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Current time:0:00Total duration:4:43

Predicting bond type (electronegativity)

AP.Chem:
SAP‑3 (EU)
,
SAP‑3.A (LO)
,
SAP‑3.A.3 (EK)

Video transcript

in other videos we had started talking about the types of bonds that might form between atoms of a given element for example if you have two metals forming a bond well you are going to have a metallic bond if you have two nonmetals nonmetals engaged in some type of bonding activity this is likely to be a covalent bond and the general rule of thumb is if you have one metal one metal and one nonmetal na one non metal and that this is likely to be an ionic bond these are the general rules of thumb what I want to do in this video is to better appreciate that bonding is really more of a spectrum there are bonds and we've talked about things like polar covalent bonds that start to look a little bit more and more ionic in nature and so that's what we're going to talk about in this video and think about it in the context of electronegativity just as a reminder we talk about electronegativity in many videos but this is the property of an atom that's in a bond to hog electrons to want the electron density to be closer to it for the electron pairs to spend more time around that particular atom so something with the high electronegativity is going to be greedier with the electrons than something with a low electronegativity we could think about the spectrum between at this end you have ionic and at this end you have covalent and one way to think about it is at the extreme left end you don't have much difference in electronegativities both atoms that are participating in the bond are roughly equal in how badly they want the electrons while in an ionic bond you have a very big difference in electronegativities so much so that one of the atoms swipes an electron from the other so one way to think about it is let me draw a little bit of an arrow here so this is increased electro negativity difference as you go from left to right and someplace in the middle or as as you go from left to right you're becoming more and more polar covalent so for example if you have a bond between oxygen and hydrogen these are both nonmetals so this will be a covalent bond by our just our general rule of thumb and actually the division between metals and nonmetals I'm gonna make it right over here is this blue line is one division you could view although things that straddle it are a little bit more interesting but oxygen and hydrogen are both non metals but you have a pretty big difference in electronegativities this right over here is electronegativity measured on a Pauling scale named after the famous biologists and chemists Linus Pauling and you can see on that scale oxygen is a three point four for one of the most electronegative atoms electronegativity trends we talked about in other videos goes from bottom left to top right the things at the top right that are not the noble gases these are the ones that really are greedy with electrons and oxygen is one of the greediest while hydrogen it's not not electronegative but it's lower at 2.20 so in this scenario those electrons are going to spend more time around the oxygen if they spend an equal amount of time that oxygen might be neutral but since they're spending a little bit more time here we'll say that has a partial negative charge the Greek lowercase letter Delta and on the hydrogen side because the shared electrons are spending more time around the oxygen than around the hydrogen you would have a partially positive charge right over there and so this would be a polar covalent bond maybe on the spectrum it sits right over there depending on how you want to how you view this scale now the other question it says okay this is a spectrum between covalent and ionic what about metallic well metallic bonds are in general going to be formed if you have two things that are not so different in electronegativity and they both have reasonably low electronegativities so that's why things on the bottom left right over here if you have two of these forming bonds with each other somehow that you are likely to have metallic bonds and that makes sense because in metallic bonds you have all the electrons kind of mixing in in a shared pool which give some of the properties like conductivity and so if you have a lot of things that are fairly similar in electronegativity and there are low in electronegativity they might be more willing to share those valence electrons in a communal pool