9.1 Naming Ions 9 - Ms. Lara La Cueva HS Science -...

Chemical Names and Formulas 253

9.1

FOCUSObjectives9.1.1 Identify the charges on mona-

tomic ions by using the peri-odic table, and name the ions.

9.1.2 Define a polyatomic ion and write the names and formulas of the most common poly-atomic ions.

9.1.3 Identify the two common end-ings for the names of most polyatomic ions.

Guide for Reading

Build VocabularyWord Parts Ask, Can you think of words that begin with the prefixes mono– and poly–? (Students may respond with words such as monotone, monochrome, polygon, or polygamy.) Discuss the meanings of these words and then ask, How do you think mon-atomic ions and polyatomic ions might differ? (A monatomic ion has one atom; a polyatomic ion has more than one atom.)

Reading StrategyCompare and Contrast As students read the section, have them make a chart that compares monatomic ions and polyatomic ions as to charge, com-position, and name endings.

INSTRUCT

Comment that you couldn’t talk with people in a different country unless you knew their language. Emphasize that chemists everywhere use the same chemical language. Ask, Why is it important that there be only one lan-guage of chemistry? (Chemists need to communicate with one another and hav-ing the same names for compounds makes this easier.)

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Section ResourcesPrint• Guided Reading and Study Workbook,

Section 9.1• Core Teaching Resources, Section 9.1

Review, Interpreting Graphics• Transparencies, T94–T95

Technology• Interactive Textbook with ChemASAP,

Problem-Solving 9.1, Assessment 9.1• Go Online, Section 9.1

Connecting to Your World

Section 9.1 Naming Ions 253

9.1 Naming Ions

In the play Romeo and Juliet,William Shakespeare wrote, “What’s in a name? That which we call a rose/By any other name would smell as sweet.” A rose is rosa in Spanish,

warda in Arabic, and julab in Hindi. To truly under-stand another culture, you must first learn the

language used in that culture. Similarly, to understand chemistry, you must learn its

language. Part of learning the language of chemistry involves understanding how to

name ionic compounds. For this you need to know how to name ions.

Guide for Reading

Key Concepts • How are the charges of Group A

metal and nonmetal ions related to their positions in the periodic table?

• How are the charges of some transition metal ions determined?

• What are the two endings of the names of most polyatomic ions?

Vocabularymonatomic ion

polyatomic ion

Reading StrategyOutlining As you read, make an outline of the most important ideas in this section. Use the red headings as the main topics and the blue headings as subtopics. Add a sentence or a note after each heading to provide key infor-mation about the topic.

Monatomic IonsIonic compounds consist of a positive metal ion and a negative nonmetalion combined in a proportion such that their charges add up to a netcharge of zero. For example, the ionic compound sodium chloride (NaCl)consists of one sodium ion (Na�) and one chloride ion (Cl�). Probably youare already familiar with the name and formula of sodium chloride, whichis common table salt. But it is important, in learning the language ofchemistry, to be able to name and write the chemical formulas for all ioniccompounds. The first step is to learn about the ions that form ionic com-pounds. Some ions, called monatomic ions, consist of a single atom with apositive or negative charge resulting from the loss or gain of one or morevalence electrons, respectively.

Cations Recall that metallic elements tend to lose valence electrons. Lith-ium, sodium, and potassium in Group 1A lose one electron to form cations.All the Group 1A ions have a 1� charge (Li�, Na�, K�, Rb�, and Cs�). Mag-nesium and calcium are Group 2A metals. They tend to lose two electronsto form cations with a 2� charge (Mg2� and Ca2�), as do all the other Group2A metals. Aluminum is the only common Group 3A metal. As you mightexpect, it tends to lose three electrons to form a 3� cation (Al3�). Whenthe metals in Groups 1A, 2A, and 3A lose electrons, they form cations withpositive charges equal to their group number. Figure 9.1 shows some of theelements whose ionic charges can be obtained from their positions in theperiodic table. The names of the cations of the Group 1A, Group 2A, andGroup 3A metals are the same as the name of the metal, followed by theword ion or cation. Thus Na� is the sodium ion (or cation), Ca2� is the cal-cium ion (or cation), and Al3� is the aluminum ion (or cation).

Figure 9.1 The representative elements shown form positive ions with charges equal to their group numbers. Applying Concepts Are the ions anions or cations?

Li Be

Na Mg

K Ca

Rb Sr

Cs Ba

Fr Ra

1A 2A

Al

3A

Answers to...Figure 9.1 cations

254 Chapter 9

Section 9.1 (continued)

Monatomic IonsUse VisualsFigures 9.1 and 9.2 Have students note that in each figure, the periodic table is shown in the background to help them locate the groups being dis-cussed. Ask, How do the ions formed by metals in Groups 1A, 2A, and 3A differ from the ions formed by non-metals in Groups 5A, 6A, and 7A? (Groups 1A, 2A, and 3A form positive ions; Groups 5A, 6A, and 7A form nega-tive ions.) Ask, Are the ions formed by the transition metals cations or anions? (They are cations.)

CLASS ActivityCLASS

Determining Ionic ChargePurpose Students gain practice in using the periodic table to determine the charge on ions.

Materials A display-size periodic table

Procedure Have one student point, one-by-one and in no particular order, to any of the elements shown promi-nently in Figures 9.1 and 9.2. Have the other students vie to identify the charge of the ion formed by each element.

TEACHER DemoTEACHER Demo

Colorful IonsPurpose Students see the various col-ors of solutions of transition metal ions and practice naming them.

Materials Beakers containing solu-tions of soluble metal salts, for exam-ple: MnCl2, FeCl2, CoCl2, NiCl2, and CuCl2, or use the ions in Figure 9.3.

Procedure Write the symbols for the metal ions on the board. Have students describe the colors of the solutions. Ask them to use Table 9.2 to write the Stock and classical names of each cat-ion. Ask students to suggest why chemists currently use only the Stock system for naming ions.

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254 Chapter 9

1A 2A 3A 4A 5A 6A 7A 8A

Li� Be2� N3� O2� F�

Na� Mg2� Al3� P3� S2� Cl�

K� Ca2� As3� Se2� Br�

Rb� Sr2� I�

Cs� Ba2�

Anions Nonmetals tend to gain electrons to form anions, so the charge ofa nonmetallic ion is negative. The charge of any ion of a Group Anonmetal is determined by subtracting 8 from the group number. Theelements in Group 7A form anions with a 1� charge (7 � 8 � �1). Thename of an anion is not the same as the element’s name. Anion names startwith the stem of the element name and end in -ide. For example, two ele-ments in Group 7A are fluorine and chlorine. The anions for these non-metals are the fluoride ion (F�) and chloride ion (Cl�). Anions of nonmetalsin Group 6A have a 2� charge (6 � 8 � �2). Group 6A elements, oxygen andsulfur, form the oxide anion (O2�) and the sulfide anion (S2�), respectively.The three nonmetals in Group 5A—nitrogen, phosphorus, and arsenic—can form anions with a 3� charge (5 � 8 � �3). These have the symbolsN3�, P3�, and As3� and are called, respectively, nitride ion, phosphide ion,and arsenide ion. Figure 9.2 shows the Group A elements that form anions.Table 9.1 summarizes the ionic charges of representative elements that canbe obtained from the periodic table.

The majority of the elements in the two remaining representativegroups, 4A and 8A, usually do not form ions.

Checkpoint What is the name of the anion N3�?

Ions of Transition Metals The metals of Groups 1A, 2A, and 3A consis-tently form cations with charges of 1�, 2�, and 3�, respectively. Many ofthe transition metals (Groups 1B–8B) form more than one cation with dif-ferent ionic charges. Some of these are shown in Figure 9.2. Thecharges of the cations of many transition metal ions must be determinedfrom the number of electrons lost. For example, the transition metal ironforms two common cations, Fe2� (two electrons lost) and Fe3� (three elec-trons lost). Cations of tin and lead, the two metals in Group 4A, can alsohave more than one charge. Table 9.2 lists symbols for common ions ofmany of the metals that form more than one ion. Two methods are used toname these ions. The preferred method is called the Stock system. In theStock system, a Roman numeral in parentheses is placed after the name ofthe element to indicate the numerical value of the charge. Table 9.2 showsthat the cation Fe2� is named iron(II) ion. Note that no space is left betweenthe element name and the Roman numeral in parentheses. The name forFe2� is read “iron two ion.” The Fe3� ion is named iron(III) ion and is read“iron three ion.” Colorful solutions of the transition metal ions Co3�, Cr3�,Fe3�, Ni2�, and Mn2� are shown in Figure 9.3.

Figure 9.3 The ions of these transition metals produce an array of colors when dissolved in water. From left to right, the ions are Co3�, Cr3�, Fe3�, Ni2�, and Mn2�.

Table 9.1

Ionic Charges of Representative ElementsN O

P S

As Se

5A 6A

F

Cl

Br

I

7A

Cr Mn Fe Co

Hg

Cu

8B7B6B

1B 2B

Figure 9.2 Note the positions of the nonmetals and the metalloid, arsenic. These elements form anions. Common transition elements that form more than one ion are also shown. Applying Concepts Do the transition metals form anions or cations?


CLASS ActivityCLASS

Symbols for Monatomic IonsPurpose Students use the periodic table for writing symbols for mona-tomic ions.

Materials Blank photocopy of the peri-odic table for each pair of students.

Procedure Have students work in pairs. Allow them to refer to their text-books or other resource materials. In the element blocks on the blank peri-odic table, have them write the sym-bols and names of the cations and anions of as many elements as possi-ble. Have them use their tables to iden-tify any trends in ionic charges. Encourage them to keep their tables for reference.

RelateDivide students into research teams to gather data about paint pigments from different sources. Possible assign-ments: (1) Examine the pigments avail-able at an art-supply store and try to tell from the names what they contain. (2) Interview an art teacher about the pigments that he or she prefers. (3) Use the library or Internet to research which pigments were available and popular during earlier eras; look for information about natural sources of pigments. (4) Invite a curator or art restorer from a local museum to talk about using pigments to repair dam-aged art, authenticate art, or unmask a forgery.

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Answers to...Figure 9.2 cations

Checkpoint

nitride ion

Special Needs For some students, the charge that results when electrons are transferred is counter-intuitive — additions result in a negative charge, subtractions result in a positive charge. Give students different-colored disks

to represent protons and electrons in neutral atoms. Remove or add electrons and ask stu-dents to find the charge of the resulting “ion.”

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An older, less useful method for naming these cations uses a root wordwith different suffixes at the end of the word. The older, or classical, nameof the element is used to form the root name for the element. For example,ferrum is Latin for iron, so ferr- is the root name for iron. The suffix -ous isused 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, Fe2�

is the ferrous ion, and Fe3� is the ferric ion, as shown in Table 9.2. Noticethat you can usually identify an element from what may be an unfamiliarclassical name by looking for the element’s symbol in the name. Thus fer-rous (Fe) is iron; cuprous (Cu) is copper; and stannous (Sn) is tin. A majordisadvantage of using classical names for ions is that they do not tell youthe actual charge of the ion. A classical name tells you only that the cationhas either the smaller (-ous) or the larger (-ic) charge of the pair of possibleions for that element.

A few transition metals have only one ionic charge. The names of thesecations do not have a Roman numeral. These exceptions include silver,with cations that have a 1� charge (Ag�), as well as cadmium and zinc,with cations that have a 2� charge (Cd2� and Zn2�). As Figure 9.4 shows,many transition metal compounds are colored and can be used as pig-ments. Pigments are compounds having intense colors that can be used tocolor other materials. For example, compounds of chromium are pigmentsused to make yellow, orange, red, or green paints. Various cadmium com-pounds range in color from yellow to red and maroon. Prussian blue is animportant pigment composed of the transition element iron combinedwith carbon, hydrogen, and nitrogen.

Figure 9.4 Many transition metals form brightly colored compounds that are used in making artists’ paints.

Table 9.2

Symbols and Names of 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

Fe2� Iron(II) ion Ferrous ion

Fe3� Iron(III) ion Ferric ion*Hg2

2�

*A diatomic elemental ion.

Mercury(I) ion Mercurous ion

Hg2� Mercury(II) ion Mercuric ion

Pb2� Lead(II) ion Plumbous ion

Pb4� Lead(IV) ion Plumbic ion

Sn2� Tin(II) ion Stannous ion

Sn4� Tin(IV) ion Stannic ion

Cr2� Chromium(II) ion Chromous ion

Cr3� Chromium(III) ion Chromic ion

Mn2� Manganese(II) ion Manganous ion

Mn3� Manganese(III) ion Manganic ion

Co2� Cobalt(II) ion Cobaltous ion

Co3� Cobalt(III) ion Cobaltic ion

Differentiated Instruction

256 Chapter 9


PharmacistAlthough pharmacists must often work in the evenings and on weekends, they are well paid and employment oppor-tunities for pharmacists during the coming decade are expected to grow faster than for many other professions. The American Association of Colleges of Pharmacy (ASCP) operates the Phar-macy College Application Service to allow students to use a single web-based application for all applications to schools of pharmacy.

Have students research chemistry-related careers in the library or on the Internet. Students can then con-struct a table that describes the nature of the work, educational and training requirements, employ-ment outlook, working conditions, and other necessary information.

CONCEPTUAL PROBLEM 9.1

Answers1. a. selenide ion, anion

b. barium ion, cationc. phosphide ion, anion

2. a. three electrons lostb. two electrons gainedc. one electron lost

Practice Problems PlusWrite the symbol (including charge) for the ion formed by each element and classify each as an anion or a cation.a. arsenic (As3–, anion)b. beryllium (Be2+, cation)c. astatine (At–, anion)d. gallium (Ga3+, cation)

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Potassium Iodide as Radiation Medicine Potassium is stockpiled for use in the event of a nuclear accident that results in fallout of radioactive iodine-131. Whether radioactive or not, absorbed iodine accumulates in the thyroid gland. If a dose of nonradioactive KI

is ingested in a timely way after a nuclear accident, iodine-131 is less likely to enter the thyroid gland. Iodine-131 has a relatively short half-life of eight days, but can cause thyroid cancer, especially in children.

Facts and Figures

256 Chapter 9

Practice Problems


Classifying and Naming Cations and AnionsWrite the symbol for the ion formed by each element. Classify the ions ascations or anions and name the ion. Potassium and iodine combine to formpotassium iodide, an additive to table salt that protects the thyroid gland.

a. potassium b. iodine c. sulfur d. lead, 4 electrons lost

Analyze Identify the relevant concepts.

a.–d. Use the periodic table or the electrons lost to write the symbol for the ion. Ions with positive charges are cations; ions with nega-tive charges are anions. Apply the rules for naming cations and anions. The names of nonmetallic anions end in -ide. Metallic cat-ions take the name of the metal. If the metal ion can have more than one ionic charge, use a Roman numeral in the Stock name or use the classical name with a suffix.

Solve Apply concepts to this situation.

a. K�: cation, potassium ion b. I�: anion, iodide ion c. S2�: anion, sulfide ion d. Pb4�: cation, lead(IV) or plumbic ion

The ions formed by metals are cations and the ions formed by nonmetals are anions. The rules for naming have been correctly applied.

PharmacistDoctors provide written instruc-tions to pharmacists about medi-cines they wish to have dispensed to their patients. It is the responsi-bility of the pharmacist to prepare the medicine and to advise the patient about possible side effects. Pharmacists also make sure that physicians have not prescribed a medicine or dosage that could harm the patient.

A person with some knowledge of chemistry and biology could become a pharmacist’s assistant

with on-the-job training. Advance-ment to the position of pharmacist requires a college degree in phar-macy. This degree includes the study of chemistry, biology, mathe-matics, and statistics. Pharmacists must also learn about the biological effects of drugs and drug interac-tions (pharmacology). To obtain a license to dispense drugs, pharma-cists are required to pass a state test and must work for a specified period of time under the supervision of another pharmacist.

Practice Problems

1. Name the ions formed by these elements and classify them as anions or cations.

a. selenium b. barium c. phosphorus

2. How many electrons were lost or gained to form these ions?

a. Fe3� b. O2� c. Cu�

For: Careers in ChemistryVisit: PHSchool.comWeb Code: cdb-1091

withChemASAP

Problem-Solving 9.1 Solve Problem 1 with the help of an interactive guided tutorial.


Polyatomic IonsDiscussWrite the following formulas on the board: NaOH, H2SO4, NH4NO3, Na2CO3. Ask students what these compounds have in common. (Students may note that they all contain oxygen.) Tell stu-dents that this is an important obser-vation, then explain that all of these compounds contain ions that are made up of more than one type of atom. In ions such as these, oxygen is almost always present.

Use VisualsTable 9.3 Call attention to how the table is divided into sections according to charge. More than half of the ions have a charge of 1–. Only two ions have charges of 3–, and both of these contain the phosphorus atom. The ammonium ion is the only common polyatomic ion with a 1+ charge, and it does not contain oxygen. The remain-ing ions have charges of 2–. Have stu-dents pick out the –ate l -ite pairs and write their formulas on the board. Have students note that the members of each pair have the same charge. It is not the charge but the number of oxy-gen atoms in the members of an -ate/-ite pair that determines the end-ings of the names.

DiscussWrite on the board the names and for-mulas of at least ten different poly-atomic ions. Purposely mismatch the names so that they do not appear with the correct formulas. Challenge stu-dents to see how quickly they can rear-range the names and formulas so that they are paired correctly.

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Answers to...Figure 9.5 The ammonium ion is a cation and does not contain oxygen.

Checkpoint

HSO3–

English Learners Have students prepare flash cards with the name of a polyatomic ion on one side and its formula on the other side. Pairs of stu-dents can use the flash cards to quiz each other on the names and formulas of these ions. Set aside a few minutes at the begin-ning or end of several class periods for this activity.

L2 Two Kinds of Bonding When an ionic compound forms between a metal ion and a polyatomic ion, the resulting compound contains both ionic bonds and covalent bonds. The atoms in all polyatomic ions are held together by covalent bonds.

Facts and FiguresDifferentiated Instruction


Polyatomic IonsSome ions, called polyatomic ions, are composed of more than one atom.The sulfate anion consists of one sulfur atom and four oxygen atoms. Thesefive atoms together comprise a single anion with an overall 2� charge. Theformula is written SO4

2�. Polyatomic ions, such as the sulfate ion, are tightlybound groups of atoms that behave as a unit and carry a charge. You cansee the structures of four common polyatomic ions in Figure 9.5.

The names and formulas of some common polyatomic ions are shownin Table 9.3 grouped according to their charges. The names of mostpolyatomic anions end in -ite or -ate. For example, notice the endings ofthe names of the hypochlorite ion (ClO�) and the hydrogen carbonate ion(HCO3

�). Also notice that three important ions have different endings. Thepositively charged ammonium cation (NH4

�) ends in -ium, and the cya-nide ion (CN�) and the hydroxide ion (OH�) end in -ide. Use Table 9.3 as areference until you have memorized its contents.

Sometimes the same two or three elements combine in different ratiosto form different polyatomic ions. You can see examples in Table 9.3. Lookfor pairs of ions for which there is both an -ite and an -ate ending, for exam-ple, sulfite and sulfate. In the list below, examine the charge on each ion inthe pair. Note the number of oxygen atoms and the endings on each name.You should be able to discern a pattern in the naming convention.

The charge on each polyatomic ion in a given pair is the same. The -iteending indicates one less oxygen atom than the -ate ending. However, theending does not tell you the actual number of oxygen atoms in the ion. Forexample, the nitrite ion has two oxygen atoms and the sulfite ion has threeoxygen atoms. All anions with names ending in -ite or -ate contain oxygen.

Checkpoint What is the formula for the hydrogen sulfite polyatomic ion?

-ite -ateSO3

2�, sulfite SO42�, sulfate

NO2�, nitrite NO3

�, nitrateClO2

�, chlorite ClO3�, chlorate

Formula Name

Charge � 1�

H2PO4� Dihydrogen

phosphate

C2H3O2� Acetate

HSO3� Hydrogen sulfite

HSO4� Hydrogen sulfate

HCO3� Hydrogen carbonate

NO2� Nitrite

NO3� Nitrate

CN� Cyanide

OH� Hydroxide

MnO4� Permanganate

ClO� Hypochlorite

ClO2� Chlorite

ClO3� Chlorate

ClO4� Perchlorate

Charge � 2�

HPO42� Hydrogen phosphate

C2O42� Oxalate

SO32� Sulfite

SO42� Sulfate

CO32� Carbonate

CrO42� Chromate

Cr2O72� Dichromate

SiO32� Silicate

Charge � 3�

PO33� Phosphite

PO43� Phosphate

Charge � 1�

NH4� Ammonium

Figure 9.5 These molecular models show the arrangement of atoms in four common polyatomic ions. Interpreting Diagrams How does the ammonium ion differ from the other three?

Nitrate ion

(NO3�)

Sulfate ion

(SO42�)

Phosphate ion

(PO43�)

Ammonium ion

(NH4�)

Table 9.3

Common Polyatomic Ions

258 Chapter 9


CLASS ActivityCLASS

Shapes of Polyatomic IonsPurpose Students visualize the geom-etry of some polyatomic ions. Materials Styrofoam balls and wooden sticks

Procedure Pairs of students can research the three-dimensional structure of one of the polyatomic ions in Table 9.3. Have them prepare a ball-and-stick model of the ion. They may wish to dif-ferentiate atoms by size or color. Make sure that they pay attention to correct geometric placement of atoms.

ASSESSEvaluate UnderstandingWrite these symbols on the chalkboard: K, NH3, CN, Mg, O, OH, Co, NH4, Pb, PO4, Ar, ClO, H2O, and Zn. Ask students to identify which species can exist as ions by simply attaching a charge. (K, CN, Mg, O, OH, Co, NH4, Pb, PO4, ClO, and Zn) For these ions, ask students to identify the charges and name the ion.

ReteachRemind students that one of the most important properties of a compound is that it is electrically neutral. Because polyatomic ions carry a charge, they are always combined with other ions in compounds.

Sodium is found in higher concentra-tions in extra-cellular fluids, such as plasma. Potassium is found in higher concentrations within cells. Both ions are involved in transmission of nerve impulses.

with ChemASAP

If your class subscribes to the Interactive Textbook, use it to review key concepts in Section 9.1.

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258 Chapter 9

Essay Sodium ions (Na�) and potassium ions(K�) are needed for the human body to function.Research where these ions are most likely to befound in the body and the roles they play. Writea brief essay describing your findings.

withChemASAP

When the formula for a polyatomic ion begins with H (hydrogen), youcan think of the H as representing a hydrogen ion (H�) combined withanother polyatomic ion. For example, HCO3

� is a combination of H� andCO3

2�

charges.

The hydrogen carbonate anion (HCO3�), the hydrogen phosphate

anion (HPO42�), and the dihydrogen phosphate anion (H2PO4

�) are essen-tial components of living systems. In contrast, the cyanide ion (CN�) isextremely poisonous to living systems because it blocks a cell’s meansof producing energy. Figure 9.6 shows some uses for compounds withhydrogen-containing polyatomic ions.

dihydrogen phosphatehydrogen phosphate

H2PO4�¡H� � HPO4

2�

hydrogen phosphatephosphate

HPO42�¡H� � PO4

3�

hydrogen carbonatecarbonate

HCO3�¡H� � CO3

2�

9.1 Section Assessment

3. Key Concept Explain how the charges of Group A metal and nonmetal ions are related to their positions in the periodic table.

4. Key Concept How are the charges of some transition metal ions determined?

5. Key Concept What are the usual endings for the names of polyatomic ions?

6. What are the charges on ions of Group 1A, Group 3A (aluminum), and Group 5A?

7. How does a polyatomic anion differ from a mon-atomic anion?

8. Write the symbol for the ion of each element. Classify the ion as an anion or a cation, and name the ion.

a. potassium b. oxygen c. tin (2 electrons lost) d. bromine e. beryllium f. cobalt (3 electrons lost)

9. Write the symbol or formula (including charge) for each of the following ions.

a. ammonium ion b. tin(II) ion c. chromate ion d. nitrate ion

Assessment 9.1 Test yourself on the concepts in Section 9.1.

Figure 9.6 Hydrogen-containing polyatomic ions are part of many compounds that affect your daily life. Sodium hydrogen carbonate, which contains the HCO3

� ion, can relieve an upset stomach.

The presence of dissolved HCO3

�, HPO42�, and H2PO4

� ionsin your blood is critical for your health. Crop dusters spread fertilizers containing HPO4

2� and H2PO4

� ions.

a

b

c

a b c

. Note that the charge on the new ion is the algebraic sum of the ionic

Section 9.1 Assessment3. The positive charge of a group A metal is

equal to its group number. The charge of a group A nonmetal is the group number minus 8.

4. from the number of electrons lost5. -ite or -ate6. Group 1A metals, 1+; Group 3A (alumi-

num), 3+, Group 5A nonmetals, 3–7. A monatomic anion is a single atom with a

negative charge; a polyatomic anion is

two or more bound atoms with a negative charge.

8. a. K+, cation, potassium ion b. O2–, anion, oxide ion c. Sn2+, cation, tin(II) ion d. Br–, anion, bromide ion e. Be2+, cation, beryllium ion f. Co3+, cation, cobalt(III) ion

9. a. NH4+ b. Sn2+ c. CrO4

2– d. NO3–

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Technology and Society 259

Pixel

Display electrode

Front plate glass

Phosphor

5 in.

Plasma TV

Today, a TV can be mounted on the wall just as if it

were a picture in a frame. The cathode ray tube (CRT),

which bulges from the back of a conventional TV, has

been replaced by plasma. Plasma is a gaseous mixture

of high-energy electrons and ions that activates tiny

fluorescent tubes in chambers called pixels. A TV

picture is created by hundreds of thousands

of pixels, each contributing a single point of

colored light. Inferring Explain why

you don’t see the points of light.

How it works A computer controls the output of each pixel individually. Varying the electrical current flowing through the cells changes the intensity of the phosphor color in any cell to create millions of colors.

Pixels A pixel is divided into three cells containing phosphors of red, green, and blue. A phosphor is a substance that emits light when excited, in this case by plasma.

Plasma TVStudents may be interested in research-ing one or more of these topics:

• What is the composition of plasma? How is it produced? What is its role in creating a colored TV picture? Are there other ways in which plasma is used today?

• What are the properties of phos-phors? What kinds of substances are they and how do they produce light?

• Color theory—how do red, green and blue light produce all imaginable col-ors of light?

• Plasma is considered a fourth state of matter. Explore the meaning of this statement.

• Explore the quality of plasma TV as compared with conventional TVs. Does the technology of plasma TV assure superior picture quality?

Answers to...Inferring They are too small.

260 Chapter 9

9.2

FOCUSObjectives9.2.1 Apply the rules for naming

and writing formulas for binary ionic compounds.

9.2.2 Apply the rules for naming and writing formulas for com-pounds with polyatomic ions.

Guide for Reading

Build VocabularyWord Parts The word compound comes from the Latin componere, which means “to put.” Parts are put together to make a whole. A com-pound always contains at least two parts. A compound with two parts is called a binary compound.

Reading StrategyAnticipation Guide Have students page through the section and note the two major headings in red. Ask, What are the two types of compounds you will be reading about? (binary ionic compounds and compounds with poly-atomic ions) Building on the vocabu-lary discussion above, ask, What do you think is the difference between a binary compound and a com-pound with a polyatomic ion? (A binary compound contains only two elements. A compound with a poly-atomic ion can contain three or more elements because a polyatomic ion can have two or more elements.)

INSTRUCT

Ask students to draw an analogy between a recipe that calls for 4 cups of tomato sauce and 1 teaspoon of salt and the formula for a chemical com-pound such as CaCl2. (Calcium and chlo-rine correspond to the ingredients tomato sauce and salt; the subscripts correspond to the quantities of the ingredients.)

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Section ResourcesPrint• Small-Scale Chemistry Laboratory

Manual, Lab 12• Guided Reading and Study Workbook,

Section 9.2• Core Teaching Resources, Section 9.2

Review• Transparencies, T96–T97


Simulation 9; Problem-Solving 9.11, 9.12; Assessment 9.2

• Go Online, Section 9.2

260 Chapter 9

9.2Naming and Writing Formulas for Ionic Compounds

At festivals throughout the summer, contestants compete for blue ribbons for the best barbecue. Some cooks say the recipe for their barbecue sauce is the key to winning and they may hint at a secret ingredient. The recipe is the formula for the sauce—a complete list of ingredients and their proportions. With the recipe, anyone could reproduce a sauce, so a cook is likely to keep a prize-winning reci-pe a closely guarded secret. Chem-istry also uses formulas, but without any secrets. Once you know the rules, you can write the formula for any chemical compound. In this section, you will learn how to write the formulas for ionic compounds.

Guide for Reading

Key Concepts • How are the names of binary

ionic compounds determined?• How do you write the formulas

for binary ionic compounds?• How do you write the formulas

and names of compounds containing polyatomic ions?

Vocabularybinary compound

Reading StrategyPredicting Before you read, pre-view the section by reading the Key Concepts, the headings, and the boldfaced sentences. Predict how you would write the formulas for binary ionic compounds. After you have read the section, check the accuracy of your prediction.

Figure 9.7 These masks are made of an ionic compound with the common name plaster of paris(CaSO4 · 2H2O). Plaster of paris is also used in wallboard.

Binary Ionic CompoundsIn the days before the science of chemistry developed, the person who dis-covered a new compound often named it anything he or she wished. It wasnot uncommon for the name to describe some property of the substance orits source. For example, a common name for potassium carbonate (K2CO3)is potash. The name evolved because the compound was obtained byboiling wood ashes in iron pots. Baking soda (NaHCO3) is added to batterto make cakes rise. Plaster of paris (CaSO4 · 2H2O) is the name for a sub-stance used in wallboard and to make face masks like those shown inFigure 9.7. Gypsum and lye are other common names of chemical com-pounds. Unfortunately, such names do not tell you anything about thechemical composition of a compound or give you any indication abouthow it is related to other compounds.

The French chemist Antoine-Laurent Lavoisier(1743–1794) determined the composition of manycompounds in his experiments to show how chemicalcompounds form. As more and more compoundswere identified, Lavoisier recognized that it wasbecoming impossible to memorize all the unrelatednames of the compounds. He worked with otherchemists to develop a systematic method for namingchemical compounds. Their work is the basis fornaming compounds today.

260 Chapter 9


Binary Ionic Compounds

Word OriginsA binary star is a system of two stars that revolve around each other.

RelateAsk, Do you or someone you know have a nickname? Does the nick-name tell something about the per-son?(Students will have a variety of responses.) Guide students to recog-nize that nicknames are somewhat like the common names used to describe compounds. Use sodium carbonate (Na2CO3) as an example. Its common name is soda or soda ash. Ask, Which tells you more about the compound, soda or sodium carbonate? (sodium carbonate).

CLASS ActivityCLASS

Naming Ionic Binary CompoundsPurpose Students practice naming binary compounds.

Materials chalkboard, chalk

Procedure Divide the class into teams. Have each team write the names of ionic compounds on a sheet of paper as you write formulas on the board. Use chlorides, bromides, phos-phides, and oxides of the elements of Groups 1A, 2A, and aluminum in 3A. Mix in sulfides, oxides, chlorides, and bromides of lead, tin, iron, cobalt, cop-per, and zinc. Have the teams compare their lists of names. When a discrep-ancy occurs, have them discuss it and come to agreement on the correct name. Save the lists of names for the activity on page 263.

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Answers to...Figure 9.8 2+ and 4+

Checkpoint

2+ and 4+

Less Proficient ReadersCut index cards to obtain pieces that are one-third and two- thirds of a card. Keep some cards whole. On some whole cards, mark three large positive signs; on others mark three large negative signs. Mark some of the one-third pieces with single positive signs; others with single negative signs. Mark the two-thirds pieces with two positive signs or two negative signs. On the opposite side of

each card, write the formula for an ion hav-ing the appropriate charge. Have students match single positive and negative signs. Have them match double positive signs with double negative signs and with two single positive signs. Continue with all possible combinations. Then have students turn the cards over to see the formulas of the ionic compounds they produced.

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Section 9.2 Naming and Writing Formulas for Ionic Compounds 261

Word OriginsNaming Binary Ionic Compounds A binary compound is composedof two elements and can be either ionic or molecular. If you know the for-mula for a binary ionic compound, you can write its name. First you mustverify that the compound is composed of a monatomic metallic cation anda monatomic nonmetallic anion. The compound Cs2O is composed of themetal cesium and the nonmetal oxygen. Both cesium and oxygen are GroupA elements, so each ion has only one charge. To name any binary ioniccompound, place the cation name first, followed by the anion name. Thename of Cs2O, then, is cesium oxide. The name of NaBr is sodium bromideand the name of SrF2 is strontium fluoride. But suppose you want to namethe binary ionic compound CuO. Following the rule above, you would namethis compound copper oxide. However, the name copper oxide is incom-plete. Recall that copper commonly forms two cations: Cu� and Cu2�. Thenames of these ions are copper(I) ion and copper(II) ion, respectively. Howcan you tell which of these cations forms the compound CuO? Workingbackward will help. The formula indicates that the copper cation and theoxide anion combine in a 1:1 ratio. You know that the oxide anion always hasa 2� charge. Therefore, the charge of the copper cation must be 2� in orderto balance the 2� charge. The compound CuO must be copper(II) oxide.The formula for copper(I) oxide is Cu2O.

Table 9.2 lists the symbols and names of the common metal ions that formmore than one ion. Recall that the charges of monatomic anions can be deter-mined from the periodic table; those of polyatomic anions are shown in Table9.3. Using these sources, you can write the names of SnF2 and SnS2. Tin (Sn)forms cations with 2� and 4� charges. Fluorine is a Group 7A element, so thecharge of the fluoride ion is 1�. In SnF2, the ratio of cation to anion is 1:2. There-fore, the charge of the tin cation must be 2� to balance the combined 2� chargeof two fluoride ions. The name of SnF2 is tin(II) fluoride or stannous fluoride.However, the name of SnS2 is not tin(II) sulfide. Sulfur is a Group 6A element, soits charge is 2�. The charge of the tin cation must be 4� to balance the com-bined charges of two sulfur anions. Thus the name of SnS2 is tin(IV) sulfide orstannic sulfide. Figure 9.8 shows examples of uses of stannous fluoride and stan-nic sulfide.

Checkpoint What are the charges of the two ions of tin?

Binary comes from the Latin word bini meaning “two by two” or “twofold.” Binary compounds consist of two elements. Predict what a binary star might be and then check your prediction in the dictionary.

Figure 9.8 Tin(II) fluoride and tin(IV) sulfide have different compositions and uses.

Tin(II) fluoride is added to toothpastes to prevent cavities.

Tin(IV) sulfide is used in glazes for porcelain fixtures and dishes. Inferring What are the charges on the tin ions in the two compounds?

a

b

a b

262 Chapter 9


262 Chapter 9

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Writing Formulas for Binary Ionic Compounds If you know thename of a binary ionic compound, you can write its formula. Write thesymbol of the cation and then the anion. Add whatever subscripts are neededto balance the charges. The positive charge of the cation must balance thenegative charge of the anion so that the net ionic charge of the formula iszero. The ionic compound potassium chloride is composed of potassiumcations (K�) and chloride anions (Cl�), so potassium chloride is a binaryionic compound. The charge of each K� cation is balanced by the charge ofeach Cl� anion, so in potassium chloride, the potassium and chloride ionscombine in a 1:1 ratio. Thus the formula for potassium chloride is KCl. Thenet ionic charge of the formula unit is zero.

The binary ionic compound calcium bromide is composed of calciumcations (Ca2�) and bromide anions (Br�). The two ions do not have equalnumerical charges. Thus each calcium ion with its 2� charge must com-bine with (or be balanced by) two bromide ions, each with a 1� charge.That means that the ions must combine in a 1:2 ratio, so the formula forcalcium bromide is CaBr2. The net ionic charge of the formula unit is zero.

Figure 9.9 shows one step in the process of making steel from iron ore.Hematite, a common ore of iron, contains iron(III) oxide. What is the for-mula for this compound? Recall that a Roman numeral in the name of anion shows the charge of the metal ion. Thus iron(III) oxide contains Fe3�

cations combined with oxide anions (O2�). How can you balance a 3�

charge and a 2� charge? You must find the least common multiple of thecharges, which is 6. Iron’s three charges taken two times equals six (3 � 2� 6). Oxygen’s two charges taken three times also equals six. Thus twoFe3�cations (a 6� charge) will balance three O2� anions (a 6� charge). Thebalanced formula, then, is Fe2O3.

Another approach to writing a balanced formula for a compound is touse the crisscross method. In this method, the numerical value of thecharge of each ion is crossed over and becomes the subscript for the otherion. Notice that the signs of the charges are dropped.

The formula is correct because the overall charge of the formula is zeroand the subscripts are in the lowest whole number ratio.

Fe O

Fe2O3

2(3�) � 3(2�) � 0

3 � 2 �

Simulation 9 Simulate combining ions and deriving the chemical formulas for several ionic compounds.

Figure 9.9 In the process for making steel, iron is extracted from hematite, an ore containing iron(III) oxide. Applying Concepts What is the formula for iron(III) oxide?

For: Links on Ionic Compounds

Visit: www.SciLinks.orgWeb Code: cdn-1092


Making and Naming an Ionic CompoundPurpose Students see a reaction in which an ionic compound is formed and then name the compound and write its formula.

Materials 1 g powdered zinc, 4 g iodine (I2), watch glass, eyedropper, 8 mL water

Safety Wear goggles and perform the demo in a fume hood. Place the zinc iodide in a plastic or cardboard con-tainer and dispose of it in an approved landfill site.

Procedure Wear safety goggles and use a fume hood. Mix 1 g of powdered zinc (Zn) and 4 g of iodine (I2) on a watch glass. With an eyedropper, care-fully add 8 mL of water, one drop at a time. After the reaction is complete, show students the zinc iodide that was formed. Write the formula unit for zinc iodide (ZnI2) along with its name on the chalkboard. Ask, What happened to elemental Zn and I2 during the reaction?(Zinc and iodine reacted to form an ionic compound composed of Zn2+ and I– ions.) Use the criss-cross method to show how the formula unit for zinc iodide was derived. Why is ZnI2 named zinc iodide and not zinc(II) iodide?(Zinc forms only one ion.)Expected Outcome The masses of Zn and I2 are the stoichiometic amounts. The reactants should be used up and white, crystalline ZnI2 formed.

Download a worksheet on Ionic Compounds to complete, and find additional teacher support from NSTA SciLinks.

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Lattice Energy in Ionic Bonding Ionic compounds tend to be stable—energy in the form of heat or electricity is needed to decompose them. Thus, energy must be released when ionic bonds form. But the released energy is not primarily from the trans-fer of electrons. Forming a cation is an endo-thermic process. In addition, both the metal and the nonmetal must be vaporized—another endothermic process—before

electron transfer can take place. Some energy (electron affinity) is released when the non-metal gains one or more electrons, but this is not enough to make the entire process exo-thermic. It is lattice energy that makes the dif-ference. Lattice energy is the energy released when gaseous cations and anions settle into the orderly crystal structure characteristic of a solid ionic compound.

Facts and Figures

The copyright holder has not granted permission to display this imagein electronic format. Please see the teacher's edition of your textbookfor this image.


Answers to...Figure 9.9 Fe2O3

Checkpoint

The charges are balanced and the subscripts are in the lowest whole number ratio.

CLASS ActivityCLASS

Formulas for Binary Ionic CompoundsPurpose Students become more pro-ficient in writing formulas.

Materials The lists of names of ionic compounds generated in the activity on p. 261.

Procedure Have teams of students write the formulas for the names on the lists. When the formulas on two or more lists do not agree, have the teams resolve the discrepancy by using the criss-cross method to write the formula on the board.


Answers10. a. BaS b. Li2O c. Ca3N2 d. CuI211. a. NaI b. SnCl2 c. K2S d. CaI2

Practice Problems PlusWrite formulas for these compounds.a. lithium fluoride (LiF)b. aluminum chloride (AlCl3)c. sodium nitride (Na3N)d. ferric oxide (Fe2O3)

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Section 9.2 Naming and Writing Formulas for Ionic Compounds 263

If you use the crisscross method to write the formula for some com-pounds such as calcium sulfide (Ca2� and S2�), you will obtain the resultCa2S2. The 2:2 ratio of calcium and sulfide ions is not the lowest wholenumber ratio. The formula for calcium sulfide is CaS.

Of course, if the magnitudes of the charges of the cation and anion arethe same, as they are in this case, the ions combine in a 1:1 ratio and thecharges are balanced.

Checkpoint Explain why the formula CaS is correct.

Ca S2 � 2 �

Ca2S2 reduces to CaS1(2�) � 1(2�) � 0


Writing Formulas for Binary Ionic CompoundsWrite formulas for these binary ionic compounds.

a. copper(II) sulfide, shown in the photo b. potassium nitride


Binary ionic compounds are composed of a mon-atomic cation and a monatomic anion. The ionic charges in an ionic compound must balance (add up to zero), and the ions must be in the lowest whole number ratio. The symbol for the cation appears first in the formula for the compound.


Write the symbol and charge for each ion in each compound.a. Cu2� and S2� b. K� and N3�

Balance the formula using appropriate subscripts.

a.

b.

The ions are in the lowest whole number ratio, and the net ionic charge is zero: 1(2�) � 1(2�) � 0 and 3(1�) � 1(3�) � 0.

Cu S2 � 2 �

CuS

K N1 � 3 �

K3N

Practice Problems

10. Write formulas for compounds formed from these pairs of ions.a. Ba2�, S2� b. Li�, O2�

c. Ca2�, N3� d. Cu2�, I�

11. Write formulas for these compounds.a. sodium iodide b. stannous chloridec. potassium sulfide d. calcium iodide withChemASAP


264 Chapter 9


Compounds with Polyatomic Ions


Making and Naming Lead CarbonatePurpose Students watch the form-ation of an ionic precipitate and postu-late possible formulas.

Materials 50 mL 0.1M lead(II) nitrate, 50 mL 0.1M sodium carbonate, 100-mL beaker.

Procedure Wear goggles and gloves. Slowly mix the two solutions. Make sure students see the precipitate of lead carbonate that forms. Write on the board the symbols or formulas for the four ions that are in the two solutions: Pb2+, NO3

–, Na+, CO32–. Tell students

that the two solutions contained these four ions and that the precipitate is an ionic compound formed by the combi-nation of two of them. Ask students to list all possible formula units for the solid and to name each possibility. Identify the solid as lead(II) carbonate (PbCO3).

Safety Wear goggles and gloves because lead(II) nitrate is toxic. For dis-posal, combine the reaction mixture with 10 g of solid NaCl in a beaker. Stir and allow to settle. Filter or decant to isolate the precipitate. Place the dry precipitate in a plastic or cardboard container and dispose of it in an approved landfill. Flush the filtrate down the drain with excess water.

Use VisualsFigure 9.10 Tell students that the compounds mentioned in this caption are only a small fraction of the com-pounds with polyatomic ions that they may encounter daily. Ask, What are the formulas for calcium carbonate, lead(II) sulfate, ammonium sulfate, and ammonium phosphate?(CaCO3, PbSO4, (NH4)2SO4, (NH4)3PO4)

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Gifted and TalentedHave interested students research the possi-ble mechanisms for the alleviation of symp-toms of bipolar disorder by lithium ions. Challenge students to explain why other Group 1A ions, such as sodium and potas-

sium, which are normally present in substan-tial concentrations in the body, do not have the same effects as lithium ions even though they have the same charge.

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264 Chapter 9

Compounds with Polyatomic IonsThe pearl and the oyster shell shown in Figure 9.10 are both made of cal-cium carbonate (CaCO3). Calcium carbonate is obviously not a binary com-pound because it contains more than two elements. Remember that an -ateor -ite ending on the name of a compound indicates that the compoundcontains a polyatomic anion that includes oxygen. This compoundcontains one monatomic ion (Ca2�) and one polyatomic ion (CO3

2�).Figure 9.10 also shows a typical automobile battery called a lead storagebattery. The energy-producing reaction inside the battery uses the ioniccompound lead(II) sulfate (PbSO4), which consists of the monatomic ionPb2� and the polyatomic ion SO4

2�. The fertilizer mixture also shown in theillustration could have been produced from such compounds as potassiumhydrogen phosphate (K2HPO4), potassium sulfate (K2SO4), or sodiumnitrate (NaNO3). Each contains a polyatomic anion. How would you writethe formula for an ionic compound with a polyatomic ion? You would dowhat you did for binary ionic compounds. Write the symbol for thecation followed by the formula for the polyatomic ion and balance thecharges. For example, calcium nitrate is composed of a calcium cation(Ca2�) and a polyatomic nitrate anion (NO3

�). In calcium nitrate, twonitrate anions, each with a 1� charge, are needed to balance the 2� chargeof each calcium cation.

1(2�) � 2(1�) � 0

The charge is balanced and the ions are in the lowest whole numberratio, so the formula is correct. Parentheses are used around the nitrate ionin the formula because more than one nitrate anion is needed. The sub-script 2 that follows the parentheses shows that the compound containstwo nitrate anions. Use parentheses to set off the polyatomic ion in a for-mula only when the compound contains more than one polyatomic ion.The formula for strontium sulfate, SrSO4, has no parentheses because onepolyatomic sulfate anion balances the charge of the strontium cation.

Checkpoint When are parentheses used in a formula containing a polyatomic ion?

Ca 2 � (NO3)

Ca(NO3)2

1 �

Figure 9.10 Some examples of ionic compounds containing polyatomic ions are shown.

Oysters produce calcium carbonate to form their shells and sometimes pearls.

Lead(II) sulfate is an important component of an automobile battery. Compounds such as ammonium sulfate or ammonium phosphate are common fertilizers.

a

b

c

ca b



CLASS ActivityCLASS

Naming and Writing FormulasPurpose Students gain experience in naming and writing formulas for com-pounds with polyatomic ions.

Procedure Divide the class into groups of two to four students. Have one student in each group randomly chose ions from Tables 9.2 and 9.3. The other member or members of the group must write the formula and name the compound. Rotate the posi-tion of “ion chooser” through the group. All students in the group should agree on the names and formulas.

RelateMilk of magnesia, shown in the Con-ceptual Problem photo, is a suspension of magnesium hydroxide (Mg(OH)2) in water and is useful as an antacid and laxative. In the stomach, the hydroxide ion reacts with excess acid that causes the discomfort of indigestion. In larger amounts, magnesium hydroxide also acts as a muscle relaxant and relieves constipation.


Answers12. a. (NH4)2SO3 b. Ca3(PO4)213. a. LiHSO4 b. Cr(NO2)3

Practice Problems PlusWrite formulas of compounds formed from these pairs of ions:a. Pb2+, NO3

–(Pb(NO3)2)b. iron(III) ion and sulfate ion (Fe2(SO4)3)c. Cr3+, OH– (Cr(OH)3)d. sodium ion and hydrogen phos-phate ion (Na2HPO4)

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Answers to...

Checkpoint

Parentheses are used in a formula when the formula contains more than one unit of the same polyatomic ion.

Lithium carbonate is a compound composed of lithium cations (Li�)and polyatomic carbonate anions (CO3

2�).

In lithium carbonate, two lithium cations, each with a 1� charge, areneeded to balance the 2� charge of one carbonate anion. Parentheses arenot needed to set off the polyatomic carbonate anion. Lithium carbonatecan be prescribed for patients who have mood disorders, such as manic-depressive or bipolar disorder. A person with bipolar disorder experiencesdistressing mood swings, from elation to depression and back again.The exact mechanism is not known, but lithium ions may exert a mood-stabilizing effect on neurotransmission. Neurotransmission is the processby which “messages” are sent and received between nerve cells, includingthose in the brain.

Li 1 � 2 �(CO3)

Li2CO3


Writing Formulas for Compounds with Polyatomic IonsWhat are the formulas for these ionic compounds?

a. magnesium hydroxide, shown in the photo as milk of magnesia

b. potassium sulfate


Write the formula for each ion in the order listed in the name. Use subscripts to balance the charges. If more than one polyatomic ion is needed to balance a formula, place the poly-atomic ion formula in parentheses, followed by a subscript showing the number needed.


a.Mg 2 � 1 �(OH)

Mg(OH)2

Two hydroxide anions with 1� charges are needed to balance the 2� charge on one magnesium cation. The formula for magne-sium hydroxide must make use of paren-theses.

b.

Two potassium cations with 1� charges are needed to balance the 2� charge on one sulfate anion. The formula for potassium sulfate is K2SO4.

K 1 �

K2SO4

2 �(SO4)

Practice Problems

12. Write formulas for compounds formed from these pairs of ions.a. NH4

�, SO32�

b. calcium ion, phosphate ion

13. Write formulas for these compounds.a. lithium hydrogen sulfateb. chromium(III) nitrite withChemASAP


Chem_Chap09.fm Page 265 Friday, May 21, 2004 6:53 AM

Lithium Carbonate as MedicationWhen John Cade, a doctor in the Victoria Department of Mental Health in Victoria, Australia, injected guinea pigs with a lithium salt of uric acid in 1949, he found that the usually hyperactive animals became calm and lethargic for a period of time. After fur-ther experimentation, Cade injected a severely disturbed patient with lithium car-

bonate. The results were so astonishingly positive for this patient, and for many others who followed, that within 10 years the treat-ment had spread throughout Europe and into the United States. Patients who had been confined to mental institutions for vir-tually their entire lives were able to return to normal living.

Facts and Figures

266 Chapter 9


Section 9.2 Assessment14. Write the name of the cation followed by

the name of the anion.15. Write the symbol of the cation followed

by the symbol of the anion, then use sub-scripts to balance the charges.

16. Write the symbol for the metal ion fol-lowed by the formula of the polyatomic

ion and balance the charges. Name the cation first followed by the anion.

17. a. BeCl2 b. Cs2S c. Nal d. SrO18. a. Cr(NO2)3 b. NaClO4

c. Mg(HCO3)2 d. Ca(C2H3O2)219. a. incorrect; charges are not balanced,

MgSO4 c. incorrect; charges are not bal-anced, BeCl2

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Handbook

Naming Compounds with Polyatomic Ions You have learned towrite formulas for compounds containing polyatomic ions when you weregiven their names. Now, if you were given the formulas for these com-pounds, could you name them? When naming compounds containingpolyatomic ions, follow these guidelines. First, recognize that the com-pound contains a polyatomic ion. If the ion is unfamiliar, find its name inTable 9.3. How would you name the compound LiCN? You could easilythink that this compound is composed of individual atoms of lithium, car-bon, and nitrogen. But you know that lithium is a Group 1A element andthat this group forms 1� ions. In addition, carbon is a Group 4A elementthat does not form a monatomic ion. From this you might suspect that thecarbon and nitrogen atoms are part of a polyatomic ion with a 1� charge.Table 9.3 confirms your conclusion and tells you that the ion’s name is cya-nide ion. To name a compound containing a polyatomic ion, statethe cation first and then the anion just as you did in naming binary ioniccompounds. The name of LiCN is lithium cyanide.

The compound NaClO is used as a bleach and a disinfectant for swim-ming pools, as shown in Figure 9.11. The metallic cation in this compoundis sodium (Na�), a Group IA element that forms 1� cations. The poly-atomic ion must be ClO�. This ion is called hypochlorite ion, so the namefor NaClO is sodium hypochlorite.

Some ionic compounds containing polyatomic ions do not include ametal cation. Instead, the cation may be the polyatomic ammonium ion(NH4

�). What is the name of (NH4)2C2O4? The ammonium cation has acharge of 1�. The anion must have a charge of 2� to balance the combined2� charge of two ammonium ions. Table 9.3 shows that the name of theanion C2O4

2� is oxalate ion, so (NH4)2C2O4 is named ammonium oxalate.


Figure 9.11 Sodiumhypochlorite (NaClO) is often added to the water in swimming pools to keep bacteria at a safe level.


14. Key Concept Describe how to determine the names of binary ionic compounds.

15. Key Concept Describe how to write the for-mulas for binary ionic compounds.

16. Key Concept How do you write the formulas and the names of compounds with polyatomic ions?

17. Write the formula for these binary compounds. a. beryllium chloride b. cesium sulfide c. sodium iodide d. strontium oxide

18. Write the formula for these compounds contain-ing polyatomic ions.

a. chromium(III) nitrite b. sodium perchlorate c. magnesium hydrogen carbonate d. calcium acetate

19. Identify any incorrect formulas. Explain your answer.a. Mg2(SO4)3 b. Rb3Asc. BeCl3 d. NaF

Successful treatment of bipolar disorder often involves the use of lithium carbonate. Refer to page R9 to read more about this disorder. Write a short report summarizing what you learn.

ASSESSEvaluate UnderstandingWrite the following cations on one side of the board: NH4

+, Mg2+, Pb4+. Write the following anions on the other side of the board: Br–, S2–, PO4

3–. Ask stu-dents to write formula units for all the possible ionic compounds that these ions could form and name them. Ask them to explain how they arrived at their answers.

ReteachPoint out that three things must be considered when naming an ionic compound: (1) the identity of the ions, (2) the order of the names, and (3) the possibility that an element may form cations with more than one charge.(1) For binary compounds, ions can be identified from their symbols. The suf-fix -ide is used when naming the non-metal ion. For compounds with polyatomic ions, the polyatomic ion can be obtained from Table 9.3(2) The name of the cation always pre-cedes the name of the anion. (3) For elements that form more than one cat-ion, the correct charge is shown by a Roman numeral in parentheses directly after the cation name. Ask stu-dents to use the three-step naming procedure to name FeN and Mg(NO3)2. (iron(III) nitride and magnesium nitrate)

Elements Handbook

Individuals with bipolar disorder have difficulty functioning because of mood swings from elation to depression. Lithium carbonate is effective in regulating the patient’s mental state.

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Small-ScaleLAB

Small-ScaleLAB

Names and Formulas for Ionic Compounds

Objective After completing this activ-ity, students will be able to:• recognize and describe precipitates.• write the names and formulas for the

precipitates.

Only the ions in parentheses in Figures A and B can form precipitates.

Prep Time I hour

Class Time 30 minutes

Safety Students should wear safety goggles, lab apron, and gloves.

Expected Outcome For Figure A, only d did not produce a precipitate. For Figure B, d, h, and l produced no pre-cipitates.

Analyze and Conclude1. AgNO3 and Na2SO4 did not form a

precipitate.2. a. Ag2CO3, silver carbonate b. Ag3PO4,

silver phosphate c. AgOH, silver hydroxide (Note: This is Ag2O, silver oxide.) d. No visible reaction e. PbCO3, lead(II) carbonate f. Pb3(PO4)2, lead(II) phosphate g. Pb(OH)2, lead(II) hydroxide h. PbSO4, lead(II) sulfate i. CaCO3, calcium carbonate j. Ca3(PO4)2, calcium phosphatek. Ca(OH)2, calcium hydroxide l. CaSO4, calcium sulfate

Solution Preparation

0.05M AgNO3 2.1 g in 250 mL

0.2M Pb(NO3)2 16.6 g in 250 mL

0.5M CaCl2 13.9 g in 250 mL

1.0M Na2CO3 26.5 g in 250 mL

0.1M Na3PO4 9.5 g Na3PO4 · 12H2O in 250 mL

0.5M NaOH 20.0 g in 1.0 L

0.2M Na2SO4 7.1 in 250 mL

0.2M CuSO4 12.5 g CuSO4 · 5H2O in 250 mL

0.2M MgSO4 6.0 g in 250 mL

0.1M FeCl3 6.8 g FeCl3· 6H2O in 25 mL of 1.0M NaCl (for sta-bility); dilute to 250 mL

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You’re The Chemist1. d, h, l, no visible reaction a. Fe2(CO3)3

iron(III) carbonate b. FePO4, iron(III) phosphate c. Fe(OH)3, iron(III) hydroxidee. MgCO3, magnesium carbonate f. Mg3(PO4)2, magnesium phosphate g. Mg(OH)2, magnesium hydroxide i. CuCO3, copper(II) carbonatej. Cu3(PO4)2, copper(II) phosphate k. Cu(OH)2, copper(II) hydroxide

2. a. 2Fe3+ + 3CO32– → Fe2(CO3)3(s)

b. Fe3+ + PO43– → FePO4(s)

c. Fe3+ + 3OH– → Fe(OH)3(s)e. Mg2+ + CO3

2– → MgCO3(s)f. 3Mg2+ + 2PO4

3– → Mg3(PO4)2(s)g. Mg2+ + 2OH– → Mg(OH)2(s)i. Cu2+ + CO3

2– → CuCO3(s)j. 3Cu2+ + 2PO4

3– → Cu3(PO4)2(s)k. Cu2+ + 2OH– → Cu(OH)2(s)

For EnrichmentHave interested students design and carry out an experiment in which they make a measure-able amount of one of the precipitates, sepa-rate it, dry it, and determine its mass.

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Small-Scale Lab 267

Small-ScaleLAB

Small-ScaleLAB

Names and Formulas for Ionic CompoundsPurposeTo observe the formation of compounds, and to write their names and formulas.

Materials

• pencil

• paper

• ruler

• reaction surface

• spatula

• chemicals shown in Figure A

ProcedureOn separate sheets of paper, draw two grids similar to Figure A. Make each square 2 cm on each side. Draw black Xs on one of the grids. Use the other grid as a data table to record your observations. Place a reaction surface over the grid with black Xs and add the chemicals as shown in Figure A.

AnalyzeUsing your experimental data, record the answers to the following questions below your data table.

1. Describe each precipitate (solid product) that forms. Use terms such as milky, grainy, cloudy, or gelatinous. Which mixture(s) did not form a precipitate?

2. Write the formulas and names of the chemical com-pounds produced in the mixings.

You’re The ChemistThe following small-scale activities allow you to develop your own procedures and analyze the results.

1. Analyze It! Repeat the experiment, using the chemi-cals in Figure B. Identify the precipitates, write their formulas, and name them.

2. Explain It! In ionic equations, the precipitate is written to the right of an arrow, and the ions that produced it are written to the left. Write ionic equations for the precipitates formed from the reactions related to Figure B. For example:

2Ag� � CO32� ¡ Ag2CO3

a e i

b f j

c

d h l

Na2CO3

(CO32�)

AgNO3

(Ag�)

Pb(NO3)2(Pb2�)

CaCl2(Ca2�)

Na3PO4

(PO43�)

NaOH

(OH�)

Na2SO4

(SO42�)

g k

Figure A

a e i

b f j

c

d h l

Na2CO3

(CO32�)

Na3PO4

(PO43�)

NaOH

(OH�)

Na2SO4

(SO42�)

g k

FeCl3(Fe3�)

MgSO4

(Mg2�)

CuSO4

(Cu2�)

Figure B

268 Chapter 9

9.3

FOCUSObjectives9.3.1 Interpret the prefixes in the

names of molecular com-pounds in terms of their chemi-cal formulas.

9.3.2 Apply the rules for naming and writing formulas for binary molecular compounds.

Guide for Reading

Build VocabularyWord Parts The word prefix comes from the Latin word praefigere meaning “to fasten before.” Tell students they will learn to fasten a prefix such as di-, tri-, tetra- to the names of elements to indi-cate how many atoms of each element are in a formula of a molecular com-pound.

Reading StrategyVisualize Encourage students to visu-alize the meaning of the prefixes used in binary molecular compounds. Write some names on the chalkboard, for example, carbon tetrachloride. Then draw one circle representing carbon and four circles representing chlorine. All the circles combined constitute the five atoms in CCl4. Ask, How many cir-cles should I draw for fluorine in sul-fur hexafluoride)?(six) How many should I draw for sulfur? (one)

INSTRUCT

The prefix milli- means one-thousandth of something and the prefix kilo- means 1000 of something. Ask, How many milligrams of gold are in one gram of gold? (1000) How many milligrams are in one kilogram of gold? (1,000,000) Based on $12,500 for a kilogram, is one cent the actual value for one milligram? (The price is actually one and one-quarter cent.)

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Section 9.3• Core Teaching Resources, Section 9.3• Transparencies, T98


Assessment 9.3• Go Online, Section 9.3

268 Chapter 9

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9.3Naming and Writing Formulas for Molecular Compounds

Gold was one of the first metals to attract human attention. When gold was discovered in California in the late 1840s, people from all over the world came to find it and make their fortune. Today, gold is still greatly prized and valued. Whereas one milligram of gold is worth only about one cent, one kilogram of gold is worth approx-imately $12,500. In this case, using the correct prefix (milli- or kilo-) makes quite a difference! Prefixes are important in chemistry, too. In this section, you will learn how prefixes in the name of a binary molecular compound tell you its composition.

Guide for Reading

Key Concepts • What does a prefix in the name

of a binary molecular compound tell you about the compound’s composition?

• How do you write the formula for a binary molecular compound?

Reading StrategyMonitoring Your UnderstandingBefore you read, preview the Key Concepts, the headings, the bold-faced sentences, and the visuals. List two things you expect to learn. After reading, state what you learned about each item you listed.

Naming Binary Molecular CompoundsRecall that binary ionic compounds are composed of the ions of two ele-ments, a metal and a nonmetal. Binary molecular compounds are alsocomposed of two elements, but both elements are nonmetals and they arenot ions. These differences affect the naming of these compounds and theirformulas. Binary molecular compounds are composed of molecules, notions, so ionic charges cannot be used to write formulas or to name them. Inaddition, when two nonmetallic elements combine, they often do so inmore than one way. For example, the elements carbon and oxygen com-bine to form two invisible gaseous compounds, CO and CO2, which areillustrated in Figure 9.12. How would you name a binary compound formedby the combination of carbon and oxygen atoms? It might seem satisfac-tory to call it carbon oxide. However, the two carbon oxides, CO and CO2,are very different compounds. Sitting in a room with small amounts of thecarbon oxide CO2 in the air would not present any problems. You exhaleCO2 as a product of your body chemistry. Thus it is normally present in theair you breathe. On the other hand, if the same amount of the other carbonoxide, CO, were in the room, you could die of asphyxiation. The binarycompound CO is a poisonous gas that interferes with your blood’s ability tocarry oxygen to body cells. Obviously, a naming system that distinguishesbetween these two compounds is needed.

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Naming Binary Molecular Compounds

CLASS ActivityCLASS

Naming Binary Molecular CompoundsPurpose Students convert the subscripts in a formula to prefixes in the name.

Materials paper and pencil

Procedure Have students make a chart with three columns: element name, number of atoms, and prefix. Have them fill in the columns for N2O and then name the compound. For example:

The name is dinitrogen monoxide. Write the molecular formulas for other com-pounds on the board and have students add them to their charts. Some possibil-ities are CCl4, PBr5, and P4S3.

DiscussStudents may be interested in knowing how the order of the elements in the names of most molecular compounds is established. Ordinarily, the less electro-negative element appears first in the name. For example, a compound con-taining carbon and sulfur is carbon disul-fide (CS2). Carbon is less electronegative than sulfur so it appears first. Electroneg-ativity increases from left to right on the periodic table and decreases from top to bottom. Thus the first element in the name and formula is the element further to the left, for example, disulfur dichlo-ride (S2Cl2). For elements in the same col-umn, the element nearer the bottom of the table goes first, for example, iodine heptafluoride (IF7).

Download a worksheet on Carbon Monoxide for students to com-plete, and find additional teacher support from NSTA SciLinks.

Nitrogen 2 di-Oxygen 1 mono-

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Answers to...

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-ide

Differentiated InstructionGifted and TalentedIncreasingly large quantities of the binary molecular compound CO2 are released into the atmosphere annually by the burning of fossil fuels. Once in the atmosphere, carbon dioxide traps solar energy near Earth’s sur-

face. As a result, some scientists predict that over time global temperatures will rise. Ask students to learn more about global warm-ing and prepare an oral or written report or a poster that explains it.

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Section 9.3 Naming and Writing Formulas for Molecular Compounds 269

Prefix Mono- Di- Tri- Tetra- Penta- Hexa- Hepta- Octa- Nona- Deca-

Number 1 2 3 4 5 6 7 8 9 10

Just as prefixes in the masses of gold samples distinguish between largeand small samples, so prefixes in the names of binary molecular com-pounds help distinguish compounds containing different amounts of thesame two elements. The prefix in the name of a binary molecular com-pound tells how many atoms of each element are present in each molecule ofthe compound. Table 9.4 lists the prefixes used to name binary molecularcompounds. According to the table, the prefix mono- indicates the pres-ence of one oxygen atom in CO. The prefix di- indicates the presence of thetwo oxygen atoms in CO2. The two compounds of carbon and oxygen, COand CO2, are thus named carbon monoxide and carbon dioxide, respec-tively. Laughing gas is the common name for the gaseous compound dini-trogen monoxide (N2O), which is used as an anesthetic. When inhaled, N2Otends to make people laugh. Notice that the second element in the nameends with -ide. The names of all binary molecular compounds end in -ide.Also note that the vowel at the end of a prefix often is dropped when thename of the element begins with a vowel. For CO, you would write carbonmonoxide, not carbon monooxide. If just one atom of the first element is inthe formula, omit the prefix mono-.

Here are some guidelines for naming binary molecular compounds.First, confirm that the compound is a binary molecular compound—thatis, a compound composed of two nonmetals. The name must identify theelements in the molecule and indicate the number of each atom of eachelement. Name the elements in the order listed in the formula. Use prefixesto indicate the number of each kind of atom. Omit the prefix mono- whenthe formula contains only one atom of the first element in the name. Thesuffix of the name of the second element is -ide. Now, apply these guide-lines to naming N2O. The formula shows that the compound consists oftwo nonmetals, so it is a binary molecular compound. Two atoms of nitro-gen are combined with one atom of oxygen. Thus the prefix of nitrogen isdi- and the prefix of oxygen is mono-. The name of the compound is dini-trogen monoxide. Using the same guidelines, the name of SF6 is sulfurhexafluoride. Notice that it is not necessary to use the prefix mono- beforesulfur. What about the compound Cl2O8? This binary molecular compoundconsists of two chlorine atoms (prefix di-) and eight oxygen atoms (prefixocta-). The name is dichlorine octoxide.

Checkpoint What suffix ends the names of all binary molecular compounds?

For: Links on Carbon Monoxide

Visit: www.SciLinks.orgWeb Code: cdn-1093

Table 9.4

Prefixes Used in Naming Binary Molecular Compounds

Figure 9.12 Carbonmonoxide and carbon dioxide are two invisible, gaseous compounds of carbon and oxygen. Carbon dioxide is a product of respiration.

Carbon monoxide is a toxic product of incomplete burning, such as occurs in automobile engines and faulty furnaces.

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270 Chapter 9


Section 9.3 Assessment20. Prefixes indicate the number of atoms of

each element in a molecule of the com-pound.

21. Write the symbols for each element with a subscript corresponding to the prefix before each element in the name.

22. a. nitrogen trichloride b. boron trichloride c. nitrogen triiodide d. sul-fur trioxide e. dinitrogen tetrahydridef. dinitrogen trioxide

23. a. carbon disulfide b. CBr4 c. dichlo-rine heptoxide d. P2O3

24. a. PCl5 b. IF7 c. ClF3 d. IO225. No; the correct name is silicon tetrachloride.

270 Chapter 9

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Writing Formulas for Binary Molecular CompoundsSuppose you know the name of a molecular compound and want to write theformula. Use the prefixes in the name to tell you the subscript of eachelement in the formula. Then write the correct symbols for the two elementswith the appropriate subscripts. A simple example is silicon carbide. Siliconcarbide is a hard material like diamond. It is used as an abrasive and for cuttingand grinding, as shown in Figure 9.13. The name silicon carbide has no pre-fixes, so the subscripts of silicon and carbon must be one. Thus the formula forsilicon carbide is SiC. The name of another binary molecular compound is dini-trogen tetroxide. The prefix di- before nitrogen tells you that the compoundcontains two nitrogen atoms; the prefix tetra- tells you that the molecule alsocontains four oxygen atoms. Thus the formula for dinitrogen tetroxide is N2O4.


20. Key Concept What information do prefixes in the name of a binary molecular compound tell you about the composition of the compound?

21. Key Concept Describe how to write the for-mula of a binary molecular compound.

22. Write the names for these molecular compounds. a. NCl3 b. BCl3 c. NI3

d. SO3 e. N2H4 f. N2O3

23. Write the formulas or names for these molecular compounds.

a. CS2 b. carbon tetrabromide c. Cl2O7 d. diphosphorus trioxide

24. Write the formulas for these binary molecular compounds.

a. phosphorus pentachloride b. iodine heptafluoride c. chlorine trifluoride d. iodine dioxide

25. The name a student gives for the molecular compound SiCl4 is monosilicon trichloride. Is this name correct? Explain.

Covalent Bonds In Section 8.1, you learned about covalent bonds. Are the bonds between silicon and chlorine in silicon tetrachloride (SiCl4) single bonds? Justify your answer by drawing an electron dot struc-ture of silicon tetrachloride.


Figure 9.13 A grinding wheel made of silicon carbide (SiC) can shape even the toughest materials. Inferring Whatcauses the sparks?

Writing Formulas for Binary Molecular Compounds

RelateStudents may be interested in knowing that the hardness of substances such as silicon carbide have been quantified using the Mohs scale, which ranges from zero to 10. Tell students the graphite in their pencils has a rating of 0.5 Mohs. Diamond is the hardest mineral at 10 Mohs and silicon carbide is 9.3.

ASSESSEvaluate UnderstandingChallenge students to name the follow-ing pairs of compounds and to identify what each pair has in common: PBr3 and CrBr3, N2O and Na2O, CI4 and PbI4, P2O3and Fe2O3

(Each pair consists of a binary molecular compound and a binary ionic com-pound with one element in common.)

ReteachHave students write the names of these binary molecular compounds: NO, SiO2, N2O4, ClF3. (nitrogen monoxide, silicon dioxide, dinitrogen tetroxide, chlorine triflu-oride) Have students write the formulas for these compounds: arsenic pentachlo-ride, iodine tribromide, tetraphosphorus hexoxide. (AsCl5, IBr3, P4O6)

Connecting Concepts

Yes, chlorine can form only one bond; silicon can form four. An electron dot structure shows silicon sharing one electron with each chlorine for a total of eight electrons around silicon. Each chlorine also is surrounded by eight electrons.

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9.4

FOCUSObjectives9.4.1 Apply three rules for naming

acids.9.4.2 Apply the rules in reverse to

write formulas of acids.9.4.3 Apply the rules for naming

bases.

Guide for Reading

Build VocabularyConnect the Terms Ask students if the words acid or acidic are applied to any foods they eat. (lemons, tomato sauce, vinegar) One of the characteris-tics of acids is a sour taste. A base is a sort of chemical opposite. Together an acid and a base neutralize each other, which means their individual charac-teristics are nullified.

Reading StrategySummarize Encourage students to summarize the rules for naming acids in their own words.

INSTRUCT

Ask, Why is an attack by a formicine ant not usually serious for a human? (It would take more of the poison than a tiny ant could produce to be fatal for a person.) Can you imagine conditions under which a formicine attack might be serious for a person?(If many more than one ant attacked at once.) Tell students that among acids, formic acid (methanoic acid) is not especially strong.

Naming AcidsUse VisualsFigure 9.14 Ask, What inference can you make about the vulnerability of glass to reaction with hydrofluoric acid compared to the vulnerability of wax? (Apparently, glass reacts with hydrofluoric acid, but wax does not.) Would a glass bottle be an appropri-ate container for hydrofluoric acid? (No, the bottle would react with the acid.)

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Section 9.4• Core Teaching Resources, Section 9.4• Transparencies, T99


Assessment 9.4• Go Online, Section 9.4

Connecting to Your World

Section 9.4 Naming and Writing Formulas for Acids and Bases 271

9.4Naming and Writing Formulas for Acids and Bases

Some ants can give painful stings when threatened or disturbed. Certain ant species called formicines have poison glands that produce venom containing formic

acid. Formicines protect themselves by spraying this venom on their predators. Formic acid

can stun or even kill the ants’ most com-mon enemies. A formicine attack on a human, however, is much less severe. The contact of formic acid with the

skin usually results only in blistering. In this section, you will learn the names

and formulas of some important acids such as formic acid.

Guide for Reading

Key Concepts • What are the three rules for

naming acids?• How are the formulas of acids

determined?• How are bases named?

Vocabularyacid

base

Reading StrategyComparing and ContrastingWhen you compare and contrast things, you examine how they are alike and how they are different. After you have read this section, list similarities and differences between acids and bases and how they are named.Naming Acids

Acids are a group of ionic compounds with unique properties. As you willsee in Chapter 19, acids can be defined in several ways. For now, it isenough to know that an acid is a compound that contains one or morehydrogen atoms and produces hydrogen ions (H�) when dissolved inwater. Acids have various uses, one of which is shown in Figure 9.14. Whennaming an acid, you can consider the acid to consist of an anion combinedwith as many hydrogen ions as are needed to make the molecule electri-cally neutral. Therefore, the chemical formulas of acids are in the generalform HnX where X is a monatomic or polyatomic anion and n is a subscriptindicating the number of hydrogen ions that are combined with the anion.

Figure 9.14 To create designs such as this on glass, the glass is first coated with wax and the design is drawn through the wax. When the glass is dipped into hydrofluoric acid (HF), the acid etches (eats away) the glass wherever the wax has been removed.

272 Chapter 9


Use VisualsTable 9.5 Remind students that all acids have hydrogen as one compo-nent. It is the anion combined with hydrogen that identifies the acid. Call attention to the first column in which the endings of anions are given. Ask stu-dents to name some anions with the endings -ide, -ite, and -ate. (They may mention chloride, bromide, nitrite, sulfite, carbonate, formate, among others) Call attention to the third column. Ask, When the anion ends in -ide, what does the acid name begin with? (hydro-) What does the acid name end with? (-ic) Have students name an acid containing the bromide anion. (hydro-bromic acid) Continue the questioning and naming through the other two rows of the table and encourage stu-dents to use the table until they are comfortable with naming acids.

Writing Formulas for AcidsDiscussThe table for naming acids is also the table for writing formulas for acids, but it must be used in reverse. Give stu-dents an acid name, for example, per-chloric acid. Ask, What does the -ic ending tell you? (There is no hydro- in the name, so -ic means the anion ends in -ate.) Ask, What is the name and for-mula for the anion? (perchlorate, ClO4

–) Ask, How many hydrogen atoms will combine with the per-chlorate ion? (one, HClO4)

Download a worksheet on Acids for students to complete and find addi-tional teacher support from NSTA SciLinks.

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Facts and Figures

272 Chapter 9

Anion

ending Example Acid name Example

-ide chloride, Cl� hydro-(stem)-ic acid hydrochloric acid

-ite sulfite, SO32� (stem)-ous acid sulfurous acid

-ate nitrate, NO3� (stem)-ic acid nitric acid

Name Formula

Hydrochloric acid HCl

Sulfuric acid H2SO4

Nitric acid HNO3

Acetic acid CH3COOH

Phosphoric acid H3PO4

Carbonic acid H2CO3

Table 9.5

Naming Common Acids

Three rules can help you name an acid with the general formula HnX. Readthe rules and the examples carefully. Notice that the naming systemdepends on the name of the anion. Each of the rules deals with an anionwith a different suffix: -ide, -ite, and -ic.

1. When the name of the anion (X) ends in -ide, the acid namebegins with the prefix hydro-. The stem of the anion has the suffix -icand is followed by the word acid. Therefore, HCl(aq) (X � chloride) isnamed hydrochloric acid. H2S(aq) (X � sulfide) is named hydrosulfuricacid.

2. When the anion name ends in -ite, the acid name is the stem ofthe anion with the suffix -ous, followed by the word acid. Thus H2SO3

(aq) (X � sulfite) is named sulfurous acid.

3. When the anion name ends in -ate, the acid name is the stem ofthe anion with the suffix -ic followed by the word acid. Thus HNO3(aq)(X � nitrate) is named nitric acid.

The three rules are summarized in Table 9.5. Use the table to help youwrite acid names until you become an expert.

Writing Formulas for AcidsIf you know the name of an acid, you can write its formula. Use therules for writing the names of acids in reverse to write the formulasfor acids. For example, what is the formula of hydrobromic acid? FollowingRule 1, hydrobromic acid (hydro- prefix and -ic suffix) must be a combina-tion of hydrogen ion (H�) and bromide ion (Br�). The formula of hydrobro-mic acid is HBr. How do you write the formula for phosphorous acid? UsingRule 2, hydrogen ion and phosphite ion (PO3

3�) must be the componentsof phosphorous acid. The formula of phosphorous acid is H3PO3. (Note: Donot confuse phosphorous with phosphorus, the element name.) Finally,what is the formula for formic acid, the defensive weapon of the ants youread about in Connecting to Your World? According to Rule 3, formic acid(-ic ending) must be a combination of hydrogen ion (H�) and formate ion(HCOO�). The formula for formic acid is HCOOH.

Many industrial processes, including steel and fertilizer manufactur-ing, use acids. In the laboratory, you will regularly use a few common acidssuch as those listed in Table 9.6. You should become familiar with theirnames and formulas.

Checkpoint When does an acid name begin with the prefix hydro-?

For: Links on AcidsVisit: www.SciLinks.orgWeb Code: cdn-1094

Table 9.6

Common Acids

A Toxic Environmental GasThe binary molecular compound carbon monoxide is a colorless, odorless, flammable gas that is highly toxic to humans. Upon inha-lation, carbon monoxide binds to the hemo-globin molecules in red blood cells, where it replaces oxygen. It binds to hemoglobin about 200 times more effectively than oxygen does, keeping the red blood cells from carry-ing oxygen to body tissues. Thus, even at low levels, carbon monoxide is a fast-acting

poison that may cause serious illness or death. At peak traffic times, the level of carbon mon-oxide around roadways may reach as high as 100 parts per million (ppm) of air. In the U.S., automobiles must have catalytic converters that change toxic carbon monoxide to carbon dioxide. Carbon monoxide is also present in cigarette smoke. It takes several hours to replace the carbon monoxide in a smoker’s blood after only one cigarette.


Names and Formulas for BasesRelateSodium hydroxide is a powerful base. It can turn wood into the mushy pulp from which paper is made. It breaks up and dissolves the greasy matter that clogs drains. Care must be taken to pro-tect the body when using strong bases.

ASSESSEvaluate UnderstandingDivide students into an even number of groups, and assign to each a num-ber of the polyatomic ions listed in Table 9.3. (Omit the hydroxide ion and ammonium ion.) Have the groups write the formulas for the acids corre-sponding to each assigned anion by adding the correct number of hydro-gen atoms. Then ask students to name the acids on a separate piece of paper. Have them exchange papers with another group and write the formulas for the acid names they receive.

ReteachUse the names of the six common acids in Table 9.6 as models. Ask stu-dents to name the anion and write the formulas using Table 9.5.[icon] Writing Activity

Annual production of sulfuric acid is over 150 million tons. The usual method for manufacturing is the con-tact process. Fertilizer, detergents, gasoline, explosives, and textiles are some of the products requiring sulfu-ric acid in their preparation.

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Section 9.4 Assessment26. See the rules for naming on the SE facing

page (page 272).27. The rules for writing the names of acids

are used in reverse to write the formulas for acids.

28. The name of the cation is followed by the name of the anion.

29. a. nitrous acid b. permanganic acidc. hydrocyanic acid d. hydrosulfuric acid

30. a. lithium hydroxide b. lead(II) hydroxide c. magnesium hydroxided. aluminum hydroxide

31. a. base b. acid c. base d. base32. a. H2CO3 b. H2SO3 c. Fe(OH)3

d. Sr(OH)233. acid, hydrogen; base, hydroxide ion

Section 9.4 Naming and Writing Formulas for Acids and Bases 273

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Names and Formulas for BasesAnother group of ionic compounds is the bases. A base is an ionic com-pound that produces hydroxide ions when dissolved in water. Basesare named in the same way as other ionic compounds—the name of the cat-ion is followed by the name of the anion. For example, sodium hydroxide(NaOH) is a base used in making paper, cleaners, and soap, as shown in Fig-ure 9.15. To write the formulas for bases, write the symbol for the metal cat-ion followed by the formula for the hydroxide ion. Balance the ioniccharges just as you do for any ionic compound. For example, aluminumhydroxide consists of the aluminum cation (Al3�) and the hydroxide anion(OH�). You need three hydroxide ions to balance the 3� charge of the alu-minum cation. Thus the formula for aluminum hydroxide is Al(OH)3. Insome bases, the cation is not a metal ion but a polyatomic ion. For exam-ple, in ammonium hydroxide (NH4OH), the cation is NH4

�.


26. Key Concept List the rules for naming acids.

27. Key Concept How are the formulas for acids determined?

28. Key Concept How are bases named?

29. Give the names of these acids. a. HNO2 b. HMnO4

c. HCN d. H2S

30. Write the names of these bases. a. LiOH b. Pb(OH)2

c. Mg(OH)2 d. Al(OH)3

31. Identify each compound as an acid or a base. a. Ba(OH)2 b. HClO4

c. Fe(OH)3 d. KOH

32. Write the formulas for these compounds. a. carbonic acid b. sulfurous acid c. iron(III) hydroxide d. strontium hydroxide

33. What element generally appears in the formula of an acid? What ion generally appears in the formula of a base?

Report Investigate the importance of sulfuric acid in the economy. Write a brief report that includes information on the manufacturing process, the annual output, and the variety of ways in which H2SO4 is used.


Figure 9.15 Sodium hydroxide is an important industrial and consumer product. Recycled paper and wood are digested with NaOH to make pulp in the first step in making paper.

Cleaners containing NaOH cut through heavy grease. An important use of sodium hydroxide is in making soap. Inferring Why is the woman in the second photo wearing gloves?

a

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Answers to...Figure 9.15 She is protecting her hands from corrosive NaOH.

Checkpoint

when the anion ends in -ide.

274 Chapter 9

9.5

FOCUSObjectives9.5.1 Define the laws of definite

proportions and multiple proportions.

9.5.2 Apply the rules for naming chemical compounds by using a flowchart.

9.5.3 Apply the rules for writing the formulas of chemical com-pounds by using a flowchart.

Guide for Reading

Build VocabularyList the Parts You Know A scientific law is a statement of a relationship that is invariable so far as it is known. Thus, the law of definite proportions and the law of multiple proportions are invari-able statements governing the forma-tion of compounds.

Reading StrategyThink Aloud As you familiarize students with the flowcharts in Figures 9.20 and 9.22, verbalize the routes to a name or formula by asking and answering the questions posed at each intersection.

INSTRUCT

Ask, What would be the ratio of can-dles to birthday cake at a seven-teenth birthday? (17:1) What would be the ratio of candles on two birth-day cakes, one at a seventeenth birthday and the other at a fourth birthday? (17:4)

The Laws of Definite and Multiple ProportionsUse VisualsFigure 9.16 Ask students to use the models to determine the formulas for the two compounds. (H2O and H2O2) Ask, In what other way can you tell that the two compounds are differ-ent? (One bleaches cloth, the other does not.)

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Section 9.5• Core Teaching Resources, Section 9.5 • Transparencies, T100–T103


Problem-Solving 9.34, Assessment 9.5

274 Chapter 9

Water

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Hydrogen

peroxide

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9.5 The Laws Governing Formulas and Names

A birthday cake for a four-year-old has four candles. The ratio of candles to birthday cake is 4:1. A sixteen-year-old’s birthday cake has 16 candles. The ratio of candles to cake is also a whole number ratio, 16:1. Is there a whole number ratio between the numbers of candles on one cake at two diffe-rent birthdays? For the sixteenth and fourth birthdays, the ratio is 16:4 or 4:1. In chemistry, similar relationships exist among the masses of elements as they combine in compounds.

Guide for Reading

Key Concepts • What are the two laws that

describe how compounds form?• How do you use a flowchart to

write the name of a chemical compound?

• What four guidelines should you follow to write the formula of a chemical compound?

Vocabularylaw of definite proportions

law of multiple proportions

Reading StrategyRelating Text and Visuals As you read, use Figure 9.20 and Figure 9.22 to help you become thoroughly familiar with writing the names and formulas for chem-ical compounds.

The Laws of Definite and Multiple ProportionsThe rules for naming and writing formulas for compounds are possibleonly because compounds form from the elements in predictable ways.

These ways are summed up in two laws: the law of definite propor-tions and the law of multiple proportions.

The Law of Definite Proportions A chemical formula tells you, bymeans of subscripts, the ratio of atoms of each element in the compound.Ratios of atoms can also be expressed as ratios of masses. Magnesium sul-fide (MgS) is composed of magnesium cations and sulfide anions. If youcould take 100.00 g of magnesium sulfide and break it down into its ele-ments, you will obtain 43.13 g of magnesium and 56.87 g of sulfur. The Mg:Sratio of these masses is 43.13/56.87 or 0.758:1. This mass ratio does notchange no matter how the magnesium sulfide is formed or the size of thesample. Magnesium sulfide illustrates the law of definite proportions,which states that in samples of any chemical compound, the masses of theelements are always in the same proportions. Because atoms combine insimple whole-number ratios, it follows that their proportions by mass mustalways be the same.

The Law of Multiple Proportions Figure 9.16 shows two compounds,water (H2O) and hydrogen peroxide (H2O2). Although these compounds areformed by the same two elements, they have different physical and chemi-cal properties. Each compound obeys the law of definite proportions. Inevery sample of hydrogen peroxide, 16.0 g of oxygen are present for each1.0 g of hydrogen. The mass ratio of oxygen to hydrogen is always 16:1. Inevery sample of water, the mass ratio of oxygen to hydrogen is always 8:1. Ifa sample of hydrogen peroxide has the same mass of hydrogen as a sampleof water, the ratio of the mass of oxygen in the two compounds is exactly 2:1.

16 g O 1in H2O2 sample that has 1 g H28 g O 1in H2O sample that has 1 g H2 � 16

8 � 21 � 2 : 1

Figure 9.16 Water and hydrogen peroxide contain the same two elements, but they have different properties.

Water does not bleach dyes. Hydrogen peroxide is a bleach.

ab


DiscussStudents may be able to understand the law of multiple proportions more easily by thinking in terms of atoms. One atom of carbon in CO2 has the same mass (12 amu) as one atom of carbon in CO. One atom of oxygen (16 amu) combines with 12 amu of carbon in CO. Two atoms of oxygen (32 amu) combine with 12 amu of carbon in CO2. The ratio of the masses of oxygen in the two compounds is 32:16 or 2:1.

Use VisualsFigure 9.17 Ask students, How many grams of B are in compound X? (2 g) How many grams of B are in com-pound Y? (2 g) Thus two compounds have the same masses of B. Ask, What is the ratio between the masses of A in these two compounds that have equal masses of B? (10 g:5 g or 2:1) Ask students to name the law illustrated by the figure and define it in their own words. (the law of multiple proportions; When two compounds are formed from the same two elements, and you take a certain mass of one of the elements, the masses of the other element in the two compounds that combined with that cer-tain mass are in a whole number ratio).

Math Handbook

[Math Handbook]

For a math refresher and practice, direct students to using a calculator, page R62.

Sample Problem 9.1

Answer34. 2:1

Practice Problems PlusIn the compound iron oxide, also known as rust, the mass ratio of iron to oxygen is 7:3. A 33-g sample of a com-pound composed of iron and oxygen contains 10 g of oxygen. Is the sample iron oxide? Explain your answer. (Yes, because the ratio in the compound is 2.3:1 and the ratio in iron oxide is 2.3:1)

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Proust’s Law In the early 1800s, many scientists were studying chemical reactions by carefully mea-suring the masses of reactants and products. The French scientist Joseph Proust (1766–1844) demonstrated that samples of copper carbonate always contain 5.3 parts by mass of copper to 4 parts of oxygen and 1 part of car-

bon. The principle embodied in this discovery became known as Proust’s Law and later as the law of definite proportions. Proust’s experiments inspired John Dalton to think in terms of atoms. With atoms in mind, Dalton designed experiments that soon led to the law of multiple proportions and Dalton’s atomic theory.

Facts and Figures

Section 9.5 The Laws Governing Formulas and Names 275

Math Handbook

YA B

10g 2g

Compound Y

12g� �

5g 2g 7g

Compound X

A B� � X

Practice Problems

Practice Problems

Using the results from studies of this kind, John Dalton stated the lawof multiple proportions: Whenever the same two elements form more thanone compound, the different masses of one element that combine with thesame mass of the other element are in the ratio of small whole numbers.Figure 9.17 illustrates the law of multiple proportions.

SAMPLE PROBLEM 9.1

Calculating Mass RatiosCarbon reacts with oxygen to form two compounds. Compound A con-tains 2.41 g of carbon for each 3.22 g of oxygen. Compound B contains6.71 g of carbon for each 17.9 g of oxygen. What is the lowest wholenumber mass ratio of carbon that combines with a given mass of oxygen?

Analyze List the knowns and the unknown.

Knowns• Compound A � 2.41 g C and 3.22 g O• Compound B � 6.71 g C and 17.9 g OUnknown• Lowest whole number ratio of carbon per gram of oxygen in the two

compounds � ?Apply the law of multiple proportions to the two compounds. For eachcompound, find the grams of carbon that combine with 1.00 g ofoxygen by dividing the mass of carbon by the mass of oxygen. Thenfind the ratio of the masses of carbon in the two compounds bydividing the larger value by the smaller. Confirm that the ratio is thelowest whole number ratio.

Calculate Solve for the unknown.

•

•

Compare the masses of carbon per gram of oxygen in the compounds.

The mass ratio of carbon per gram of oxygen in the two compounds is 2:1.

Evaluate Does the result make sense?

The ratio is a low whole number ratio, as expected. For a given mass ofoxygen, compound A contains twice the mass of carbon as compound B.

Compound A 2.41 g C3.22 g O �

0.748 g C1.00 g O

Compound B 6.71 g C17.9 g O �

0.375 g C1.00 g O

0.748 g C 1in compound A20.375 g C 1in compound B2 � 1.99

1 � roughly 21 � 2 : 1

34. Lead forms two compounds with oxygen. One contains 2.98 g of lead and 0.461 g of oxygen. The other contains 9.89 g of lead and 0.763 g of

oxygen. For a given mass of oxygen, what is the lowest whole number mass ratio of lead in the two compounds?

Figure 9.17 The diagram illustrates the law of multiple proportions. Two compounds, X and Y, contain equal masses of element B. The ratio of the masses of A in these compounds is 5:10 or 1:2 (a small whole number ratio). Applying Concepts Would the ratio be different if samples of X and Y contained 3 g of B?

For help with using a calculator go to page R62.

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Answers to...Figure 9.17 No, as long as the two samples have the same mass of B.

276 Chapter 9


Practicing Skills: Naming Chemical CompoundsUse VisualsFigure 9.18 Have students read the first paragraph on this page and exam-ine the photograph. Discuss the impor-tance of naming conventions for compounds. Explain that chemists need to be able to understand papers written by colleagues and to repro-duce experimental results. Focus on the problems that could occur if com-mon names in multiple languages were the norm. Ask, Why would knowing the correct name for a chemical be important to a poison-control center worker? (The worker needs to know the specific chemical ingested before offering a solution. Administering an antidote for the wrong chemical could cause further harm.)

RelateAsk students to think of other situa-tions where specific names are impor-tant for accurate or fast results. (When you are ordering items by telephone or on the internet) Ask, Why do many bureaucratic agencies use social security or driver’s license numbers instead of people’s names? (Many people could have the same name.)

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Special Needs Students who have difficulty with mathemat-ics may need extra help with the laws of defi-nite proportions and the law of multiple proportions. Assign such students to work

with students with strong math skills. Encour-age students with strong math skills to develop ways of sharing their problem-solv-ing techniques with others.

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276 Chapter 9

Figure 9.18 If someone ingests a poison, the poison control center can provide information about what immediate action to take. Inferring What informa-tion about the poison would be most helpful to the center?

Figure 9.19 A variety of compounds create a colorful display in the clay cliffs at Gay Head, Massachusetts on the island of Martha’s Vineyard. Each colored compound can be named by the methods you are learning if you know the compound’s formula.

Practicing Skills: Naming Chemical CompoundsIn the average home, you can probably find hundreds of chemicals, includ-ing cleaning products, drugs, and pesticides. Figure 9.18 shows a typicalwarning label on a product that tells about its possible dangers. Most peo-ple would not know what to do if some of these chemicals accidentallymixed together and began to react or if a small child ingested one. A phonecall to a poison control center can provide lifesaving information to victimsof such poisonings. But a poison control center can be much more effectiveif the caller can supply some information about the name or formula of thesubstance.

In this chapter, you learned two basic skills that could help you to dealwith an emergency involving chemicals: writing chemical formulas andnaming chemical compounds. If this is the first time you have tried to mas-ter these skills, you may feel a little overwhelmed. For example, you mayfind it difficult to know when you should or should not use prefixes andRoman numerals in a name. Or you may have trouble determining if acompound’s name should end in -ate, -ide, or -ite. The flowchart in Figure9.20 provides you with a sequence of questions for naming a compoundwhen you know its formula. Follow the arrows and answer the ques-tions on the flowchart to write the correct name for a compound. Thesequence of questions can help you name chemicals you may have in yourhome as well as the colorful compounds that create the picturesque land-scape of Gay Head, Massachusetts shown in Figure 9.19.

The flowchart shows the routes to the names of several compounds:HNO3, N2O3, BaS, Li2CO3, CuSO4, and FeCl2. Apply the general formula QxRy

to each compound. Q and R can be atoms, monatomic ions, or polyatomicions. For example, to name HNO3, let H � Q and NO3 � R. Follow the firstarrow down to the question Q � H? The answer is yes, so the arrow to theright tells you that the compound is an acid. You can then follow the rulesfor naming acids. HNO3 is nitric acid.

To name N2O3, let Q � N and R � O. The answer to the question Q � H?is no, so follow the arrow down. Does the compound have more than twoelements? The answer is no, so follow the arrow to the left. The compoundis binary and its name ends in -ide. Is Q a metal? The answer is no, so youmust use prefixes in the name, which is dinitrogen trioxide.


Use VisualsFigure 9.20 Tell students that the flowchart is like a road map. At every intersection you need to make a deci-sion and when you make the right decisions you are led to your destina-tion (the correct name for the com-pound). Lead them through a few examples asking them to respond to the questions at each intersection. Then have volunteers from the class take the lead to continue the exercise.

Use VisualsFigure 9.21 Students may ask about the two forms of copper sulfate (white and blue). Tell them that the blue form is called a hydrate because it has water molecules incorporated into its crystal structure. In the hydrate, each formula unit of CuSO4 is accompanied by five molecules of water. Ask, Would equal masses of the white and the blue compounds contain the same num-ber of formula units of copper sul-fate? (No, some of the mass of the hydrate is water.)

RelateWhile students are involved in devel-oping their skills in writing formulas for ionic and molecular compounds, you may have the opportunity to comment on the characteristics of representative ionic and molecular compounds found in Figure 9.20. For example, call atten-tion to the high melting points of ionic compounds. Iron(II) chloride melts at 677°C; lithium carbonate at 723°C. In addition, a large amount of energy (heat of fusion) is required to melt these ionic compounds. By contrast, the molecular compound dinitrogen trioxide melts at –101°C and methane at –182°C.

Make the point that ionic and molecu-lar compounds do not differ just in the way that they are named but funda-mentally in the bonding that holds the atoms together in the compound.

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Answers to...Figure 9.18 the formula, the name, and possibly the concentration

Checkpoint

Q is Mg2+; R is SO4

2–.

Gifted and TalentedChallenge advanced students to use the flowchart as a model for writing a computer program for naming chemical compounds.

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Compound is binary; name ends in -ide.

Compound is an acid. (HNO3, nitric acid)

Compound is binary molecular; use

prefixes in the name. (N2O3, dinitrogen trioxide)

Name the ions. (Li2CO3, lithium

carbonate)

Name the ions.(BaS, barium sulfide)

Name the ions; use aRoman numeral with the cation.

(FeCl2, iron(II) chloride)

Compound contains a polyatomic ion; name generally ends in -ite or -ate.

Name the ions; use a Roman numeral

with the cation. (CuSO4, copper(II) sulfate)

yes

yes

yesyes

QxRy

no

no

no

no

no

yes

Q � H?

> 2 Elements?

Q � Group A?Q � Metal?

Q � Group A?

Another example shown on the flowchart is CuSO4. In this case, Q � Cuand R � SO4. Q does not equal H. The compound does have more than twoelements, so it contains a polyatomic ion. Thus you should expect that thename will end in -ite or -ate. The answer to the next question, Q � Group A?is no, so you must name the ions and use a Roman numeral to identify thecharge of the transition metal. The name is copper(II) sulfate. A sample ofcopper(II) sulfate is shown in Figure 9.21. Practice with the other com-pounds listed above, and then use the flowchart when doing namingexercises. Soon you won’t need it anymore.

Checkpoint Identify Q and R in the compound MgSO4.

Figure 9.20 This flowchart will help you name chemical compounds. Begin with the letters Q and R in the general formula QxRy. Q and R can be atoms, monatomic ions, or polyatomic ions.

Figure 9.21 Dry copper sulfate is a white solid, as shown on the right. When water is added, the white solid absorbs water into its crystal structure and turns blue.


278 Chapter 9


Practicing Skills: Writing Chemical FormulasDiscussHave students summarize the rules for writing formulas and naming com-pounds. Point out that naming com-pounds and writing formulas becomes easier with practice because chemical names and formulas are systematized. Ask students to consider how difficult the task would be if the names were assigned randomly. Because chemists adhere to an established system of naming, it is possible to quickly locate information on physical constants such as melting point, boiling point, and density in chemical handbooks such Lange’s Handbook of Chemistry, The Merck Index, and the CRC Handbook of Chemistry and Physics. The Merck Index is particularly helpful to organic chem-ists interested in the synthesis and identification of a particular com-pound. Encourage students to look for these books in their local public library.

ASSESSEvaluate UnderstandingGive students formulas for compounds and have them use Figure 9.20 to determine their names. Then give them names for different compounds and have them use Figure 9.22 to write their formulas.

ReteachReview the four guidelines for writing chemical formulas by asking students in turn what it means when each of the following is included in the name of a compound: an -ide ending, an -ite or -ate ending, a prefix, or a Roman numeral. Then give them the following names of compounds containing one of these components: hydrogen cyanide, potas-sium chromate, sulfur tetrafluoride, cop-per(I) chloride. Ask them to use Figure 9.22 to determine their formulas.

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Other Molecular CompoundsThe binary molecular compounds constitute only a small fraction of molecular compounds. An enormous number of compounds contain-ing principally carbon, hydrogen, oxygen, nitrogen, and sulfur are classified as organic

chemicals. A different, more complex but pre-cise system of naming makes it possible for large and complex molecules to be precisely identified.

278 Chapter 9

Practicing Skills: Writing Chemical FormulasIn writing a chemical formula from a chemical name, it is helpful toremember the following guidelines.

1. An -ide ending generally indicates a binary compound.

2. An -ite or -ate ending means a polyatomic ion that includes oxy-gen is in the formula.

3. Prefixes in a name generally indicate that the compound ismolecular.

4. A Roman numeral after the name of a cation shows the ioniccharge of the cation.

These guidelines and the questions in the flowchart in Figure 9.22 willhelp you write the formula for a compound when you know its name. Forexample, use the flowchart to write the formula for sodium chromate. Thename does not contain prefixes, so it is ionic. The ions are sodium ion andchromate ion. Follow the arrows to the right and left. Sodium is a Group Aelement, so use the periodic table or Table 9.1 to obtain its ionic charge(1�). Chromate ion is a polyatomic ion, so use Table 9.3 to obtain itscharge (2�). Balance the charges to obtain the formula Na2CrO4. Practiceformula writing using the flowchart until you don’t need it anymore.

no

Use Table 9.1for charges.

Use Table 9.3for charges.

Uses prefixes to write formula.

Give charges for cations.

Use crisscross method. Add parentheses for any multiple

polyatomic ions.

Molecular

compound

Group A

elements

Roman

numerals

Name of Compound

yes

Polyatomic

ions

Balance

charges

Identify symbols.

Contains

prefixes?

Ionic compound

Figure 9.22 This flowchart will help you write a chemical formula when given a chemical name. Interpreting Illustrations What are the two types of chemical compounds whose formulas you can write using this flowchart?

Facts and Figures



Quick LABQuick LAB

Making Ionic CompoundsPurposeTo mix solutions containing cations and anions to make ionic compounds.

Materials

• 9 small test tubes

• test tube rack

• paper, pencil, ruler

• 6 solutions in plastic dropper bottles containing the following ions:Solution A (Fe3� ion)Solution B (Ag� ion)Solution C (Pb2� ion)

Solution X (CO32� ion)

Solution Y (OH� ion)Solution Z (PO4

3� ion)

Procedure

1. Label three test tubes A, three test tubes B, and three test tubes C.

2. Add 10 drops (approximately 0.5 mL) of solutions A, B, and C to appropriately labeled test tubes.

3. Add 10 drops of solution X to one test tube of A, 10 drops to one test tube of B, and 10 drops to one test tube of C. Observe each for the formation of a solid.

4. Make a 3-by-3 inch grid in which to record your obser-vations. Label the rows A, B, and C. Label the columns X, Y, and Z. Describe any solid material you observe.

5. Repeat Step 3, adding 10 drops of solution Y to test tubes A, B, and C. Record your observations.

6. Repeat Step 3, adding 10 drops of solution Z to test tubes A, B, and C. Record your observations.

Analyze and Conclude

1. Some ionic compounds are insoluble (do not dissolve in water). Explain what you observed.

2. Write the formula for each ionic compound formed.

3. Name each ionic compound formed.

4. Will mixing any cation with any anion always lead to the formation of an insoluble ionic compound? Explain.


35. Key Concept What two laws describe how chemical compounds form?

36. Key Concept How should you use a flowchart to name a chemical compound?

37. Key Concept What are four guidelines for writing the formulas of chemical compounds?

38. Two compounds containing copper and oxygen were found to contain the following masses:

Compound A: 32.10 g Cu and 17.90 g ClCompound B: 23.64 g Cu and 26.37 g Cl

Are the compounds the same? If not, what is the lowest whole number mass ratio of copper that combines with a given mass of chlorine?

39. Name these compounds. a. CaCO3 b. PbCrO4 c. SnCr2O7

40. Write formulas for these compounds. a. tin(II) hydroxide b. barium fluoride

41. Identify the incorrect names or formulas. a. calcium(II) oxide b. aluminum oxide c. Na2C2O4 d. Mg(NH4)2

Ionic Bonds Review ionic bonds in Section 7.2 and show by means of electron dot structures why an ionic compound always has a charge of zero. Use magnesium bromide as an example.

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Quick LABQuick LAB

Making Ionic CompoundsObjective Students form precipitates and write their formulas and names.

Skills Focus Observing, applying the rules for naming compounds and writ-ing their formulas

Prep Time 30 minutes

Advance Prep Prepare 0.1M FeCl3, 0.05M AgNO3, 0.2M Pb(NO3)2, 1.0M Na2CO3, 0.5M NaOH, 0.1M Na3(PO4)2.Class Time 20 minutes

Expected Outcome A precipitate forms in every tube.

Analyze and Conclude 1. An insoluble compound formed in

every tube.2. Fe2(CO3)3, Fe(OH)3, FePO4, Ag2CO3,

AgOH, Ag3PO4, PbCO3, Pb(OH)2, Pb3(PO4)2

3. iron(III) carbonate, iron(III) hydroxide, iron(III) phosphate, silver carbonate, sil-ver hydroxide, silver phosphate, lead(II) carbonate, lead(II) hydroxide, lead(II) phosphate.

4. No, sodium chloride, for example, is soluble.

For Enrichment Students can support their answer to question 4 by testing solutions A, B, and C with 0.1M Na2SO4. (A precipitate of PbSO4 will form, but Fe3+ and Ag+ will not form precipitates.)

Connecting Concepts

Magnesium loses its two valence electrons. Two bromine atoms each gain one electron.

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Answers to...Figure 9.22 ionic compounds and binary molecular compounds

Section 9.5 Assessment35. law of definite proportions and law of

multiple proportions36. Follow the arrows and answer the ques-

tions on the flowchart. 37. See the four guidelines on the facing SE

page (page 278).38. no; 2:139. a. calcium carbonate b. lead(II)

chromate c. tin(II) dichromate

40. a. Sn(OH)2 b. BaF241. a. incorrect; a Roman numeral is not used

with a Group A metal, calcium oxideb. correct c. correct d. incorrect; ammonium ion, a polyatomic cation, will not form a compound with a monatomic cation.

9.1 Naming Ions 9 - Ms. Lara La Cueva HS Science -...

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