Student
Naming Ionic Compounds
NGSSS: SC.912.P.8.7: Interpret formula representations of molecules and compounds in terms
of composition and structure. Write chemical formulas for simple covalent (HCl, SO2, CO2, and
CH4), ionic (Na+ + Cl− → NaCl) and molecular (O2, H2O) compounds. Predict the formulas of
ionic compounds based on the number of valence electrons and the charges on the ions.
Background:
Once an atom "ionizes" (gives up or captures valence electrons) the ion has a (+) or (-) charge.
When two oppositely charged ions come together they bond chemically, meaning they are
electrostatically attracted to each other. In order to write the correct chemical formula we need
to make sure all the (+) and (-) charges cancel each other out so that the net charge of the
compound is zero.
The math here is very straightforward - every negative charge has to be balanced out by a
positive charge. This is what makes compounds charge neutral.
The easiest compounds to balance the charges are the ones with a 1:1 charge ratio.



Lithium's ion Li1+ bonds with chlorine's ion Cl1- to form Lithium Chloride, LiCl.
Magnesium's ion Mg2+ bonds with oxygen's ion O2- to form Magnesium oxide, MgO.
Aluminum's ion Al3+ bonds with nitrogen's ion N3- to form Aluminum nitride, AlN
Notice that you don't see any subscripts in the chemical formulas above because we don't write
subscripts for compounds whose charges already equal to zero.
When you don't have a 1:1 ratio you have to find the combination that balances all of the
charges



Lithium's ion Li1+bonds with oxygen's ion O2- to form Lithium oxide, Li2O
Magnesium's ion Mg2+ bonds with nitrogen's ion N 3- to form Magnesium nitride, Mg3N2.
Aluminum's ion Al3+ bonds with chlorine's ion Cl1-to form Aluminum chloride, AlCl3
Let's walk through one visually
Ask yourself (self?)
what number will
both charges divide
evenly into?
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Here 2+ and 3- will
both divide evenly into
6 so your target
numbers are 6 and -6.
Since 6 and -6 will
cancel to 0 divide each
target by the charge to
get each subscript.
The final formula.
Wasn't that easy?
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Student
Monoatomic vs. polyatomic ions and the compounds they form
All of the examples above contained monoatomic ions (ions with ONE element). But nature is
full of polyatomic ions, too. Polyatomic ions are made up of more than one element. Polyatomic
ions include ions like NO31- (the nitrate ion) and CO32- (the carbonate ion).
The idea of charge balancing compounds with polyatomic ions is the same. You just need to be
careful about using parentheses as needed. The general rule is: If you only need 1 of the
polyatomic ions then you don't need to surround them with parentheses. If you need 2 or more
of a polyatomic ion then you do need to put them in parentheses so it's clear which subscript
belongs to the polyatomic ion and which subscript is there as the charge balancing "inventory"
number. Here are some examples:



Lithium's ion Li1+bonds with the nitrate ion NO31- to form Lithium nitrate LiNO3
Magnesium's ion Mg2+ bonds with the nitrate ion NO31- to form Magnesium nitrate
Mg(NO3)2
Aluminum's ion Al3+ bonds with the carbonate ion CO32- to form Aluminum carbonate
Al2(CO3)3
Notice you still start by looking for that lowest common multiple to find your target number. Once
you have your targets, divide each target by the charge on the associated ion to find the
subscript.
Purpose of Lab/Activity:
 To assemble and create as many different and non-repeating compounds as possible
using the ion/polyatomic ion template
 Based on the charges of the ions, apply the concept that a compound must have a net
charge of zero
 To be able to write the names of simple ionic formulas that use ions and polyatomic ions
Safety: Always wear safety goggles in the lab.
Vocabulary: Formula, ionic compounds, net charge, ion, polyatomic ion, valance electrons,
charge
Materials (individual or per group):
 Ion/polyatomic ion template paper
 1 or more color pencils
 scissors
 glue stick
 copy paper
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Student
Procedures:
1. Using the ion/polyatomic ion template, color the positive ions completely
2. Negative ions are half-colored. Draw a diagonal line in each negative ion box, and
shade in the bottom half for each negative ion.
3. Cut out all of the boxes from the ion/polyatomic ion template.
4. Preassemble compounds on your desk following the rules that no two compounds can
be repeated, and that the net charges of each compound must equal to zero.
5. Glue the compounds to a sheet of paper.
6. Name all compounds using the rules for nomenclature of ionic compounds and
polyatomic ions
7. Cleanup and Disposal- Follow your teacher's instructions for returning the coins.
Observations/Data: Use the following Ion/Polyatomic Ion Template for the lab
Ion/Polyatomic Ion Template
2-
SO3
2-
SO3
2-
SO3
2-
SO3
2-
SO3
2-
SO3
-
NO2
-
NO2
-
2-
3-
3-
-
3-
3-
-
3-
3-
-
3-
3-
-
3-
3-
-
3-
3-
PO3
-
SO4
NO3
PO4
2-
CO3
+
NH4
2+
Ca
-
NO3
2-
+
2+
Ca
-
NO3
2-
+
2+
Ca
-
NO3
2-
+
2+
Ca
-
2-
+
2+
-
2-
+
NH4
2+
SO4
2-
NO2
-
NO2
-
NO2
+
2-
PO4
SO4
2-
PO4
SO4
2-
PO4
SO4
2-
NO3
NO3
CO3
CO3
CO3
CO3
CO3
PO3
PO3
PO3
PO3
PO3
NH4
NH4
NH4
NH4
OH
OH
OH
OH
OH
OH
2+
3+
5+
2+
2+
3+
5+
2+
Be
K
+
PO4
SO4
NO2
-
PO4
K
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Be
B
B
P
P
Ca
Ca
+
+2
+
+2
+
+2
+
+2
+
+2
+
+2
Na
Na
Na
Na
Na
Na
Ba
Ba
Ba
Ba
Ba
Ba
3+
4+
3+
4+
3+
4+
3+
4+
3+
4+
3+
4+
Al
Al
Al
Al
Al
Al
Pb
Pb
Pb
Pb
Pb
Pb
2+
Mg
Mg
2+
Mg
Mg
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Student
Data Analysis/Results:
1. Use your own words to describe how you organized your thoughts when you carried out
this experiment?
2. How could you make the lab more efficient?
3. Predict what would happen if you used large ion combinations instead of smaller ion
combinations in making compounds.
Conclusions:
1. List and describe at least 3 sources of error observed during this activity that could have
led to poor results.
2. Use your knowledge for ionic nomenclature to name each compound listed.
a. Na3N
______________________
b. CaF2
______________________
c. FeO
______________________
d. Al2S3
______________________
e. MgSe
______________________
f. CoBr2
______________________
g. CuCl2
______________________
h. LiBr
______________________
i. SnS2
______________________
j. Sr3P2
______________________
3. Write the names for each of the following compounds that use polyatomic ions.
a. NaNO3 ______________________
b. BaSO4 ______________________
c. Fe2O3 ______________________
d. CrPO3 ______________________
e. (NH4)2O ______________________
f. RbNO2 ______________________
4. Write the correct symbols with the correct subscripts for each of the following
compounds.
a. Aluminum phosphate
______________________
b. Potassium nitrate
______________________
c. Sodium hydrogen carbonate ______________________
d. Calcium carbonate
______________________
e. Magnesium hydroxide
______________________
f. Ammonium nitrate
______________________
g. Tin(II) nitrate
______________________
h. Iron(III) phosphate
______________________
i. Copper(I) sulfate
______________________
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Page 80