hello and welcome to the chemistry
solution this tutorial is on drawing
Lewis structures for molecules with
resonance structures sometimes more than
one correct lewis structure can be drawn
for a molecule let's try the lewis
structure for no.3 - and no three - has
24 valence electrons so when we draw the
lewis structure for no.3 we start by
placing the central atom in the middle
and draw it bonded to all of the other
atoms we've now used six electrons then
we fill in the octets of the atoms
saving the central atom for last at this
point
I've included all 24 valence electrons
so what's wrong with this structure what
you'll notice is that nitrogen doesn't
have an octet of electrons and so to
give nitrogen an octet we will move one
pair of electrons from one of the oxygen
atoms in to create a double bond now all
of the atoms have an octet but did I
have to move the electrons from the
oxygen on the left to create a double
bond and the answer is no I could have
moved I could have created a double bond
between nitrogen and any of the oxygen
atoms and these equivalent structures
are called resonance structures
something that's important to remember
is that resonance structures differ only
in the electron pairs and not in the
placement of atoms if you change the
placement of atoms then you're changing
the actual molecule the other thing to
remember is that Lewis structures are
just representations of the actual
structures and so the actual structure
is a hybrid of these resonance
structures so if I had a collection of
no.3 minus molecules I wouldn't see the
double bond between nitrogen and oxygen
in varying positions in fact I would see
all equivalent bonds between the
nitrogen and oxygen atoms and this is
because instead of that double bond
existing between one nitrogen and one
oxygen atom it's actually shared between
all three oxygen atoms and so it
sometimes helpful to compare resonant
structures to mixing different colors of
paint for example if I were to mix red
paint and blue paint I wouldn't have
paint that oscillated between red and
blue being red sometimes and blue
sometimes I would have paint that was
purple that was a mixture of the two
colors and it's the same way with
resonance structures I don't see this
double bond switching positions in
different molecules the structure is
actually a hybrid of these three
structures and we just draw them all out
separately to represent this how many
resonance structures are possible for
the molecule so2 so2 has 18 valence
electrons when we draw the structure for
so2 we start by placing the central atom
in the middle and draw a bonded to each
of the oxygen atoms remember that there
are two electrons in each bond so as of
now I've used four electrons then I
start by filling in the octets of the
remaining atoms saving the central atom
for last so this structure includes all
18 valence electrons but sulfur doesn't
have an octet which means that we need
to move two electrons from one of the
oxygen atoms in to form a double bond
giving all atoms in the structure an
octet but this double bond could have
been placed between sulfur and either
oxygen atom so in this case the molecule
so2 has two resonance structures and
again remember that the actual structure
for so2 is actually a hybrid or a
mixture of these two structures thanks
for watching the chemistry solution we
hope you enjoyed this tutorial
you
