hey guys I wanted to show you some more stuff with chemdoodle this
time I wanted to use the 3d software rather than the 2d software that I've
shown you a couple of times previously and I wanted to use this one because
it's really great for visualizing molecules in three dimensions so what I
want to use this for today is to build upon what we've already learned about
VSEPR theory and molecular geometry so if you haven't seen my first tutorial on
this in the general chemistry playlist go ahead and check that out because
that's sort of the basics about VSEPR theory and now I want to use now I want
to build on that and use this software to talk a little bit about bond angles
and also some of the molecular geometries that we didn't talk about
before so just to show you what this thing can do here's methane and I've
drawn this the way we might on a piece of paper just with a C and some H's and
of course we know that that doesn't accurately represent the geometry so
what I want to show you here is the way that we can actually use this software
to show us what the correct geometry of any molecule is gonna be so we can go
over here to optimize and use this minimization option and that is going to
use the rules of chemistry to go ahead and calculate what the geometry of the
molecule must be so this looks like it makes a lot more sense right this is
what methane looks like we know that this carbon atom is sp3 hybridized and
therefore it's gonna adopt this tetrahedral geometry and we can drag
this around and and get everything looking you know look at it from all
angles so that it's not just a three-dimensional representation on a
piece of paper we really can turn this all around and make sure that the shape
feels really intuitive in our minds and another thing that we can also do is
verify some bond angles so we can use this tool over here so let's select
these three atoms and we can see 109.47 that's about 109.5 which
is exactly what we expect for a molecule that has tetrahedral electron domain
geometry and molecular geometry as there are no lone pairs there just to show one
other thing here that's kind of fun we can turn auto optimize on so if we turn
that on that is going to ensure that if we want to manipulate this molecule in
any way it is going to stay optimized so I can drag this around by the carbon
atom I can drag this around by one of the hydrogen atoms and we can see that
it will always retain the same geometry and the same bond angles okay so that is
methane now I want to talk about some of the other molecular geometries we know
that within any electron domain geometry there can be multiple molecular geometries
so what if we change this to a nitrogen and then let's get rid of a hydrogen
okay so that's ammonia we've got NH3 now the thing is just by deleting that
hydrogen and changing this to a nitrogen this may not be the precise correct
geometry so let's go ahead and optimize again okay so we have optimized and
let's go ahead and turn auto optimization on as well just to make
sure this stays correct and now we can drag this around and we can see this
geometry because we know that the nitrogen has a lone pair so we're gonna
have to visualize that lone pair right here because nitrogen has five valence
electrons so three one goes to each covalent bond
and then there's a lone pair left over so that's why we get this trigonal
pyramidal looking situation and now let's go ahead and calculate the bond
angles so we've got 108.12 I've seen this as low as 107 but ballpark it's
it's correct and we the thing that's important to understand is that this is
less than what we saw for methane right now and the reason for that is because
of the enhanced repulsion that is offered by a lone pair so this lone pair
up here is going to repel the other groups
more so than a covalent bond to another hydrogen atom would so we do want to
keep that in mind when assessing molecular geometry and bond angles lone
pairs will repel neighboring electron density more than a covalent bond to a
hydrogen atom so or any atom so for methane we saw 109.5 for ammonia with
that one lone pair we're seeing about 108 so let's continue this trend why
don't we go ahead and turn this into an oxygen and then let's get rid of one
more hydrogen okay so we've got water we've got H2O there and let's optimize
again because once again the bond angles are gonna change slightly so we do have
to re optimize in order to get this correct and again let's turn auto
optimize on and now we can look at this and it looks a little bit different
right we can see that this is a little bit different than ammonia we do see the
bent shape right we see that bent shape very clearly because oxygen now has two
lone pairs one going away from us one going towards us to retain that
tetrahedral electron domain geometry but the shape is going to be bent and once
again we can get these bond angles and we might predict that it's going to be
even less than for ammonia because we have now two lone pairs that are
repelling and they're going to repel these hydrogen atoms more so than we saw
for methane or even ammonia so now we see about 104.5 so that is now
significantly less than the 109.5 that we saw for methane so that's what we
want to understand that we already looked at methane ammonia and water in
my previous VSEPR tutorial I did want to talk about these bond angles that is
important so now let's go ahead and look at some other electron domain geometry
and some of the molecular geometries that
we didn't talk about let's do let's put a phosphorus and let's do PCl5
so we've got a phosphorus atom and we've got five chlorine atoms and we've drawn
that however we wish and let's go ahead and minimize and that is going to be our
geometry for PCl5 so we can clearly see that this has adopted a trigonal
bipyramidal molecular geometry right we can see this triangular plane and then
the pyramids extending on either side so clearly the phosphorus atom is sp3d
hybridized right and that's because we've got it's got five valence
electrons and so we need one valence electron for each of the five bonds and
this is the furthest way that these five groups can be and this is an interesting
electron domain geometry because it is the one that has two different bond
angles we've got ninety degree bond angles here but within the plane of this
triangle we've got 120 degree bond angles so it's kind of like trigonal
planar and and and linear combined so that's an interesting one now let's make
some modifications just like before so we can talk about some of these other
ways this can be so what if we what if we go ahead and get rid of one of these
let's turn this into sulphur and then let's turn these into fluorines so now
we have SF4 okay we have SF4 let's get the right geometry there so that's what
this is gonna look like and if we turn this thing around we can see that it
resembles it's still very similar right but the difference is that we're missing
this group over here because this is occupied by a lone pair right sf6 sulfur
has six valence electrons so four of them go to create these covalent bonds
and then we have a lone pair right there okay and this is called a
seesaw shape this is this has seesaw molecular geometry which makes sense if
we kind of look at it like this right it's like a seesaw it's kind of like
right this is one kid sitting here one kid sitting there and that can go like
that so that's what we mean by seesaw and so that's one way that we can do
that now let's continue here so why don't we go ahead and get rid of one of
these another one of these and let's turn that into chlorine so ClF3
actually is a molecule that works so let's go ahead and optimize that so this
is what we get and we call this t-shaped so this is still sp3d hybridized we know
that that chlorine has seven valence electrons and so it's going to use three
to make these covalent bonds and then it has two lone pairs left over right four
five six seven those are going to occupy these locations that were occupied by
atoms in the original electron domain geometry when we had PCl5 so we've gone
from trigonal bipyramidal to seesaw to t-shaped okay and if we got rid of one
more we could get linear so sp3d has a variety of molecular geometries within
the overall electron domain geometry of trigonal bipyramidal so the the
orientation of all the groups is the same but it's interesting what happens
as we start to replace atoms with lone pairs okay so that's that let's go ahead
and try let's put a sulfur atom and let's do SF6 so once again we can draw
that however we want we're just putting six fluorine atoms on a sulfur atom and
let's go ahead and minimize here
and there is the octahedral geometry that we would expect so let's zoom in
there okay so that is what we're looking at this perfectly symmetrical situation
that is octahedral and any of any of these four right we can see this as sort
of the the square base and then we can put the pyramid up there the pyramid up
there so it's like two square pyramids fused together so that's octahedral now
let's change this a little bit let's get rid of one of these fluorines
and let's turn this into bromine okay so we've got BrF5 now and let's make sure
that this is looking correct and so this is an interesting situation we actually
did not see this in my previous tutorial this is called square pyramidal right so
this is square pyramidal because we've got so bromine has seven valence
electrons and so it's gonna use five of them for these five covalent bonds but
then seven minus five we've got two left over that's gonna be this lone pair down
here so that is going to repel the electron density just as if bond to an
atom would and we're gonna retain this overall configuration so this is square
pyramidal and we're looking at sp3d2 hybridized complexes so SF6 was sp3d2
and so is BrF5 with that lone pair five atoms one lone pair six electron domains
overall and let's go ahead and do one more so let's get rid of one more atom
and let's change this to xenon so this is this is a xenon atom and now we we
didn't maybe necessarily even know that some noble gases can make covalent bonds
xenon can because it's large enough so let's go ahead and minimize that again
and we can very clearly see our square planar configuration here so
this is very interesting because it looks like it would be incorrect just
the way that when we draw methane like this when we draw methane like this it's
incorrect because methane there are only four electron domains and so that's an
sp3 hybridization that's got to be tetrahedral but now xenon tetrafluoride
xenon has eight valence electrons remember it's got its valence shell full
so it has eight valence electrons it's going to use four for these four
covalent bonds but then it has two lone pairs left over and because of the way
those repel each other those will prefer to be directly opposite one another
rather than say one here and one here with just a 90-degree angle those lone
pairs because they repel even more so than these atoms they're gonna want to
have a 180 degree they're gonna want to be completely opposite each other so
this is the correct geometry it's not from methane but it is for xenon
tetrafluoride because of those additional lone pairs so this is the
square planar molecular geometry for an over overall octahedral electron domain
geometry that we get when we replace two atoms with two lone pairs so that's it I
just wanted to cover some of these electron don't these some of these
molecular geometries we didn't talk about previously so for sp3d that was
our seesaw and our T shaped and then eventually getting to linear and then
for the sp3d2 we also saw square pyramidal and we also saw
square planar so that's just to show you some of these additional geometries and
just help you visualize once again we are using we are using chem doodle 3d to
do this which is tremendously helpful once again you can make you can
construct any molecule any molecule you want you can go over here and build it
with carbon atoms or you can input whatever other elements you want and
then just go ahead and optimize it and it'll show you what the geometry must be
for a small molecule or a large one as well
and so that's the chemdoodle 3d I've also shown you chemdoodle 2d in the
past and those can come together as a bundle the it's called iChemLabs so I
chem labs produces both of these software's and they're very affordable
and very useful for a variety of purposes whether you're in general
chemistry or organic chemistry or any other chemistry course so I definitely
encourage you to check those out and I'll see you guys next time