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consider this molecule
what are the bond orders for each Bond
shown in this diagram
so let's start with the CH Bond what is
the bond order
for bonds that are not involved in
resonance
the bond basically tells you the bond
order
so for a single Bond the bond order is
one
for double bond the bond order is two
and for a triple bond the bond order is
3.
now for bonds that are involved in
resonance you can have fractional Bond
orders
so for the CH Bond that's simply a
single Bond so that's going to have a
bond order of one
every
single bond that we see here
that doesn't participate in resonance
has a bond order of one
the double bond has a bond order of two
the triple bond has a bond order of
three
now let's focus on this group right here
I'm going to redraw it like this
and let's show the lone pairs
so we have two lone pairs on the
carbonyl oxygen three lone pairs on the
other one
now
if there were no resonance structures
you'd assume that this would have a bond
order of two
but because we can draw
a resonance structure
the bond order is going to be different
if we take a lump here
we can use it to form a pi Bond and we
can break this Pi Bond put in two
electrons on that oxygen
so this oxygen will now have two the
other one will have 3 and the negative
charge
so now looking at this particular Bond
would you still say it has a bond order
of two
because here it looks like it has a bond
order of one
it turns out that the the actual answer
is going to be an average of those two
numbers it's 1.5
so the way you would calculate bond
order
is you would look at the number of bonds
of the atoms that participate in
resonance
so that would be three bonds here
and you would divide those three bonds
which
are basically part of those two atoms
so those three bonds are connected to
those two atoms not including the
central atom
so you can think of it as the three
bonds being shared across two atoms
so you get a bond order of 1.5
and it makes sense
here it looks like it's two here it's
one the resonance hybrid is actually an
average of the two
so it's 1.5
so that's the bottom order
for the two carbon oxygen bonds
now what about the solve for oxygen
bonds what's the bond order there
first let's calculate it and then let's
make sense of it this negative charge
can be shared among these three oxygen
atoms so all of those three oxygen atoms
they can have a single Bond or a double
bond
so to calculate the bond order
we have five Bonds in this system of
resonance
and those five bonds are spread out
across three oxygen atoms
so 5 divided by 3 that's 1.67
now let's draw the resonance structures
for this group
so this is one form
we can also put the oxygen there I mean
the negative charge on that oxygen
and we can also put the negative charge
on the oxygen in the bottom
so let's focus on this Bond
here it appears to have a bond order of
two
here it looks like it's one and here it
looks like it's two
if we were to average two one and two
what would what number will we get
so two plus one plus two
that's three numbers so we're going to
divide it by the three numbers
so we get five over three
so the bond order
for the sulfur oxygen
is 1.67 or 5 over 3.
so what it really means is that
out of the three resonance forms
two of them is going to have a double
bond one is going to have a single Bond
so you get an average of 1.67
so that's another way to picture a bond
order and now you know how to calculate
it when dealing with Organic resonance
structures
