Electronegativity

what I want to talk about in this video are the notions of electronegative elect electro negativity negative negativity and a closely and a closely related idea of electron affinity electron affinity and they're so closely related that in general if something has a high electronegativity they have a high electron affinity but what does this mean well electron affinity is how much does that atom attract electrons how much does it like electrons does it want nessa does it maybe want more electrons electronegativity is a little bit more specific it's when that atom is part of a covalent bond when it is sharing electrons with another atom how likely is it or how badly does it want to hog the electrons in that covalent bond or what do I mean by hogging electrons so let me make let me write this down so so how badly badly wants to hog and this is an informal definition clearly hog electrons keep-keep the electrons to spend more of their time closer to them then to the other party in the covalent bond and this is how how how much they like attract electrons or how how how much affinity they have towards electrons so how much they want want electrons and you can see that these are very these are very related notions this is within the context of a covalent bond how much electron affinity is there while this you could think of it as a slightly broader notion but these two trends go absolutely in line with each other and to think about to just think about electronegativity make it a little bit more tangible let's think about one of the most famous sets of covalent bonds and that's what you see in a water molecule water as you probably know is h2o you have an oxygen atom and you have two hydrogen's each of the hydrogen's have one valence electron and the oxygen has we see here in its outermost shell it has one two three four five six valence electrons one two three four five six valence electrons and so you could imagine hydrogen would be happy if it was able to somehow pretend like it had another electron then it would have an electron configuration a stable first shell that only requires two electrons the rest of them require eight hydrogen would feel hey I'm stable like helium if it could get another electron and oxygen would feel hey I'm stable like neon if I could get two more electrons and so what happens they share each other's electrons this this electron could be shared in conjunction with this electron for this hydrogen so that hydrogen can kind of feel like it's using both and it gets more stable it stabilizes the outer shell or it stabilizes the hydrogen and likewise that electron could be can be shared with the hydrogen and if the hydrogen can kind of feel more like helium and then this oxygen can feel like it gets its it's a quid pro quo it's getting something exchanged for something else it's getting the electron an electron it's sharing electron from each of these hydrogen's and so it can feel like it's that that it stabilizes it similar to a similar to a neon but when you have these covalent bonds only in the case where they're equally electronegative would you have a case where maybe there shouldn't even there what what happens in the rest of the molecule might matter but when you have something like this where you have oxygen hydrogen they don't have the same electronegativity oxygen likes to hog electrons more that hydrogen does and so these electrons are not going to spend an even amount of time here I did it kind of just drawing these you know these valence electrons as these dots but as we know the electrons are in this kind of blur around around the around the actual nuclei around the atoms that make up the atoms and so in this type of a covalent bond the electrons the two electrons that this bond represents are going to spend more time around the oxygen than they are going to spend around the hydrogen and these these two electrons are going to spend more time around the oxygen that are going to spend around the hydrogen and we know that because oxygen is more electronegative and we'll talk about the trends in a second this is a really important idea in chemistry and especially later on as you study organic chemistry because because we know that oxygens more electronegative and the electrons spend more time and around oxygen around hydrogen it creates a partial negative charge on this side and partial positive charges on this side right over here which is why water has many of the properties that it does that it and we go into much more depth in that in other videos and also when you study organic chemistry a lot of the likely reactions that are going to happen can be predicted or a lot of the likely molecules that form can be predicted based on electronegativity and especially when you start going into oxidation numbers and things like that electronegativity will tell you a lot so now that we know what electronegativity is let's think a little bit about what is as we go through as we start as we go through a as we go through a period as say as we start in Group one and we go to group and as we go all the way all the way to let's say the halogens all the way up to the yellow column right over here what do you think is going to be the trend for electronegativity and once again one way to think about it is think about the extremes think about sodium and think about chlorine and I encourage you to pause the video and think about that assuming you've had a go at it and it's in some ways the same idea or it's a similar ideas ionization energy an Electra something like sodium has only one electron in this outermost shell it would be hard for it to complete that shell and so to get to a stable state it's much easier for it to giveaway that one electron that it has so it can get to a stable configuration like neon so this one really wants to give away an electron and we said we saw in the video on ionization energy that's why this has a low ionization energy it doesn't take much energy to in a gaseous state to remove an electron from sodium but chlorine is the opposite it's only one away from completing its shell the last thing it wants to do is give away electron it wants an electron really really really really badly so it can get to a configuration of argon so it can complete its third shell so the logic here is that sodium wouldn't wouldn't mind giving away an electron while chlorine really would love an electron so chlorine is more likely to hog electrons while sodium is very unlikely to hog electrons so this trend right here if when you go from the left to the right your electronegativity let me write this you're getting more electronegative more electro electronegative as you as you go to the right now what do you think the trend is going to be as you go down as you go down in a group what do you think the trend is going to be as you go down well I'll give you a hint think about think about atomic radii and given that positive didn't think about what do you think the trend is are we going to get more or less electronegative as we move down so once again I'm assuming you've given a go at it so as we know from the video and atomic radii our atom is getting larger and larger and larger as we add more and more and more shells and so cesium has one electron in in its outermost shell and the sixth shell while say lithium has one one electron everything here all the Group one elements have one electron its outermost shell but that 55th electron that one electron the atom of shown cesium is a lot further away than the outermost electron in lithium or in hydrogen and so because of that it's it's it's it's well one there's more interference between that electron and the nucleus from all the electrons in between them and also it's just further away so it's easier to kind of grab it off so cesium is is very likely to give up is very likely to give up electrons it's much more likely to give up electrons than hydrogen so as you go down a given group you're becoming less less electronegative electronegative so what what are based on this what are going to be the most electronegative of all the atoms well they're going we're going to be the ones that are in the top and the right of the periodic table there going to be these right over here these are going to be the most electronegative sometimes we don't think as much about the noble gases because they aren't they aren't really that reactive they don't even form covalent bond because they're just happy well these characters up here they sometimes will form covalent bonds and when they do they really like to hog those electrons and what are the least electronegative sometimes called very electro positive well these things down here in the bottom left these over here they have only you know in the case of cesium they have one electron to give away that would take them to a stable state like like xenon or in the case of these others in these group two elements you might have to give away two but it's much easier to give away two than to gain a whole bunch of them and they're big they're big atoms so those outermost electrons are getting less attracted to the positive nucleus so the trend in the periodic table is you go from the bottom left to the top right you're getting more more electro electro negative