NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
While there are many thousands of different chemical compounds there is a very definite system
of nomenclature whereby we can name or write chemical formulas for most compounds. We
divide the compounds into two main types – binary compounds and ternary compounds.
I.
Binary Compounds
All true binary compounds contain only two elements. The name of every binary compound ends
with “ide.” Binary compounds come in three types. They are:
Type I ………. the metal forms only one type of cation
Type II ……… the metal forms two or more types of cations
Type III …….. contains only nonmetals
We will look at each type, one at a time.
Type I Binary Compounds
For Type I binary compounds the metal present can be found in either Group 1 or Group 2 on
the periodic table. The naming system for this type of compound is quite simple and is found
below.
1.
2.
3.
4.
Rules for naming Type I binary compounds
The cation is always name first and the anion second.
A simple cation (obtained from a single atom) takes its name from the name of the
element.
A simple anion (obtained from a single atom) is named by taking the first part of the
element name (the root) and adding the letters “IDE.”
Write the name for the compound by combining the names of the ions.
When naming Type I binary compounds:
name of first element
root + ide
The root is merely an abbreviation for the name of the second element. The roots of the most
commonly used elements are listed in the following table.
Roots of the most commonly used elements.
arsenic
bromine
carbon
chlorine
fluorine
hydrogen
iodine
= arsen
= brom
= carb
= chlor
= fluor
= hydr
= iod
nitrogen
oxygen
phosphorus
selenium
sulfur
tellurium
Page 1 of 13
= nitr
= ox
= phosph
= selen
= sulf
= tellur
NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Examples:
Name the compound RbI.
 Rb is the chemical symbol for rubidium.
 I is the chemical symbol for iodine, whose root is “iod.” Add the “ide” ending to get
iodide.
 Put the pieces together to get the name rubidium iodide.
Name the compound CaO.
 Ca is the chemical symbol for calcium.
 O is the symbol for oxygen, whose root is “ox.” Add the “ide” ending to get oxide.
 Put the pieces together to get the name calcium oxide.
Name the compound Li3N.
 Li is the chemical symbol for lithium.
 N is the chemical symbol for nitrogen, whose root is “nitr.” Add the “ide” ending to
get nitride.
 Put the pieces together to get the name lithium nitride.
Write the formula for potassium sulfide.
 The chemical symbol of potassium is K. K is in the 1st column of the periodic table,
therefore, its ionic charge is +1.
 Sulfide is derived from sulfur, whose symbol is S. Its ionic charge is -2.
+1 -2



So far we have… K S.
The total positive charge must balance the total negative charge. Therefore, we need
2 K atoms to give a total positive charge of +2. This balances the -2 charge on the
sulfur.
Putting it all together we have K2S.
Write the formula for magnesium chloride.
 The chemical symbol of magnesium is Mg. Mg is in the 2nd column of the periodic
table, therefore, its ionic charge is +2.
 Chloride is derived from chlorine, whose symbol is Cl. Its ionic charge is -1.



+2
-1
So far we have… Mg Cl
The total positive charge must balance the total negative charge. Therefore, we need
2 chlorine atoms to give a total negative charge of -2. This balances the charge on the
magnesium.
Putting it all together we have MgCl2.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Type II Binary Compounds
For Type II binary compounds the metal present is NOT found in either Group 1 or Group 2 on
the periodic table. The naming system for this type of compound is found below.
1.
2.
3.
4.
Rules for naming Type II binary compounds
The cation is always named first and the anion second.
A simple cation (obtained from a single atom) takes its name from the name of the
element. Include a Roman numeral to indicate the ionic charge on the metal cation.
A simple anion (obtained from a single atom) is named by taking the first part of the
element name (the root) and adding the letters “IDE.”
Write the name for the compound by combining the names of the ions.
When naming Type II binary compounds:
name of first element (Roman numeral)
root + ide
Roman Numerals
1..........I
6
VI
2..........II
7..........VII
3..........III
8..........VIII
4..........IV
9..........IX
5..........V
10........X
Examples:
Name the compound FeCl2.
 Fe is the chemical symbol for iron.
o Fe is not in Group 1 or Group 2; therefore a Roman numeral is needed in the
name. We’ll come back to that shortly.
 Cl is the chemical symbol for chlorine, whose root is “chlor.” Add the “ide” ending
to get chloride.
 At this point we have iron (??) chloride.
 To find the Roman numeral …
o Find the charge of the anion.
 Cl has a -1 charge.
o Multiply times the number of those atoms to get the total negative charge.
 There are 2 Cl atoms.
 2 times -1 = -2.  total negative charge.
o Balance total negative charge with total positive charge.
 The total negative charge of -2 must be balanced with a total positive charge
of +2.
o Divide the total positive charge by the number of atoms to get Roman numeral.
 There is only 1 Fe
 +2 divided by 1 = +2. The Roman numeral is II.
 Put the pieces together to get the name iron (II) chloride.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Name the compound PbS2.
 Pb is the chemical symbol for lead.
o Pb is not in the Group 1 or Group 2; therefore a Roman numeral is needed.
 S is sulfur, whose root is “sulf.” Add the “ide” ending to get sulfide.
 At this point we have lead (??) sulfide.
 To find the Roman numeral …
 S has a charge of -2.
 There are 2 sulfur atoms so … 2 x -2 = -4.  total negative charge
 The total positive charge must be +4.
 There is 1 lead atom so … +4 ÷ 1 = +4. The Roman numeral is IV.
 Put the pieces together to get the name lead (IV) sulfide.
Write the formula for nickel (III) oxide.
 The chemical symbol of nickel is Ni. The ionic charge is +3, as given by the Roman
numeral.
 Oxide is derived from oxygen, whose symbol is O. Its ionic charge is -2.
+3 -2



So far we have Ni O.
In order to balance the charges we find the least common multiple (LCM) of 3 and 2.
The LCM is 6. We need two Ni atoms (+6 ÷ +3 = 2) and three O atoms (-6 ÷ -2 = 3)
to balance the charges.
Putting it all together we have Ni2O3.
Write the formula for lead (IV) nitride.
 The chemical symbol of lead is Pb. The ionic charge is +4.
 Nitride is derived from nitrogen, whose symbol is N. Its ionic charge is -3.
+4 -3



So far we have Pb N.
The LCM of 4 and 3 is 12. We need three Pb atoms (+12 ÷ +4 = 3) and 4 N atoms
(-12 ÷ -3 = 4) to balance the charges.
Putting it all together we have Pb3N4.
Write the name for iron (II) oxide.
 The chemical symbol of iron is Fe. The ionic charge is +2.
 Oxide is derived from oxygen, whose symbol is O. Its ionic charge is -2.
+2



-2
So far we have Fe O
Since the charges already balance there is no additional work to be done.
Putting it all together we have FeO.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Type III Binary Compounds
Type III binary compounds contain no metal atoms. The naming system for Type III compounds
uses prefixes to indicate the number of each atom present. The naming system for this type of
compound is found below.
1.
2.
3.
4.
Rules for naming Type III binary compounds
The first element in the formula is named first, and the full element name is used.
The second element is named as though it were an anion: root + ide.
Prefixes are used to denote the numbers of atoms present. (See table below)
The prefix mono- is never used for naming the first element.
When naming Type III binary compounds:
prefix + name of first element
Prefixes
1..........mono
2..........di
3..........tri
4..........tetra
5..........penta
prefix + root + ide
6..........hexa
7..........hepta
8..........octa
9..........nona
10........deca
Examples:
Name the compound NO2.
 N is the chemical symbol of nitrogen. Since there is only one nitrogen atom AND it
is the first element the prefix mono is not used.
 O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get
oxide. There are two oxygen atoms so we also add the prefix di to get dioxide.
 Put the pieces together to get the name nitrogen dioxide.
Name the compound N2O.
 N is the chemical symbol of nitrogen. Since there are two nitrogen atoms we need to
add the prefix di to get dinitrogen.
 O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get
oxide. There is only one oxygen atom we add the prefix mono (mono IS used for the
second element) to get monoxide.
 Put the pieces together to get the name dinitrogen monoxide.
Write the formula for carbon tetrachloride.
 The chemical symbol of carbon is C. There is no prefix before carbon in the
chemical name, therefore, there is only 1 C atom in the chemical formula.
 Tetrachloride has the prefix tetra which means there are 4 atoms present. Chloride is
derived from chlorine, whose symbol is Cl. Thus, there are 4 Cl atoms in the
chemical formula.
 Putting it all together we have CCl4.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Write the formula for dinotrogen pentaoxide.
 The prefix di means 2. Thus there are 2 N atoms in the chemical formula.
 The prefix penta means 5. Thus, there are 5 O atoms in the chemical formula.
 Putting it all together we have N2O5.
II.
Ternary compounds
Ternary compounds are easy to spot. They usually contain three different elements but may
contain more. A ternary compound contains a polyatomic ion. A polyatomic ion is made up of
two or more atoms that act as a single unit and have an electric charge.
Nearly all polyatomic ions have a negative charge which means they will be at the end of the
chemical formula and name. One notable exception is the ammonium ion (NH4+). MEMORIZE
THIS ION.
The names of nearly all polyatomic ions end with the letters –ate or –ite. Beware three
exceptions: cyanide (CN-), hydroxide (OH-), and peroxide (O22-). These ions end with “ide”
which can trick into thinking you have a binary compound when you actually have a ternary
compound.
The naming system for ternary compounds is much the same as that for Type I and Type II
binary compounds. The main difference is that you do not change the name of a polyatomic ion.
When naming compounds whose first member is a polyatomic
ion use the following system:
name of polyatomic ion
root + ide
Examples:
Name the compound NH4Cl.
 NH4+ is ammonium
o No Roman numeral is needed because ammonium always has a charge of +1.
 Cl is chlorine, whose root is chlor. Add the “ide” ending to get chloride.
 Answer…ammonium chloride
Write the formula for ammonium sulfide.
 Ammonium is NH4+. Charge …+1.
 Sulfide is S. Charge …-2


+1
-2
So far we have NH4 S.
Balance the charges to get (NH4)2S.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
When naming compounds whose second member is a polyatomic
ion use the following system:
name of first element (R.N.?)
name of polyatomic ion
Examples:
Name the compound Na2SO4.
 Na is the symbol for sodium
o Sodium is in Group 1 so no Roman numeral is needed.
 SO42- is the formula of the sulfate ion.
 Put the pieces together to get the name sodium sulfate.
Name the compound CrPO4.
 Cr is the chemical symbol for chromium.
o Cr is not in Group 1 or Group 2; therefore, a Roman numeral is needed.
 PO43- is the formula of the phosphate ion.
 So far we have chromium (??) phosphate.
 To find the Roman numeral
o The phosphate ion has a charge of -3.
o There is only one phosphate ion so the total negative charge is -3.
o The total positive charge must be +3 to balance the total negative charge.
o Since there is only one chromium atom it gets the entire +3 charge. The Roman
numeral is III.
 Putting it all together we have chromium (III) phosphate.
Write the formula for potassium cyanide.
 The chemical symbol of potassium is K. The absence of a Roman numeral indicates
that potassium can be found in either Group 1 or Group 2. Its ionic charge is +1.
 The formula for the cyanide ion is CN- and its charge is -1.


+1
-1
So far we have K CN.
The charges already balance so the formula is KCN.
Write the formula for iron (III) chromate.
 Iron is Fe. The Roman numeral indicates a charge of +3.
 Chromate is CrO42-. Its charge is -2.



+3
-2
So far we have Fe CrO4.
In order to balance the charges we need two iron atoms and three chromate ions.
Putting it together we have Fe2(CrO4)3.
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
When naming compounds composed of two polyatomic ions use
the following system:
name of polyatomic ion
name of polyatomic ion
Examples:
Name the compound NH4CN.
 NH4+ is ammonium
 CN- is cyanide
 Answer … ammonium cyanide
Write the formula for ammonium sulfate.
 Ammonium is NH4+.
 Sulfate is SO4-2.
 Answer … (NH4)2SO4.
III.
Naming Polyatomic Ions That Contain Oxygen
There are many atoms that form several different polyatomic ions with oxygen. The naming
system for these ions is based on two things: the most common ion in each series and the number
of oxygen atoms compared to the most common ion. The ones that concern us most are the ions
of phosphorus, sulfur, nitrogen, chlorine and carbon. MEMORIZE THESE IONS IMMEDIATELY!
CO32- = carbonate
ClO3- = chlorate
NO3- = nitrate
PO43- = phosphate
SO42- = sulfate
When naming oxygen containing polyatomic ions:
One more oxygen than the most common ........... per ___ ate
Most common .......................................................... ___ ate
One less oxygen than the most common.....................___ ite
Two less oxygen than the most common ...........hypo ___ ite
Examples:
PO53PO43PO33PO23SO52SO42SO32SO22-
= perphosphate
= phosphate (most common)
= phosphite
= hypophosphite
= persulfate
= sulfate (most common)
= sulfite
= hyposulfite
(Note: Some of these ions do not exist in the
real world. They are written here to show
how to use the naming system.)
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NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
IV.
Naming Acids
For this class, all acids begin with H (hydrogen). The names of all acids end with the word
“acid.” There are two types of acids: those that contain oxygen and those that do not.
1.
2.
Naming acids that DO NOT contain oxygen
Take the name of the anion, add the prefix “hydro” and change the ending to “ic.”
Add the word “acid.”
When naming acids that DO NOT contain oxygen:
hydro + root of second element + ic
acid
Examples:
Name the compound HF.
 We know this is an acid because the chemical formula starts with “H.”
 Take the name of the anion (fluoride) add the prefix “hydro” and change the ending
to “ic”: hydrofluoric
 Finally, add the word “acid.”
 hydrofluoric acid
Name the compound HCN.
 We know this is an acid because the chemical formula starts with “H.”
 There is no oxygen present so we start with the prefix “hydro.”
 Next, take the name of the anion (cyanide) and change the ending to “ic”:
hydrocyanic
 Finally, add the word “acid.”
 hydrocyanic acid
Write the formula for hydrobromic acid.
 We know the formula starts with “H” because it is an acid. The charge on H is +1.
 We also know that the acid does not contain oxygen because of the “hydro” prefix.
 Removing the “hydro” and “ic” leaves us with “brom”, the root of bromine or Br.
The charge on bromine is -1.


+1
-1
So far we have H Br
Balance the charges to get the formula HBr.
Write the formula for hydrosulfuric acid.
 We know the formula starts with “H” because it is an acid. The charge on H is +1.
 We also know that the acid does not contain oxygen because of the “hydro” prefix.
 Removing the “hydro” and “ic” leaves us with sulfur. The charge on sulfur is -2.


+1 -2
So far we have H S
Balance the charges to get the formula H2S.
Page 9 of 13
NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
1.
2.
3.
Naming Acids that DO contain oxygen
Find the name of the polyatomic ion.
Change “ate” to “ic” or “ite” to “ous.”
Add the word acid.
When naming acids that DO contain oxygen:
name of polyatomic ion root + ic/ous
acid
(Change “ate” to “ic” or “ite” to “ous”)
Examples:
Name the compound HClO4.
 We know this is an acid because it starts with “H.”
 ClO4- is the perchlorate ion.
 Change the “ate” to “ic” and get perchloric.
 Add the word acid and get perchloric acid.
Name the compound H2SO3.
 We know this is an acid because it starts with “H.”
 SO32- is the sulfite ion.
 Change the “ite” to “ous” and get sulfous.
 Add the word acid and get sulfous acid.
o The name is actually sulfurous acid, which differs from the root for sulfur.
Write the formula for phosphorous acid.
 The word acid tells us the first element is “H.” The charge on H is +1.
 We also know it is a ternary acid because the prefix “hydro” (meaning binary acid) is
missing.
 Change “ous” to “ite” to get phosphite. The formula for phosphite is PO33-.
 Putting it together and balancing the charges we get H3PO3.
Write the formula for carbonic acid.
 The name tells us the first element is “H.” The charge on H is +1.
 We also know it is a ternary acid because the prefix “hydro” (meaning binary acid) is
missing.
 Change “ic” to “ate” to get carbonate. The formula for carbonate is CO32-.
 Putting it together and balancing charges we get H2CO3.
Page 10 of 13
NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Common Polyatomic Ions
Formula
Name
NH41+
ammonium
C2H3O21-
acetate
CO32-
carbonate
HCO31-
hydrogen carbonate or bicarbonate
ClO1-
hypochlorite
ClO21-
chlorite
ClO31-
chlorate
ClO41-
perchlorate
CrO42-
chromate
Cr2O72-
dichromate
CN1-
cyanide
OCN1-
cyanate
SCN1-
thiocyanate
OH1-
hydroxide
NO21-
nitrite
NO31-
nitrate
MnO41-
permanganate
PO43-
phosphate
HPO42-
hydrogen phosphate
H2PO41-
dihydrogen phosphate
SO32-
sulfite
SO42-
sulfate
HSO41-
hydrogen sulfate or bisulfate
S2O32-
thiosulfate
AsO33-
arsenite
AsO43-
arsenate
C2O42-
oxalate
O22-
peroxide
Page 11 of 13
NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Assignment
Name each of the following compounds.
1.
MnO
26.
Cu(OH)2
2.
ZnBr2
27.
PCl5
3.
Ca(ClO3)2
28.
LiNO3
4.
BaSO4
29.
KH2PO4
5.
AgNO3
30.
CuCN
6.
H2S
31.
KHCO3
7.
CaO
32.
NaHSO4
8.
H2CO3
33.
Li2S2O3
9.
Mg3(PO4)2
34.
H3PO4
10.
K2CrO4
35.
MgSO4
11.
NaI
36.
Ca3(AsO3)2
12.
Al(NO2)3
37.
SiO2
13.
ZnSe
38.
CuCl
14.
Sn(MnO4)2
39.
KClO4
15.
ICl5
40.
CdSO3
16.
CoSO3
41.
NaBr
17.
HF
42.
P2O3
18.
Fe2(SO4)3
43.
HClO
19.
Sn(Cr2O7)2
44.
N2O4
20.
AsBr3
45.
NaH
21.
KCN
46.
WN2
22.
NH4OH
47.
PbC2O4
23.
Fe(ClO4)3
48.
H2Se
24.
HNO2
49.
H3PO2
25.
CS2
50.
CaH2
Page 12 of 13
NAMING CHEMICAL COMPOUNDS & WRITING CHEMICAL FORMULAS
Write the formula for each of the following compounds.
51.
tin (II) nitrate
76.
calcium bicarbonate
52.
zinc phosphate
77.
magnesium hydroxide
53.
hypophosphorous acid
78.
zinc bisulfate
54.
iron (III) chloride
79.
mercury (I) oxide
55.
lithium sulfide
80.
chlorous acid
56.
silver oxalate
81.
lead (IV) sulfide
57.
perchloric acid
82.
calcium acetate
58.
potassium permanganate
83.
sodium phosphate
59.
strontium hypochlorite
84.
gold (III) oxide
60.
copper (I) sulfite
85.
phosphorous acid
61.
carbon disulfide
86.
hydroiodic acid
62.
calcium oxide
87.
sodium fluoride
63.
barium carbonate
88.
diarsenic pentoxide
64.
antimony (III) dichromate
89.
sulfur dibromide
65.
silicon dioxide
90.
aluminum sulfate
66.
iron (II) carbonate
91.
dinitrogen trisulfide
67.
sodium cyanide
92.
nickel (III) iodide
68.
carbon tetrafluoride
93.
scandium (III) phosphate
69.
cesium iodide
94.
platinum (II) perchlorate
70.
sodium chromate
95.
sodium dihydrogen phosphate
71.
hydrosulfuric acid
96.
sulfurous acid
72.
aluminum oxide
97.
strontium carbonate
73.
ammonium thiocyanate
98.
copper (II) hydroxide
74.
boron trifluoride
99.
bismuth (III) oxalate
75.
radium sulfate
100.
diphosphorous pentaselenide
Page 13 of 13