3
Chemical Compounds
Section Objectives
1. Know and apply the conventions used in determining oxidation states.
Because oxidation state is a formal rather than an experimental concept, it is possible to
devise a rigid set of rules that work in all but the most unusual circumstances. One set of
rules is given below.
1.
2.
3.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Method of applying the rules
Apply the rules from the top to the bottom of the list.
Search the list to find a rule that fits. Apply it.
Then start again at the top of the list to find the next rule that fits.
Oxidation State rules
The OS (oxidation state) of all uncombined elements = 0.
The sum of the OS in compound = 0.
The sum of the OS in an ion = ionic charge.
Alkali metals (group 1A) have OS = +1.
Alkaline earth metals (2A) have OS = +2.
F has OS = -1 and H has OS = +1.
O has OS = -2.
Cl, Br, I (in order) have OS = -1.
S, Se, Te (in order) have OS = -2.
N, P, As (in order) have OS = -3.
2. Know the names, formulas, and charges of ions in the following tables and be
able to write formulas and names of the compounds formed from these ions.
Names, Formulas, and Charges of Some Common Ions
Iron (III) or ferric
Al3+ Aluminum
Au3+ Gold (III) or auric
Fe3+
Cobalt (II) or
H
Hydride
Sn2+ Tin (II) or stannous
Co2+ cobaltous
Cobalt (III) or
Mn2+ Manganese (II) Sn4+ Tin (IV) or stannic
Co3+ cobaltic
Copper (I) or
Ni2+ Nickel (II)
Pb2+ Lead (II) or plumbous Cu+
cuprous
2+ Zinc
4+
2+
Lead (IV) or plumbic Cu
Copper (II) or cupric
Zn
Pb
2+
Chromium (II) or
Mercury (I) or
Cd
Cadmium
Cr2+ chromous
Hg22+ mercurous
Chromium (III) or
Mercury (II) or
Ag+
Silver
Cr3+ chromic
Hg2+ mercuric
Gold (I) or
Au+
Fe2+ Iron (II) or ferrous
aurous
NH4
Names, Formulas, and Charges of Some Common Polyatomic Ions
Ammonium
Sulfate
Hypofluorite
SO42FO-
C2H3O2-
Acetate
HSO4-
Hydrogen sulfate
ClO-
CO32-
Carbonate
SO32-
Sulfite
ClO2-
Chlorite
-
+
HCO3C2O42-
Hydrogen sulfite
ClO3
Chlorate
S2O32-
Thiosulfate
ClO4-
Perchlorate
Cyanide
HS-
Hydrogen sulfide
BrO-
Hypobromite
OCN
Cyanate
OH
-
SCN-
Thiocyanate
O22-
CN
-
Hydrogen carbonate
HSO3
Oxalate
-
Hypochlorite
Hydroxide
BrO3
Bromate
Peroxide
BrO4-
Perbromate
-
Hypoiodite
NO2
-
Nitrite
CrO4
Chromate
IO
NO3-
Nitrate
Cr2O72-
Dichromate
IO3-
Iodate
PO43-
Phosphate
MnO4-
Permanganate
IO4-
Periodate
HPO42H2PO4-
2-
-
2-
Hydrogen phosphate
MnO4
Manganate
Dihydrogen phosphate
The lists presented above may seem rather extensive, but they contain practically all the
ions you are likely to encounter in AP Chemistry. (You may get a few more in
September, but this will give you a good start!)
Naming an ionic compound is simple. Write down the name of the cation (positive ion),
followed with a space, and then the name of the anion (negative ion).
Writing formulas from names is not quite so simple. The formula contains more than just
the symbols for the cation and anion. The cation and anion symbols are multiplied so
that the total charge from the cations just balances the total charge of the anions. The
total cation charge plus the total anion charge equals zero.
Cations
M+
[NH4+]
-
X
MX
-
[F ]
2-
X
Anions
[SO42-]
M
2+
M
3+
[Al ]
[NH4F] M2X [(NH4)2SO4]
MX2 [CaF2] MX
[CaSO4]
MX3 [AlF3] M2X3 [Al2(SO4)3]
M4+
[Ce4+]
MX4 [CeF4]
2+
[Ca ]
3+
MX2
[Ce(SO4)3]
X3-
[PO43-]
M 3X
[(NH4)3PO4]
M3X4 [Ce3(PO4)4]
M3X2 [Ca3(PO4)2]
MX
[AlPO4]
3. Be able to write formulas and names of simple binary covalent compounds and
of binary acids.
Covalent compounds are formed between nonmetallic elements. The names of binary
covalent compounds are obtained from the names of the two elements. The elements are
named in the same order as they appear in the formula. The first element name is
unchanged; the ending of the second becomes “-ide.” The element names have prefixes
depending on the subscript of that element in the formula, except that the prefix mono(meaning one of) is rarely used for the first element in a formula. Other prefixes are: di =
2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, nona = 9, and deca = 10.
Binary acids consist of hydrogen and a nonmetal. HCl is a binary acid. The name of a
binary acid has the prefix “hydro-” and the suffix “-ic” surrounding the root name of the
element. HCl is hydrochloric acid. The binary acid names are used when the compound
is dissolved in water, that is, in aqueous solution. When the compound is not an aqueous
solution the name is the same as any ionic compound.
4. Use oxidation states to name oxoacids and oxoanions.
Salts and acids of chlorine oxoanions
Ox.
State
+1
Salt
Example
Acid
Example
Hypo- -ite
NaClO
Sodium hypochlorite
NaClO2
Sodium chlorite
NaClO3
Sodium chlorate
NaClO4
Sodium perchlorate
Hypo- -ous
HClO
Hypochlorous acid
HClO2
Chlorous acid
HClO3
Chloric acid
HClO4
Perchloric acid
+3
-ite
+5
-ate
+7
Per-
-ite
-ous
-ic
Per-
-ic
All oxoanions of the same family with the same oxidation state have similar names.
Another generality is that the –ate anion and the –ic acid endings are used when the
oxidation state of the central atom equals the periodic table family number. The only
exceptions to this occur in the halogens, where the –ate and the –ic endings correspond to
a +5 oxidation state and the noble gases where they correspond to +6.
5. Use solubility rules to predict products of reactions.
The attached table of rules is one form of the solubility rules. You are responsible for
learning these rules in some format. Each textbook gives a slightly different
approach.
SOLUBILITY RULES
LEARN!!
The solubility of a solute is the amount that can be dissolved in a given quantity of
solvent at a given temperature. For example, the solubility of lead (II) nitrate is
56 g/100 mL at 20oC. The solubilities of ionic solids in water vary over a wide range of
values. For convenience, we divide compounds into three categories called soluble,
slightly soluble and insoluble. Insoluble is a relative term and does not mean that no
solute dissolves! Compounds are classified as insoluble if their solubility is less than
0.1 g/100 mL of water. On the other hand, soluble compounds are those whose
solubilities are greater than 1.0 g/100 mL of water. The following “solubility rules”
summarize the solubilities of various compounds in water at 25oC.
1. All Group IA salts are soluble (aq).
2. All ammonium salts are soluble (aq).
3. All salts containing nitrate, acetate, chlorate and perchlorate are soluble (aq).
4. All salts containing halides (chlorides, bromides, iodides, and fluorides) are
soluble (aq) EXCEPT silver, mercury(I) and lead (s). (Lead halides are soluble in
hot water.)
5. All sulfate salts are soluble (aq) EXCEPT barium, calcium, strontium, silver,
mercury(I) and lead (s).
6. All salts containing carbonates, phosphates, and chromates are insoluble (s) EXCEPT
for rules #1 and 2 (aq).
All sulfide salts are insoluble (s) EXCEPT for rules #1 and 2 and calcium, strontium,
and barium (aq).
All hydroxide salts are insoluble (s) EXCEPT for rules #1 and 2 and barium and
strontium (aq). (Calcium hydroxide is very slightly soluble.)
Note: Rule #8 is the one that varies from text book to text book and causes the most
trouble for people writing net ionic equations. Are the Group IIA hydroxides soluble or
not? At best they are only moderately soluble – barium and strontium are a little more
soluble than calcium and usually are called soluble. Calcium hydroxide is usually called
insoluble.