Chemistry, Chapter 9, Balancing Equations from sentences Notes
Chemistry, like many of your other classes, is a class the builds as you go. If you don’t learn one topic, you may not do well in the next top. Here are some things you MUST know in order to do well the rest of the year.
I. The diatomic elements These elements, when not combined with something else, are always found in pairs. Hydrogen (H), Nitrogen (N), Oxygen (O), Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I). I don’t care how you memorize them, you just need to do it. I do it by their position in the periodic table. There are a number of mnemonic devices. Here are two: Oh I Have Nice Closet For Brooms.
Horses Need Oats For Clear Brown I’s. I personally like the 2nd one better since it lays out the elements in the order that they are on the chart. However you do it, MEMORIZE THEM!
1 / H / He2 / Li / Be / B / C / N / O / F / Ne
3 / Na / Mg / Al / Si / P / S / Cl / Ar
4 / K / Ca / Sc / Ti / V / Cr / Mn / Fe / Co / Ni / Cu / Zn / Ga / Ge / As / Se / Br / Kr
5 / Rb / Sr / Y / Zr / Nb / Mo / Tc / Ru / Rh / Pd / Ag / Cd / In / Sn / Sb / Te / I / Xe
II. Know how to name binary molecular compounds (covalent bonds) from Chapter 8
(p. 248).
1. The first element is named first, using the entire element name.
2. The second element is named using its root and adding the suffix –ide.
3. Prefixes are used to indicate the number of atoms of each element.
4. This means you have to KNOW the prefixes. (Remember that the first element almost never uses the prefix mono).
Examples:
NF would be “Nitrogen trifluoride”
CClwould be “Carbon tetrachloride”
Sulfur hexafluoride would be SF
Silicon dioxide would be SiO
III. Try to learn the element abbreviations. Some of them are based
on ancient element names, so they may not match the letters
in the name.
Iron = Fe Iodine = I, Lead = Pb
IV. Know what the meaning of the different metal ions are.
In other words, what does it mean to be Iron (II)? It means that it would be Fe.
On the other hand Iron (IV) would be written Fe.
As we talked about when you first learned them, the only metal ion where the number in the name does not match the charge is Mercury (I). Mercury (I) = Hg. For all other metal ions, the roman numeral in the parenthesis IS the charge on the ion.
Tin (II) = Sn, Chromium (III) = Cr, Cobalt(III) = Co, etc, etc.
V. Know the difference between a polyatomic ion and part of a binary molecular compound.
Magnesium Sulfide = MgS Magnesium Sulfate = MgSO
VI. When you are writing compounds, do look at the charges on the ions, and then balance them out so that the compound is neutral.
Ex 1: Iron(II) Chloride------Iron II = Fe Chloride = Cl
If you combine them: FeCl, the charges will add to 2 – 1, which does not equal zero.
To get them to balance, you must have: FeCl That way, the two Chlorines have a total charge of -2, which balances the +2 in the iron.
Ex 2: Iron (II) Phosphate Iron II = Fe Phosphate = PO
Putting them together: FePO
Again, the charges will not add to zero. The smallest number that 2 and 3 will both go into is six, so we need to make it so both the iron and phosphate have a total charge of 6 or -6.
Fe(PO)
This shows the compound with the charges. Without the charges, it would be:
Fe(PO)
VII. Once you have a compound balanced and you are working in an equation to balance it, you NEVER change the subscripts on the compound, you balance the equation only be changing the coefficients in front of the compounds.