Condensed structures

- Let's say we're given the molecular formula C three H eight O, and we're asked to draw a Lewis dot structure. So on the left here is one possible Lewis dot structure that you can draw that has that molecular formula. There are three carbons, one, two, three. There's one oxygen, right here. And if you count up the hydrogens you will get eight. And this Lewis dot structure, let me go ahead and write that, this is a Lewis dot structure here, this one shows all of the bonds. So all the bonds are drawn in. But it takes a lot of time to draw in all the bonds and so we could represent this molecule in different ways. We could condense this Lewis structure a little bit. So this is equal to the structure I'm about to draw. And we'll focus in on the carbon I just circled there in red. So that carbon is this one right here. That carbon is bonded to an OH, so we can say this is an OH right here. Putting lone pairs of electrons on the oxygen. And that carbon is also bonded to this hydrogen, let me draw in that hydrogen. On the right side that carbon in red is bonded to this carbon in magenta. And the carbon in magenta is bonded to three other hydrogens. So we could represent that as a CH three. So I could write CH three here, and the carbon in red is this one and the carbon in magenta is this one. On the left side, the carbon in red is bonded to another carbon in blue and the carbon in blue is bonded to three hydrogens, so there's another CH three on the left side, so let me draw that in, so we have a CH three on the left and the carbon in blue is directly bonded to the carbon in red. So this is called a partially condensed structure so this is a partially condensed, partially condensed structure. We haven't shown all of the bonds here but this structure has the same information as the Lewis structure on the left. It's the same molecule it's just a different way to represent that molecule. We could keep going. We could go for a fully condensed structure. So let's do that. Focus in on the carbon in red. So this one right here. So let me draw in that carbon over here. So that's that carbon. That carbon is bonded to two CH three groups. There's a CH three group on the right, so there's the CH three group on the right. And there's a CH three group on the left. So I could write CH three and then I could write a two here which indicates there are two CH three groups bonded to directly bonded to the carbon in red. What else is bonded to the carbon in red? There's a hydrogen, so I'll put that in. So the carbon is bonded to a hydrogen. The carbon is also bonded to an OH, so I'll write in here an OH. This is the fully condensed version, so this is completely condensed and notice there are no bonds shown. Right, there are no bonds drawn in here, you have to infer you have to infer the bonding from the condensed. All right, let's start with the condensed and go all the way to a Lewis structure, so we'll start with a condensed and then we'll do partially condensed structure, and then we'll go to a full Lewis structure. Just to get some more practice here. So I'll draw in a condensed one, so we have CH three, three and then COCH three. All right let's turn that into a partially condensed structure. So this carbon in red right here we're gonna start with that carbon, so I'll start drawing in that carbon right here. What is bonded to that carbon? Well, we have CH three groups and we have three of them. So there are three CH three groups directly bonded to that carbon. So let me draw them in. So here's one CH three group here is another CH three group, and then finally here's the third CH three group. So this carbon in red over here is this carbon. The carbon in red is also bonded to an oxygen all right, so we need to draw in an oxygen next. So now we have our oxygen. Notice the carbon in red now has an octet of electrons around it. The oxygen is bonded to another CH three group. So the oxygen is bonded to another CH three and let's draw that in so we have our CH three and since we're doing a partially condensed I won't draw in those bonds. We have CH three like that. I could put in my lone pairs of electrons on the oxygen to give the oxygen an octet of electrons. And now we have our partially condensed structure. If we want to expand it even more, and draw the full Lewis structure, again we start with the carbon in red. So here's the carbon in red, and that carbon is bonded to another carbon and this carbon is bonded to three hydrogens, so I draw in those three hydrogens. So this CH three group that I just drew is this one. All right, next, we have a CH three group on the left side, so I need to draw in a CH three on the left, hopefully I have enough room to do that. I'll squeeze it in here, so we have our hydrogens, and that's our second CH three group. So let me circle it in green here. So here's a CH three. And then finally we have let me make this blue down here, we have another CH three group, so I'll draw that one in. So we have another CH three, we'll make room for all these hydrogens here. And that's the one in blue. So we're drawing out all of the bonds now in our full Lewis structure. Next we have an oxygen, so we have an oxygen right in here, with two lone pairs of electrons on the oxygen. The oxygen is bonded to another CH three. So let me let me pick a color here for that one. So we have another CH three on the right, and let's draw it in. There's a carbon with three bonds to hydrogen. So that's our last CH three group, so let me circle it. This one right here is this one. So that's an important skill, being able to go from a condensed to a partially condensed, to a full Lewis dot structure, and also going the opposite direction. Going from Lewis to partially condensed, and finally to condensed. And usually you'll only see these used for small molecules. Right, it's obviously it's obviously easy to work with when you have small molecules. When you have large molecules this doesn't work very well and you'll see almost exclusively bond line structures used to represent larger organic molecules. And we'll look at those in the next video.