General Chemistry – Basic Concepts, Atoms, Molecules, & Ions – Simple Compounds

General Chemistry – Basic Concepts, Atoms, Molecules, & Ions – Simple Compounds


In this video we’re going to learn to name
and write the formulas for simple compounds: ionic compounds, polyatomic ions in ionic
compounds and some simple molecular compounds. For ionic compounds we can start with something
relatively simple NaCl. Na as we know from the periodic table is sodium. We’ll capitalize
that and then CL is chlorine. In this case we know that it is chloride so the way this
works is the positive ion and from the location of sodium in a periodic table we know that
it has a +1 charge because it’s in the first column group 1A and chlorine likes to have
a negative charge. We’re gonna change the suffix of chorine to ide to suggest that it’s
negative or to indicate that it’s negative, so sodium chloride. Another compound Li2O
in this case again notice that we’re putting the element that’s going to be a cation first
and we know that lithium is group 1A again so we’re going to have a positive charge and
oxygen is in ground 6A so if we added 2 electrons, -2 we would get to the noble gas configuration
so we’re gonna have a -2 charge on our oxygen. This is going to give us Llithium oxide and
again for the anion we’re gonna chnge the suffix and put ide. Now notice that the name
lithium oxide does not indicate the two lithiums in Li2O but we know that we have to have 2
lithium atoms or cations to match the charge of the oxygen so therefore we do not need
to indicate in ionic compounds how many elements are going together or ions are going together
to make these compounds. These are relatively simple and notice that I’m changing I’m staying
with main group. If we look at a transition metal so FeF3 we know that this is iron but
iron is a transition metal so we don’t know what the charge is right off the bat. We know
that fluoride is a -1 and we know that in this molecule we have three of those so our
overall charge is going to be -3. If we’re going to balance our charge in this ionic
compound what is the charge that’s necessary for our iron? Well if we have three -1 that’s
-3 we’re gonna need a +3 so therefore this is going to Fe+3 with three fluoride ions
to indicate that in the name we’re gonna put iron (III) and then fluoride so for our transition
metals and for those metals that do not have a definite charge as a cation we’re gonna
use the roman numeral system behind. Let’s try a couple where we go from the name to
the formula. So magnesium oxide we know that magnesium Mg is in the second column or group
2A so that’s can have a +2 charge and oxygen that we’ve already looked at has a -2 so therefore
we balance that +2 -2 that’s zero so we can just say him MgO as the formula. Let’s try
another one chromium (III) oxide here we know gonna be Cr +3 and oxygen -2 now we need to
balance this so the correct formula here if we have +3 and -2 well we’re going to have
to have two chromiums which brings up this charge to +6 and we’ll need three oxygens,
3 times -2 will give us -6 so we balance our charge so this would be the correct formula
for chromium (III) oxide. These were some simple ionic compounds. We can make these
slightly more complicated by starting to use polyatomic ions. In polyatomic ions we need
to learn the polyatomic ions. I’m gonna list out a few here but the list is a little longer
than this depending on the text you’re using. There’s usually only one common cation that’s
ammonium NH4+. For the anion’s there’s a really long list. We have hydroxide OH-, cyanide
CN-, nitrite NO2-, nitrate NO3-, notice here that the ite had one less oxygen than the
ate. This is a common system. Carbonate CO3-2, bicarbonate or often called hydrogen carbonate
HCO3-, sulfite SO3-2, sulfate SO4-2, phosphate PO4-3, perchlorate ClO4-, and acetate this
a molecular polyatomic acetate is CH3CO2-. Now when we get a simple compound with a polyatomic
like KNO3 notice that the polyatomic is written together. We know that the potassium ion combines
with the nitrate and so we get potassium nitrate. Let’s look at another example for polyatomics.
Notice that we’re still using the atomic nomenclature system here let’s take in parentheses NH4
to the 2 and then SO4. We know the NH4 is ammonium and the SO4-2 is sulfate. You can
see here that we had to have two ammoniums for the one sulfate but in the name it’s just
ammonium sulfate since we know the charges of these two polyatomics we should have been
able to figure out the name. One more example calcium going the other way calcium carbonate
again calcium is group 2 so that’s gonna have a +2 and carbonate we have to know what that
polyatomic is we know it’s -2 so therefore our formula is just CaCO3. This is our simple
ionic compounds those with just simple ions, cations, and anions and those with polyatomics.
Now let’s look at some molecular compounds. If we look at two carbon with one oxygen and
carbon with two oxygens if we tried to use the ionic naming system this would just be
carbon oxide but we can see here we have two different forms that’s because we’re sharing
electrons not having a cation and in anion so when we go to a molecular compound, ones
with covalent bonds we need a different name. What we’ll use is for CO that is a carbon
with one oxygen so we’ll use the prefixes for one mono we delete one oxygen from mono
to get the oxide so monoxide, carbon monoxide with the CO2 we have carbon again to start
but now we have two oxygens so we’re going to use dioxide to indicate two. This is the
way that we can indicate the right number. Notice here that we cannot rely on the cation
or the anion to figure out how many of the two elements put together so we have to be
explicit about that and we use the prefixes to get us the right number. Let’s try N2O5,
with N2O5 we have two nitrogens so that’s gonna be dinitrogen the oxygen now we have
pentoxide so dinitrogen pentoxide so we have two nitrogens and five oxygens now there are
some caveats to this. One of them is those that contain hydrogen another is those that
have specific common names and then we’ll also look quickly at organic compounds. So
if we look at hydrogens they often use non-systematic names so if we look at HCl we’re going to
call that hydrogen chloride it looks like a follows the ionic or simple name we just
leave out the mono but if we go to something like H2S this also does not have an indication
that we have two hydrogens so here we have hydrogen sulfide. So you see when hydrogen
we live out the prefixes so it’s a non-systematic naming system and this is very common for
anything that contains hydrogen. But we also have some compounds like NH3 that uses a common
name nothing that’s really related to any of the elements in there for these there’s
a set of common names we’re going to need to know. This one you’ll see quite often this
is ammonia and you may be familiar with that and another one where we do not use its non-systematic
or systematic name dihydrogen oxide or hydrogen oxide but its common name—water. The other
one we need to watch for are organic compounds specifically hydrocarbons for the hydrocarbons
we’re gonna learn a list of names or IUPAC names. This is a group of names that have
been decided on and are the official chemical names for these compounds. For this video
I’m just gonna start with a few–one carbon two carbons and an organic hydrocarbon with
three carbons for the first one the IUPAC approved name is methane, for two carbons
ethane, for three carbons propane. It’s usually best to know all of the IUPAC names for hydrocarbons
all the way up to 10 carbons but for this video we just wanted to get you started. Now
you should be able to name simple ionic compounds, ionic compounds that contain polyatomics,
and some simple molecular compounds.

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