http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson31.htm
Vocabulary
oxidation number
polyatomic ion
The charge or apparent charge that an atom in a compound or ion
would have if all the electrons in its bonds belonged entirely to the
more electropositive atom.
An electrically charged species formed by covalent bonding of atoms
of two or more different elements, usually non-metals.
Review Answers
1.
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
353
AlF3 . . . . . . . . . . . . aluminum fluoride
K2S . . . . . . . . . . . . potassium sulfide
.
CaI2 . . . . . . . . . . . . calcium iodide
Rb2O . . . . . . . . . . . rubidium oxide
.
H3N . . . . . . . . . . . . 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
NaC2H3O2 . . . . . . . . . .
sodium acetate
Mg(NO3)2 . . . . . . . . . .
magnesium nitrate
(NH4)2CrO4 . . . . . . . . .
ammonium chromate
(NH4)2S . . . . . . . . . . . . . ammonium sulfide
Ca(OH)2 . . . . . . . . . . . . calcium hydroxide
.
BaCr2O7 . . . . . . . . . . . . barium dichromate
.
H3PO4 . . . . . . . . . . . . . . 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 Fe2O3. 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 Fe2O3, 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.
354
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.
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.
355
•
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.
(Intermediate)
_____________________________________________________
_____________________________________________________
_______________________________________________
_______________________________________________
___________________________________________________
_______________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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
(Intermediate)
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
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
cation
chemical nomenclature
356
An ion with a negative charge.
An ion with a positive charge.
The system for naming chemical compounds.
ionic bond
polyatomic ion
The electrostatic attraction between ions
of opposite charge.
A group of atoms bonded to each other
covalently but possessing an overall
charge.
Review Answers
1.
Calcium fluoride
Ammonium chromate
Potassium carbonate
Sodium chloride
Lead (II) oxide
Copper (II) sulfate
Hydrogen carbonate
Calcium nitrate
Magnesium hydroxide
Tin (IV) oxide
2.
Na2CO3
Ca(OH)2
Fe(NO3)3
MgO
Al2S3
Cu2Cr2O7
(NH4)2SO4
Fe3(PO4)2
H3N
Pb(SO4)2
357
CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook
materials for the K-12 market both in the U.S. and worldwide. Using an open-content, webbased collaborative model termed the “FlexBook,” CK-12 intends to pioneer the generation
and distribution of high-quality educational content that will serve both as core text as well
as provide an adaptive environment for learning.
Copyright © 2009 CK-12 Foundation, www.ck12.org
Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material)
is made available to Users in accordance with the Creative Commons Attribution/NonCommercial/Share Alike 3.0 Unported (CC-by-NC-SA) License (http://creativecommons.
org/licenses/by-nc-sa/3.0/), as amended and updated by Creative Commons from time
to time (the “CC License”), which is incorporated herein by this reference. Specific details
can be found at http://about.ck12.org/terms.