In the last video, I talkedabout some of the weaker intermolecular forces orstructures of elements. The weakest, of course, was theLondon dispersion force. In this video, I'll start withthe strongest structure, and that's the covalent network. So if you have a covalentnetwork crystal- and let me actually define theword crystal. Crystal is just when you havea solid, where the molecules that make up the solid arein a regular, relatively consistent pattern, and this isversus an amorphous solid, where everything is kind of justa hodge-podge and there's different concentrations ofdifferent things, of different ions, and different molecules,and different parts of the solid. So crystal is just a veryregular structure.
Ionic bond: bond in which one or more electrons from one atom are removed and attached. Other types of bonds include metallic bonds and hydrogen bonding. Their strength indicates that the atoms are difficult to separate, but malleability.
Ice is a crystal, because onceyou get the temperature low enough in water, the hydrogenbonds form a crystal, a regular structure. And we've talked aboutthat a bunch. But the strongest of all crystalstructures is the covalent network.
And the biggest, or the prime,example of that is carbon when it forms a diamond. So in the covalent network,carbon has four valence electrons, so it alwayswants four more. So when carbon shares withitself, it's very happy. So what it can do is it can formfour bonds to four more carbons, and then each of thosecarbons can form four more bonds to fourmore carbons. And this, one, 1, 2, 3, andit just keeps going on.
This is the structureof a diamond. And the reason why this is sucha strong structure is because you can almost viewthe entire- in fact, you should view the entire diamondas one molecule, because they all have covalent bonds. These are actual sharing ofelectrons, and these are actually the strongest ofall molecular bonds. So you can imagine if the entiresolid is made out of this network of carbons,you're going to have an extremely strong, extremely highboiling point substance, and that's why a diamond is sostrong, and that's why it's so hard to boil a diamond.
Now, the next two, and itdepends on your special cases of the next most solid versionof a solid, and it depends which case you're talkingabout, one are the ionic crystals, and I'll do them bothhere, because one isn't necessarily- ionic crystal-and the next is the metal. Well, it's not the next. They're kind of themetallic crystal. And these bonds, I mean, let'ssay the most common ionic molecule or- that's notexactly the right word, because to some degree, let'ssay if I had some sodium and some chloride- and justremember, what happens with sodium chloride is sodium herereally has one extra electron that it's dying to lose. Chlorine has seven electronsand it's dying to get a new one.
So sodium essentially donatesits electron to chlorine, and then the chlorine becomesnegative, the sodium becomes positive, and they want to benear each other, right? So you have a positive sodiumion and a negative chlorine ion, and the structure of thisis going to look something like this, where they'reall- so let me do the sodium in green. So you have a bunch of sodiumions that are positive, and then you have a bunch ofchlorine ions that are maybe- this isn't the exact way thatthey actually are, but I think you get the idea, that one atomis positive and one atom is negative, so they really,really want to be close to each other. And so this is a pretty strongbond, and it has very- not a very high boiling point. It can have a pretty highboiling point, and this type of structure is actuallyquite brittle. So if you take some dry tablesalt, not dissolved in water, if you have a big block of itand you slam it with a hammer, you'll see that you'll get,like, a big slice of it. It'll just fall off, right?
Because you're essentially justcutting it along one of these lines really fast. That'sthe interesting thing.
Whenever you do something ona macroscale, like cut something, you reallyfundamentally are breaking atomic bonds. So the strength of the atomicbonds really do tell you about how hard or strongsomething is. Now, the metallic crystal we'vetalked a lot about. Metals, they like to get rid oftheir electrons, or not get rid of them, they liketo share them. So what happens is, let's say inthe case of iron, you have a bunch of iron atoms.This is all iron. And their electrons are allowedto roam free in the neighborhood. These are all the electrons.
They're allowed to roam free. And because of this, it formsthis sea of electrons that are negative, and that makes ita very good conductor of electricity.
And, of course, since the ironatoms have allowed their electrons to roam, they allbecome slightly positive. And so they're kind of embeddedin this mesh or this sea of electrons. And so the metallic crystals,depending on what cases you look at, sometimes they'reharder than the ionic crystals, sometimes not. Obviously, we could list a lotof very hard metals, but we could list a lot ofvery soft metals. Gold, for example. If you take a screwdriver and ahammer, you know, pure gold, 24-carat gold, if you take ascrewdriver and hit it onto the gold, it'll dentit, right?
So this one isn't as brittleas the ionic crystal. It'll often mold to whatyou want to do with it. It's a little bit softer. Even if you talk about very hardmetals, they tend to not be as brittle, because the seaof electrons kind of gives you a little give when you'removing around the metal. But that's not to saythat it's not hard.
In fact, sometimes that givethat a metal has, or that ability to bend or flex, iswhat actually gives it its strength because it's allowed tokind of deflect the force. So the strength, and I'vetouched on this, it also goes into the boiling point.
So because these bonds arepretty strong, it has a higher boiling point. If you just took salt crystaland tried to boil it, you'd have to add a lot of heatinto the system. So this has a higher boilingpoint than say- I mean, definitely things that have justvan der Waals forces like the noble gases, but it'll alsohave a higher boiling point than, say, hydrogenfluoride. Hydrogen fluoride, if youremember from the last video, just had dipole-dipole forces. But what's interesting aboutthis is they have a very high boiling point unless they'redissolved in water.
So these are very hard, highboiling point, but the ionic crystals can actually bedissolved in water. And when they are dissolvedin water, they form ionic dipole bonds. What does that mean? Ionic dipole or ionicpolar bonds. And this is a situation wherethe sodium- and this is actually why it dissolvesin water.
Because the water molecule,we've gone over this tons of times, it has a negative end,because oxygen is hoarding the electrons, and then the hydrogenends are positive because the electron's prettystripped of it. So when you put these sodium andchloride ions in the room, or in the water solution, thepositive sodiums want to get attracted to the negative sideof this dipole, and then the negative chlorides, Cl minus,want to go near the hydrogens. So they kind of getdissolved in this.
They don't necessarily want tobe- they still want to be attracted to each other, butthey're still also attracted to different sides of the water,so it allows them to get dissolved and go withthe flow of the water. So in this case, when youactually dissolve an ionic crystal into water, as an ioniccrystal, not a good conductor of electricity, not alot of charge that is really movable in this state. But here, all of a sudden, wehave these charged particles that can move. And because they can move, allof a sudden, when you put salt, sodium chloride, inwater, that does become conductive.
So anyway, I wanted you to beat least exposed to all of these different formsof matter. And now, you should at least geta sense when you look at something and you should atleast be able to give a pretty good guess at how likely it isto have a high boiling point, a low boiling point, oris it strong or not. And the general way to look atit is just how strong are the intermolecular bonds. Obviously, if the entirestructure is all one molecule, it's going to be super-duperstrong.
And on the other hand, if you'rejust talking about neon, a bunch of neon molecules,and all they have are the London dispersionforces, this thing's going to have ultra-weak bonds. So a gas is almost itsmost natural state. If you get super, super cold,you might be able to get it to a fluid, and then everythingin between. Anyway, hopefully, youfound that useful.