Chemical Nomenclature
Polyatomic Ions & Their Rules
Start by memorizing the six “-ate” polyatomic ions shaded in below. They set the pattern for
the polyatomic ions formed by elements beneath them in the periodic table.
BO33borate
CO32carbonate
NO3nitrate
PO43phosphate
SO42sulfate
ClO3chlorate
AsO43arsenate
SeO42selenate
BrO3bromate
IO3iodate
Naming Oxyanions
# of O Atoms
Once you know the “-ate” ions you can figure out the rest by adding or removing oxygen atoms.
Prefix
Root
Suffix
per–
root
–ate
--
root
–ate
–1 O atom
root
–ite
root
–ite
+1 O atom
–2 O atom
hypo–
Odds & Ends
Memorize the extra ones below that don’t follow the above patterns.
NH4
+
H3O+
Cation
ammonium ion
C2H3O2–
hydronium ion
HCO3–
Anions
acetate ion
OH
Anions
hydroxide ion
bicarbonate ion
C2O42−
oxalate ion
CrO42−
chromate ion
MnO4–
permanganate ion
CN–
cyanide ion
O22−
peroxide ion
Cr2O72−
dichromate ion
S2O32−
thiosulfate ion
–
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Greek Prefixes
When naming molecular compounds (those composed of two nonmetals), we use the
appropriate Greek prefix and change the ending of the second nonmetal to “–ide”.
Number
1
Prefix
mono-
Number
6
Prefix
hexa-
7
8
9
10
heptaoctanonadeca-
(don’t use with 1st nonmetal)
2
3
4
5
ditritetrapenta-
The preferred form of monooxide is “monoxide”.
Naming Acids
Acid formulas always begin with H and end with (aq) meaning they are in aqueous
solution (dissolved in water). Acids are basically anions combined with one or more H+
ions. Figure out the name of the anion to name the acid, or vice-versa.
Anion Ending
root-ide
root-ate
root-ite
Acid Name
hydro- root -ic acid
root-ic acid
root -ous acid
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