>> Hello and welcome to the Penguin Prof Channel.
And welcome back to the Fabio Playlist.
If you have not yet met Fabio, you can click there
or in the description box, and watch our introduction.
And we also did a video where we introduced you
to molecular model building,
in so much as why you shouldn't be scared of it.
And we promised you that we would dive deeper
into molecular model kits, and today is the day.
>> Yes. When you are looking at molecular models,
there are two general ideas.
There's a ball and stick model and a wireframe model.
The ball and stick is a very simple model.
It's very popular in introductory organic chemistry.
And it has balls that are representative of atoms
and sticks that are bones.
So you just make bones by inserting in the premade holes,
and you make a carbon hydrogen bone.
>> Isn't it magical?
>> So if you want to make, for example, methane that looks
like carbon, hydrogen, hydrogen, hydrogen, hydrogen, CH4,
you do this four times, and you end up with methane.
And you see it is tetrahedral shape
and corresponds to these four.
If you want to make ethane, which has carbon carbon bond
and has CH3, CH3, you pretty much do the same thing.
And can you make it?
>> Sure.
It's what I live for.
Actually, this was the kind of kit that I had when I was
in organic chemistry, and I'm
to blame any future arthritis I have in my later years
to these little ball and stick models.
>> [inaudible] I have two CH3 units that you put together,
and you have ethane that looks exactly like this.
>> It's kind of pretty.
And, you know, I think even though these are simple models
so far, the thing to think about is that you're gaining practice.
The goal is that you're going to need to be able to look
at structures on paper and imagine them
in your mind in three dimensions.
And by building models, this is how you're going
to get that skill.
>> Yes. And so if you have on paper something that looks
like this, now you have a carbon carbon double bond,
this is ethylene.
And you want to build it with your models,
you use still the normal sticks for the carbon hydrogens
but to make the double bond, you need to use the flexible ones.
So you can actually take two CH3 units and you insert them
like that so you get one bond and make the second bond,
you do this, and then you bend it.
And you end up with ethylene,
you have double bonds and four hydrogens.
>> Can you make a triple bond?
>> You can do that, yeah.
You can do the same thing, if you want to make triple bond,
you just so you make a second one that looks like this.
Now the hydrogens are sticking out 180 degrees.
You end up with these.
>> That's kind of cute.
I like this one.
Now, don't fooled, they don't have this kind
of curvature, right?
It's just, this is the logistics of using these kind
of ball and stick models.
>> Yes. Actually, this idea, this way of making models,
comes directly from Jacobus van 't Hoff, who believed
that atoms were small triangles [inaudible] model,
and specifically, carbon atoms were tetrahedral in shape,
and they made carbon carbon bonds just
by joining [inaudible].
So in about 1874, he came
out with the very first molecular model set made
out of paper.
And he had tetrahedral carbons.
So his models were not very different from these.
>> Hey. Is this what you were using my cereal boxes
for the other day?
>> Yes.
>> Just can't leave him alone for a minute.
Look at this.
So they were made out of paper, like this?
>> Yes, exactly like this.
And he was saying that if you draw the two tetrahedral
by vertex, you make a carbon carbon bond.
And you make ethane like this.
So the center is the carbon carbon bond
and these are the three hydrogens on one side
and three hydrogens on the other side.
>> Oh, I see that, I see that.
>> Then if you want to make a carbon carbon double bond,
you would join these vortexes and these vortexes.
So if they are joined through an edge,
and that's the carbon carbon double bond.
>> Wait, wait.
That's this one?
>> Yes. And the hydrogens are sticking
out where I have my fingers here.
And if you want to make a carbon triple bond, you have one, two,
and three vortexes, so they are attached by a face,
and you have the two hydrogens sticking out like that.
>> Now, I have to say,
you'd have to be a pretty creative thinker to look
at that and imagine this.
But you know for a first go, that's not bad.
>> van 't Hoff was a genius.
>> Okay, so how long did this model that he came up with,
how long did that last?
>> Yes, now we know that this is actually not true,
and that atoms are not small triangles matter
with a specific shape, but it took Linus Pauling in 1931
with his hydrogenation theory,
to come up with a better explanation.
And actually, the wireframe models are based
on Pauling's hydrogenation idea.
They are less intuitive, but they're a lot more accurate.
So if you see you have a lot of different pieces
and they have written on the arm, it says, SP-3 in this case.
So you can separate SP-3 as carbon [inaudible] as always.
And these are SP-2 hydrogenated carbons,
it is written on the side as well.
>> I can verify that.
>> And you have an awful lot of pieces
that you actually will not need.
>> Oh, nice, okay.
>> Those are metals.
>> Yeah, not for today.
>> Carbon makes four bonds, this piece has only two,
so you have to join two together and they will snap like that
to make methane, in this case.
>> So I have to say that something that students struggle
with these wireframes is that these pieces all
by themselves don't actually represent anything,
in that sense.
It's not like you can clearly see like with the ball
and stick, oh, that's the atom, that's the bond.
You have to actually put them together like this and then --
actually, if we stick the hydrogens on there,
it's going to be even more clear,
the comparison between the two.
Okay, so now they look much more similar.
There's some real advantages to this.
>> Yes. Not many hydrogens are not specified
as you don't draw normally in organic chemistry.
So you would say this is methane.
And if you want to make ethane, let's say it's CH3, you join two
of them like this and then you can simply make the carbon
carbon bond like that.
And that's the equivalent of these.
If you want to make a double bond, now you have
to use different pieces.
You take a double bond piece and an SP-2 carbon.
Now, these per se don't represent anything but you need
to put them together, but it's not together in the same way.
And you will end up with ethane, which is ethane,
which is you see the correspondences are pretty much
the same.
The main problem with this way of presentation is
that the angles inside the hydrogen carbon hydrogen bond
are fixed at 109, which is the right angle.
While if you want to make ethane, like this,
these angles should be 120
because they're 360 divided by 3.
So this angle is slightly too small.
And these models are very good for very simple molecules,
but they won't actually be accurate enough
when you start building up.
While these are 120 and they are a lot more faithful
to the right bond angle.
We see that in a minute.
So for example, if you make benzine, that's 6H6,
it's six hydrogen with three double bonds in it.
And if you build it, you end up building it like this,
and you see that the angles do not match.
So this angle is a lot smaller than this angle,
which is not what supposed to look like.
And in the wireframe, you see that the angles are correct,
they're all 120 degrees, they're all the same.
So there are real [inaudible],
because if you start making big bundles with this ball
and stick approach, the hosts just won't match.
>> So I hope that you guys can see that there are advantages
and disadvantages to both of these types of models.
And you know, my suggestion would be that you got to get
out there, you got to play with these things,
and start to see how they work,
and start to translate what you're seeing on paper
to what you can build in three dimensions.
And I think we're going to go from here,
and the next video is discussing those hashes and wedges
that you guys draw all the time.
And students really hate those.
But, you know, get used
to drawing these things and building them.
And trust me, it's going to make a big difference.
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Bye, bye.