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Chapter 4.3b Molecular Nomenclature
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welcome to the second video for chapter
four section three
on chemical nomenclature and we're
picking up where we left off with
molecular compounds
so if you have a molecular compound
rather than an ionic compound we
need to be able to name these with
unique and recognizable names in the
same way that we needed to
name our ionic compounds um but things
are a little bit trickier because we
need to know
what element comes first with ionic
compounds we could choose the
uh the element that was the cation which
is usually the metal
but here with molecular compounds we
don't have any cations or anions
and so we need to choose a system to
choose which element
goes first and what we do is choose the
element that is further towards the left
of the periodic table or further towards
the bottom and essentially what that is
is the more metallic
element so the closer towards the metals
that that element is
that element goes first then
we are going to use greek prefixes to
specify any ratios that we need to
so for example uh molecular compounds can
can
exist in many different uh combinations
of numbers of the same kind of element
and we need to um we need to specify
what how many elements or how many of
each type of element are in the specific
compound that we're looking at
the one exception is if the first
element uh there's only one of that
then we can drop the mono prefix so i've
put the greek
prefixes over here just for your
reference um we went over those in the
ionic compound video but here they are again
again
and uh so once we've decided which
element goes first we've used our greek prefixes
prefixes
we're going to use the eyed suffix on
the second element just like we did
with the ionic compounds so here's an
example we're going to go ahead and name
this molecule uh it consists of carbon
and two oxygen atoms
so we start out by figuring out who goes
first so we need to look at our periodic
table and identify which element is
further towards the left
or towards the bottom here carbon is
clearly further towards the left
so it will be the first atom we should
choose what prefix we use
here there's only one carbon atom and
it's the first one so we can drop
the mono prefix so we'll just write carbon
carbon
and then we'll use our prefix for the
number of oxygen
atoms and it's two so di and then oxide
so this is carbon dioxide all right
let's do a couple of
uh more examples so this next one we've
got nitrogen
and oxygen so we need to identify which
element is further towards the left or
towards the bottom
we see that nitrogen is further towards
the left so we will start off with that
we need to use the greek prefix dye for two
dinitrogen and then there are four oxygens
oxygens
so tetra the thing is that now we've got
a vowel next to a vowel so we've got
this a from
tetra and then we have oxide so when
there's an
a next to the o and oxide i just tetra
oxide is clumsy and so we drop that a
uh we can do another one so phosphorus
and fluorine
we look here and we see that phosphorus
is further towards the left
and the bottom than fluorine so we will
start off with phosphorus there's only
one of it we can drop that monoprefix
whoops phosphorus and then our prefix
here is five
penta and then
our element is fluorine and so that
phosphorus pentafluoride so that is how
you name
simple uh molecular compounds
there are a few special types of
molecular compounds that i'm going to
talk about and these are acids
the first kind of acid that we're going
to deal with is binary acids and so
those are things that can
contain a hydrogen and then one other
kind of element
so for example hbr is a binary acid and
so is hcl
so we'll use these two as examples as
we're naming these
if we were just to name these using our
rules we would wind up with hydrogen
bromide and that is in fact what this is
called when it's in its gaseous phase
but if you dissolve this guy into water
it becomes an acid and we need to
specify that it's acidic
so what we do is we go ahead and look at
this hydrogen and we call it hydro as a prefix
prefix
so we use this prefix hydro and then we
take the second element
which is here bromine and we use an ick
suffix on that element so bromine
becomes bromic
and then we add acid to the end of the word
word
so if we do this again we can look at
this one hcl if this is
aqueous dissolved in water it's an
acidic solution and we need to specify
that so it's going to become
hydro for the hydrogen and then
caloric whoops chloric
so that's in a nutshell how you name
binary acids
all right and then the last kind of
compound that we're going to talk about
are oxyacids and these are
a special type of acid that contain hydrogen
hydrogen
oxygen and at least one other element
and so often what we'll see
is that these are hydrogen combined with
a polyatomic ion that has oxygen in it
there's a whole process for naming these
and it always starts out with
we need to omit the hydrogen which means
we figure out what our root
anion is so we're going to look and see
what kind of polyatomic anion is this
that's different by one hydrogen and
what we see
is this is acetate it's c2h3
oh minus or equivalently written a
different way
ch3coo minus but with that extra
so once we know that base name of the ion
ion
of the anion then we can go ahead and
name our acid so what we're going to do is
is
leave out the hydrogen we're just going
to start right off with our anion
and then we're going to think about the
ending of that thing
so we're going to change any endings
that are eight
with ick so we're going to convert this
guy over from
acetate to acetic
and then we add acid
so oops acid not added
let me just fix that typo real quick
acid there we go so uh you may recognize
this as vinegar acetic acid this is vinegar
vinegar
all right so let's do a few more um this
one we recognize
that this is no3 minus with a hydrogen
out front
so again we take this ending and we
switch it from eight
to ick so this becomes nitric
acid all right so this next one's a
little bit tricky
so ah this is not an anion a polyatomic
anion that you know from the list that i
had in the last video
um but if you read your textbook you'll note
note
that if you have a a polyatomic that's
different than
one of the other ones just based by one
oxygen we've got some naming conventions
so nitrate one oxygen less than nitrate
becomes nitric
so this is no2 minus this becomes uh
sorry um one oxygen less than eight
is it so this is nitrite and when we
replace that ending the nitrite becomes
nitrous so this becomes nitrous
acid so there's some more naming
conventions with the
polyatomic ions in your textbook in
chapter 4.3
and i suggest that you read those just
so that you're familiar with them i
didn't cover them in depth
in either of these um videos just for
time but it's a good idea to go ahead
and read those
all right and then the last acid that
i'm going to do is this guy so this
one's a little bit odd because there's
two hydrogens
but that's totally just for charge
balance right because sulfate as we
recognize so4 is a two minus
um hydrogen tends to make a plus one
cation so
uh in fact it's all it makes is a plus
one cation
so we need two of them for charge
balance uh this has exactly the same
naming conventions as everybody else
this is the sulfate ion
and we do our uh our process so we
take um sulfate and um
sulfur is a little bit odd um if we just
followed the rules this would be sulfite
acid but it sounds weird so we use sulfuric
sulfuric
so we just go back to the actual name of
the element in the attic
um and sulfur is just sounds better so
this is sulfuric acid
so that is the naming convention for
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