V. NOMENCLATURE
A. Oxidation Numbers (Oxidation States)
The ox. num. of an atom indicates the number of electrons it has lost or gained, either
fully or partially.
1. Rules of the game:
a) In a simple ionic compound the ox. st. (ox. num.) of an atom is the same as its
charge.
Example(1): MgS
Example(2): Na2O
b) The sum of the ox. num.'s in a neutral compound = zero.
Example(3): Al2O3
Example(4): FeCl3
c) In a covalent compound the ox. st. of an atom indicates the number of electrons
partially lost or gained.
Example(5): From its dot formula, determine the oxidation state of each atom in HF
Example(6): From its dot formula, determine the oxidation state of each atom in H 2O
Example(7): From its dot formula, determine the oxidation state of each atom in OF2
Example(8): From its dot formula, determine the oxidation state of each atom in CO2
57 NOMENCLATURE / Oxidation Numbers
d) The ox. st. of any element is zero.
Example(9): He
Example(10): Cl2
e) The sum of the ox. states in a polyatomic ion = its charge.
We will come back to this after we do “Predictable atoms” below
2. Predictable atoms in a compound
a) Group VII: F will always be -1 when it is in a compound.
Cl, Br, and I will be -1 if the atom is the most EN in the compound.
Example(11): NaF
Example(12): HF
Example(13): ClF
Example(14): BrCl
Example(15): HBr
b) Group VI: Oxygen will be -2 in a compound, except when with F or in a
peroxide.
S, Se and Te will be -2 if the atom is the most EN in the compound.
Example(16): Na2O
Example(17): Cl2O
58 NOMENCLATURE / Oxidation Numbers
Example(18): OF2
Example(19): H2O2 (hydrogen peroxide)
Example(20): What is the ox. st. of sulfur in each of the following:
Na2S
H2 S
S2
SCl2
SO2
SO3
Example(21): What is the highest ox st S can obtain? Why?
Example(22): What is the lowest ox st S can obtain? Why?
c) Group V: N and P will be -3 if the atom is the most EN in the compound.
d) Group I Metals: - will always be +1 in a compound.
e) Group II: atoms will always be +2 in a compound.
f) H is +1 when bonded with something more EN than itself.
(Assume H has the lowest EN of the nonmetals.)
H is -1 when with something less EN than itself.
Example(23): HI
Example(24): NaH
59 NOMENCLATURE / Oxidation Numbers
Back to rule 1e) The sum of the ox. states in a polyatomic ion = its charge.
Example(25): What is the ox. st. of sulfur in MgSO4
Example(26): What is the ox. st. of sulfur in SO42-
Example(27): What is the ox. st. of phosphorus in PO43-
Example(28): What is the ox. st. of each Cr in Cr2O72-
60 NOMENCLATURE / Ionic Compounds
B. Nomenclature of Ionic Compounds
1. Simple Ionic Compounds
a) Positive ox. st. atom is written first in the formula.
(This is true for all nomenclature, with the exception of organic compounds and a few historically named
compounds.)
b) Pos. ox. st. atom(s): ordinary elemental name.
c) Neg. ox. st. atom(s): root name + IDE ending.
Example(1): Name NaCl
Example(2): Name CaBr2
Example(3): Name Al2S3
Example(4): What is the formula of lithium nitride?
2. Compounds With A Metal That Can Display More Than One Ox. St.
a) New Nomenclature System: named like simple ionic, except a Roman numeral
is used to indicate the ox. st. of each metal atom. All of the ions that you are
required to know are on page 63.
Example(5): Name FeCl2 and FeCl3
Example(6): Name CuO and Cu2O
Example(7): Name SnS2
Example(8): What is the formula of mercury (II) nitride?
61 NOMENCLATURE / Ionic Compounds
b) Old System: metal is named with its Latin root name + IC or OUS ending.
IC ending for the higher ox.st., OUS ending for the lower. All of the ions that
you are required to know are on page 62.
Example(9): Name FeCl2 and FeCl3
Example(10): Name CuO and Cu2O
Example(11): What is the formula of stannic fluoride?
3. Polyatomic Ions
Some polyatomic ions follow a systematic method of nomenclature (most of the oxygen
containing ions, see the rules below), other do not follow a system. All of the ions that
you are required to know are on page 62.
a) Root name of the non-oxygen atom plus the ending ATE or ITE . The ATE and
ITE endings indicate a polyatomic ion containing oxygen.
b) When there are 2 ions possible between an the element and oxygen use :
ATE for the one with more oxygen, ITE for the one with less oxygen
Example(12): Name SO42- and SO32-
Example(13): Name NO31-and NO21-
c) If there is only one ion, the ATE ending is used.
Example(14): Name PO43-
Example(15): Name CO32-
62 NOMENCLATURE / Ionic Compounds
d) More than two ions
Example(16): Name the following:
ClO41ClO31ClO21ClO1-
d) Polyatomic ions combined with one hydrogen ion
When we study acid-base theory you will see where these ions come from.
In the new system H is named as hydrogen since it has a positive ox. st.
In the old system the presence of hydrogen is indicated with “bi”.
Example(17): Name HCO31-
Example(18): Name HSO41-
4. Putting it altogether
Example(19): Name Na2SO3
Example(20): Name Al(HCO3)3
Example(21): Name Fe(NO3)2
Example(22): What is the formula of calcium hydrogensulfate?
Example(23): What is the formula of mercury(II) phosphate?
Example(24): What is the formula of ferric sulfate?
63 NOMENCLATURE / Ionic Compounds
You should learn the names, formulas, and charges/oxidation states of the following
common ions.
H+
hydrogen
H-
hydride
Li+
lithium
F-
fluoride
Na+
sodium
Cl-
chloride
K+
potassium
Br-
bromide
Mg2+
Magnesium
I-
iodide
Ca2+
calcium
O2-
oxide
Sr2+
strontium
S2-
sulfide
Ba2+
barium
N3-
nitride
Al3+
aluminum
P3-
phosphide
Ag+
silver
NO3-
nitrate
Zn2+
zinc
NO2-
nitrite
Fe2+
iron(II), [ferrous]
SO42-
sulfate
HSO4-
Fe3+
iron(III), [ferric]
SO32-
sulfite
HSO3-
Cu+
copper(I), [cuprous]
ClO4-
perchlorate
Cu2+
copper(II), [cupric]
ClO3-
chlorate
Hg+
mercury(I), [mercurous]
ClO2-
chlorite
Hg2+
mercury(II), [mercuric]
ClO-
hypochlorite
Sn2+
tin(II), [stannous]
CO32-
carbonate
Sn4+
tin(IV), [stannic]
PO43-
phosphate
H3O+ hydronium
OH-
hydroxide
NH4+
CN-
cyanide
ammonium
HCO3-
C2H3O2- acetate
MnO4-
permanganate
hydrogen sulfate
[bisulfate]
hydrogen sulfite
[bisulfite]
hydrogen carbonate
[bicarbonate]
64 NOMENCLATURE / Covalent Compounds
C. Nomenclature of Simple Covalent
Simple covalent compounds are named like simple ions except when there is more
than one atom of any type, a prefix is used to indicate the number.
Number Prefix
2
3
4
5
6
di
tri
tetra
penta
hexa
Example(1): Name CO2
Example(2): Name SCl4
Example(3): Name H2O
Example(4): What is the formula of dinitrogen trioxide?
Example(5): What is the formula of carbon monoxide?