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TABLE 4.5
Figure 4.3
A flow chart for naming acids. The
acid is considered as one or more
H1 ions attached to an anion.
Does the anion contain oxygen?
Names of Acids That
Do Not Contain Oxygen
No
Acid
Name
HF
HCl
HBr
Hl
HCN
H2S
hydrofluoric acid
hydrochloric acid
hydrobromic acid
hydroiodic acid
hydrocyanic acid
hydrosulfuric acid
hydro+ anion root
+ -ic
hydro(anion root)ic acid
HNO3
HNO2
H2SO4
H2SO3
H3PO4
nitric acid
nitrous acid
sulfuric acid
sulfurous acid
phosphoric
acid
acetic acid
HC2H3O2
-ate
anion or element root
+ -ous
(root)ous acid
Names of Some
Oxygen-Containing
Acids
Name
Check the ending
of the anion name.
-ite
TABLE 4.6
Acid
Yes
anion or element root
+ -ic
(root)ic acid
The application of rule 2 can be seen in the names of the acids of the
oxyanions of chlorine, as shown below. The rules for naming acids are given
in schematic form in Figure 4.3. The names of the most important acids are
given in Table 4.5 and Table 4.6. These should be memorized.
Acid
Anion
Name
HClO4
perchlorate
perchloric acid
HClO3
chlorate
chloric acid
HClO2
chlorite
chlorous acid
HClO
hypochlorite
hypochlorous acid
Writing Formulas from Names
Objective: To learn to write the formula of a compound, given its name.
S
TOP TEN
First Letters of Last Names
in the United States
Letter
1.
2.
3.
4.
5.
6.
8.
9.
10.
S
B
M
K
D
C, P
G
L
A
Percent
9.8
7.0
6.5
6.4
5.9
5.5
5.2
5.0
4.8
o far we have started with the chemical formula of a compound and decided on its systematic name. Being able to reverse the process is also important. Often a laboratory procedure describes a compound by name, but
the label on the bottle in the lab shows only the formula of the chemical it
contains. It is essential that you are able to get the formula of a compound
from its name. In fact, you already know enough about compounds to do
this. For example, given the name calcium hydroxide, you can write the formula as Ca(OH)2 because you know that calcium forms only Ca2 ions and
that, since hydroxide is OH, two of these anions are required to give a neutral compound. Similarly, the name iron(II) oxide implies the formula FeO,
because the Roman numeral II indicates the presence of the cation Fe2 and
the oxide ion is O2.
We emphasize at this point that it is essential to learn the name, composition, and charge of each of the common polyatomic anions (and the
NH4 cation). If you do not recognize these ions by formula and by name,
you will not be able to write the compound’s name given its formula or the
compound’s formula given its name. You must also learn the names of the
common acids.
4.6 Writing Formulas from Names
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Example 4.9
Writing Formulas from Names
Give the formula for each of the following compounds.
a. potassium hydroxide
e. calcium chloride
b. sodium carbonate
f. lead(IV) oxide
c. nitric acid
g. dinitrogen pentoxide
d. cobalt(III) nitrate
h. ammonium perchlorate
Solution
Name
Formula
Comments
a. potassium hydroxide
KOH
Contains K and OH.
b. sodium carbonate
Na2CO3
We need two Na to balance CO32.
c. nitric acid
HNO3
Common strong acid; memorize.
d. cobalt(III) nitrate
Co(NO3)3
Cobalt(III) means Co3; we need three NO3 to balance
Co3.
e. calcium chloride
CaCl2
We need two Cl to balance Ca2; Ca (Group 2) always
forms Ca2.
f. lead(IV) oxide
PbO2
Lead(IV) means Pb4; we need two O2 to balance Pb4.
g. dinitrogen pentoxide
N2O5
di- means two; pent(a)- means
five.
h. ammonium
perchlorate
NH4ClO4
Contains NH4 and ClO4.
Self-Check Exercise 4.8
Write the formula for each of the following compounds.
a. ammonium sulfate
d. rubidium peroxide
b. vanadium(V) fluoride
e. aluminum oxide
c. disulfur dichloride
Focus Questions
Sections 4.4–4.6
1. What patterns can you see in Table 4.4 that reduce the number of
polyatomic ions you need to memorize? (Hint: Try grouping the ions by
common elements or suffixes.)
2. Once you have identified that a compound contains a polyatomic ion,
how is naming it different from naming a binary compound?
3. How can you tell if a compound should be named an acid?
4. Use the flow chart in Figure 4.3 to name the following:
a. HClO4
b. HNO2
c. HBr
d. H2SO4
5. When writing a formula from a chemical name, how can you tell how
many of each element or polyatomic ion to put in the formula?
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Chapter 4 Nomenclature