Ch 105 – Naming Inorganic Compounds
Fall, 2015
There is a systematic procedure for naming inorganic compounds. This note presents the rules for the
simplest compounds. The rules differ for ionic and molecular compounds, so the first order of business is
to determine which type of compound you’ve got. In a nutshell, if the compound contains both metal and
non-metal elements, the compound will be ionic. If the compound contains only non-metal elements, the
compound will be molecular. There are (as usual) exceptions to this simple rule, but we will stick by this
rule in this course. Once the type of compound is determined, you should go to the set of rules appropriate
for that type of compound.
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Ionic Compounds
For the most part, an ionic compound contains a cation (usually a metal ion) and an anion (containing,
usually, non-metal elements). The naming of an ionic compound most often involves just naming the two
ions. The cation is named first and the anion is named second. It seems that nothing can be so simple,
however, and the special considerations that arise will be outlined in this note.
A large number of ionic compounds are binary. That is, they contain only two elements (one metal and
one non-metal). The first set of rules will cover this case. A second set of ionic compounds contain two ions,
but one or both of the ions may be polyatomic. The naming is similar to that for binary compounds, but it
is necessary to know the special names for the polyatomic ions. The additional complications having to do
with additional hydrogens being added to a polyatomic ion and the hydration of a salt will round out this
section.
1. Begin with binary compounds. It is simply a matter of naming the two elements: the cation name
first and then the anion name.
(a) Cation name
i. Metals with unambiguous charge
• Cases you should know:
metal
alkali metal
alkaline-earth metal
Al
charge
+
2+
3+
• Just name the element
• Examples:
Mg2+
Al3+
Cs+
Ag+
1
magnesium
aluminum
cesium
silver
ii. Metals with ambiguous charge
• Any metal that is not listed above will be considered to be ambiguous.
• Determine the charge on the cation. This can often be done by knowing the charge on
the anion. For instance, halogens have a − charge, oxygen has a 2− charge, . . . .
• Name the element and add the charge in roman numerals in parentheses.
• Examples:
Cr6+
W4+
Fe3+
Ru8+
chromium(VI)
tungsten(IV)
iron(III)
ruthenium(VIII)
(b) Anion name
• Obtain the unambiguous stem – rough rule is to drop suffix: “-on”, “-ogen” or “-ygen”,
“-ium”, “-ine” and then add the suffix “ide”.
B5−
boride
C4−
carbide
Si4−
silicide
N3−
nitride
P3−
phosphide
As3−
arsenide
Sb3−
antimonide
O2−
oxide
S2−
sulfide
Se2−
selenide
Te2−
telluride
F−
fluoride
Cl−
chloride
Br−
bromide
I−
iodide
• One more case that arises (rarely) is H− , the hydride ion.
(c) Examples:
MgCl2
MgO
BeSe
Li3 N
SrBr2
FeCl2
FeCl3
CrO
Cr2 O3
CrO3
magnesium chloride
magnesium oxide
beryllium selenide
lithium nitride
strontium bromide
iron(II) chloride
iron(III) chloride
chromium(II) oxide
chromium(III) oxide
chromium(VI) oxide
2. Next, come the pseudobinary compounds, ionic compounds with polyatomic ions. These are handled
in pretty much the same way as binary compounds, using the names of the polyatomic ions in the
appropriate places.
(a) Polyatomic cations
• The only polyatomic cation we will encounter is the ammonium ion, NH4 + .
(b) Polyatomic anions
• Polyatomic ions are treated as a unit and have special names:
2
ion
NO−
3
OH−
C 2 H3 O −
2
CN−
MnO−
4
ClO−
3
CO2−
3
SO2−
4
CrO2−
4
PO3−
4
name
nitrate
hydroxide
acetate
cyanide
permanganate
chlorate
carbonate
sulfate
chromate
phosphate
• The book has a table (Table 3.4 on p. 91) of polyatomic ions that you are expected to
memorize. Many of these polyatomic anions are what are known as oxyanions. In hopes it
will help you remember the names of these ions, a separate discussion of these ions is presented
below.
(c) Examples:
Na2 SO4
Sr(NO3 )2
Al(OH)3
Cu(CN)2
sodium sulfate
strontium nitrate
aluminum hydroxide
copper(II) cyanide
(d) Oxyanions
Many of the polyatomic anions come from the class of anions called oxyanions. They are formed
from what are known as ternary acids – we’ll see more of these a bit later. For now, we’ll just
work with the oxyanions, which are polyatomic anions containing a non-metal element and oxygen.
These anions have special names that must be memorized.
i. Use the unambiguous stem of the non-oxygen element to construct the name.
ii. Start with the standard oxyanion, which are presented in the following table. This list must
be memorized.∗ The name of the standard oxyanion is formed by adding “-ate” to the stem.
BO3−
3
borate
NO−
3
nitrate
PO3−
4
phosphate
AsO3−
4
arsenate
CO2−
3
carbonate
SO2−
4
sulfate
SeO2−
4
selenate
TeO2−
4
tellurate
ClO−
3
chlorate
BrO−
3
bromate
IO−
3
iodate
iii. If one oxygen atom is removed from the standard oxyanion, change “-ate” to “-ite”. Examples:
PO3−
3
SO2−
3
NO−
2
ClO−
2
phosphite
sulfite
nitrite
chlorite
∗ There is actually a mnemonic that has been developed for the oxyanions. See S. Hawkes, J. Chem. Ed. 67, 149 (1990).
It produces a table for the number of oxygen atoms that is easily remembered as well as a table for the charge that is easily
remembered. You may try this if it helps.
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iv. If two oxygen atoms are removed from the standard oxyanion, change “-ate” to “-ite” and
add the prefix “hypo-”. Examples:
PO3−
2
ClO−
hypophosphite
hypochlorite
v. If one oxygen atom is added to the standard oxyanion, add the prefix “per-” (and keep the
“-ate” suffix). Example:
ClO−
4
perchlorate
(e) Examples:
NaClO3
K2 SO4
Ba(IO4 )2
BaSO3
AlPO2
sodium chlorate
potassium sulfate
barium periodate
barium sulfite
aluminum hypophosphite
(f) It is possible to form an oxyanion with one or more protons (H+ ) added to it. For such an anion,
use the same name as the anion without the protons, but also specify the number of hydrogens
added using greek prefixes. Examples:
H2 PO−
4
HSO−
4
dihydrogen phosphate
hydrogen sulfate
KH2 PO2
NaHCO3
potassium dihydrogen hypophosphite
sodium hydrogen carbonate
3. Hydrated salts are salts that have water molecules embedded in a regular way into the crystal. These
are true compounds and not simply mixtures of water and salt. As a result, they have well-defined
names. To name a hydrated salt, use the standard name for the ionic part, but specify the number of
water molecules per formula unit using greek prefixes. Examples:
CuSO4 · 5H2 O
Na2 CO3 · 10H2 O
2
copper(II) sulfate pentahydrate
sodium carbonate decahydrate
Molecular compounds
For molecular compounds, the rules are not quite as varied. We will stick with binary compounds and
acids.
1. Special cases – some molecular compounds have special names that must simply be memorized. Some
examples:
H2 O
NH3
N2 H4
PH3
water
ammonia
hydrazine
phosphine
2. For other cases, specify the {first element name} followed by the {second element name}; use the rules
for an elemental cation for the first element (just the element name) and the rules for an elemental
anion for the second element (with an “ide” suffix). Also, specify the number of atoms of each type
using greek prefixes
4
number
1
2
3
4
5
prefix
mono
di
tri
tetra
penta
number
6
7
8
9
10
prefix
hexa
hepta
octa
nona
deca
3. Exception: do not use “mono” with the first element name.
4. Examples
Cl2 O7
CO
CO2
N2 O 5
P4 O10
dichlorine heptoxide
carbon monoxide
carbon dioxide
dinitrogen pentoxide
tetraphosphorus decoxide
5. Acids take up a set of rules all their own.
(a) Binary Acids
Many binary molecular compounds that contain hydrogen and another non-metal element will
break apart when dissolved in water, forming H+ ions and the corresponding anion. Such a
solution is acidic, and the compound, when placed in water, is named as an acid. So, for instance,
HCl as a gas is called hydrogen chloride, but when it is placed in water, it is called hydrochloric
acid.
i. Gas phase molecular name is “hydrogen hunambiguous stemiide” (e.g., hydrogen chloride).
For the acid, remove “-gen” from “hydrogen” and “ide” from the second element name – also
remove any prefix there might be on “hydrogen”. Put the two element names together and
add “-ic acid” (e.g., “hydrogen chlor ide” −→ “hydrochlor ic acid”
ii. Examples
HBr
HCN
H2 S
hydrobromic acid
hydrocyanic acid
hydrosulfuric acid
(b) Oxyacids
These acids can be viewed as protonated oxyanions. [Many textbooks generate oxyanions from
oxyacids, but either way is perfectly acceptable.] If the name of the associated oxyanion is known,
the name of the oxyacid is easily generated.
i. Determine the associated oxyanion. For instance, the oxyanion associated with H2 SeO4 is
SeO2−
4 , the selenate ion.
ii. If the oxyanion name ends with “-ate”, replace this with “-ic acid”. For instance, H2 SeO4 is
associated with the “selenate” ion, so this acid is called “selenic acid”.
iii. If the oxyanion name ends with “-ite”, replace this with “-ous acid”. For instance, HClO is
associated with the “hypochlorite” ion, so this acid is called “hypochlorous acid”.
iv. Examples:
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H2 SO4
H3 PO3
HNO2
HClO2
HClO4
H3 PO2
HClO
sulfuric acid
phosphorous acid
nitrous acid
chlorous acid
perchloric acid
hypophosphorous acid
hypochlorous acid
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Practice examples
On the following pages are two sets of problems to help you practice your nomenclature skills. Set A has the
answers printed at the end of this note. Set B does not. One column of each list has the molecular formula
or formula unit. You are to give the names for these compounds. The other column has a list of compound
names. You are to provide the correct molecular formula or formula unit for these.
Set A – Answers at end
1. Ca(OH)2
1. phosphorus trichloride
2. Ag3 PO4
2. bismuth(III) cyanide
3. AgCN
3. krypton difluoride
4. MgS
4. aluminum bromate
5. (NH)2 SO4
5. hypophosphorous acid
6. ZnSe
6. bismuth(III) oxide
7. Cd(CN)2
7. strontium hydrogen carbonate
8. Ba(IO3 )2
8. gold(I) iodide
9. CuSO3
9. chromium(III) iodide
10. CuI
10. manganese(II) hydroxide
11. Fe(NO3 )3
11. lithium arsenide
12. Hg2 Cl2
12. arsenic(III) sulfate
13. H2 SO3
13. tin(IV) chloride
14. MnCO3
14. nickel(II) periodate
15. Mn(OH)3
15. dichlorine heptoxide
16. Ni(ClO)2
16. xenon tetroxide
17. CrAsO4
17. antimony(III) sulfide
18. SnBr4
18. hydrosulfuric acid
19. CrF2
19. sodium chlorite
20. Bi2 O5
20. mercury(II) cyanide
21. CsClO3
21. ammonium sulfite
22. HI(aqueous)
22. cobalt(II) tellurite
23. Sr(IO)2
23. lead(II) carbonate
24. RbH2 AsO3
24. zinc phosphide
25. HBrO4
25. copper(II) silicide
26. Ra(OH)2
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Set B – No answers
1. silver phosphate
1. Cu3 (AsO4 )2
2. cobalt(II) chloride
2. Bi2 (CO3 )3
3. beryllium nitrite
3. Mn2 O3
4. iron(III) iodate
4. Hg2 SO4
5. ammonium nitrate
5. NI3
6. aluminum sulfide
6. Co3 (BO3 )2
7. zinc periodate
7. CsIO
8. lead(II) borate
8. BN
9. arsenic(III) cyanide
9. CdHPO2
10. nickel(II) arsenite
10. LiOH
11. iodine heptoxide
11. Zn(OH)2
12. barium silicide
12. Ra3 (PO4 )2
13. gold(I) sulfite
13. Fe(BrO3 )3
14. barium hypobromite
14. As(ClO4 )5
15. calcium hydride
15. MgHBO3
16. dinitrogen pentoxide
16. HF
17. antimony(II) sulfide
17. SrCO3
18. magnesium oxide
18. Be(OH)2
19. iodine monochloride
19. SnO2
20. rubidium carbonate
20. AuF3
21. sulfur hexafluoride
21. Fe2 (TeO4 )3
22. calcium phosphide
22. I2 O5
23. manganese(II) oxide
23. PtCl4
24. copper(II) telluride
24. OsO4
25. chromium(II) bromide
25. H3 BO3
26. barium borate
26. InCl
27. bromine trichloride
27. UF6
28. cerium(IV) sulfate
28. H3 AsO3
29. MnO
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Answers to set A
1. calcium hydroxide
1. PCl3
2. silver phosphate
2. Bi(CN)3
3. silver cyanide
3. KrF2
4. magnesium sulfide
4. Al(BrO3 )3
5. ammonium sulfate
5. H3 PO2
6. zinc selenide
6. Bi2 O3
7. cadmium cyanide
7. Sr(HCO3 )2
8. barium iodate
8. AuI
9. copper(II) sulfite
9. CrI3
10. copper(I) iodide
10. Mn(OH)2
11. iron(III) nitrate
11. Li3 As
12. mercury(I) chloride
12. As2 (SO4 )3
13. sulfurous acid
13. SnCl4
14. manganese(II) carbonate
14. Ni(IO4 )2
15. manganese(III) hydroxide
15. Cl2 O7
16. nickel(II) hypochlorite
16. XeO4
17. chromium(III) arsenate
17. Sb2 S3
18. tin(IV) bromide
18. H2 S
19. chromium(II) fluoride
19. NaClO2
20. bismuth(V) oxide
20. Hg(CN)2
21. cesium chlorate
21. (NH4 )2 SO3
22. hydroiodic acid
22. CoTeO3
23. strontium hypoiodite
23. PbCO3
24. rubidium dihydrogen arsenite
24. Zn3 P2
25. perbromic acid
25. Cu2 Si
26. radium hydroxide
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