Formulas of Compounds
I.
Formula writing for ionic compounds
A.
B
Systematic Chemical Names
IUPAC- International Union of Pure and Applied Chemistry set the ground rules
for naming
1.
Inorganic compounds- those not containing carbon
a.
Positive portion comes first.
b.
Negative portion comes last.
There are additional rules if the compound is binary, ternary or higher or takes the
form of acids, bases or salts.
Writing formulas
1. Now we can use names and formulas of cations and anions to write formulas
of compounds.
2. In these formulas, the sum of the total cation and anion charges must be zero.
3. We use subscripts to balance the charges.
4. In most cases, we write the cation first and then the anion. (Positive first).
5. Rules for writing formulas:
a. By convention, the simplest whole number ratio of the elements is
usually used for writing formulas (empirical formula).
b. Only a single formula can be written for any compound.
C
Examples:
1.
Ba+2 + F-1  BaF2
2.
Al+3 + Br-1  AlBr3
3.
Li+1 + SO4-2  Li2SO4
4.
5.
NH4+ + SO3-2  (NH4)2SO3
Sr+2 + PO4-3  Sr3(PO4)2
The use of parenthesis in formula writing is also very important, it is used when a
polyatomic ion is present in the formula. The subscript tells the reader how many
molecules of the polyatomic ion are present. The rule is adhered to without fail unless
there is only one ion present in which case the parenthesis are not used. Ex (NH4)2SO4
the 2 means there are 2 ammonium ions present.
Solve the following
+
Li
Ca2+
Sr2+
Cs1+
Fe3+
Cr+
Cu2+
FLiF
CaF2
SrF2
CsF
FeF3
CrF
CuF2
S2Li2S
CaS
SrS
Cs2S
Fe2S3
Cr2S
CuS
N3Li3N
Ca3N2
Sr3N2
CsN3
FeN
Cr3N
Cu3N2
P3Li3P
Ca3P2
Sr3P2
Cs3P
FeP
Cr3P
Cu3P2
ILiI
CaI2
SrI2
CsI
FeI3
CrI
CuI2
Se2Li2Se
CaSe
SrSe
Cs2Se
Fe2S3
Cr2Se
CuSe
ClLiCl
CaCl2
SrCl2
CsCl
FeCl3
CrCl
CuCl
IONS
IONS
Fluoride
Iodide
Nitride
Oxide
Sulfide
Bromide
F-
I-
N3-
O2-
S2-
Br-
Aluminum
Al3+
AlF3
AlI3
AlN
Al2O3
Al2S3
AlBr3
Gallium
Ga3+
GaF3
GaI3
GaN
Ga2O3
Ga2S3
GaBr3
Potassium
K+
KF
KI
K3N
K2O
K2S
KBr
Strontium
Sr2+
SrF2
SrI2
Sr3N2
SrO
SrS
SrBr2
Barium
Ba2+
BaF2
BaI2
Ba3N2
BaO
BaS
BaBr2
Lithium
Li+
LiF
LiI
Li3N
Li2O
Li2S
LiBr
Calcium
Ca2+
CaF2
CaI2
Ca3N2
CaO
CaS
CaBr2
Magnesium
Mg2+
MgF2
MgI2
Mg3N2
MgO
MgS
MgBr2
Sodium
Na+
NaF
NaI
Na3N
Na2O
Na2S
NaBr
Beryllium
Be2+
BeF2
BeI2
Ba3N2
BeO
BeS
BeBr2
Bonding and Naming
Combine the following ions to make balanced compounds. The name on the negative
will end in “ide.”
Ion(+)
Ion(-)
Compound
Name
Mg2+
Cl-
MgCl2
Magnesium chloride
Li+
P3-
Li3P
Lithium phosphide
Be2+
N3-
Be3N2
Beryllium nitride
K+
Se2-
K2Se
Potassium selenide
Ca2+
I-
CaI2
Calcium iodide
Al3+
S2-
Al2S3
Aluminum sulfide
H+
O2-
H2O
Hydrogen oxide
WATER