to change the amount of lone pairs on the central atom that's when your molecular geometry will change so in our case since we haven't added any lone pairs the molecular geometry will be the exact same as our electron geometry move or not so now let's look at something that has three different electron groups so in our case let's start off with this first type boron is our central atom and I'm gonna count again so I'm gonna see how many bonds and lone pairs are on my central atom so looking at our central atom there's only one two three and there are no lone pairs so in our case our electron geometry is going to be known as trigonal planar and our molecular geometry is also the same it will be trigonal planar because there are no lone pairs on your central atom of boron now let's look at a different type so let's say if we're comparing this to let's compare this to something that actually has lone pairs on your central atom so in this case we're gonna have one and two bonds now I want to make a note here that I did not count the double bond as two bonds okay I only counted the double bond as one bond when we're trying to figure out our electron group so in our case we're only going to have two bonds two double bonds but they're still going to just count as two bonding groups or bonds plus that lone pair on sulfur which is our central atom so in our case our total electron groups would be that three so that's why in this case if the electron geometry would have been trigonal planar because there are three electron groups however now that we added a lone pair on our central atom then it's known as bent for our molecular geometry so that's that's that special case right there that we're seeing whenever we start to add lone pairs on the central atom our molecular geometry will change and we're gonna keep seeing this so let's try another one and then I also wanted to make it out that for Vesper Theory Vesper Theory is kind of that more of that 3d structure that I really kind of showed here with our bond angles so that is something that you have to know let me go ahead and go back to Vesper Theory as a whole so for linear the overall structure is gonna be 180 degrees and I make sense it's just a perfect line right if we go back way back when to geometry remember that a perfect line is gonna be 180 degrees now that's the same concept here for linear make sense why it's called geometry and if people ever asked will I ever use this again you are now right so in this case also for trigonal planar we're gonna have different bond angles as well so whenever we don't have any lone pairs then we're just gonna have at least four trigonal planar we're gonna have 120 degrees as we see on this one now when we start adding lone pairs on our central atom then the bond angles will decrease so in our case we're gonna say that it's now less than 120 degrees on this overall this structure of bent for a trigonal planar electron geometry so let me go back to what I'm trying to say and it'll make more sense once we see this structure so now going back to the Vesper theory of this structure remember that Vesper theory is just saying that electrons want to be our atoms want to be as far away as possible because our electrons are going to repel and they don't want to be you know by each other so that's why I'm spacing everything out and it's actually symmetrical so in our case this would have been 120 degree angle all throughout and that's best for theory I'm also going to show that with our bent structure here where those lone pairs actually start to literally Bend like I want you to think of it as like a weight those electrons electrons tend to like let's say if this is our bond right then our electrons typically actually make it Bend because it's sitting on top so that's the concept there so that's why it's a little bit less than 120 degrees and we'll keep going all right so our other type is known as tetrahedral now tetrahedral will have four electron groups on our central atom so let's check that we'll start with ch4 which is this example and our electron groups as mentioned before are our bonds plus our lone pairs and we're specifically focusing on the central atom alright so in our case we're going to focus on carbon and we're going to count how many bonds there are so there is 1 2 3 & 4 so there's 4 bonds but no lone pairs on carbon so in our case we would have an electron geometry of tetrahedral as well as a molecular geometry of Tata hydro now we'll continue on let's do another type so in this case on PCL 3 we're going to have 1 2 & 3 bonds so 3 bonds plus there's one lone pair on our central atom of phosphorus giving us 4 electron groups so that's why this would have been for now our electron geometry is going to be tetrahedral because our electron geometry only focuses on the overall electrons surrounding our central atom so that's why this when we add those bronze plus those lone pairs from our central atom that gave us four four electron groups tells us our electron geometry is tetrahedral now we just added one lone pair on our central atom so in our case we're no longer going to have a molecular geometry of tetrahedral instead they is known as trigonal pyramidal so as we keep adding more lone pairs the name for the molecular geometry will change and it will not be the same as your electron geometry remember the molecular geometry just focuses on the shape of the structure it's a more like it's more description scripted overall like let's say bent right you're later gonna see something that's known as t-shaped and it's really just telling you what type of shape this overall is now we'll keep going with this another example on our central atom of sulfur let's count those bonds again so in our case we're gonna have one and two so we have two bonds and then looking at our central atom of sulfur we're gonna have one and two lone pairs so two plus two gives us four electron groups so this would be an electron geometry of a tetrahedral but we added two lone pairs on our central atom so the molecular geometry is known as bent which makes sense right you can literally tell up the shape of this is bending those lone pairs are kind of just acting as a weight and it starts to bend that bond just to make room because electrons once again are repelling against each other and they don't want to be close to each other so that's our Vesper theory and I'm going to show you what all of these really look like I also wanna make a note that you're probably gonna see a lot of these where you're gonna have something that's wedged which is this so this is a wedged and then this is a dashed line or bond now let's say let's talk about just what in the world that means so if something is wedged that means it's coming towards you all right so it's coming right out of I want you to think of out of the board or out of the page it's literally just going towards you okay now if something is dashed you can't see it it's behind something else or behind the other like I would say like this one is in the back and you really can't see it so anytime there is a - bond that is not in your eyesight or in your eye level like you can't see it anything that is a solid line you can't see it it is in your eye sight your eye eyeline and then anything that is wedged is literally coming right towards you all right is that making some sense guys so I could even kind of think about it this way here I oftentimes do this with students now let's look at it this way so it makes so much more sense okay okay sharpies so let's say we're doing something like I'm gonna go back to something like trigonal planar and we have these three bonds right all right so looking at this it's a little bit tough to say but there we go looking at this I want you to think of the pink this this lighter pink coming towards you so that's going to be wedged now this next one the blue that is right here that's still in your eyesight right you can still see that now or in your eye line so you can still see that so this would just be a single line now you can barely see this hot pink right it's a kind of hidden behind here so that's going to be dashed so anything that's kind of hiding in the back like if we were to kind of move this this is coming towards you right so that's going to be wedged this is a solid line because you can still see it and however it's kind of hard to see all the way in the back this hot pink sharpie that's going to be dashed so that's kind of essentially what we're looking at with a 3d structure Vesper is a way to draw a 3d structure 2d right so this is kind of like the the easier way to look at it and that's essentially what actually a lot of you guys probably have done with different 3d models or those kits that you have that you have to work in in lab so continuing on with that concept this is the proper way that you would actually draw a tetrahedral structure in Vesper theory now this is what it would look like and everything's kind of nicely spaced apart and as I mentioned that wedge is coming towards you that - is going in the back and this is another way of drawing trigonal pyramidal in Vesper theory just looking at it this way we're in said everything is now kind of making room for those lone pairs on top and then lastly I kind of drew this one in the bent structure is once again having those two lone pairs on top two lone pairs on top and that's making room and kind of bending the rest of that structure so that is tetrahedral let's keep going so I also want to make a note that some of you guys depending on what class you're in whether you're in high school you might just stop at tetrahedral or if you're in a kind of like a prep class a chemistry prep class or introductory class you might just stop here as you continue with chemistry you will see these next geometries so depending on what major you are or just where you are along with chemistry but we'll still get into that now the next type is going to have five electron groups let's look at that so our electron groups in our case let's focus on this first compound right lewis structure and looking at our central atom of phosphorus let's count how many bonds there are so remember electron groups I'm gonna keep repeating this our bonds plus our lone pairs and then if at any point you guys have any questions go ahead and leave them the chat or you can literally ask the question and I will answer that I definitely see that there's a button that says on the screen ask a question and I will be happy to answer your eyes this question another thing by the way as more and more people come enjoying the session definitely let want need help with overall so next week's tutoring session is to be announced just because I want to know what you guys need this these sessions are really designed for you so please in the chat let me know what you're still struggling on and I will help you out and we can talk about that next Sunday alright so continuing on with us let's look at our central atom of phosphorus and we'll see that we have one two four in five electron groups or bonds in general five bonds because there are no lone pairs on your central atom so in our case we're gonna have five electron groups and the electron geometry is going to be trigonal bi-pyramidal alright then now since there are no lone pairs the molecular geometry will be the exact same as our electron geometry so it's also trigonal bi-pyramidal now let's keep going that with a different type there's several different types of these now let's look at the next compound or the next lewis structure and we'll focus on sulfur as our central atom counting our bonds 1 2 3 & 4 so we have four bonds plus there is there's only one lone pair on our central atom so that gives us still five electron groups making it an electron geometry of trigonal bi-pyramidal now if we add one lone pair then it falls near this category and i've often times seen it as seesaw you in some books it could also be known as sawhorse who comes up with these right now seesaw is really kind of just showing the overall shape that um suppose what looks like a seesaw now if we were to see that in a Vesper theory this is kind of what it would look like where your lone pair on that central atom is here and once again that's - meaning we can't see it right it's hidden in the back and then here we'll see that this fluorine is coming right towards you right at you and then this flooring is hidden in the back as well and then these two fluorines on top are in your eyeliner in your eyesight so you can definitely see those so in that case as I mentioned our electron geometry for that case would have been trigonal bi-pyramidal but our molecular geometry since we added one lone pair would be known as seesaw or sawhorse okay now continuing on another type there's so many types now I'm going to look at this structure and count how many bonds again and bromine our central atom so we'll count one two and three bonds our lone pairs on our central atom are one in two so we still have the five electron groups so once again our electron geometry is going to be trigonal bi-pyramidal however since we added two lone pairs on our central atom that is known as t-shaped so t-shaped if we were to draw this as my Vesper Theory it literally looks like a tea right literally looks like a tea so that's why they're defining as that and that's kind of another thing why I keep saying that molecular geometry is really describing this shape of the structure and this is it the best you know example to really show that yes it really does look like a tea alright continuing on let's look at xenon and that's our central atom we'll have one and two bonds on our central atom but looking at how many lone pairs we have one two and three so we still have five electron groups because remember electron groups are our bonds plus our lone pairs and in our case we said we had two bonds plus three of our lone pairs giving us five electron groups so still going with this concept that it has five electron groups our electron geometry would then be trigonal bi-pyramidal and then our overall molecular geometry would be known as linear and that's just because there are three lone pairs on your central atom all right there's one more there's one more goodness all right this next group is known as octahedral all right so an octahedral it just means that there are six and I know that's kind of deceiving right octa typically means H but in our case octahedral is going to refer to six electron groups overall so in our first case we'll see that sulfur has six bonds altogether and we'll count that so on our central group there's one two three four and five and six so right then and there are electron geometry would have been octahedral there are no lone pairs on your central atom making it octahedral for your molecular geometry and then now we'll add some lone pairs to change our molecular geometry so in our case we'll see for our next structure the iodine is our central atom alright let's count those bonds so one and two three four and five there are five bonds plus the one lone pair making it six electron groups so our electron geometry would be octahedral now we added one lone pair so now we have a different type of molecular geometry which is a square pyramidal and will keep going and then just to kind of show this again this is the overall Vesper theory once more I'm going to go back to all of the different bond angles so several different teachers or professors will tell you that you do have to remember them I'll teach you a kind of a trick as to how to remember all of your bond angles just so you don't have to memorize every single one and then in our case let's keep going our next structure looking at bromine we're gonna have one two three four five bonds again five bonds and only one lone pair so that's just another example of square pyramidal and we see that because there are five bonds and there's one lone pair on your central atom of bromine and we'll keep going so the next four xenon will count how many bonds we have in total we have one two three and four bonds and we have two lone pairs on our central atom so looking back at that whenever we have six electron groups we're going to have electron an electron geometry of octahedral but our molecular geometry will change because we added two lone pairs on our central atom so in our case it's known as square planar so this is an example of square planar and this is what it would look like as our Vesper theory all right and as mentioned let me know if you guys have any questions at any point and I'm gonna go back to just the Vesper theory and then we'll get into polarity all right so for best for theory a lot of times you will have to know all the bond angles and it's not as bad as it seems so everything is ordered depending on the electron groups and as I mentioned we have something like you know whether it's two three four electron groups five or six and we mentioned that that too would have been typically linear and I'm just talking about the electron geometry at the moment and three electron groups would have been trigonal planar and four would have been tetrahedral five trigonal bi-pyramidal and then six would have been octahedral so in our case I kind of want you to think of these as like little groups or little families okay so everything that only has two electron groups is going to have 180 degrees overall anything that has three electron groups will have something around 120 degrees now if there are lone pairs on your central atom then it would be less than 120 degrees for those that have three electron groups alright following me a little bit so now I'm going to go to the next type and then if it's tetrahedral tetrahedral meaning that it's going to be four different electron groups then it is typically 109 degrees for your bond angle however when we start adding lone pairs like these two that means it's going to be less than 109 degrees so anytime you are adding lone pairs on your central atom that is going to be less than the typical bond AIM angle of that group and we'll keep going and we'll keep seeing that so now for a trigonal by pyramidal this is where it's a little bit different where we're gonna have something known as axial and equatorial now all this is really saying is and I'll zoom in for this is these that are perfectly ninety degrees as we can see here these are all ninety degrees those are known as axial okay so think of it kind of like axial like maybe like the y-axis alright going back to math that's movie it's something that we can remember equatorial would have been been those on the side making it more of a hundred and twenty degrees and this is specifically for our five electron groups where we would have we would have 90 degrees and 120 typically now for octahedral you're going to typically have ninety degrees all throughout because that's just how you're able to space everything symmetrical and then we'll see that here so however when we start to add lone pairs as I mentioned that's where we get that less than ninety degrees right because typically off to octahedral will have ninety degrees with the and that's that's overall that's kind of the main they main concept here is every single time you'll see those lone pairs kind of scrunching it together you will have less than and I needed grease alright so that was a quick little trick to how to remember all of your bond angles as I mentioned before that depending on what electron group it's in it would be like let's say I'm gonna go over this real quick again that this first one would have been 180 degrees then the third one trigonal planar or with three electron groups that would have been 120 add a lone pair it's less than 120 same thing with tetrahedral it's typically at 109 and then add a lone pair it's less than 109 those are your typical ones everything thereafter as we mentioned with five electron groups would have been 120 and at 90 degrees 90 degrees on your axial and then 120 on your equatorial alright and then octahedral as I mentioned would have been ninety degrees or less if we add a lone pair now let's jump into the concept of polarity I know this is a big concept you will continue to see polarity and overall just the concept as a whole polarity is really gonna focus mostly on the concept of electronegativity and electronegativity is really just how attractive the atom is meaning how how can this atom attract other electrons okay and there are more attractive atoms in our periodic table or elements in our periodic table and as you can see here this is the overall electronegativity trend now I also included the values specifically of the electronegativity on each that you can kind of compare the values so essentially what this is saying is that we will increase as we move to the left of the periodic table and then as we I said left to the right of the periodic table and as we go up in the periodic table it will increase as shown by the arrows here and then I also highlighted your most electronegative atom which is fluorine so at any point if you're forgetting you know what's the trend for electronegativity I want you to think of whatever is closest to fluorine is then the most electronegative all right and then we'll see that here that a lot of times student students think that I'm not sure you know is oxygen or chlorine more electronegative if I'm comparing those two and it's actually oxygen so oxygen would have been a lot more electronegative versus chlorine and you can tell that by the actual values that's kind of something to note is that really the higher up it is and especially like that's really right next to fluorine rather than being under fluorine that would then be more electronegative as you can tell but we'll go over this now how does this tie in to polarity good question good question let's say if we were to have something like HF in our case we're going to compare our overall polarities as a whole now polarity I want you to think of it like a tug-of-war all right so if we're if we're looking at this go back to that table for polarity the most electronegative atom wins the tug-of-war okay so I want you to think of it as let's say anything in that is like furthest away from fluorine is going to be very weak all right so think of someone who just isn't strong all right and then rather fluorine is like a bodybuilder all right can you get that visual in your mind all right so in that case if we were to go back to this and we're looking at that tug-of-war who's going to win that tug-of-war fluorine would because fluorine is a lot more electronegative or a lot stronger and then this is what's known as a dipole moment so a dipole moment is the idea of the tug-of-war where in our case it's really just a pool of electrons so as we mentioned electronegativity is how attractive that atom is to other electrons so in our case since fluorine is the most electronegative in this case it will pool or win that tug-of-war and create a dipole moment which is really just a pool of electrons okay so that's kind of what I'm kind of initiating or trying to have you think about now they're all are also other things relative to polarity we're also going to get into symmetry and how that can change and we'll get into that so just keep thinking about that concept that everything that is closest to fluorine is more electronegative so I want you to think they're really really strong they're bodybuilders up in this little area and then everything thereafter is just weak all right so oh he's kind of think of that you know tug-of-war like who's gonna win that tug-of-war overall so we'll keep going with that and we'll do a bunch of examples now this table is really really helpful because this is talking about whether just the overall molecular geometry or molecular shape is going to make it polar or nonpolar and we'll go over over ulis amount of examples for us to really understand this concept all right so let's kind of just look at this overall we're our first type would have been linear and then what this is this chart is trying to say is that anything that's linear meaning that we would actually have only two bonds on our central atom remember that so if we have two bonds on our central atom or two electron groups on our central atom then and and if they're connected to the same exact atom then it would be non polar and the concept here is because if we were to let's actually look at an example this is a perfect example carbon dioxide so if we were to look at the Lewis structure of carbon side and look at this as we know that oxygen is very electronegative because it's right next to fluorine on our periodic table so since it's very electronegative I want you to think of this as you know they're the bodybuilders again or they're really strong and we're trying to compare and see who's gonna win that fight or who's gonna win that tug-of-war now in our case since they're both oxygen they're both the same strength on equal sides or the same atoms on equal sides they're gonna cancel each other out so if something is symmetrical it would be nonpolar yes do you catch that so anything that is symmetrical will be nonpolar something that is not symmetrical will be polar all right so that's something to definitely know and we'll get into all these different concepts continuing on so what would happen here is our oxygen would pull one way the other oxygen would pull the other way and essentially there would be no about dipole moment meaning no one wins that tug-of-war it's an equal pool of electrons so they just end up kind of going nowhere and that's why this would have been non-poor because there is no dipole moment and then I realized that one is asked a question and he asked how to determine polarity of our geometrical shapes for Vesper theory and I'm answering that right now we're going over that completely right now and we'll keep doing more examples so let's say if we had this other example of HCN now there are two completely different atoms on either side right yeah this is still linear and we'll notice this this is linear because there are only two electron groups right let's go back to that concept so electron groups are our bonds plus our lone pairs so in our case we're not going to count that triple bond as three bonds we're only going to counted as one all right so in our case we only have two bonds and it's linear and that's going to look like what this table is saying whenever we have totally different atoms on opposite sides then it's no longer symmetrical because there are different atoms then that would most likely be polar and we'll see that so going back to this structure think about that tug-of-war once more where nitrogen and let's actually go back to our electron electronegativity and nitrogen has an electronegativity of three yet hydrogen has 2.1 so nitrogen would be stronger right it's a lot more electronegative so that's why it would win that tug-of-war so in our case hydrogen would not be able to compete with nitrogens pull of electrons so that's why this structure would have a dipole moment so once again dipole moment just means that there it's a pool of electrons that they don't cancel each other out and that someone wins that tug of war and in our case this would be cooler so that's a good example of that and we'll keep going and then now looking at the next type of structure which our molecular geometry would have been bent and this bent shape is referring to and it doesn't show it here is referring to there being some sort of lone pairs on that central atom overall and in our case let's go ahead and do something like water this is a very good example you're gonna keep saying this example so definitely know the structure of water now if we're looking at water let's go ahead and kind of practice also doing our electron geometry as well as our molecular geometry so let's figure out our electron groups as a whole so electron groups let's add those bonds on our central atom of oxygen which is one and two and then we'll have two lone pairs on our central atom of oxygen so right then in there if we count this one two three and four we'll have four different electron groups four electron groups would then give us an electron geometry a tetrahedral but our molecular geometry as we just said before was bent because there are two lone pairs on our central atom so since this is bent what would happen because of those lone pairs it would actually make it very electronegative or it would make it cooler because and even just looking at the atoms as a whole I want you to see that oxygen as we said it was very electronegative hydrogen is not so what would happen our dipole moment or who would win the tug-of-war it would look like this and then what I'm drawing is religious I'm showing this as a dipole moment that's what that arrow signifies and that arrow is just telling you what where is the pool of electrons that we're gonna see and this would have been our dipole moment as a whole and then another way that you can also see this as you can see that hydrogen would have been pulling the opposite direction and it's really small because it's very wee and then the reason why I'm drawing the arrow even larger is because I'm showing that oxygen would win and that's where the overall dipole moment would be because oxygen would win that tug of war I'm gonna keep referring to that and in our case this would be very polar so water is very very polar so that concept will continue on and on when you guys get further on in chemistry actually this semester the school year when you guys get into solutions or things like that and I'll touch on that again so another thing to mention is typically when you have lone pairs on your central atom that adds to polarity or that adds to that electronegativity I want you to think that a lot of times with lone pairs that are on your central atom that will make your structure polar typically all right I don't want to say always with chemistry but typically those lone pairs on your central atom will make your compound or your structure polar and will still keep going with these examples so that that kind of went back to this bent shape where it's always going to be polar now let's look at our other types of molecular shape or or structure and we're gonna see something like a trigonal planar now if we were to have the exact same atoms all throughout and it's all consistent then we said that's something that is symmetrical would be nonpolar right anything that has symmetry or a symmetrical is nonpolar something that is not symmetrical will most likely be polar so in our case let's do another example like that here we have trigonal planar how do we know that because there are three bonds or electron groups on your central atom that gives us trigonal planar now going back to this though chlorine is relatively electronegative I would say now it's going to be strong so everything is going to pull in opposite directions and because these are perfect we spaced out as we said a hundred and twenty degrees all of these would cancel each other out and think about it is if we were to have that tug-of-war that rope and we're pulling this all in the exact degree where everything is symmetrical with each other and it's the exact same bodybuilder or the exact same person pulling that rope no one would win right they would get exhausted and then just say we're done but no one would win because no one wins that tug-of-war since it's symmetrical and since it's all equal poles all throughout so since there is no dipole moment or pool of electrons then we would say that this is nonpolar so anytime we have a compound that is trigonal planar and all of the atoms surrounding which we're saying here chlorine chlorine and chlorine since all of them are symmetrical or all throughout our chlorine it would be nonpolar and then let's see what else we can say nice touch all right however if we were to then say something else that was trigonal planar but it was no longer symmetrical and let me see if I even have I think I have an example of that I do perfect here it is so let's compare this one and let's see that this is trigonal planar once again we know that because this is one two and three bonds or electron groups on your central atom and this trigonal planar we can tell that we said that fluorine was the most electronegative atom so it's the stronger one so in our case fluorine would pull on that direction and then hydrogen is very very weak in electronegativity so what won't want doesn't really do much so in our case the one that would win or the dipole moment or a pool of electrons would be on fluorine so right then and there and then what I'm signifying here overall is really just the concept that this is where our pool of electrons would be our fluorine since they're on opposite sides and though everything is symmetrical our fluorine would pull in one direction and it would actually be polar in this case so it really does depend on symmetry it also depends on electronegativity when we're looking at polarity and we'll keep going with these concepts and then symmetry I'm really talking about these different types of geometries now we just went over that trigonal planar and whenever we have two of the same atoms but the last atom is not the same that would give us something that is polar now our next two cases are going to be tetrahedral I did include other larger electron group structures just so we can practice that as well so our next one is a tetrahedral structure remember tetrahedral has four electron groups and then in our case if it's symmetrical again then that means it's nonpolar so if we were to have all of these atoms being the exact same atom that you would cancel each other out because they're symmetrical and they're all the same so let's look at an example of that so let's say if we had this going back to the structure of ch4 and hydrogen and I wanted to include this case because this is actually known as a hydro carbon what's a hydrocarbon a hydrocarbon is a compound that consists of only hydrogen and carbon which is this one right this only contains a ch4 this only contains hydrogen and carbon so this is ch4 hydro carbons all hydro carbons are non polar nonpolar that's something to definitely note whenever you just see any sort of lewis structure that only has hydrogen and carbons throughout nothing else then that will be nonpolar and then we also see that here that even though they're all pooling opposite directions they all have very very small electronegativity because hydrogen doesn't really have much electronegativity and then we'll see here that everything is pulling in the opposite but symmetrical way and no one wins that tug-of-war so once again this is nonpolar and it will keep going with this our next one is tetrahedral once again it's going to be polar and the reason why it's going to be polar is because we no longer have that symmetry here you'll see that there are three different types or sometimes even two and two but they're not all the same atom is what I essentially want to say is that though it's such a he'd role they're not all going to be the exact same atom this is the one exception that I will say with symmetry and we focus on electronegativity so you could draw this structure few different ways you can draw the structure and I'm going to say like this would have been a ch2cl2 so you can draw in this structure a different way where we rearrange our chlorine and our hydrogen to look like this right so in our case if we rearrange this compound or the solute structure in this second form that would have been you know applied to the rule of it being symmetrical and in that case then being nonpolar because these two chlorine would then pull in opposite directions and cancelling each other out and that's what you would think and you would write a non-polar but sadly that would be wrong so in our case it's a little bit different here because of the possibility of drawing this other structure as this other way where we're gonna we're gonna put the chlorines on the opposite side so we're gonna put the chlorines here and hydrogen's on the other side we said that hydrogen is not electronegative whatsoever but chlorine is so in our case I still want you to think about tug-of-war and chlorine would be pooling in this direction but hydrogen would then be pulling the opposite but doesn't really do much because it's not very electronegative so in our case you would win the tug-of-war or that pool of electron electrons would have been the chlorine so in our case this would have been polar so be aware of that if you if you see anything that maybe it seems like it's going to be symmetrical but you can draw it a different way to make it polar then it has a possibility of being polar all right so it does depend on how it is you draw that lewis structure so definitely practice those lewis structures and I would also say don't just stop there and think that like let's say if you were to just see the overall structure or the overall formula chemical formula and you saw this and you said you know what it has it has an equal amount of atoms surrounding that central atom of carbon it has two hydrogen and two chlorine that has to be symmetrical so it's nonpolar don't do that - really really guarantee that you get the answer right I really recommend you to actually draw out the Lewis structure and then and specifically I'm just really like comparing it and and as I mentioned really see if there's any other way that you can also draw the Lewis structure that might make the atom polar especially in this case especially in tetrahedral in that scenario alright so for Shore draw out the structure let's keep going alright so there's another type of tetrahedral and we'll see that here and then this is going back to just looking at that lone pair on that central atom of nitrogen alright so in our case this might seem to be polar or nonpolar so if we were to look at it maybe you might have drawn this a little bit differently and you would have thought that you know what this might be if you were to have said that this is probably something like this and you were to then say okay well everything is pretty symmetrical if I were to chalk this right along the middle and you that seems to be nonpolar because it's symmetrical not the case so in our case whatever as I mentioned whenever we add those lone pairs to our central atom it then makes it polar alright so how I have it drawn above right here is the proper way so another thing too is if you really can't tell from looking at the the drawing or the Lewis structure try to draw it as a Vesper best investment theory overall to see how everything is just angled because whenever we put a lone pair as we mentioned before these bond angles will then decrease so before as I mentioned anything that is tetrahedral as we saw here those bond angles would have been 109 degrees however when we start to add those lone pairs it's less than 109 degrees and it's just because these lone pairs are starting to kind of push the other like I'm really want you to think of it as it's pushing or bending just to make room for those lone pairs because because once again those electrons are repelling each other and they need to have that extra space so in our case this would have been polar because fluorine is very electronegative it's actually the most electronegative and then fluorine is pulling in this direction alright and this is an it's just not symmetrical because the nitrogen is pulling in the opposite direction and then who's gonna win well the fluorines gonna win because it's gonna really cool in that direction however nitrogen is still adding and still putting up a fair fight but because it is not equal it's not an equal pool of electrons if they wouldn't cancel each other out all right so that's another concept to really think about is if they have that imbalance where it's it's literally they're going back and forth or one would just instantly kind of win that tug-of-war which in our cases is fluorine then we can see that okay that's a possibility another thing that actually could even we could have even seen is just looking back at those lone pairs and just said okay well that's going to add two polarity so right then and there I can say it's going to be polar so definitely watch out for that and then we'll see a couple of a couple other types and once again this is now going back to symmetry so let's just focus on something like this and this is going to be trigonal bi-pyramidal because there are 1 2 3 4 & 5 overall bonds or electron groups on our central atom of phosphorous so in our case if we see that it's symmetrical which we do everything is perfectly aligned and I know this is kind of hard to see but it would have been aligned everything is pulling in opposite directions and no one wins that tug-of-war or no there are no unequal pools of electron and I this is really once again going to be nonpolar and these are just great representations of these another kind of concept here would have been let's say if we had something that was octahedral then going back to these types of structures something like this all throughout then once again because this is symmetrical right then and there we can just instantly tell it is nonpolar all right is this making sense we can keep going back to other types we have a little bit of time left and if at any point does anyone have any questions I'm leaving the chat let me know if you have any questions that you want me to go over and also let me know what you want me to cover next week at any point leave a comment below or a chat in the chat definitely let me know and I'm gonna keep going with just these other types that we've saw before all right so we got back to something like this and let's just practice doing a few of these all right so going back to these let's just kind of look at will this be polar would this be nonpolar and focusing on this structure because there is a lone pair on that central atom of phosphorous boom polar because of that lone pair overall we can then say okay that's gonna add to our electron pool and then therefore it would be polar so anytime we really see those lone pairs on our central atom that adds to polarity polar as a whole now I'm gonna keep going to another type and looking at this one and we'll see that okay if we have two lone pairs on sulfur and then also even just looking at hydrogen as a whole we said that that's very very small and that's not really gonna do much at all so in our case hydrogen is weak as we said before in electronegativity so that will barely pull anything and sulfur because it has those two lone pairs and it is more electronegative than hydrogen would pull in that direction causing a dipole moment which we said was just a pool of electrons this would then be polar all right let's do a few more all right let's see what else you can look at this is a good one so let's go back to this one and check and see what this would have been so we mentioned before that this was a molecular geometry of bent and once again we have those lone pairs and even though even though oxygen is very electronegative and it's pulling in this direction because of those lone pairs we're going to have a dipole moment and that will add to polarity as a whole making it polar we're going to keep saying stuff like that so we really mentioned that trigonal planar when all of the atoms surrounding are the exact same they would cancel each other out making it nonpolar and we covered that and then going back to this one remember that anything that's linear and it has that symmetry and there are no lone pairs whatsoever making it nonpolar making sense let's do another type that I mentioned since we have a little bit more time let's say I were to construct this crazy-looking structure and if we were to look at something like this and just think what in the world is going on there are two central atoms carbon and carbon I have no idea if it's polar or nonpolar remember that hint that I told you that anything that is a hydrocarbon right hydrocarbon meaning it only consists of hydrogen and carbon makes it non polar nonpolar right then in there anything that only consists of hydrogen and carbon makes it non polar alright guys so thank you so much for tuning in and joining everything definitely let me know in the chat what you want me to go over next Sunday and I will be you know letting you know what I'm going to be going over as a whole another thing is please help me get to 10,000 subscribers when we get to that subscriber mark then what I will be doing is an eight-hour live tutoring session eight hours I know so an eight hour live tutoring session before your finals just to really help you guys out so you don't have to stress so much and didn't really get these concepts down and just refresh your memory on everything you can also then use that time to ask me questions and we can really just study and work on these concepts together so share my videos let me I definitely let other people know about just me in general my channel anyone that you can think of that will benefit from these chemistry videos anyway in your chemistry class teachers and so on so thank you so much guys for for being here and I will see you next Sunday take care [Music]

Channel: Melissa Maribel

Views: 100,724

Rating: 4.9514523 out of 5

Keywords: Electron geometry, molecular geometry, polarity, chemistry, VSEPR, VSEPR theory, nonpolar, polar, lewis structure, Valence, Repulsion, Electron, bent, octahedral, linear, electron pair geometry, electron groups, bonds, lone pairs, tetrahedral, ap chem, ap chemistry, bond polarity, trigonal planar, electronegativity, dipole moment, molecular shape, valence shell pair repulsion theory, electronegative, bond angles, trigonal bipyramidal, t-shaped, square planar, seesaw, dat, mcat, chem, science, VESPR

Id: XbSW2x35OeU

Length: 62min 24sec (3744 seconds)

Published: Tue Oct 24 2017