1. Chapter 9 Chemical Names and Formulas 9.1 Naming Ions
9.2 Naming and Writing Formulas for
Ionic Compounds
9.3 Naming and Writing Formulas for
Molecular Compounds
9.4 Naming and Writing Formulas for
Acids and Bases
9.5 The Laws Governing How
Compounds Form
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2. Do you speak “Chemistry”?
CHEMISTRY & YOU
Do you speak “Chemistry”?
Try looking at the ingredient label on a household product—a bottle of shampoo, a tube of toothpaste, a box of detergent. Do the names of the ingredients make sense?
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3. The first step is to learn about the ions that form ionic compounds.
Monatomic Ions
Learning the language of chemistry is important to be able to name and write the chemical formulas for ionic compounds.
The first step is to learn about the ions that form ionic compounds.
Monatomic ions, consist of a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons.
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4. Monatomic Ions How can you determine the charges of monatomic ions?
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5. Monatomic Ions
Cations
Metals in Groups 1A, 2A, and 3A form cations with positive charges equal to their group number.
The charge of the cations of many transition metal ions must be determined from the number of electrons lost.
The charge of any ion of Group A nonmetals is determined by subtracting 8 from the group number.
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6. Recall that metallic elements tend to lose valence electrons.
Monatomic Ions
Cations
Recall that metallic elements tend to lose valence electrons.
All the Group 1A ions have a 1+ charge (Li+, Na+, K+, Rb+, and Cs+).
Group 2A metals, tend to lose two electrons to form cations with a 2+ charge (Mg2+ and Ca2+).
Aluminum is the only common Group 3A metal, and tends to lose three electrons to form a 3+ cation (Aℓ3+).
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7. Monatomic Ions
Cations
The names of the cations of Group 1A, Group 2A, and Group 3A metals are the same as the name of the metal, followed by the word ion or cation.
Thus, Na+ is the sodium ion (or cation), Ca2+ is the calcium ion (or cation), and Aℓ3+ is the aluminum ion (or cation).
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8. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
Many of the transition metals (Groups 1B–8B) form more than one cation with different ionic charges.
Transition metal iron forms two common cations, Fe2+ (two electrons lost) and Fe3+ (three electrons lost).
Cations of tin and lead, the two metals in Group 4A, can also have more than one common ionic charge.
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9. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
Two methods are used to name ions that can have more than one common ionic charge.
The preferred method is called the Stock system.
The other is the Classical method.
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10. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
In the Stock system, a Roman numeral, in parentheses, is placed after the name of the element to indicate the charge.
The cation Cr2+ is written chromium(II) ion and is read “chromium two ion.”
The Cr3+ ion is written chromim(III) ion and is read “chromium three ion.”
No space is left between the element name and the Roman numeral in parentheses.
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11. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
A few transition metals have only one ionic charge.
The names of these cations do not have a Roman numeral.
Exceptions include silver, with a 1+ charge (Ag+), as well as cadmium and zinc, with a 2+ charge (Cd2+ and Zn2+).
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12. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
The Classical method uses a root word with different suffixes at the end of the word.
ferrum is Latin for iron, so ferr- is the root name for iron.
stunnum is Latin for tin, so stann- is the root for tin.
wolfram is Latin for tungsten, so wolfr- is the root for tungsten.
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13. Metals That Form More Than One Ion
Monatomic Ions
Metals That Form More Than One Ion
The Classical method uses a root word with different suffixes at the end of the word.
The suffix -ous is used to name the cation with the lower of the two ionic charges.
The suffix -ic is used with the higher of the two ionic charges.
Using this system, Sn2+ is the stannous ion, and Sn4+ is the stannic ion.
The disadvantage of classical names is that they do not tell you the actual charge of the ion.
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14. Monatomic Ions
Symbols and Names of Other Common Metal Ions With More Than One Ionic Charge
Symbol
Stock Name
Classical Name
Cu+
Copper(I) ion
Cuprous ion
Cu2+
Copper(II) ion
Cupric ion
Pb2+
Lead(II) ion
Plumbous ion
Pb4+
Lead(IV) ion
Plumbic ion
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15. Nonmetals in Group 7A form a 1– charge (7 – 8 = –1).
Monatomic Ions
Anions
Nonmetals in Group 7A form a 1– charge (7 – 8 = –1).
Nonmetals in Group 6A form a 2– charge (6 – 8 = –2).
Nonmetals in Group 5A form a 3– charge (5 – 8 = –3).
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16. Monatomic Ions
Anions
Anion names start with the stem or root of the element name and end in -ide.
For example, two elements in Group 7A are fluorine and chlorine. The anions for these nonmetals are the fluoride ion (F–) and the chloride ion (Cℓ–).
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17. Naming Cations and Anions
Sample Problem 9.1
Naming Cations and Anions
Name the ion formed by each of the following elements:
potassium
lead, 4 electrons lost
sulfur
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18. Analyze Identify the relevant concepts.
Sample Problem 9.1 1
Analyze Identify the relevant concepts.
You can use the periodic table to determine the charge of most Group A elements. Ions with positive charges are cations; ions with negative charges are anions. The names of nonmetallic anions end in -ide. Metallic cations take the name of the metal. Some metals, including transition metals, can form more than one cation. Use a Roman number in the Stock name or use the classical name with a suffix to name these metals.
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19. Solve Apply concepts to the situation.
Sample Problem 9.1
Solve Apply concepts to the situation.
Write the symbol for the element.
a. K
b. Pb
c. S 2
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20. Solve Apply concepts to the situation.
Sample Problem 9.1
Solve Apply concepts to the situation.
Determine the charge of the ion formed by the element.
a. K 1+
b. Pb 4+
c. S 2– 2
A negative charge means electrons gained; a positive charge means electrons lost.
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21. Solve Apply concepts to the situation.
Sample Problem 9.1
Solve Apply concepts to the situation.
Determine whether the ion is a cation or an anion.
a. K 1+ K+ is a cation.
b. Pb 4+ Pb4+ is a cation.
c. S 2– S2– is an anion. 2
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22. Solve Apply concepts to the situation.
Sample Problem 9.1
Solve Apply concepts to the situation.
Apply the appropriate rules for naming the ion. Use a Roman numeral if necessary.
a. K+ is named potassium ion.
b. Pb4+ is named lead(IV) or plumbic ion.
c. S2– is named sulfide ion. 2
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23. What type of elements (metals or nonmetals) tends to form cations
What type of elements (metals or nonmetals) tends to form cations? What type of elements tends to form anions?
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24. Metals tend to form cations. Nonmetals tend to form anions.
What type of elements (metals or nonmetals) tends to form cations? What type of elements tends to form anions?
Metals tend to form cations. Nonmetals tend to form anions.
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25. Polyatomic Ions
Polyatomic Ions
How do polyatomic ions differ from monatomic ions? How are they similar?
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26. Polyatomic Ions
Unlike a monatomic ion, a polyatomic ion is composed of more than one atom. But like a monatomic ion, a polyatomic ion behaves as a unit and carries a charge.
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27. The sulfate anion consists of one sulfur atom and four oxygen atoms.
Polyatomic Ions
The sulfate anion consists of one sulfur atom and four oxygen atoms.
These five atoms together comprise a single anion with an overall 2– charge.
The formula is written SO42–.
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28. Polyatomic Ions
You can see the structure of the sulfate ion along with three other common polyatomic ions below.
Ammonium ion
(NH4+)
Nitrate ion
(NO3–)
Sulfate ion
(SO42–)
Phosphate ion
(PO43–)
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29. Common Polyatomic Ions
Charge
Formula
Name 1–
HSO4–
NO2–
CℓO–
Hydrogen sulfate
Nitrite
Hypochlorite 2–
SO32–
SO42–
CO32–
Sulfite
Sulfate
Carbonate 3–
PO43–
Phosphate 1+
NH4+
Ammonium
The names and formulas of some common polyatomic ions are shown here.
Note that the names of most polyatomic ions end in -ite or -ate.
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30. Common Polyatomic Ions
Charge
Formula
Name 1–
HSO4–
NO2–
CℓO–
Hydrogen sulfate
Nitrite
Hypochlorite 2–
SO32–
SO42–
CO32–
Sulfite
Sulfate
Carbonate 3–
PO43–
Phosphate 1+
NH4+
Ammonium
Sometimes the same two or three elements combine in different ratios to form different polyatomic ions.
Look for pairs of ions for which there is both an -ite and an -ate ending, for example, sulfite and sulfate.
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31. SO32−, sulfite SO42–, sulfate NO2–, nitrite NO3–, nitrate
Polyatomic Ions
Note the number of oxygen atoms and the endings on each name. You should be able to discern a pattern in the naming convention.
-ite -ate
SO32−, sulfite SO42–, sulfate
NO2–, nitrite NO3–, nitrate
CℓO2–, chlorite CℓO3–, chlorate
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32. The -ite ending indicates one less oxygen atom than the -ate ending.
Polyatomic Ions
The charge is the same on each polyatomic ion in a pair for which there is both an -ite and an -ate ion.
The -ite ending indicates one less oxygen atom than the -ate ending.
The ending does not tell you the actual number of oxygen atoms in the ion.
For example, the nitrite ion has two oxygen atoms, and the sulfite ion has three oxygen atoms.
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33. For example, HCO3– is a combination of H+ and CO32–.
Polyatomic Ions
When the formula for a polyatomic ion begins with H, you can think of the H as representing a hydrogen ion (H+) combined with another polyatomic ion.
For example, HCO3– is a combination of H+ and CO32–.
Note that the charge on the new ion is the sum of the ionic charges of the two component ions.
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34. Polyatomic Ions
Hydrogen carbonate anion (HCO3–), Hydrogen phosphate anion (HPO42–), and Dihydrogen phosphate anion (H2PO42–) are essential components of living systems.
The presence of these ions dissolved in your blood is critical for your health.
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35. Polyatomic Ions
Sodium hydrogen carbonate, containing the HCO3– ion, can relieve an upset stomach.
In contrast, the cyanide ion (CN–) is extremely poisonous to living systems because it blocks a cell’s means of producing energy.
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36. Compare and Contrast the -ate and -ite versions of a polyatomic ion
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37. Compare and Contrast the -ate and -ite versions of a polyatomic ion
Compare = both made using the same elements with the same ion charge
Contrast = -ate has one more oxygen atom than the -ite version
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38. Key Concepts
When the metals in Groups 1A, 2A, and 3A lose electrons, they form cations with positive charges equal to their group number.
The charges of the cations of many transition metal ions must be determined from the number of electrons lost.
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39. Key Concepts
The charge of any ion of a Group A nonmetal is determined by subtracting 8 from the group number.
Unlike a monatomic ion, a polyatomic ion is composed of more than one atom. But like a monatomic ion, a polyatomic ion behaves as a unit and carries a charge.
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40. END OF 9.1
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