today we're gonna practice naming ionic compounds. so first given the name we
want to provide the molecular formula. so we have aluminum oxide, potassium sulfate,
and iron 3 sulfide. then given the molecular formula we want to provide the
name. so we have Mg3N2, Mn3(PO4)2, and FeCl2. so if you're not sure how to
approach this go ahead and check out my tutorial on naming ionic compounds
that'll tell you everything you need to know and when you're ready give these a try.
so let's take these first three where we're given the name. now let's try
aluminum oxide. so we know these are ionic compounds so what we have to do is
figure out exactly what ions these are. so if we have an aluminum ion what's
going to be the charge on that ion? what is the common charge for aluminum? well
that is going to be Al 3 plus and we can tell because of where it is on the
periodic table. we know that if it loses three electrons it will gain noble gas
electron configuration, so that will be the common ion for aluminum and thus in
aluminum oxide we know we have Al 3 plus. then for oxide we know that that is
going to be O 2 minus. the suffix IDE whenever we see oxide or fluoride or
chloride we know that that is an anion with noble gas electron configuration so
oxygen has to gain two electrons to attain neon electron configuration so
that is the oxide ion so we have Al 3 plus, and O 2 minus and if these are going
to come together to form aluminum oxide which is a neutral compound what ratio
must these come together in in order to form a neutral compound?
well we know we're gonna need two aluminum ions for every three oxide ions
because that is going to add up to six positive charges and six negative
charges right 2 times 3 plus is 6 plus and 3 times 2 minus is 6 minus that is
how we're going to balance the charges on these ions so that is the ratio of
these ions in this compound and so we can just write that out as a molecular
formula Al2O3. now let's move on to potassium sulfate
so potassium, what is a potassium ion? well that is going to be K plus because
if potassium loses one electron it will attain noble gas electron configuration
so that is the common charge for potassium
now how about sulfate sulfate is a polyatomic ion it is SO4 2 minus and
that's just something we kind of have to know we're gonna have to memorize some
of these polyatomic ions so sulfate is SO4 with a 2 minus charge so once again
what is the ratio in which these must come together in order to generate a
neutral compound well we have a 1 plus charge and we have a 2 minus charge so
we're going to need 2 potassium ions for every sulfate ion so that we have 2 plus
and 2 minus and that will generate a neutral charge overall so we put those
together and we get K2SO4 that is potassium sulfate. now moving on to iron
3 sulfide well iron 3 without the 3 we wouldn't be too sure because iron as a
transition metal is capable of multiple oxidation states but here that's what
the Roman numeral is for 3 means 3 plus so when we see iron 3 we know that we
have Fe 3 plus ions and then sulfide just like oxide is S 2 minus. sulfur
needs to gain two electrons to attain noble gas electron configuration so that
is the sulfide ion. now once again what is the ratio in which these ions must
come together in order to generate a neutral compound
well we have three plus and we have 2 minus so what we have to do is have two
iron ions and three sulfide ions that will give us 6 plus and 6 minus that is
neutral overall so we have two irons and three sulfides and we can write that out
as Fe2S3. so these are the molecular formulas that correspond to these names
now let's look at these molecular formulas and write the names so we have
Mg3N2 so Mg3 those are three magnesium ions
those are Mg 2 plus ions and we just refer to the cation by the name of
element so that is just going to be magnesium and then the anion therefore
must be the nitride ion. we have N 3 minus, that's when nitrogen gains 3
electrons to attain neon electron configuration and so we have 3 Mg 2
pluses and 2 N 3 minuses and that gives us magnesium nitride. now moving on
we have manganese we have 3 manganese ions and in this case these are going to
be Mn 2 plus and we just refer to them as manganese. and then we have 2
phosphate ions those are PO4 3 minus, and so we have 3
manganese ions, we have 2 phosphate ions, those come together to form manganese
phosphate. and lastly FeCl2 we are not sure immediately what kind of iron ion
this is but let's look at the anion first. we have 2 chloride ions those are
Cl minus anions those each have a minus 1 charge so that totals to a minus 2
charge overall in that formula unit so in order to balance out the minus 2
charge to generate a neutral compound we are going to need to have iron 2 plus or
iron in oxidation state 2, that means this must be
iron II chloride as opposed to iron III chloride which would have to be FeCl3 so
we have iron 2 chloride and a nickname is ferrous chloride we can also call
this ferrous chloride whereas if iron was in oxidation state 3
that would be ferric but it's in 2, so this is iron 2 chloride or ferrous
chloride. and these are the names associated with these molecular formulas.