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Ch 5.4c MO Pi and whole MO diagram | General Chemistry | YouTubeToText
YouTube Transcript: Ch 5.4c MO Pi and whole MO diagram
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so we have two more 2p orbital uh
atomic orbitals that we still have to
work with so
these two over here remember those are
the ones that are off axis to each other
if you remember from valence bond theory
those are the leftover orbitals that
were available for pi
bonding so these 2p are also degenerate
from each other
and then we can have these kind of
interactions on here so remember back from
from
uh valence bond theory we might get
something like this
with it and and they're perpendicular to
the bond itself
you can have your wave character down here
here
uh and then when the orbital lobes are
matching up the atomic orbitals are
matching up you get some bonding here
and then you get some bonding there and
that's our valence bond theory
so this occurs again in a molecular
orbital theory
so we can form a bonding interaction
down here
so if we take this 2p over here and
we're just going to draw one of them
they're both degenerate down here but
there are just 90 degrees from each other
other
they're going to have a positive and a
positive and negative and negative
we're going to take them down here
they're going to match up with each other
other
and their wave characters are going to
match up for constructive interference
so we end up getting some electron
density here electron density here
we end up getting a picture of that
and then we get lots of electron density here
here
and here so we end up getting the the bond
bond
density is above and below the bond itself
itself
we already know that we call these pi interactions
interactions
and we're going to indicate this comes
from the pi
of the 2p so if we were to get a nice
that you'll see you will see your
electron density looks something
like that on there
so and then we draw the correlation
lines remember that they
are degenerate from each other there's
two sets of them they're just
offset by 90 degrees from each other
we can think about what happens is if we
have a
negative wave character on this side and
a positive wave character on this side
so we end up getting a degenerate kind of
of
um orbital and if they are opposite wave
characters from each other
so we have positive negative over here
and then we have a negative and a
positive here
this is going to cause destructive interference
interference
when you add those wave functions over
there so you end up getting these kinds
of orbitals down here
you get this positive um this negative
then here they actually
and then you get an antibonding interaction
interaction
and we are going to call this the pi star
star
of the 2p and we can and if it's an
anti-bonding interaction it is actually
going to
increase in energy on here
so they are higher in energy remember this
this
y-axis is energy on here
and then when you actually start to see
some nicer drawings of this you'll see something
something
like this so this is the kind of bonding
and kind of the pictures
you should be able to imagine for what's
happening in these
anti-bonding kind of orbitals
then what we can do is actually take all
of this
together and combine it into an entire
molecular orbital diagram
and when we combine it into the entire
molecular orbital diagram
we're going to draw this reaction
coordinate diagram
on here the y-axis is going to be energy
again and then we have our
um the 2s and the 2p
of one of the atoms and our 2s and the 2p
2p
of course people always ask what happens
to the 1s
the 1s remember our inner core electrons
the only thing that we are interested
are the valence electrons so when we're
only interested in the valence electrons
we can go ahead and say the inner core
electrons like the 1s
is not going to do anything so they do
not show up
on our overall molecular orbital diagram
so then we can go ahead and draw our mo
diagram in the middle
over here is is our mo's on here we can
draw our correlation lines to show where
those orbitals actually came from
and this is our sigma that comes from
the 2s
this is our sigma that comes sigma star
from r2s
so remember that the sigma star has to
be higher in energy
than the other two and then we have our 2p
2p
over here we we can form our 2p
2p
our sigma star
that is due to the 2p and we can draw
and then we can't ignore our pi bonds
that happen in there so i'm just going
to draw them in here as a back in an envelope
envelope
we have our pi star uh
molecular orbital and our pi
inner molecular orbital and those are
both to the 2p
so we can go ahead and draw our
correlation lines
from the 2p so this middle portion
represents our molecular orbital diagram
and then we can start to fill in
electrons with that
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