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Ch 5.3 multiple bonds and delocalization | General Chemistry | YouTubeToText
YouTube Transcript: Ch 5.3 multiple bonds and delocalization
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our next section of of
our studies is going to be the origins
of multi-bonds and you saw a quick
preview of this but it's worth mentioning
mentioning
again so let's take a look at this
ethene molecule where we have a c double bonded
bonded
c on here so we already know based on
our v
valence bond theory that we should have
a sigma bond and
a pi bond and now that we have hybridization
hybridization
we can say that the hybridization for
the carbon atom
has three electron domains so you need
three atomic orbitals to actually form
the hybridization
so both of these carbon atoms are going
to be sp2
hybridized carbon atoms
and as a reminder where did these sp
hybridize orbitals
so we look at the 2p orbitals remember
we can only form hybrid orbitals from
the valence electrons
on here so you have your 2s your 2p we took
took
these three to hybridize to form
our sp2 hybridized orbital
and we're left over here with another p orbital
orbital
so that p orbital remember our pi
bonds are usually formed by p orbitals
so this actually forms
our pi bond on here
so each one of those carbons
has a p orbital
the atomic orbitals or above the bonds
that can form some sort of bonding
kind of interaction on here
so as a reminder your sp2 hybridized orbitals
orbitals
so your sp2 form
all of your sigma bonds on here
and then your pi bonds are formed by the leftover
leftover
p orbitals in the carbon atom
and that can be extended to the triple bond
bond
so we go back to this kind of molecule
over here that we saw earlier we have sp
hybridized so what we did with that sp
is we took
our 2p orbitals and our 2s and we took
these two and find
the uh these
sp hybridized and then we still have our
two p orbitals
so in this kind of a picture we can have this
this
kind of bonding in here this is our sp
so the yellow ones are our sp
hybridized orbitals then our two left
over p orbitals
can actually form our pi bonds
so we end up getting electron density above
above
and below and also another set
perpendicular to it so this is also behind
behind
that over there with the blue atomic orbitals
orbitals
so this is what really is powerful about valence
valence
bond theory is that we can get an actual picture
picture
of what the bonding actually looks like
and we can describe the bonding as
a series of sigma bonds and pi bonds
what this will also allow us to do is to understand
understand
something else a little bit more
complicated and what we can also understand
understand
is this concept of delocalization
on here so this is actually the lewis
structure of the benzene model
model and it's very flawed because we
have to draw two different lewis structures
structures
to kind of explain what is actually
going on
in here because in reality what we have
is some sort of molecule
that we can express kind of like this
where we have electron density
that is in a circular kind of fashion
so all of these atomic orbital are these
uh carbon atoms
are all sp2 hybridized which means that
there is a p
orbital to form those pi interactions
and then all the carbon atoms will have
some sort of p
orbital that is available for bonding
and this creates the ring of electron density
density
the benzene ring
so to give you a better picture of this
what we can do is we can go to this
website kentube3d.com
and we can look at the benzene orbitals
on here
so here's a picture of the benzene
orbitals on here
so uh in the picture in the upper right
hand corner you can see the sp2
hybridized forms all the sigma bonds
on here so we can go ahead and first
think about all the sp2
hybridized orbitals and they form these
kind of orange kind of orbitals on here
so that works really great and then what
we have left over
are our remaining p orbitals that are
drawn above and below
and what we end up getting is a ring of
electron density
and this is what we call delocalized
electrons and that's really important
for this benzene molecule
so we end up getting these p orbitals
that can form this ring like of
electron density on here
and then if we actually show the
resulting bonding orbital
on here we see that we end up getting a
whole bunch of pi
interactions above and below
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