7/19/2015
Writing Balanced Formulas
For Ionic Compounds
Writing Formulas for
Ionic Compounds
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 Why is the formula for calcium carbonate
is CaCO3?
When Metal is Common Ion or NH4+
With Monatomic Ions and Polyatomic Ions
From Ion Formulas
From Names
Writing Balanced Formulas
for Ionic Compounds
Writing Balanced Formulas
for Ionic Compounds
Ions combine to form compounds with a net
charge of zero.
 Ions combine to form
compounds with a net
charge of zero.
Formula
 KBr
 CaCl2
 Na2S
Ions per Formula Unit
1 K+ and 1 Br
1 Ca2+ and 2 Cl
2 Na+ and 1 S2
 Mg(NO3)2
1 Mg2+ and 2 NO3
Writing Balanced Formulas
for Ionic Compounds
Test Your Understanding
Ions combine to form compounds with a net
charge of zero.
 For each pair of ions, write the formula for
the compound formed from these ions.
a) K+ and N3
b) Al3+ ion and NO3
c) Al3+ ion and SO42
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7/19/2015
Writing Balanced Formulas for
Ionic Compounds
Common Monatomic Ions
 To write the formula of an ionic compound from
its name, we need to think about the charges of
the ions in the compound.
Anions end in -ide
 Remember that the charges of most “common
monatomic ions” can be determined from their
positions on the periodic table.
 Some polyatomic ion formulas/charges must be
memorized (see learning objectives/handout).
Writing Formulas with
Monatomic Ions from Names
 Let’s practice writing ionic compound
formulas from names.
Name
Ions
Formula
magnesium chloride
potassium sulfide
aluminum oxide
PT follows
Polyatomic Ions you should
know
Polyatomic Ions
Anions usually end in –ate or ite
 Nitrate
 Bicarbonate
 Bromate
 Chlorate
 Periodate
 Cyanide
 Hydroxide
 Acetate
 Chromate
 Sulfate
 Carbonate
 Peroxide
 Phosphate
 Ammonium
cation
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7/19/2015
Writing Formulas with
Polyatomic Ions from Names
 Let’s practice writing ionic compound
formulas from names.
Name
Ions
Formula
calcium carbonate
potassium phosphate
aluminum hydroxide
Test Your Understanding
 Pay attention to suffixes. Write the correct
formula for each compound. Refer to a periodic
table.
Name
Ions
Formula
aluminum chloride
sodium carbonate
calcium nitrate
calcium nitride
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