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- In other videos, we had started talking
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about the types of bonds that might form
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between atoms of a given element.
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For example, if you have two metals forming a bond,
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well, you are going to have a metallic bond.
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If you have two nonmetals,
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engaged in some type of bonding activity,
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this is likely to be a covalent bond.
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And the general rule of thumb is
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if you have one metal,
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and one nonmetal,
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that this is likely to be an ionic bond.
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These are the general rules of thumb.
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What I wanna do in this video is to better appreciate
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that bonding is really more of a spectrum.
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There are bonds,
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and we've talked about things like polar covalent bonds,
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that start to look a little bit more and more
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ionic in nature.
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And so that's what we're gonna talk about in this video
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and think about it in the context of electronegativity.
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Just as a reminder, we talk about electronegativity
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in many videos,
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but this is the property of an atom that's in a bond
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to hog electrons,
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to want the electron density to be closer to it
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for the electron pairs to spend more time
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around that particular atom.
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So, something with a high electronegativity
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is going to be greedier with the electrons
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than something with a low electronegativity.
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We can think about the spectrum between
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at this end you have ionic,
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and at this end you have covalent.
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And one way to think about it is at the extreme left end,
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you don't have much difference in electronegativities.
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Both atoms that are participating in the bond
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are roughly equal in how badly they want the electrons.
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While in an ionic bond,
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you have a very big difference in electronegativities,
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so much so that one of the atoms swipes an electron
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from the other.
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So, one way to think about it is,
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let me draw a little bit of an arrow here,
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so this is increased electronegativity
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difference as you go from left to right.
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And some place in the middle,
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or as you go from left to right,
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you're becoming more and more polar covalent.
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So for example, if you have a bond
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between oxygen and hydrogen,
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these are both nonmetals.
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So this will be a covalent bond
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by just our general rule of thumb.
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And actually the division between metals and nonmetals,
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I'm gonna make it right over here,
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it's this blue line is one division you could view,
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although things that straddle it
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are a little bit more interesting.
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But oxygen and hydrogen are both nonmetals,
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but you have a pretty big difference in electronegativities.
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This right over here is electronegativity
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measured on a Pauling scale,
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named after the famous biologist and chemist, Linus Pauling,
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and you can see on that scale oxygen is a 3.44,
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one of the most electronegative atoms.
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Electronegativity trends, we talk about in other videos,
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goes from bottom left to top right.
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The things at the top right that are not the noble gases,
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these are the ones that really are greedy with electrons.
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And oxygen is one of the greediest.
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While hydrogen, it's not not electronegative,
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but it's lower, at 2.20.
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So in this scenario,
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those electrons are going to spend more time
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around the oxygen.
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If they spent an equal amount of time,
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that oxygen might be neutral,
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but since they're spending a little bit more time here,
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we'll say that has a partial negative charge,
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the Greek lowercase letter delta,
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and on the hydrogen side
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because the shared electrons are spending more time
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around the oxygen than around the hydrogen,
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you would have a partially positive charge right over there.
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And so this would be a polar covalent bond.
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Maybe on the spectrum it sits right over there,
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depending on how you wanna,
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how you view this scale.
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Now the other question you say is
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okay, this is a spectrum between covalent and ionic,
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what about metallic?
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Well, metallic bonds are in general going to be formed
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if you have two things that are not so different
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in electronegativity,
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and they both have reasonably low electronegativities.
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So that's why things on the bottom left right over here,
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if you have two of these forming bonds
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with each other somehow,
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that you're likely to have metallic bonds.
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And that makes sense because in metallic bonds
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you have all the electrons kind of mixing in
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in a shared pool,
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which gives some of the properties like conductivity.
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And so if you have a lot of things
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that are fairly similar in electronegativity,
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and they're all low in electronegativity,
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they might be more willing to share those valence electrons
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in a communal pool.
