Inorganic Nomenclature
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C ONCEPT
Concept 1. Inorganic Nomenclature
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Inorganic Nomenclature
Lesson Objectives
• Given the formulas, the student will correctly name binary ionic compounds, compounds containing metals
with variable oxidation numbers, and compounds containing polyatomic ions.
• Given the names, the student will provide formulas for binary ionic compounds, compounds containing metals
with variable oxidation numbers, and compounds containing polyatomic ions.
Naming Binary Ionic Compounds
Binary ionic compounds are compounds that contain only two kinds of ions regardless of how many of each ion is
present. To name such compounds, you name the metal first and then you name the non-metal except you drop the
ending off the non-metal and add "ide".
Examples
MgCl2 . . . . . . . . . . . . magnesium chloride
NaBr . . . . . . . . . . . . sodium bromide
AlF3 . . . . . . . . . . . . aluminum fluoride
K2 S . . . . . . . . . . . . potassium sulfide
CaI2 . . . . . . . . . . . . calcium iodide
Rb2 O . . . . . . . . . . . . rubidium oxide
H3 N . . . . . . . . . . . . hydrogen nitride
There is no need to attempt to indicate how many of each ion is present because all these ions have only one oxidation
number and therefore these are the only possible compounds between the two ions.
Naming Compounds Containing Polyatomic Ions
When naming a compound containing a polyatomic ion, the name of the polyatomic ion is not changed in any way
regardless of whether it is written first or last in the formula. If the formula contains a positive polyatomic ion
in place of the metal and a regular non-metal, the polyatomic ion is named with no change in its name and the
non-metal is named with its ending replaced by “ide.” If the compound contains a regular metal and the non-metal
is a polyatomic ion, both the metal and the polyatomic ion are named with no changes. If both the metal and the
non-metal are replaced with polyatomic ions, the polyatomic ions are named with no changes in either name.
Examples
NaC2 H3 O2 . . . . . . . . . . . . sodium acetate
Mg(NO3 )2 . . . . . . . . . . . . magnesium nitrate
(NH4 )2CrO4 . . . . . . . . . ammonium chromate
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(NH4 )2 S . . . . . . . . . . . . ammonium sulfide
Ca(OH)2 . . . . . . . . . . . . calcium hydroxide
BaCr2 O7 . . . . . . . . . . . . barium dichromate
H3 PO4 . . . . . . . . . . . . hydrogen phosphate
Once again, no effort is made to indicate how many of each ion is present because these are the only possible
compounds between these substances.
Naming Compounds Containing Variable Oxidation Number Metals
Metals with variable oxidation numbers may form different compounds with the same non-metal. Iron, for example,
may form FeO and Fe2 O3 . These are very different compounds with different properties. When we name these
compounds, it is absolutely vital that we clearly distinguish between them. They are both iron oxides but in FeO,
iron is exhibiting an oxidation number of 2+ and in Fe2 O3 , it is exhibiting an oxidation number of 3+. The rule
for naming these compounds is to insert the oxidation number of the iron with Roman numerals in parentheses after
the name iron. These two compounds would be named iron (II) oxide and iron (III) oxide. When you see that the
compound involves any of the variable oxidation number metals (iron, copper, tin, lead, nickel, and gold), you must
determine the oxidation number of the metal from the formula and insert Roman numerals indicating that oxidation
number.
Suppose we wish to name the compound CuSO4 . Because we have memorized the six metals that have variable
oxidation numbers, we immediately recognize that copper is one of them and that we must indicate the oxidation
number in the name of this compound. We also have memorized the polyatomic ion sulfate and recognize that
its oxidation number is 2−. Since this compound formed with one ion of copper and one sulfate ion, the copper
ion in this compound must have an oxidation number of 2+ (they reacted one to one). Therefore, the name of the
compound is copper (II) sulfate.
How about SnS2 ? Tin is a variable oxidation number metal. We need a Roman numeral in the name of this compound.
The oxidation number of sulfur is 2−. Two sulfide ions were necessary to combine with one tin ion. Therefore, the
oxidation number of the tin must be 4+ and the name of this compound is tin (IV) sulfide.
Examples:
PbO . . . . . . . . . . . . lead (II) oxide
NiCl . . . . . . . . . . . . nickel (I) chloride
FeI2 . . . . . . . . . . . . iron (II) iodide
Fe2 (SO4 )3 . . . . . . iron (III) sulfate
AuCl3 . . . . . . . . . . . . gold (III) chloride
CuO . . . . . . . . . . . . copper (II) oxide
PbS2 . . . . . . . . . . . . lead (IV) sulfide
The most common error made by students in naming these compounds is to choose the Roman numeral based on
the number of atoms of the metal. The Roman numeral in these names is the oxidation number of the metal and
the oxidation number is used as explained previously. For example, in PbS2 , the oxidation state of lead (Pb) is +4
so the Roman numeral following the name lead is “IV.” Notice that there is no four in the formula. As in previous
examples, the empirical formula is always the lowest whole number ratio of the ions involved. Think carefully when
you encounter variable oxidation number metals. Make note that the Roman numeral does not appear in the formula
but does appear in the name.
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Concept 1. Inorganic Nomenclature
Lesson Summary
• Ionic charge is determined by electron configuration, ionization energy, and electron affinity. Atoms with low
ionization energy and high electron affinity tend to lose electrons. Atoms with high ionization energy and high
electron affinity tend to gain electrons. Atoms with high ionization energy and low electron affinity tend to
neither gain nor lose electrons.
• The number of electrons gained or lost is determined by the electron configuration. Metals tend to lose all of
their valence electrons. Non-metals tend to gain enough electrons to complete their outermost energy level.
• Ionic bonds are formed by transferring electrons from metals to non-metals after which the oppositely charged
ions are attracted to each other.
• Ionic compounds form crystal lattice structures rather than molecules.
• Binary ionic compounds are named by naming the metal first followed by the non-metal with the ending of
the non-metal changed to “ide.”
• Compounds containing polyatomic ions are named with the name of the polyatomic ion in the place of the
metal or non-metal or both with no changes in the name of the polyatomic ion.
• Compounds containing variable oxidation number metals are named with Roman numerals in parentheses
following the name of the metal and indicating the oxidation number of the metal.
Review Questions
1. Name the following compounds.
CaF2
(NH4 )2CrO4
K2CO3
NaCl
PbO
CuSO4
H2CO3
Ca(NO3 )2
Mg(OH)2
SnO2
2. Write the formulas from the names of the following compounds.
Sodium carbonate
Calcium hydroxide
Iron (III) nitrate
Magnesium oxide
Aluminum sulfide
Copper (I) dichromate
Ammonium sulfate
Iron (II) phosphate
Hydrogen nitride
Lead (IV) sulfate
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Further Reading / Supplemental Links
Website with lessons, worksheets, and quizzes on various high school chemistry topics.
• Lesson 5-4 is on Naming Compounds.
• http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson54.htm
Vocabulary
anion An ion with a negative charge.
cation An ion with a positive charge.
chemical nomenclature The system for naming chemical compounds.
ionic bond The electrostatic attraction between ions of opposite charge.
polyatomic ion A group of atoms bonded to each other covalently but possessing an overall charge.
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