Hello, my name is Charlie Arbuiso and I will be your chemistry teacher.
Since I said that the first time I have taught you a lot of chemistry. Below, in somewhat reverse order, is what you should already know how to do, how to understand, and how to deal with. Nothing in our class ever goes away for long. Moles is gone today, but after Chemical Reactions, it comes back big time. We left naming compounds and writing formulas for a while when we did Mole Math, but now, all of those compounds are back in reactions. If you see anything that you don’t know, you should ask about it. Ask a smart friend who remembers everything, or ask me, your chemistry teacher.
Sucrose is table sugar, with formula of C12H22O11. It has a molar mass and percent comp by mass as follows:
If you have two pounds of sugar (908 grams of sucrose), how many grams are carbon, how many grams are oxygen and how many grams are hydrogen? (this is a percent comp by mass problem).
908 grams X .421 = 382 grams carbon
908 grams X .064 = 58 grams hydrogen
908 grams X .515 = 468 grams oxygen
……………………………….908 grams total
Moles are central to chemistry. One mole is equal to different things.
1 mole = 6.02 x 1012 particles. Particles can be atoms, or molecules, or even Formula Units (FU’s). As you remember different substances come in different kinds of particles. Most elements come in atoms, individual tiny parts that exist as single particles, though often stuck together. Seven elements are unstable alone and form pairs when pure. HONClBrIF twins are H2, O2, N2, Cl2, Br2, I2, and F2 all exist as diatomic molecules when pure. Each “hydrogen” is really two atoms bonded into one molecule. That is the smallest stable bit of hydrogen. All of the HONClBrIF Twins can bond other ways to get stable, they are not always diatomic.
Ionic compounds, like NaCl or MgO exist in a crystal form (or can be dissolved into water) and “you can’t have just one”. You can imagine having one unit of the formula of an ionic compound even if you can’t have just one in your hand. If you had Avogadro’s number of them, you’d have a mole of these FU’s, but you can’t ever have just one.
1 mole = 22.4 Liters of any gas, as long as the gas is at STP or standard temperature and pressure. in our class it’s always STP until we get to gas chemistry, and then we’ll play around more with the math. If gas is colder it gets smaller. If you heat a gas it gets larger. All gases are at whatever pressure they are. If you squeeze them the pressure increases. if you let them expand, the pressure drops. At STP though, one mole of any gas fits exactly into 22.4 liters of volume.
1 mole = the molar mass of the substance. Element molar masses are on the periodic table, the atomic mass but with a unit of grams per mole. Diatomic HONClBrIF Twins need to have their atomic mass doubled, since there are two atoms bonded together (not just one).
Compound molar masses can be calculated as shown above with sucrose. Always do molar mass on the left side, and add below the math. Percent comp by mass goes on the right side.
When doing mole math, decide carefully where the problem starts, and put that measurement over one into a decimal. Use the proper conversion equality to move from mass to moles, or moles to particles, or liters to moles (or the reverse direction). Always watch your sig figs. Use units. When you don’t use units, if you are a genius it won’t matter. If you fall just below the genius level, a lack of units is a sure way to get lost in the math, and you will not get a correct answer. If there were an easier way to do this I would show you. There is not. Do the math, all of it.
When it comes to naming compounds, the first thing to decide is if the first element in the formula (or name) is a metal or nonmetal. If it’s a metal then it is an ionic compound. If it’s a nonmetal then it’s a molecular compound.
Ionic compounds come in flavors: monoatomic ions form when elements on the periodic table ionize. Metals lose electrons to become cations. Nonmetals gain electrons to form into anions. Metals lose enough electrons to become isoelectric to the noble gases. That means they end up with an electron orbital system matching a noble gas. They do not become noble gases! Nonmetals gain enough electrons to become isoelectric to noble gases as well. They do not become noble gases, they end up with similar numbers of electrons in their orbitals, like noble gases. The naming rules for these ionic compounds is easy to follow:
1st name rule: state the name of the metal atom as it is on table S.
2nd name rule: state the name of the anion while changing the ending to an “-ide”.
Examples include sodium chloride, magnesium oxide, and aluminum phosphide.
The metals in the middle of the periodic table, the transitional metals, follow slightly different rules. If in their box on the table, top right corner, has more than one + number, that atom can make more than one kind of cation. They do not follow the “simple” isoelectric rules. We don’t have to understand the deeper reasons why, but we do have to realize that copper (for example) can make a Cu+1 cation or a Cu+2 cation as well.
In order to keep track of which “copper bromide” you have, you could resort to saying the formulas only, but NY State Education wants to make sure you name them with words too. Just remember that the Cu+1 cation would be called copper (I) because the Roman Numeral I matches the +1 charge of that cation. The other is called the copper(II) cation, the Roman Numeral of “two” matches the charge of the cation.
Copper (I) bromide would be CuBr, while Copper (II) bromide would be CuBr2. The +2 cation requires two negative one bromides to bond with.
Some transitional metals have just a single ion charge, like silver. Ag+1 is the only cation silver can make. We don’t use a Roman Numeral when naming silver ionic compounds, we don’t need to differentiate between the silver cations, there is ONLY one silver cation.
These are all “monoatomic” ions, one atom becomes one cation or one anion at a time. There are also “polyatomic” ions listed on table E. These are when two or more atoms bonded together gain or lose a few electrons, acting like a cation, or an anion but as a small group.
We never change the polyatomic ion names to end in ide. We sometimes need to combine more than one polyatomic ion in one formula, and that requires parenthesis to do that. Examples are sodium hydroxide NaOH, or calcium carbonate CaCO3, or ammonium bromide NH4Br. When there are more than one polyatomic ion in one formula, we use this form: Aluminum hydroxide is Al(OH)3 while magnesium hydroxide is Mg(OH)2. Ammonium phosphate is (NH4)3PO2 and Ammonium dichromate is (NH4)2Cr2O7.
We only use parenthesis when there is more than one polyatomic ion. Sodium hydroxide forms in a one to one ration, no need to use ( )’s.
Molecular componds use NO METALS or ions. If your first name starts with a nonmetal you are a molecular compound. Examples are carbon dioxide, dihydrogen monoxide, and ammonia (nitrogen trihydride).
The naming rules are simple too. The first name rule is that if you start with a single atom in the compound, just say the name of the atom. The second atom always gets a prefix name. The second name also ends with an “ide”.
CO2 is carbon dioxide.
One carbon atom (just say carbon) and the second name must get a prefix, 2 is “di”.
PCl3 is phosphorous trichloride.
A single atom of phosphorous (say phosophorous) and the 2nd name gets a prefix, 3 = tri.
If the first part is “a multiple” then the first name gets a prefix as well. The second name gets a prefix always.
H2O which is dihydrogen monoxide, N2O5 is dinitrogen pentoxide.
The first 10 prefixes must be memorized. They are: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, and deca.
Keep studying! 15 minutes every day. Do that and you will be 79 (golden!).