Binary Compounds of Cations with Variable Charges:
Common Name System
Here is what the IUPAC currently says about the “Common Name” system: "The following systems are in use but not
recommended: The system of indicating valence by means of the suffixes -ous and -ic added to the root of the name of the
cation may be retained for elements exhibiting not more than two valences."
List of some common chemical roots
Element
root
iron
"ferr-"
lead
"plumb-"
copper
"cupr-"
Element
chromium
tin
cobalt
root
"chrom-"
"stann-"
"cobalt-"
Element
gold
manganese
mercury
root
"aur-"
"mangan-"
"mercur-"
Example #1: FeO
 The first part of the name is the root of the first element in the formula plus a suffix. For iron the root to use is "ferr-". The
suffix will be either "-ous" or "-ic." The compound using the lower of the two possible charges will use the "-ous" ending and
the higher will use "-ic." The anion is named in the usual manner of stem plus "ide."
o For example, iron takes on a +2 value and a +3 value. As you begin to learn these values, the question of lower
and higher becomes much easier. Consult your blue sheet, too.
 The answer to this example is ferrous oxide.
Example #2: Fe2O3
 Since this ion has the higher of the two charges, the term "ferric" is used.
o The answer to this example is ferric oxide.
Example #3: CuCl2
 The first part of the name comes from the first element's root: cupr-.
o Two chlorides equal -2, so the Cu must be +2. "-ic" is used because +2 is the HIGHER of the two charges
copper is known to have.
 This compound is named cupric chloride.
Example #4: SnO
 The first part of the name comes from the first element's root: stann-.
o One oxygen = negative 2, so the one tin equals +2. The tin must equal +2 because you must create a formula
with zero total charges. "-ous" is used because +2 is the LOWER of the two charges tin is known to have.
 This compound is named stannous oxide.
Symbol
Cu+
Cu2+
Fe2+
Fe3+
Sn2+
Sn4+
Cr2+
Cr3+
Mn2+
Mn3+
Systematic name
(Stock system)
copper(I)
copper(II)
iron(II)
iron(III)
tin(II)
tin(IV)
chromium(II)
chromium(III)
manganese(II)
manganese(III)
Practice Problems
Common
name
cuprous
cupric
ferrous
ferric
stannous
stannic
chromous
chromic
manganous
manganic
Systematic name Common
Symbol (Stock system) name
Hg22+
mercury(I)
mercurous
2+
Hg
mercury(II)
mercuric
Pb2+
lead(II)
plumbous
Pb4+
lead(IV)
plumbic
Co2+
cobalt(II)
cobaltous
Co3+
cobalt(III)
cobaltic
Ni2+
nickel(II)
nickelous
Ni4+
nickel(IV)
nickelic
Au+
gold(I)
aurous
Au3+
gold(III)
auric
Write the correct name for:
1) CrS
8) SnCl2
15) FeBr3
22) SnO2
29) CuCl2
2) PbBr4
9) HgO
16) HgF2
23) PbO2
3) Pb2N2
10) Sn3P4
17) CuS
24) Fe2O3
4) Fe2S3
11) Cr2S3
18) SnI4
25) CuI
5) FeI2
12) PbCl2
19) Hg2O
26) Hg2Cl2
30) Hg2O2 [Hint:
the answer to this
is different from #9
and #19. Hint: look
up peroxide]
6) Hg2F2
13) Sn3N4
20) Pb3P4
27) CuO
7) Cu2S
14) FeS
21) MnO
28) Sn3N2