EXPERIMENT 3
Nomenclature and Formula Writing
Outcomes
After completing this experiment, the student should be able to:
1. Recognize anions and cations and balance charges to write formulas for compounds.
2. Interpret chemical formulas.
3. Identify types of chemical compounds, and names of cations and anions.
4. Name inorganic compounds when formula is given and write the formula of a compound when
the name is given.
Introduction
Writing Chemical Formulas
The chemical formula for a compound is the short hand definition of a chemical substance. From a
chemical formula one can identify the elements present in the chemical substance, the ratio in which they
are combined and the number of atoms of each element present in the compound.
Elements in the periodic table are also classified as s-, p- and d-block elements based on the distribution
of electrons into s-, p- or d-orbitals. The elements belonging to s- and p-block elements are often referred
to as main group elements, whereas the d-block elements are referred to as transition elements. Metal
atoms during chemical reactions loose electrons to form cations whereas non-metals gain electrons to
form anions with the exception of hydrogen. Hydrogen atom can either loose or gain electrons during
chemical reactions, and thus, can form a cation as well as an anion. The main group elements generally
loose or gain a fixed number of electrons, and thus, form ions with fixed charges (Figure 3.1).
Figure 3.1. Main group elements and charges of the ions they form.
p-block
S-block
IA
H+
IIA
IIIA
VIA
VIIA
N3-
O2-
F-
P3-
S2-
Cl-
Li+
Be2+
Na+
Mg2+
Al3+
K+
Ca2+
Ga3+
Se2-
Br-
Rb+
Sr2+
In3+
Te2-
I-
Cs+
Ba2+
Fr+
Ra2+
Transition elements (d-block)
Noble Gases
IVA VA
In Summary:
13


Group IA, IIA and IIIA form ions with +1, +2 and +3 charges respectively.
Nonmetals are in the upper right hand portion of the periodic table.
o Group VIIA often forms ions with a -1 charge.
o Group VIA often forms ions with a -2 charge.
o Group VA often forms ions with a -3 charge.
On the other hand, the transition metals and some p-block elements (post-transition metals) are capable of
loosing multiple electrons and form cations with multiple charges (Figure 3.2)
Figure 3.2. Ions of some transition metals and post-transition metals.
IA
IIA
IIIA
IIIB
Sc3+
IVB
Ti2+
Ti4+
VB
VIB
Cr2+
Cr3+
VIIB
Mn2+
Mn3+
[
IB
Cu+
Cu2+
IIB
Zn2+
Y3+
Ag+
Cd2+
Sn2+
Sn4+
La3+
Au+
Au3+
Hg+
Hg2+
Pb2+
Pb4+
2+
Fe
Fe3+
VIIIB ]
Co2+ Ni1+
Co3+ Ni2+
Ni3+
IVA
Naming of various cations and anions listed in Figures 3.1 and 3.2 has been shown below in Tables 3.1 –
3.3. A list of polyatomic ions and their naming are shown in the Table 3.4.
Types of compounds: Depending on the type of elements and/or groups of atoms (polyatomic ions)
present, there are at least 5 major categories of compounds (described below).
1. Binary ionic compounds are composed of charged ions that are held together by a strong
electrostatic force, and essentially means that only two different elements are involved. Binary ionic
compounds are of two types.
i. Type 1 binary ionic compounds – Are made up of two elements and are composed of metallic
positive ions (cations) with fixed charges and nonmetal negative ions (anions). The metals that
from type-1 binary ionic compounds include elements from groups 1A, 2A; and Al, Ga and In
from group 3A, as well as elements Zn, Cd and Ag from transition metals (Table 3.2). Various
nonmetals found in ionic compounds and their common charges are shown in Table 3.3, and
Figure 3.2.
Example:
Calcium chloride - CaCl2.
ii. Type 2 binary ionic compounds – Are also made up of two elements and are composed of
metallic positive ions (cations) and nonmetal negative ions (anions). All metals except those
which from type I binary ionic compounds, form type II compounds. These metals can have
multiple charges (shown in Table 3.3 and Figure 3.2).
Examples:
Iron(II) chloride – FeCl2. (Iron has +2 state)
Iron(III) chloride – FeCl3 (Iron has +3 state)
2. Compounds with polyatomic ions: These are ionic compounds that contain a cation such as an
ammonium or a metallic ion, and polyatomic anion. The most common polyatomic ions are shown
in Table 3.4.
Examples:
Sodium phosphate – Na3PO4
Ammonium nitrate - NH4NO3
14
Cobalt(II) sulfate – CoSO4
3. Molecular compounds: In these compounds the elements are held together by covalent bonds or
shared pairs of electrons. Molecular compounds are also referred to as Type 3 binary compounds.
They are made up of only nonmetals. See Figure 3.1 for the location of nonmetals in the periodic
table.
Examples:
Hydrogen chloride – HCl
Dinitrogen pentoxide – N2O5
4. Binary acids:
Acids: Many compounds that contain hydrogen are often referred to as acids. Acids when dissolved
in water release hydrogen ions (H+) into solution. When a substance is dissolved is water, it is
referred to as an aqueous solution and is designated by the symbol (aq) written after the formula of
the compound. In the case of acids, the designation (aq) shows that the ions are present in aqueous
(water) solution.
-
Binary acids are compounds formed between hydrogen ion (H+) and other non-metal aniona (e.g., F ,
- -2
Cl , Br , I and S ) and dissolved in water.
Examples:
Hydrochloric acid – HCl(aq)
Hydrosulfuric acid – H2S(aq).
5. Oxyacids: These are compounds formed between hydrogen (H+) and polyatomic anions containing
oxygen.
Examples:
Sulfuric acid – H2SO4(aq)
Nitric acid – HNO3.(aq)
Rules for writing chemical formulas: The following are simple rules used for writing chemical
formulas.

Rule 1: Write the symbol for the metallic element first. Then, write the symbol for the nonmetallic element.

Rule 2: Write the combining capacities for the elements (charges).

Rule 3: Criss-cross the combining capacity numbers (Remember the compounds are neutral,
therefore the sum of positive and negative charges must equal to zero). Use subscripts to indicate
the number of atoms each element the compound has in it (if the element has only one atom, then
no subscript is needed for that element) (See examples below).

Rule 4: Writing formulas for compounds that contain polyatomic ions: The rules above also
apply when writing formulas of compounds containing polyatomic ions, except that in order to
indicate more than one polyatomic ion in the formula, put parentheses around the polyatomic ion
before writing the subscript (See example below).
Examples: Write the formulas for calcium chloride, sodium oxide and ammonium sulfate.
15
Table 3.1: List of type I metals and the charges on the cations they form
Metal (symbol)
Ion
Cation Name
Metal
Ion
+
Lithium (Li)
Li
Lithium
Strontium (Sr)
Sr2+
Sodium (Na)
Na+
Sodium
Barium (Ba)
Ba2+
Potassium (K)
K+
Potassium
Aluminum (Al)
Al3+
Rubidium (Rb)
Rb+
Rubidium
Gallium (Ga)
Ga3+
Cesium (Cs)
Cs+
Cesium
Indium (In)
In3+
Beryllium (Be)
Be2+
Beryllium
Zinc (Zn)
Zn2+
Magnesium(Mg)
Mg2+
Magnesium
Cadmium (Cd)
Cd2+
Calcium (Ca)
Ca2+
Calcium
Silver (Ag)
Ag+
Cation Name
Strontium
Barium
Aluminum
Gallium
Indium
Zinc
Cadmium
Silver
Table 3.2: List of common non-metals and the charges on the anions they form
Nonmetal
Symbol for Ion
Base Name
Anion name
–
Fluorine (F)
F
FluorFluoride
–
Chlorine (Cl)
Cl
ChlorChloride
–
Bromine (Br)
Br
BromBromide
–
Iodine (I)
I
IodIodide
2–
Oxygen (O)
O
OxOxide
2–
Sulfur (S)
S
SulfSulfide
3–
Nitrogen (N)
N
NitrNitride
3–
Phosphorus (P)
P
PhosphPhosphide
Table 3.3: Some metals that form cations with multiple charges – type II metals
Metal
Ion
Name
Metal
Ion
Name
2+
2+
Chromium
Cr
Chromium(II) or Chromous Tin (Sn)
Sn
Tin(II) or Stanous
(Cr)
Cr3+
Chromium(III) or Chromic
Sn4+
Tin(IV) or Stanic
2+
+
Iron (Fe)
Fe
Iron (II) or Ferrous
Mercury
Hg
Mercury (I) or Mercurous
(Hg)
Fe3+
Iron (III) or Ferric
Hg2+ Mercury (II) or Mercuric
Cobalt (Co)
Co2+ Cobalt (II) or Cobaltous
Lead (Pb)
Pb2+
Lead(II) or Plumbous
3+
4+
Co
Cobalt (III) Cobaltic
Pb
Lead(IV) or Plumbic
+
+
Copper (Cu)
Cu
Copper (I) or Cuprous
Gold (Au)
Au
Gold(I) or Aurous
2+
3+
Cu
Copper (II) or Cupric
Au
Gold(III) or Auric
Note: In classical style of naming compounds the name of the cation with lesser charge ends with a suffix
“ous”and higher charge ends with a suffix “ic”. The classical naming system is not commonly used,
however, texbooks in the areas of biological and health science continue to use this system and student
must be aware of it.
Table 3.4: Common polyatomic anions, their formulas and charges
Name
Formula Name
Ammonium
NH4+
Acetate
Hydroxide
OH
Cyanide
Nitrate
NO3
Carbonate
Nitrite
NO2
Hydrogen sulfate (bisulfate)
Formula
CH3COO–
CN–
CO32HSO416
Hypochlorite
ClO–
Hydrogen phosphate
–
Chlorite
ClO2
Sulfate
Chlorate
ClO3
Sulfite
Perchlorate
ClO4
Peroxide
Hydrogen carbonate (bicarbonate)
HCO3
Phosphate
Note: Ammonium ion is the only polyatomic ion with the positive charge.
HPO42SO42SO32–
O22–
PO43-
Nomenclature
The elements shown in the periodic table can combine with each other and form many compounds.
Chemists have identified and/or created millions of compounds. A systematic method of naming these
chemical compounds is therefore very important to distinguish them from each other and this process is
referred to as nomenclature. Nomenclature in chemistry was devised by International Union of Pure and
Applied Chemistry (IUPAC). As per the IUPAC method of naming compounds, every chemical
compound can be given a name that not only identifies it uniquely but also defines its chemical structure.
Naming inorganic compounds with examples:
As you learned in chemical formula writing experiment, inorganic compounds may be divided into five
categories shown below. The procedures used to name the compounds in each of the categories with
examples are described below.
1. Binary ionic compounds
a. Naming Type 1 binary compounds: Type 1 binary ionic compounds are made up of two
elements and are composed of metallic cations and nonmetal anions. Type 1 metal cations
exhibit fixed charges. The metals that form type-1 binary ionic compounds include elements
from group 1A (except hydrogen), 2A, elements Al, Ga and In from group 3A, and elements Zn,
Cd and Ag from transition metals (Table 3.1). The various nonmetals and their common charges
in ionic compounds are shown in Table 3.2.
Rules:
1. Order the names for ions - first the cation, then the anion.
2. Name of cation: Same as the name of element from the periodic table (Table 3.3).
3. Name of the anion: Derived from the root of the element's name plus the suffix "-ide."
4. Combine the names of cation and anion to generate the name of the compound.
Summary:
Example: Write the name for: KCl
Step 1: In the above example, the cation derived from potassium and anion derived from
chlorine.
Step 2: Cation = potassium (K+). Anion = chloride (Cl-).. (Root = chlor- plus the ending "-ide" =
chloride).
Step 3: The name of the compound is = Potassium chloride.
b. Naming Type 2 binary ionic compounds: Type 2 binary ionic compounds are made up of
two elements and are composed of metallic cations with variable charges and nonmetal
anions. Some of the metals that form type 2 binary ionic compounds are shown in Table 3.3s.
Rules
1. Order the names for ions - first the cation, then the anion.
2. Determine the charge on cation based on the type of anion and subscripts.
17
3. Name of cation with its charge in parenthesis as Roman numeral: Name of cation is same as
the name of element from the periodic table.
4. Name of the anion: Derived from the root of the element's name plus the suffix "-ide."
5. Combine the names of cation with Roman numeral and anion to generate the name of the
compound.
Summary:
Example: Write the name for: PbCl4
Step 1: In the above example, the cation is derived from lead (Pb) and anion is derived from
chlorine.
Step 2: Lead (Pb) is a transition element and can have multiple charges and the charge on Pb has
to be represented by a Roman numeral. Here is how to determine its value:
1. Multiply the charge of the anion (Cl-) by its subscript. Ignore the fact that it is
negative. In this example it is: 1 x 4 = 4.
2. Divide this result by the subscript of the cation (Pb). This is the value of the Roman
numeral to use. In this example, it is 4 ÷ 1 = 4.
3. The value of the Roman numeral equals the positive charge on the cation in this
formula. Since the result of step #2 is 4, we then use Lead (IV) for the name.
Note: There is no space between the name and the parenthesis.
Step 3: Cation = Lead(IV) (Pb4+); Anion = chloride (Cl-); (Root = chlor- plus the ending "-ide"
= chloride).
Step 4: The correct name of the example is Lead(IV) chloride.
Classical method of naming type-2 binary ionic compounds: In classical style of naming type two
binary ionic compounds, the name of the cation with lesser charge ends with a suffix “ous”and higher
charge ends with a suffix “ic”. Although, the classical naming system is not commonly used in
chemistry anymore, the texbooks in the areas of biological and health science continue to use it.
Therefore the students must be aware of this system of naming compounds as well.
Example: Write the name for: PbCl4 as per the classical system of naming compounds.
The steps used in this type of naming is same as above except for the following:
 In the above example the cation is Pb4+ [Lead(IV)] and anion is Cl-(chloride)
 From Table 5.4, it is apparent that the Lead has two cations, Pb2+ (Plumbus) and Pb4+
(Plumbic).
 Therefore, as per the classical system of naming PbCl4 is named as - Plumbic chloride.
2. Naming molecular compounds: In these compounds the elements are held together by covalent
bond(s) or shared pair(s) of electrons. Molecular compounds are also referred to as Type 3 binary
compounds. They are made up of only non-metals.
Rules:
1.
Look at first element and name it (the element to the left side retains its name).
2.
Derive the name for the second element by adding -ide to the root of elemental name.
3.
Use Greek prefixes for number of atoms: mono, di, tri, tetra, penta, hexa, hepta, octa,
nona, deca, and write the name.
Summary:
Example: Write the name of the following formula: N2O5
18
Step 1: Look at first element and name it. The first element is = Nitrogen.
Step 2: Look at second element. Use root of its full name (Ox- plus the ending "-ide." The anion
= oxide.
Step 3: Determine the Greek prefixes for number of atom based on subscripts. In this case “di”
for nitrogen and “penta” for oxide.
Step 4: Write the name of the compound using Greek prefixes (step 3) and names written in steps
1 and 2. The name of the compound N2O5 = Dinitrogen pentoxide.
Note: If the subscript for the first element is “mono” the Greek prefix is ignored for
the first element but not for the second element.
3. Compounds with polyatomic ions: These are ionic compounds that contain a cation such as an
ammonium or a metallic ion, and polyatomic anions. The most common polyatomic ions are shown
in Table 5.5.
Rules:
1. Order the names for ions - first the cation, then the polyatomic anion.
2. Name of cation: Same as the name of element from the periodic table.
3. If the cation is a transition element, the name of cation should be followed by Roman numeral
indicating the charge in parenthesis.
4. Name of the anion: same as name of polyatomic ion.
5. Combine the names of cation and anion to generate the name of the compound.
Summary:
a. If the metal present in the compound is one of the metals shown in Table 5.2.
b. If the metals present in the compound is one of the metals shown in Table 5.4
Example 1:
Write the name of Na3PO4.
Step 1: Names of ions: Cation – sodium (Na+) and polyatomic anion – Phosphate (PO43-).
Step 2: Cation is not from a transition metal.
Step 3: Name of compound: Sodium phosphate.
Example 2:
Write the name of Fe(NO3)3
Step 1: Names of ions: Cation – Iron (Fe3+) and polyatomic anion – Nitrate (NO3-).
Step 2: Cation is a transition metal and carries a charge of 3+ - Iron(III).
Step 3: Name of compound: Iron(III) nitrate.
Classical method of naming compounds: The procedure described under type 2 binary ionic
compounds also applies under example 2. Accordingly, classical name of Fe(NO3)3 is Ferric
nitrate.
4. Binary acids: These are compounds formed between hydrogen (H+) and other non-metals (e.g., F, Cl,
Br, I and S) and dissolved in water. Writing names of binary acids is as follows
Rules:
1. Check to make sure the compound begins with hydrogen (all acids must begin with a hydrogen)
and the formula ends with “(aq).”
2. To be a binary acid, the second element must be a nonmetal.
3. To name a binary acid the hydrogen is named “hydro”
4. The second element is named with its root name followed by a suffix “ic” and the word “acid”.
Summary:
19
Example:
Write the name of: HBr(aq).
Step 1: The compound starts with hydrogen and the formula ends with “(aq)”, therefore it is an
acid and the name must start with “hydro.”
Step 2: The second element in the compound is Br, which is a nonmetal, therefore a binary
acid.
Step 3: The root name for Br is “brom” and with the suffix “ic” added it is named as “bromic
acid)
Step 4: Complete name = Hydrobromic acid.
5. Oxyacids: These are compounds formed between hydrogen (H+) and polyatomic ions containing
oxygen.
Rules:
1. Check to make sure the compound begins with hydrogen (all acids must begin with hydrogen).
2. To be an oxyacid, the compound must contain a polyatomic ion containing oxygen.
3. Only polyatomic ion is used in naming oxyacids.
4. Name the polyatomic ion changing the ending as follows:
If the polyatomic ion ends with “ate” change its ending to “ic”
If the polyatomic ion ends with “ite” change its ending to “ous”
The name is followed by the word “acid.”
Summary:
If the oxyanion name ends with “ate”:
Example 1: Name the following compound: H2SO4(aq).
Step 1: The compound contains hydrogen and sulfate (a polyatomic ion)
Step 2: Name of polyatomic ion is “Sulfate.” As per rules, its name is modified by replacing
“ate” by “ic”, i.e., Sulfate  Sulfuric.
Step 3: The name should end with the word acid.
Step 4: Therefore the name of H2SO4 is Sulfuric acid.
If the oxyanion name ends with “ite”:
Example 2: Name the following compound: H2SO3(aq).
Explanation: The difference between this and the above example is that the polyatomic ion is
SO32- - sulfite. Therefore as per rules, its name is modified by replacing “ite” by “ous.”
Therefore the name of H2SO3 is Sulfurous acid.
Writing formulas of inorganic compounds from names
Many a times you are given names of compounds and asked to write formulas. The rules for writing
formulas from names are somewhat simpler. Shown below are rules and some examples of how to write
formulas of compounds from their names.
Rules:
Rule 1: First write the name of the compound, and identify the names and symbols for each of the
ions.
Rule 2: Look up the charge (oxidation numbers) of the elements or polyatomic ions involved
(Tables 3.1-3.4), and write them as superscripts to the right of the elemental symbols.
20
Rule 3: Use the correct combination of ions to produce a compound with a net charge of zero. Use
subscripts if there are >two atoms of the same element and/or parenthesis and subscripts if
there are two polyatomic ions in the formula.
Experimental Procedure
1. This experiment has different parts. Each part corresponds to a type of compound(s), formed
based on the classification described in the introduction.
2. Each table has a column of cations (more metallic elements) and a row of anions (more
nonmetallic elements).
3. Combine these cations and anions (metallic and nonmetallic elements) appropriately to determine
the formula of the compound (use the examples below as guide lines to arrive at the correct
formula).
4. Fill-in the appropriate box with the correct formula.
Example: Write the formulas of the compounds formed between the cations and anions given in
the table below:
Cl-
SO42-
Cation/anion
Cl-
SO42-
Ba2+
BaCl2
BaSO4
H+
HCl
H2SO4
Fe3+
FeCl3
Fe2(SO4)3
Cation/anion
Ba2+
H+
Fe3+
Correct answer:
5. The molecular compounds are formed due to sharing of electrons between nonmetals. When
writing formulas for molecular compounds, it is important to remember that the more metallic
element (element located to the left in the periodic table as compared to the element it is
combining with) is written first and then the nonmetallic element. The subscript number or the
number of atoms present in the formula is determined by the number of electrons they share. The
number of electrons they share can be determined from the group (column) they belong to in the
periodic table. For Example, carbon belongs to group IVa and it can share 4 electron with other
elements, whereas chlorine belongs to group VIIa and it can only share one electron.
Accordingly, carbon (C) when combined with chlorine (Cl) will result in CCl4.
Example: Write the formulas of the molecular compounds formed between the elements given in
the table below:
Element
C
F
O
21
Correct answer:
Element
C
F
O
CO2
OF2
6. Naming compounds when the formulas are given:
The rules and step-by-step procedures used to name compounds (with examples) in each of 5
categories of compounds are described in the introduction to this experiment.
Follow the directions described above and write the names of compounds from their formulas listed
in the laboratory data sheet.
7. Writing formulas of compounds when the names are given:
In this part of the experiment you are given names of compounds and asked to write formulas. The
rules and procedures for writing formulas from names (with examples) are also described in the
introduction above.
Follow the directions described above and write the formulas of compounds from their names listed
in the laboratory data sheet.
22
Experimental General Chemistry 1
Experiment 3: Nomenclature and Formula Writing
Laboratory Data Sheet:
Complete the following tables
Name: ______________________________________________
Section:
____________
Type 1 Binary Ionic Compounds
Practice
Ion
Cl-
Br-
O2-
S2-
N3-
S2-
N3-
Na+
Be2+
Ca2+
Al3+
Test
Zn2+
Ag+
In3+
Ba2+
Type 2 Binary Ionic Compounds
Practice
Ion
Cl-
Br-
O2-
Cu+
Cu2+
Pb2+
Test
Pb4+
Fe2+
Fe3+
Cd2+
23
Ionic Compounds with Polyatomic Ions
Practice
OH-
Ion
CO32-
NO3-
SO42-
PO43-
Na+
Ca2+
Cu+
Test
NH4+
Fe2+
Al3+
Molecular Compounds
Test
F
Element
Cl
Br
I
H
B
C
Binary Acids
Test
Cl-
Ion
S2-
Br-
I-
F-
H+
Test
Ion
SO42-
Oxyacids
CO32-
PO43-
NO3-
ClO3-
HCO3-
CN–
CH3COO–
H+
Type 1 Binary Ionic Compounds
Practice
Given Formula, Write the Name
Given Name, Write the Formula
Li3N
Lithium fluoride
MgS
Magnesium phosphide
KI
Potassium oxide
24
Test
ZnF2
Calcium oxide
Al2O3
Zinc sulfide
BeS
Aluminum nitride
Na2S
Silver bromide
Type 2 Binary Ionic Compounds
Practice
Given Formula, Write the Name
Given Name, Write the Formula
FeCl3
Cobalt(II) iodide
CuO
Cobalt(III) oxide
Cr2O3
Copper(II) sulfide
CrCl2
Tin(IV) chloride
Test
Pb3N2
Iron(II) oxide
SnCl4
Chromium(II) sulfide
CoI3
Chromium(III) chloride
HgS
Nickel(II) oxide
FeCl2
Lead(II) chloride
Ionic Compounds with Polyatomic Ions
Practice
Given Formula, Write the Name
Given Name, Write the Formula
CuSO4
Potassium hydroxide
Sn(CO3)2
Magnesium phosphate
KNO3
Iron(III) carbonate
MgSO4
Copper(II) nitrate
25
Test
Fe(OH)3
Ammonium hydroxide
NH4Cl
Sodium phosphate
CuNO2
Cobalt(II) sulfate
KClO3
Sodium hydrogen carbonate
Molecular Compounds
Practice
Given Formula, Write the Name
Given Name, Write the Formula
SiO2
Carbon tetrachloride
SO2
Boron triiodide
N2S3
Sulfur hexafluoride
Test
B2O3
Dinitrogen pentaoxide
IF5
Hydrogen chloride
HI
Dinitrogen monoxide
Binary Acids
Practice
Given Formula, Write the Name
Given Name, Write the Formula
HF
Hydrobromic acid
HClO3(aq)
Selenous acid
H2SO3(aq)
Nitric acid
H2CO3
Chloric acid
Test
HI
Sulfuric acid
HNO2(aq)
Perchloric acid
H3PO4(aq)
Hypochlorous acid
H2SO4
Carbonic acid
26