CH240 Chapter 1 Video 3 Electronegativity and bond polarity

Added: 2026-05-11

[00:00:02]electronegativity and bond polarity and we remember in chem one and in chem two we probably discussed electronegativity and whether molecules polar or nonpolar so what we're interested in looking at is when electrons are shared equally it is said to be nonpolar covalent bond so between carbons they're gonna be shared equally for our bond you will it'll always be a nonpolar covalent bond when electrons are shared unequally there's an unequal sharing of electrons that are bonded and it's non metal nonmetal it is said to be a polar covalent bond so we're we're gonna go with this is where do we look to find out whether they're going to be shared equally or unequally so where we get this information so hydrogen h2 are shared equally because it's an s-orbital overlapping with an s-orbital for starters they're gonna be shared equally well if I have a carbon - a fluoride the electrons are going to be closer to the fluoride then they will be to the carbon that's gonna give this fluoride a slight negative charge it's a delta and this carbon is gonna be heavy slight positive charge and we use this arrow called a dipole moment to show the direction of the electrons in other words if you look at the arrow the arrows pointing towards the fluoride fluoride which means in the electrons will be closer to the fluoride then the carbon that is like I said is known as a dipole moment it is given a symbol mu so how did we know that they're there and how we know that is based upon electronegativity so we use electronegativity to guide us in making these predictions whether a bond will be polar or nonpolar so using the periodic table and I just put part of the periodic table up there we use what is known as the poly scale where fluoride is the most electronegative it is those it has a scale of 4 where carbon is 2.5 which means that fluoride is going to pull the electrons towards it and we can use this scale as it as a model so if you remember right in your periodic table my version of the periodic table we say electronegativity increases you go to the right and we can see that and it increases as you go up and we can see that here two point six two three point four we can see that it does increase so electronegativity trend so try not can we then predict a direction of the dipole moment for the following so here we have carbon it was two point five chloride is three point two which means chlorines more electronegative so the dipole moment the electrons are going to be pulled closer to the chlorine then they will be to the carbon so if we have a carbon oxygen bond carbon is still two point five oxygen is three point four the electrons are gonna be pulled closer to the oxygen oh and I forgot remember when they're pulled that direction that means that all right whoops gonna be slight negative and that's gonna make the carbon a slight positive oxygens gonna be a slight negative carbons a slight positive so if we do this next one down here a nitrogen and sulfur nitrogen is 3.0 sulfur is 2.6 they're pretty close but they're obvious okay my pencil just disappeared the nitrogen is gonna have a slight pull giving it a slight negative charge and a sulfur then it's like positive charge if we did the carbon in the sulfur we had two point five and a two point six it is pretty much a wash this one nitrogen sulfur is close to a wash so formal charge first of all we want to look at this molecule this is some aldehyde we already know that oxygens can have a slight negative charge and carbons gonna have a slight positive charge these are not considered formal charges these are real charges or should I say partial charges they do exist because of polarity so a formal charge just provides us a method of keeping track of electrons it'll also help us on some other things too eventually so if we have and I have my method of doing formal charge so we have oxygen well we have the hydronium ion I have a method I do use available electrons let's go valence valence electrons and we're gonna do this for oxygen auction has six valence electrons where do I get that it's in column 6 of the periodic table so now the books usually provide a mathematical model that's too complicated so I do what I call my scissor method so any bond I just cut it in two with scissors so now how many electrons around it we count there's 1 2 3 4 5 5 electrons then we just subtract and it's plus 1 so it is plus 1 so remember in kim won and kim - he wrote hydronium ion and it has a positive charge and this is y so let's do this molecule so we'll do carbon and nitrogen so carbon has how many valence electrons periodic table it's in row column for nitrogen has how many valence electrons it's in row 5 so now when I get my scissors out and I just cut there cut cut every bond now we count around the carbons there's 1 2 3 4 we then subtract 4 because that's how many is around it now we get 0 nitrogen we count 1 2 3 4 we subtract 4 we get a plus 1 so with this molecule for tracking the electrons we can say it has a positive full positive charge got a slight one but a full positive charge so some common bonding patterns that you need to be familiar with so with carbon if we have four bonds or eight pairs of electrons around it that has no charge if it loses a pair of electrons it becomes positive and this in this case this is a carbo cation so the next one here it has three bonds but it also has electron pair that are not bonded this is a carbon ion so nitrogen in its normal state neutral position it's going to have three bonds and one electron pair when it then develops for bonds and it can pick up a proton or some positive charged species it's now going to become positive charged if it loses a bond but leaves the electrons then it becomes negative charged so with our oxygen oxygen normally has six ven has six valence electrons it will normally have two bonds and two pairs of electrons in its neutral state if it picks up a bond it becomes positive if it loses a bond so now it has six lone pair of electrons or six three pairs of electrons around it it is now negative this is a pattern that you're gonna see over and over and over again so we need to be very familiar with this cuz it's gonna help us with ionic structures so here I have a molecule ch3 nh3 with a positive charge how do I know the nitrogen has a positive charge when I draw the Lewis dot structure I see that the nitrogen has four bonds nitrogen normally has three bonds and one electron pair so that is why the nitrogen is positive and then there's a chloride because it ion so this would be an ionic structure here the attraction between the positive negative make an ionic compound ionic structure do not draw it this method because if you did if and I'm making a mess nitrogen has ten total electrons around it that is impossible so let's say we have this molecule here sodium acetate this is the correct ionic structure represents there's an ionic bond here between the oxygen and the sodium and since oxygen normally has what two bonds and two electron pairs for neutral now it has one bond and three electron pairs it is negative and it can be attracted into a sodium for an ionic structure it is not a true chemical bond I hate to say that is not bonded together as I have drawn here it is an electrostatic attraction this is incorrect does not listed as you drop that way it represents a covalent bond so what we're gonna find out is turn a little bit that electrons can move etc so if I have I'm just trying to think of it and it could be attracted to a potassium ion the molecule this part of the molecule is covalent but it is considered ionic structure because of the potassium and the oxide are attracted to each other electrostatic clay