Greetings. You have entered one of the serious places of this website. Wait! Don't leave. Just sit back and stay put. Remember The Joy of Metrics? Remember how it changed your life, and you aced that test? Well, you did, and it was because you took the time to learn. This section is about the MANY joys of chemical formulas and compounds. We have a test tomorrow you know. So if I were you, I would fais attention.
The Many Joys of Chemical Formulas and Compounds
Ok. So you know some common names of chemical substances. Salt, ammonia, water, snot..well, I'm gonna tell you now, THAT AIN'T GONNA CUT IT! You need to know a lot more pointless and extremely confusing stuff to get by in the chemical world. We're going to attempt (note that we don't guarantee success) to make this just a little bit easier for the slower people. So let's start with discussing the significance of a chemical formula, shall we?
THE SIGNIFICANCE OF A CHEMICAL FORMULA
So
what are these darned chemical formulas for? Well, a chemical formula indicates
the relative number of atoms of each kind in a chemical compound. (Yeah,
like we all are yearning to know that little tidbit) For a molecular
compound you get the number of atoms of each element contained in a single
molecule of the compound. Makes sense, doesn't it. For example. H2O, everyone's
FaVoRiTe compound, has 2 hydrogens and 1 oxygen. We can tell by that little
subscript there, which is not really a subscript because I don't know how
to make the 2 a subscript..but ya know what I mean...
Ionic
compounds, always wanting to be different, are different. They consist
of a network of positive and negative ions held together by mutual attraction.
How romantic. Their chemical formula represents one formula unit- the simplest
ratio of the compound's positive and negative ions. (cations and anions).
Aluminum sulfate, a very frisky
ionic compound, is shown like so:
Al2(SO4)3
AaAaAaAAaAaAaHhHhH!
That
looks complicated. But the textbook doesn't seem to think so. The subscript
2 refers to 2 aluminum atoms. OK! The subscript 4 refers to 4 oxygen atoms
in the sulfate ion. OK! The subscript 3 refers to everything inside those
parentheses, meaning theres 3 sulfate ions, with a total of 3 sulfur atoms
and a whopping 12 oxygen atoms. OK! I get this. What depresses me is that
it gets complicated later.
Monatomic
Ions
THIS
JUST IN! Ions formed from a single atom are called monatomic ions. By gaining
or losing electrons, many main group elements form ions with noble gas
configurations. You see, everyone wants to be like the noble gases, they're
so cool. When Neon walks down the hall, all of the other elements are like,
"Look at HER configuration!" All of the severely jealous elements go to
drastic measures to be like a noble gas. They go on crash diets, losing
astounding numbers of electrons. For example, group 1 metals lose one electron
to make 1+ cations, such as Na+. The nonmetals in groups 12, 16,
and 17 gain electrons. What elements will do to be cool....
BUT!
Not all main group elements readily form ions. Instead of gaining or losing
electrons, some form covalent bonds with other atoms where they share electrons.
These atoms realize that they will never be like a noble gas by themselves,
so they get in a group with some other atoms so it looks like they are
cool and have friends. But in reality, it would take all of those atoms
in the compound to be as cool as a noble gas.
I
bet you are asking yourself now, "Self, how do I name these monoatomic
irons?" Well, you can tell yourself, "Self, it's not that hard.", because
it really isn't. The cation K+ is just called "potassium cation". Anions
are different though. First, the ending of the elements name is dropped.
Then the ending "ide" is added to the root name. So F- would be "fluoride
anion."
Simple, eh?
look
out! it's
BINARY
IoNiC COMPOUNDS!!!!
I
bet you didn't expect this. Compounds composed of two different elements
are called binary compounds. In those little ionic compounds, the charges
of whatever's in there must be equal so it'll be neutral. Ya know? So,
like, the formula for such a krazy kompound can be written given the identities
of the compounds ions. For example, magnesium+bromine= magnesium bromide.
Magnesium, a group 2 metal forms an Mg2+ cation. Bromine, a halogen, forms
the Br- cation when with a metal. Think about this situation. The charges
must be equal, is that not so? So we need 2 bromides to balance that magnesium.
When writing this formula, the cation comes first. So it can be shown as
follows:
Ions
combined: Mg2+, Br-, Br- Chemical formula: MgBr2
That
was an easy one. The book says it has an "aid" for us in determining subscripts
for these ionic compounds, but I find that it's easier just to do it in
your head. Remember when you're naming these doggies that the name of the
cation comes first. So Al2O3 would be aluminum oxide.
THE
STOCK SYSTEM OF NOMENCLATURE
Eh.
I don't really wanna talk about this because I don't get it. Oh wait..I
read it and a think I do. You see, some elements have more than one charge.
Since the charge isn't indicated in the formula you gotta say which one
it is in the name. They use a roman numeral. Fe2+=Fe(II). This is how you
name a formula with the stock system:
CuCl2
Ok,
so we remember that the charges must balance in ionic compounds. Cl is
the anion here, so it has a charge of 2-. SO, the Cu must have to be 2+
to balance that little devil out. So the name for this would be copper(II)
chloride. ^_^
OxIdAtIoN
nUmBeRs!!!
Now
this is exciting stuff. I didn't bring my chemistry book home with me,
so I can't tell you what an oxidation number actually is. But I will tell
you how to assign them. To make this a little more fun, we're going to
use a real life situation!
You
are Maurice Clayborne, a worker at the Oxidation Office of Elements. Your
job is to assign each element an oxidation number so they can well, oxidate.
There is a long line of elements waiting to be assigned their numbers.
So you must get to work.
The
first elements in line are 2 hydrogens and an oxygen. They are a happily
bonded trio (polygamy is legal in element world) and they wish to each
have an oxidation number so they can oxidate. So what do you do?
Well,
you were trained at the Art of Oxidation school so you know all the rules
that one must follow when assigning oxidation numbers. One of them is that
hydrogen always has a charge of +1. So if you give that number to the two
lovely hydrogens, you will have a charge of +2. Another rule is that the
compounds must be NEUTRAL. So to balance the charges that oxygen must have
a charge of -2. It is as easy as that. One of the rules is that oxygen
almost always has a charge of -2 anyways, so it works out perfectly. You
assign these elements their numbers and they are happily on their way to
go and oxidate.
NAMING molecular COMPOUNDS
Ok, I think I was supposed to tell you this earlier. But I forgot, so here goes. To name a molecular compound, one uses prefixes.