Chemical Nomenclature
Chemical nomenclature is an important aspect of chemistry. Therefore, it is
essential to be able to go between name and formula easily. Historically, chemistry has
been plagued with common names. Chemicals were named whatever someone wanted to
call them. With rare exception, we don’t use common names anymore. However, there
are two chemicals that you must know that use common names. They are water (H2O)
and ammonia (NH3). Most people at least know the formula for water, if you don't, you
do now!
The names of the elements are common names. There is no system to their names
so you just have to learn them. There is also a small group of compounds that exist as
diatomic molecules. That is they exist with two of the same element in the compound.
For these compounds, the name of the compound is the same as the name of the element
because the compound only contains that element. They are shown below:
Name Formula
Hydrogen H2
Nitrogen N2
Oxygen O2
Fluorine F2
Chlorine Cl2
Bromine Br2
Iodine I2
Astatine At2
One good way to remember them is they are all of the ---gens. (Hydrogen,
nitrogen, oxygen and the halogens (F2, Cl2, Br2, I2, At2).
Nowadays, however, there is a system for chemical nomenclature. It is called the
IUPAC (International Union for Pure and Applied Chemistry) systematic nomenclature.
It is important to learn this system so you become fluent in the language of chemistry.
This handout is designed to help you. The diagram on the next page is a visual
representation. (In addition, in this packet, there is a PowerPoint presentation to describe
this. As nomenclature is somewhat complicated, it is recommended that you read both
this handout and the PowerPoint presentation.)
Types of Compounds
Ionic Acids
Covalent
H____(aq)
Contains a metal or a
Name has word, acid, in it
polyatomic ion Binary compound with two
nonmetals Like ionic compound where H is
Name ions the metal
Oxyacids
Representative metals
Transition metals Nonmetal Ions Binary Acids H—polyatomic ion
(All others) NO CHARGES
(Group IA, IIA, IIIA, Zn, Cd and Ag) Monatomic Polyatomic ions Name has number of each
Charge = group # Charge given (in Roman element in the compound HX(aq) Name depends on name of
Name = element name numerals) in name Charge = group # - 8 Prefix-first element prefix-
Ca2+ = calcium ion
Hydro-x-ic acid polyatomic ion
Metal name(charge) Name = stemide MEMORIZE secondide
Fe3+ = iron (III) P2O5= diphosphorus
S2- = sulfide pentoxide HI(aq) = hydroiodic acid
If ion ends in ate then acid
ends in ic acid chlorate = ClO3-
choric acid = HClO3(aq)
If ion ends in ite then acid chlorite = ClO2-
ends in ous acid chlorous acid = HClO2(aq)
Nomenclature flowchart
The first step in the system is to determine the type of compound. For
nomenclature, there are three major types of compounds. They are ionic compounds,
covalent compounds and acids. Each type of compound is named differently, therefore,
before a compound can be named, its type has to be determined. This is diagrammed on
the next page.
Types of Compounds
Ionic Acids
Covalent
Contains a metal or H____(aq)
Name has word, acid, in it
a polyatomic ion Binary compound with
two nonmetals Like ionic compound where
H is the metal
Name ions
Types of Compounds
Ionic compounds are made from ions. They always contain a metal or a
polyatomic ion (or both). How do we recognize that a compound is ionic? From the
formula, it is easy to recognize if a compound contains a metal because there will be the
symbol for a metal in the formula. (You might want to review identification of types of
elements from the periodic table.) For example, the following compounds all contain
metals in the formula (in bold) and are therefore ionic.
FeCl3, NaBr, Cr(NO3)3
If a compound doesn't contain a metal, it can also be ionic if it contains a
polyatomic ion. The best way to recognize, from the formula, if a compound has a
polyatomic ion is knowing the ions and recognizing them in the formula of a compound.
Otherwise, since polyatomic ions have at least two elements, a compound containing a
polyatomic ion will have at least three elements. Therefore, if a compound has at least
three elements, it must contain a polyatomic ion and is, therefore, ionic (Acids are an
exception, but will be discussed later.) The following all contain polyatomic ions (bold):
MgCO3, Ni(C2H3O2)2, NH4I
From the name, we can use the same criteria to determine if a compound is ionic.
We look for the name of a metal in a compound or the name of a polyatomic ion. Again,
it is always best if you are familiar with the polyatomic ions so you can recognize them.
However, another way that helps is that most (not all) polyatomic ions end in ---ate or ---
ite. If a compound ends that way it is ionic.
The following compounds are all ionic.
strontium sulfide, cobalt (II) arsenide, cesium phosphate, ammonium sulfate
(has a metal) (has a metal) (has a metal) (has polyatomic ions)
If a compound is not ionic, it is either covalent or an acid. (See Types of
Compounds flowchart) All acids have the word, "acid" in their names, so determining if
a compound is an acid, from the name, is trivial. From the formula, acids always begin
with H. Also since all acids are aqueous, they will often have the subscript (aq).
(Sometimes, however, that is not written.). All of the following are acids...the first group
from the name and the second from the formula.
hydrochloric acid, sulfuric acid, nitric acid
HI(aq), H3PO4(aq), HC2H3O2(aq)
If a compound is neither ionic nor an acid, then it must be covalent. (See Types of
Compounds flowchart) Another way to tell is that all covalent compounds are made from
two nonmetals. Again, they are easily recognized by recognition of the names of the
elements from which they are made and use of the periodic table to determine if the
elements are nonmetals. Each of the following compounds are made from 2 nonmetals
and therefore, covalent.
carbon disulfide, sulfur hexafluoride, dinitrogen pentoxide
and
PCl3, SeO2, CI4
Using, the above information, we can determine if a compound is ionic, an acid or
covalent. The examples below will illustrate this.
Example 1: For each of the following, determine if it is ionic, an acid, or
covalent: MoF6, CaCO3, HI(aq), CSe2.
Solution:
MoF6: Mo (molybdenum) is a metal: ionic
CaCO3: Ca (calcium) is a metal: ionic
HI(aq) : begins with H and is aqueous: acid
CSe2 : C (carbon) and Se (selenium) are nonmetals: covalent
Example 2: For each of the following, determine if it is ionic, an acid, or
covalent: ammonium sulfide, cesium chloride, nitrogen triiodide, telluric acid.
Solution:
Ammonium sulfide: ammonium (NH4+) is a polyatomic ion: ionic
Cesium chloride: cesium (Cs) is a metal: ionic
Nitrogen triiodide: nitrogen (N) and iodine (I) are nonmetals: covalent
Telluric acid: has the word "acid" in the name: acid.
As you can probably, see, the classification step is not very complicated. It really
is all about recognition and the ability to use the periodic table to determine if an element
is a metal or a nonmetal.
Once we have determined the type of substance, we can go from either formula to
name or from name to formula. Let's start with ionic substances. The chart below will
summarize.
Ionic
Contains a metal or a polyatomic ion
Name Ions
Representative metals Nonmetal Ions
Transition metals
(Group IA, IIA, IIIA, Zn, (All others) Monatomic Polyatomic ions
Cd and Ag)
Charge = group # Charge given (in Roman Charge = group # - 8 MEMORIZE
numerals) in name Name = stemide
Ionic Compounds
Ionic Compounds:
To determine the name or the formula we have to determine either the name or
the formula of the ions. There are 4 types of ions. They are representative metal ("A"
group) ions, transition metal ("B" group) ions, nonmetal ions and polyatomic ions.
(Please see the flow chart above.)
Representative metal ions are ions derived from the representative metals,
specifically group IA, (the alkali metals), group IIA (alkaline earth metals), group IIIA,
zinc, cadmium and silver. These elements are characterized by forming only one ion.
For these elements, the charge on the ion will be the same as the group number in which
the element is found. So alkali metals (group IA) form ions with a charge of +1, alkaline
earth metals (group IIA) form ions with a charge of +2 and group IIIA elements form a
charge of +3. Zinc and cadmium form +2 and silver, +1. Therefore, to find charge on
the ion, we simply find the element on the periodic table.
Example 3: Find the charges of the following ions: calcium ion, zinc ion,
potassium ion, aluminum ion.
Solution: calcium ion: calcium is in group IIA : Ca2+
zinc ion: Zn2+
potassium ion: potassium is in group IA: K+
aluminum ion: aluminum is in group IIIA: Al3+
The names of t hese ions are the same as the names of the elements from which
they are derived. Example 3 also illustrates this.
All other metals (the transition and post transition metals) are characterized by
forming more than one ion. For this reason, we cannot predict the charge on the ion
simply by the position of the element on the periodic table. We have to be told. The
convention is to use the element name with the charge on the ion in parentheses and in
Roman numerals. For example, Fe3+ is called, iron(III). Some more examples are shown
below:
Ion Name: Symbol and Charge
iron(II) Fe2+
tin(IV) Sn4+
tin(II) Sn2+
chromium(VI) Cr6+
If the name of the compound is given, it is easy to predict the charge on the ion
because it is given (What could be easier!)
However, to come up with the charge of the ion from a compound, we have to
look at what the metal is combined with. This will be illustrated in a later example
(Example 6).
The third type of ion is a nonmetal ion. These are ions derived from nonmetals
like sulfur, chlorine etc. To determine the charge on a nonmetal ion, we simply subtract
8 from the group number. Sulfur, for example is in group VI on the periodic table.
Therefore the ion it forms will have a charge of:
6 - 8 = -2
and the symbol will be:
S2-
Nonmetal ions are named by dropping the ending on the element name and
adding the suffix ---ide to the stem name of the element. This is summarized below:
Element Group # Charge Symbol Ion Name
oxygen 6 (6 - 8) = -2 O2- oxide
phosphorus 5 (5 - 8) = -3 P3- phosphide
iodide 7 (7 - 8) = -1 I- iodide
The last type of ions are the polyatomic ions. In this packet, there is a list of very
common polyatomic ions that you should learn. Once again, the best way to recognize
polyatomic ions is by familiarity. However, if you forget, a compound containing at least
three elements contains a polyatomic ion. Also, with some exceptions (see list) most
polyatomic ions end with the suffixes -ate or –ite.
Once we have determined the types of ions in the compound we can put them
together to come up with the formula, or use this information to come up with a name.
First, let's look at coming up with a formula from the name.
To determine the formula of an ionic compound there are 3 steps:
1. Determine the ions
2. Determine the charges on the ions.
3. Put the ions together.
Before we do an example, let's look at that last step. Recall that a compound has
no net charge. An ionic compound, however, is made from charged particles. To solve
this problem, the charges of the ions must cancel. We determine the least common
multiple (LCM) of the charges of the ions. Then we multiply each ion by an appropriate
number to bring the charges to the LCM. The numbers we multiply by become the
subscripts on the ions.
Example 4: Determine the formula for a compound made from Fe3+ and SO42-.
Ion Multiplier LCM
Fe3+ X 2 = 6
SO42- X 3 = -6
Notice that the sum of the charges is zero. The multipliers become the subscripts
and the formula is:
Fe2(SO4)3
Now let's look at some examples of going from name to formula for some ionic
compounds.
Example 5: Determine the formulas for the following: sodium oxide, barium
hydroxide, cobalt (II) iodide and ammonium sulfate
Solution:
sodium oxide:
symbols: Na, O
charges: Na: group 1 metal ==> Na+
O: group VI nonmetal ==> O2-
putting together
Na+ X 2 = 2
O2- X 1 = -2 formula = Na2O
barium hydroxide:
symbols: Ba, OH- (hydroxide is a polyatomic ion)
charges: Ba: group II metal ==> Ba2+
OH: polyatomic ion ==> OH-
putting together
Ba2+ X 1 = 2
OH- X 2 = -2 formula = Ba(OH)2
cobalt(II)bromide:
symbols: Co, Br
charges: Co: transition metal
the name says the charge is 2 ==> Co2+
Br: nonmetal in group VII ==> Br-
putting together
Co2+ X 1 = 2
Br- X 2 = -2 formula = CoBr2
ammonium sulfate:
symbols: both polyatomic ions so elements and charges
ammonium = NH4+
sulfate = SO42-
putting together
NH4+ X 2 = 2
SO42- X 1 = -2 formula = (NH4)2SO4
Let's go the other way now and determine the names of some compounds from
the formulas. The steps are:
1. Determine the types of ions.
2. Name the ions.
Example 6: Name the following: CaCl2, Sr(C2H3O2)2, FeBr2, V3(PO4)5
Solution:
CaCl2:
Ions: Ca = representative metal: calcium
Cl = nonmetal ion: chloride
calcium chloride
Sr(C2H3O2)2:
Ions: Sr = representative metal: strontium
C2H3O2 = polyatomic ion: acetate
strontium acetate
FeBr2
Ions: Fe = transition metal: iron( )
(Here, we need to determine the charge. See below)
Br = nonmetal ion: bromide
iron( ) bromide
To finish, we need to determine the charge on the iron. We can do
this by looking at what it is combined with as below where x represents the charge on the
iron. We use the same method we did above to determine formulas, but we go
backwards. We find the least common multiple. Here we have the multipliers
(subscripts)
Ion subscript LCM
Fex X 1 =
Br- X 2 = -2
Since the charge on the bromine is -1 and there are two of them, the LCM must be
2.
Ion subscript LCM
Fex X 1 = 2
Br- X 2 = -2
The total charge from the iron must be 2. Since there is only 1 iron ion, the
charge on that ion (x) must be +2 so it is iron (II). The name is, therefore,
iron(II)bromide
V3(PO4)5
ions: V: transition metal: vanadium( )
PO43-: polyatomic ion: phosphate
Like we did for the last example:
Ion subscript LCM
Vx X 3 =
3-
PO4 X 5 = -15
The LCM must be 15 and the charge on the vanadium must be 15/3 = 5 as
shown below:
Ion subscript LCM
V+5 X 3 = 15
3-
PO4 X 5 = -15
So, the name will be:
vanadium(V) phosphate
Types of Compounds
Ionic Acids
Covalent
Contains a metal or H____(aq)
Name has word, acid, in it
a polyatomic ion Binary compound with
two nonmetals Like ionic compound where
H is the metal
Name ions
Types of Compounds
Covalent compounds:
Compounds made from two nonmetals are covalent. Since they are held together
by covalent bonds, there are no ions. Since there are no ions, it is not necessary to
determine any charges as they don't exist. Also, unlike with ionic compounds, it is
difficult to predict the ratio in which nonmetals will combine. In fact some will combine
in different ratios to form different compounds. For this reason, the name tells us the
formula. The naming rule for these compounds is the following:
prefix first element name prefix second-ide
The prefixes used are mono, di, tri, tetra, penta, hexa, hepta, octa, nona, and deca
(for the numbers 1 - 10 respectively) and they literally tell us how many of each element
in the compound. Usually mono is not used for the first element. For example the
compound, P2O5 has 2 phosphorus atoms and 5 oxygen atoms. The name is therefore,
diphosphorus pentoxide (2 phosphorus, 5 oxygen). Nothing could be simpler. The most
common mistake students make with these compounds is trying to name them like they
are ionic. Don't do that! They are not ionic! The following examples will help with
nomenclature of covalent compounds.
Example 7: Name the following: CO2, PCl3, N2O
CO2 : one carbon and 2 oxygens ==> carbon dioxide
(it’s OK to say mono carbon, but usually it is not done)
PCl3: 1 phosphorus, 3 chlorines ==> phosphorus trichloride
N2O: two nitrogen, one oxygen ==> dinitrogen monoxide
Example 8: Determine the formulas of the following: carbon tetrabromide,
sulfur hexafluoride, dichlorine heptoxide
carbon tetrabromide: 1 carbon, 4 bromine ==> CBr4
sulfur hexafluoride: 1 sulfur, 6 fluorine ==> SF6
dichlorine heptoxide: 2 chlorine, 7 oxygen ==> Cl2O7
As you can see, charges won't work here, but the nomenclature is very simple.
Acid Nomenclature:
Acids
H____(aq)
Name has word, acid, in it
Like ionic compound where H is the metal
Binary Acids Oxyacids
H—polyatomic ion
HX(aq)
Hydro-x-ic acid Name depends on name of polyatomic ion
HI(aq) = hydroiodic acid
chlorate = ClO3-
If ion ends in ate then acid ends in ic acid
choric acid = HClO3(aq)
If ion ends in ite then acid ends in ous acid
chlorite = ClO2-
chlorous acid = HClO2(aq)
Acid Nomenclature
Acids are compounds that have a formula beginning with 'H' and are aqueous.
The name of an acid always has the word, "acid", in it. Please see the acid nomenclature
flowchart above. There are two kinds of acids. The first type are binary acids. These
acids have only hydrogen and some other element. Their names depend on the name of
the other element. In general, the pattern is hydro--x--ic acid, where x is the stem name
of the other element. For example, for HCl(aq) since the other element is chlorine the acid
is called hydrochloric acid. In an acid, hydrogen acts like a metal thus it has a charge of
+1. (An acid can be thought of as an ionic compound where hydrogen is the acid.)
Therefore, the subscript on the hydrogen will depend on the charge on the other element.
Since, in hydrochloric acid, chlorine has a charge of -1, we only need 1 hydrogen to
balance the charge.
Example 9: Determine the names of the following acids: HI(aq), HF(aq)
HI: hydrogen and iodine ===> hydroiodic acid
HF: hydrogen and flourine ==> hydrofluoric acid
Example 10: Determine the formulas for the following acids: hydrobromic acid,
hydrosulfuric acid.
Solution:
hydrobromic: hydrogen, H+
bromine, Br- formula: HBr(aq)
hydrosulfuric: hydrogen, H+
sulfur, S2- formula: H2S(aq)
The last type of acids are nonbinary. They contain more than two elements. In
addition, since they also contain oxygen, they are called the oxyacids. Like the binary
acids, oxyacids contain hydrogen and another ion. In this case the other ion is a
polyatomic ion. Like the binary acids, there will be one hydrogen in the formula for
every negative charge on the ion. For example, if the polyatomic ion has a charge of -2,
the subscript on the hydrogen in the acid will be 2. This is shown below.
Example 11: Find the formula of the acid made from sulfate ion.
Solution: sulfate ion is SO42-. The acid is made from hydrogen and
sulfate. Since sulfate has a charge of -2, we will need 2 hydrogens so the formula is:
H2SO4.
Nomenclature of the oxyacids is based on the nomenclature of the polyatomic
ions. (Once again you can see how important knowing your ions is!) The pattern is as
follows. If the ion ends in ---ate the corresponding acid ends in ---ic acid. If the ion
ends in ---ite the corresponding acid ends in ---ous acid. This is summarized below:
ion acid
--ate --ic acid
--ite --ous acid
This is illustrated well with the chlorine series as shown below:
ion name ion formula acid formula acid name
perchlorate ClO4- HClO4 perchloric acid
chlorate ClO3- HClO3 chloric acid
chlorite ClO2- HClO2 chlorous acid
hypochlorite ClO- HClO hypochlorous acid
Notice above that in each case the ate-ic, ite-ous rule is followed. In addition, the
other rule about the charges is followed. For each ion, the charge is -1 and each
corresponding acid has one hydrogen. The examples below will summarize acid
nomenclature.
Example 12: Name the following acids: H3PO4, H2SO3, HBrO4
Solution: H3PO4: The ion is, PO43- = phosphate so the acid is phosphoric
acid
H2SO3: The ion is, SO32- = sulfite so the acid is sulfurous acid
HBrO4: The ion is, BrO4- = perbromate so the acid is
perbromic acid
Example 13: Determine the formulas of the following acids: iodic acid, carbonic
acid, phosphorous acid.
Solution: Iodic acid is from iodate, IO3- since there is only one negative
charge, we need only one H. The acid is HIO3(aq)
Carbonic acid is from carbonate, CO32-, since there are 2 negative
charges, we need 2 H. The acid is H2CO3(aq)
Phosphorous acid is from phosphite, PO33- since there are 3
negative charges, we need 3 H. The acid is H3PO3(aq)
(One last note on acid nomenclature…acids are always in water so they have the
subscript (aq). Some substances can exist in more than one form. For example, H2S(aq) is
an acid and is named as such (hydrosulfuric acid). However H2S(g) is a covalent
compound and is called dihydrogen sulfide. For this reason, it is important to look at
phase labels.)
Now that we have summarized nomenclature, the only true way to become
proficient at it is practice. Remember the first step is to determine what type of substance
it is then use the information in this handout and the flowcharts accordingly. It is also
very important to know your polyatomic ions. The following two examples will
summarize everything.
Example 14: Name the following: NaI, MnO2, N2H4, CaCO3, HIO4(aq)
Solution: NaI: Na is a metal so this is an ionic compound. Since sodium
is a representative metal, we don't have to specify its charge. Iodine is nonmetal ion so it
ends in ide. The name is:
sodium iodide
MnO2: Manganese is a metal so this is an ionic compound.
Because manganese is a transition metal, we have to determine its charge. Oxygen has a
charge of -2 and there are 2 of them, so there is a total of -4 in the compound. Therefore,
the manganese must be +4. (To see this in more detail, review examples 5 and 6.)
Oxygen is nonmetal ion and ends in ide. The name is:
manganese (IV) oxide
N2H4: N and H are both nonmetals so this is a covalent
compound. There are 2 (di) nitrogens and 4 (tetra) hydrogens. The last nonmetal
(hydrogen) ends in ide. The name is:
dinitrogen tetrahydride
CaCO3: Calcium is a representative metal and CO32- is a
polyatomic ion. The name is:
calcium carbonate
HIO4(aq): This is an acid. It contains a polyatomic ion...IO4- which
is periodate. The ion ends in ate so the acid ends in ic acid. The name is:
periodic acid
Example 15: Determine the formulas of the following: magnesium nitride, iron
(III) acetate, sulfur dioxide, hydrofluoric acid, nitrous acid.
Solution: magnesium nitride: Magnesium is a metal so this is an ionic
compound.
magnesium ==> Mg ==> Mg2+
Mg3N2
nitride ==> N ==> N3-
iron(III)acetate: Iron is a transition metal so this is an ionic
compound.
iron(III) ==> Fe3+
Fe(C2H3O2)3
-
acetate ==> C2H3O2
sulfur dioxide: Both sulfur and oxygen are nonmetals so this is a
covalent compound. There is one sulfur and two oxygens.
SO2
hydrofluoric acid: Since it begins with "hydro" it is a binary acid
so there are only hydrogen and fluorine.
H ==> H+
HF(aq)
F ==> F-
Nitrous acid: This is not a binary acid. It is an oxyacid. Since the
acid name ends in ous acid, the ion must have been nitrite, NO2-. We have NO2- and H.
H+
HNO2(aq)
NO2-