Naming Compounds That Contain Polyatomic Ions Worksheet Page 2
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in -ite, and the name of the one with the larger number ends in -ate. For ex-
2
2
ample, SO
is sulfite and SO
is sulfate. When more than two oxyanions
3
4
make up a series, hypo- (less than) and per- (more than) are used as prefixes
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to name the members of the series with the fewest and the most oxygen
2
Note that the SO
anion has
3
atoms, respectively. The best example involves the oxyanions containing
very different properties from
chlorine:
SO
(sulfur trioxide), a pungent,
3
toxic gas.
ClO
hypochlorite
ClO
chlorite
2
ClO
chlorate
3
ClO
perchlorate
4
Naming ionic compounds that contain polyatomic ions is very similar to
naming binary ionic compounds. For example, the compound NaOH is called
sodium hydroxide, because it contains the Na (sodium) cation and the OH
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(hydroxide) anion. To name these compounds, you must learn to recognize the
Except for hydroxide, peroxide,
common polyatomic ions. That is, you must learn the composition and charge of
and cyanide, the names of poly-
each of the ions in Table 4.4. Then when you see the formula NH
C
H
O
,
atomic ions do not have an -ide
4
2
3
2
you should immediately recognize its two “parts”:
ending.
NH
C
H
O
4
2
3
2
+
–
NH
C
H
O
4
2
3
2
The correct name is ammonium acetate.
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When a metal is present that forms more than one cation, a Roman nu-
Certain transition metals form
meral is required to specify the cation charge, just as in naming Type II bi-
only one ion. Common exam-
nary ionic compounds. For example, the compound FeSO
is called iron(II)
2
ples are zinc (forms only Zn
)
4
2
2
sulfate, because it contains Fe
(to balance the 2 charge on SO
). Note
and silver (forms only Ag ). For
4
these cases the Roman numeral
that to determine the charge on the iron cation, you must know that sulfate
is omitted from the name.
has a 2 charge.
Example 4.7
Naming Compounds That Contain Polyatomic Ions
Give the systematic name of each of the following compounds.
a. Na
SO
c. Fe(NO
)
e. Na
SO
2
4
3
3
2
3
b. KH
PO
d. Mn(OH)
2
4
2
Solution
Compound
Ions Present
Ion Names
Compound Name
a. Na
SO
two Na
sodium
sodium sulfate
2
4
2
SO
sulfate
4
b. KH
PO
K
potassium
potassium
2
4
H
PO
dihydrogen
dihydrogen
2
4
phosphate
phosphate
3
c. Fe(NO
)
Fe
iron(III)
iron(III) nitrate
3
3
three NO
nitrate
3
(continued)
101
4.4 Naming Compounds That Contain Polyatomic Ions
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