5.1 Organizing the Elements

Key ConceptsHow did Mendeleevorganize the elementsin his periodic table?

What evidence helpedverify the usefulness ofMendeleev’s table?

Vocabulary◆ periodic table

In a video store, the latest movies are usually placed on the shelves inalphabetical order. Older movies are grouped into categories such asAction or Comedy. The manager has to choose a set of categories andthen place each movie in the most appropriate location.

Scientists faced a similar challenge when they looked for a logicalway to organize the elements. They had to decide what categories touse and where to place each element. An organized table of the ele-ments is one of the most useful tools in chemistry. The placement ofelements on the table reveals the link between the atomic structure ofelements and their properties.

The Search for OrderUntil 1750, scientists had identified only 17 elements. These weremainly metals, such as copper and iron. The rate of discoveryincreased rapidly as chemists began to investigate materials in asystematic way. As the number of known elements grew, so didthe need to organize them into groups based on their properties.

In 1789, French chemist Antoine Lavoisier (la VWAH zee ay)grouped the known elements into categories he called metals,nonmetals, gases, and earths. For the next 80 years, scientistslooked for different ways to classify the elements. But none oftheir systems provided an organizing principle that worked forall the known elements. A Russian chemist and teacher, DmitriMendeleev (Duh MEE tree Men duh LAY uff), would discover sucha principle.

Mendeleev’s proposal

Mendeleev’s prediction

Evidence supportingMendeleev’s table

Topic Main Idea

a. ?

b. ?

c. ?

Reading StrategyIdentifying Main IdeasCopy the table. As youread, write the main ideafor each topic.

Figure 1 Older movies in videostores are placed into categoriessuch as Drama or Comedy.

126 Chapter 5

126 Chapter 5

FOCUS

Objectives5.1.1 Describe how Mendeleev

arranged the elements inhis table.

5.1.2 Explain how the predictionsMendeleev made and thediscovery of new elementsdemonstrated the usefulnessof his periodic table.

Build VocabularyWord Forms Use the word periodical tohelp students understand the meaningof periodic. Explain that a periodical ispublished at regular intervals (weekly,monthly, or quarterly).

Reading Strategya. Mendeleev arranged the elements inorder of increasing mass so that ele-ments with similar properties were inthe same column. b. Mendeleev usedthe properties of existing elementsto predict properties of undiscoveredelements. c. The close match betweenMendeleev’s predictions and the actualproperties of new elements showed howuseful his periodic table could be.

INSTRUCT

The Search for OrderBuild Reading LiteracySequence Refer to page 290D inChapter 10, which provides theguidelines for a sequence.

Have students create a flowchartshowing the sequence of eventsdescribed in the last two paragraphson page 126. Ask, Based on yoursequence, what happened afterLavoisier grouped the knownelements into four categories?(Scientists looked for different waysto classify the elements.)Verbal, Portfolio

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Reading Focus

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Section 5.1

Print• Reading and Study Workbook With

Math Support, Section 5.1• Transparencies, Chapter Pretest and

Section 5.1

Technology• Interactive Textbook, Section 5.1• Presentation Pro CD-ROM, Chapter Pretest

and Section 5.1• Go Online, NSTA SciLinks, Periodic table

Section Resources

Group I Group II Group III Group IV Group V Group VI Group VII Group VIII

H = 1

Be = 9.4 B = 11 C = 12 N = 14 O = 16 F = 19Li = 7

Mg = 24Na = 23 Al = 27.3 Si = 28 P = 31 S = 32 Cl = 35.5Ca = 40K = 39 — = 44 Ti = 48 V = 51 Cr = 52 Mn = 55

Fe = 56, Co = 59,Ni = 59, Cu = 63.

Ru = 104, Rh = 104,Pd = 106, Ag = 108.

Os = 195, Ir = 197,Pt = 198, Au = 199.

Zn = 65(Cu = 63) — = 68 — = 72 As = 75 Se = 78 Br = 80

Cd = 112(Ag = 108) In = 113 Sn = 118 Sb = 122 Te = 125 I = 127

Ba = 137Cs = 133 Di = 138 Ce = 140 —— — — — — —

—

— — — —

(—)—

——

——Er = 178

— — —La = 180 Ta = 182 W = 184

Hg = 200(Au = 199) Tl = 204 Pb = 207Th = 231

Bi = 208U = 240

Sr = 87Rb = 85 Yt = 88 Zr = 90 Nb = 94 Mo = 96 — = 100

The Periodic Table 127

Mendeleev’s Periodic TableIn the 1860s, Mendeleev was working on a text-book to use with his chemistry students. Becausehe needed to describe 63 elements, Mendeleev waslooking for the best way to organize the informa-tion. He found a way to approach the problemwhile playing his favorite card game, a version ofsolitaire. In this game, the player sorts a deck ofcards by suit and value. To finish the game, theplayer must end up with four columns, as shownin Figure 2. Each column contains cards of a singlesuit arranged in order by value.

Mendeleev’s Proposal Mendeleev’s strategy for organizing theelements was modeled on the card game. Mendeleev made a “deck ofcards” of the elements. On each card, he listed an element’s name,mass, and properties. He paid special attention to how each elementbehaved in reactions with oxygen and hydrogen. When Mendeleevlined up the cards in order of increasing mass, a pattern emerged. Thekey was to break the elements into rows, as shown in Figure 3.

Mendeleev arranged the elements into rows in order ofincreasing mass so that elements with similar properties were in thesame column. The final arrangement was similar to a winning arrange-ment in solitaire, except that the columns were organized by propertiesinstead of suits. Within a column, the masses increased from top tobottom. Mendeleev’s chart was a periodic table. A periodic table is anarrangement of elements in columns, based on a set of properties thatrepeat from row to row.

Figure 2 A deck of cards can bedivided into four suits—diamonds,spades, hearts, and clubs. In oneversion of solitaire, a player mustproduce an arrangement in whicheach suit is ordered from ace toking. This arrangement is a modelfor Mendeleev’s periodic table.

Figure 3 This is a copy of a tablethat Mendeleev published in1872. He placed the elements ingroups based on the compoundsthey formed with oxygen orhydrogen. Using Tables Howmany elements did Mendeleevplace in Group II?

Integrate Social StudiesLavoisier based his classification ofelements on a vast amount of observeddata. He used Boyle’s definition of anelement as a substance that chemistscannot separate into simpler substances.Most of the elements Lavoisier identifiedwere elements, but his list did includeheat, light, and five oxides that scientistshad not been able to decompose. Have students consider what it means to “discover” an element by havingthem research and compare discoverydates for elements with the dates thoseelements were first isolated. (Forexample, beryllium was discovered in 1797, but it was not isolated until 1828.)Verbal, Interpersonal

Mendeleev’s Periodic TableUse VisualsFigure 3 Ask, How is the tableorganized? (Elements are arranged inorder of increasing mass.) What do thelong dashes represent? (They representundiscovered elements.) Why are masseslisted with some of the dashes, butnot with all of them? (Mendeleev wasable to predict properties for someunknown elements based on theproperties of neighboring elements.)Visual, Logical

FYIIn Section 5.1, the term mass isused as a shorthand for atomic massbecause atomic mass is not defined until Section 5.2. Mendeleev was comparing the relative atomic masses of the elements. Mendeleev attendedthe first international chemistry congressin Karlsruhe in 1860. During that meet-ing, chemists agreed on a standardmethod for calculating atomic masses.

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The Periodic Table 127

Customize for Inclusion Students

Learning DisabledTo reinforce the meaning of the word periodic,ask students to think of periodic activities intheir own lives. Make a class list of theseactivities. Organize the list by time interval:daily, weekly, monthly, yearly, and so on. Forexample, students may have a weekly music

lesson or a dance recital every six months.They celebrate a birthday once a year. You mayalso want to encourage students to think ofperiodic events that occur less frequently thanonce a year, for example, the Olympics orpresidential elections.

Answer to . . .

Figure 3 Mendeleev placed eightelements in Group II.

128 Chapter 5

Mendeleev’s Prediction Mendeleev could not make a com-plete table of the elements because many elements had not yet beendiscovered. He had to leave spaces in his table for those elements. Forexample, Mendeleev placed bromine (Br) in Group VII becausebromine and chlorine (Cl) have similar properties. This placement leftfour spaces in row 4 between zinc (Zn) and bromine. Mendeleev hadonly two elements, arsenic and selenium, to fill those spaces, based ontheir masses. He placed arsenic and selenium in the columns wherethey fit best and left gaps in the columns labeled Groups III and IV.

Mendeleev was not the first to arrange elements in a periodic table.He was not even the first to leave spaces in a periodic table for missingelements. But he was able to offer the best explanation for how the prop-erties of an element were related to its location in his table.

An excellent test for the correctness of a scientific model, such asMendeleev’s table, is whether the model can be used to make accuratepredictions. Mendeleev was confident that the gaps in his table would befilled by new elements. He used the properties of elements located nearthe blank spaces in his table to predict properties for undiscovered ele-ments. Some scientists didn’t accept these predictions. Others used thepredictions to help in their search for undiscovered elements.

Why did Mendeleev place bromine in Group VII ofhis periodic table?

Making a Model of a Periodic Table

Materialsplastic bag containing color chips

Procedure1. Remove the color chips from the bag and

place them on a flat surface, color side up.

2. Identify a property that you can use to dividethe chips into groups. Then, identify a secondproperty that you can use to order the chipsfrom top to bottom within a group.

3. Use the properties you chose to arrange thechips into a table with rows and columns.Your teacher deliberately left out a chip fromeach bag. Decide where to leave a gap in yourtable for the missing chip.

Analyze and Conclude1. Classifying What property did you use to

divide the color chips into groups? Whatproperty did you use to arrange the chipswithin a group from top to bottom?

2. Making Generalizations What patternrepeats across each row of your table?

3. Predicting Based on its location on yourtable, describe the missing chip.

4. Comparing and Contrasting Comparethe process you used to construct your tableto the process Mendeleev used to make histable. Describe similarities and differences.

For: Links to periodic table

Visit: www.SciLinks.org

Web Code: ccn-1051

128 Chapter 5

Making a Modelof a Periodic Table

ObjectiveAfter completing this activity, studentswill be able to • organize items in an array based on

properties.• predict where an additional item

would fit in an incomplete array.

Skills Focus Classifying, Inferring,Observing

Prep Time 20 minutes

Materials resealable plastic sandwichbag, different colored paint chip strips

Advance Prep For each group, collect4 strips with distinctly different colors.Make sure the color chips are about thesame size after you cut off any printingnumber codes used to identify theshades. Remove one chip from each set.Place each set of chips in a bag.

Class Time 20 minutes

Expected Outcome Students arelikely to organize chips of the same colorin columns based on the intensity of theshades so that the pattern of colorsrepeats across the rows.

Analyze and Conclude1. Students are likely to choose colorand shade. 2. Color or intensity of shade repeatsacross each row.3. Students should describe the color and approximate shade of themissing chip.4. Both processes involve selectingproperties to organize related items in a repeating pattern and predicting theproperties of missing items. However,unlike the periodic table, the order ofthe columns in the color array can bearbitrary. Visual, Logical

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Section 5.1 (continued)

Recognizing a Pattern Actions Mendeleevtook while developing his table show that herealized the table represented a fundamentalpattern in nature. First, he left gaps in the table for undiscovered elements. Second, hesometimes ignored accepted knowledge. Forexample, Berzelius had reported a formula of

Be2O3 for beryllium oxide, which (if true) wouldmean that beryllium belonged in the thirdcolumn. But, Mendeleev used beryllium to fill aspace in the second column. Third, Mendeleevdid not place all elements in order by atomicmass. He placed tellurium before iodine eventhough tellurium has a larger atomic mass.

Facts and Figures

Download a worksheet on theperiodic table for students tocomplete, and find additionalteacher support from NSTASciLinks.

Section 5.1 Assessment

Reviewing Concepts1. Describe how Mendeleev organized the

elements into rows and columns in hisperiodic table.

2. How did the discovery of new elementssuch as gallium demonstrate the usefulness ofMendeleev’s table?

3. Scientists before Mendeleev had proposedways to organize the elements. Why wereMendeleev’s efforts more successful?

4. What characteristic of solitaire did Mendeleevuse as a model for his periodic table?

5. Why did Mendeleev leave spaces in his table?

6. In general, how can a scientist test thecorrectness of a scientific model?

Critical Thinking7. Inferring Explain why it would not have

been possible for a scientist in 1750 todevelop a table like Mendeleev’s.

8. Predicting How was Mendeleev able topredict the properties of elements that hadnot yet been discovered?

Evidence Supporting Mendeleev’s TableMendeleev named missing elements after elements in thesame group. He gave the name eka-aluminum to the ele-ment that belonged one space below aluminum on thetable. (Eka is a Sanskrit word meaning “one.”) Mendeleevpredicted that eka-aluminum would be a soft metal witha low melting point and a density of 5.9 g/cm3.

In 1875, a French chemist discovered a new element.He named the element gallium (Ga) in honor of France.(The Latin name for France is Gallia.) Gallium is a softmetal with a melting point of 29.7°C and a density of5.91 g/cm3. Figure 4 shows a sample of gallium and atraffic signal that uses gallium compounds.

The properties of gallium are remarkably similar tothe predicted properties of eka-aluminum. Scientistsconcluded that gallium and eka-aluminum are the sameelement. The close match between Mendeleev’spredictions and the actual properties of new elementsshowed how useful his periodic table could be. The dis-covery of scandium (Sc) in 1879 and the discovery ofgermanium (Ge) in 1886 provided more evidence. Withthe periodic table, chemists could do more than predictthe properties of new elements. They could explain thechemical behavior of different groups of elements.

The Periodic Table 129

Writing to Persuade Write a paragraphabout Mendeleev’s periodic table. Use theparagraph to convince a reader that the peri-odic table is extremely useful to scientists. (Hint:Use specific facts to support your argument.)

Figure 4 Gallium wasdiscovered in 1875. Heatfrom a person’s hand canmelt gallium. In some trafficsignals, there are tiny lightemitting diodes (LEDs) thatcontain a compound ofgallium. Comparing andContrasting How does themelting point of gallium(29.7ºC) compare to roomtemperature (about 25ºC)?

Students may think that advances inscience are always achieved by scientistsworking alone. They should realize thatmost advances are the result of manyscientists working on different aspects ofa problem. To help students overcomethis misconception, have them researchthe Nobel Laureates in Chemistry andnote how many times the prize wasshared. Students could also look at thelists of authors in scientific journals.Logical

FYIThe initial value reported for the densityof gallium was 4.7 g/cm3, but additionaltests showed it to be 5.9 g/cm3.

ASSESSEvaluateUnderstandingAssign each student to one of the fourpages in Section 5.1. Have studentswrite a review question related to thecontent of their assigned page. Invitestudents to take turns posing theirquestions to the class. Continue untileveryone has had a turn, or until thequestions become repetitive.

ReteachUse Figure 3 to review Mendeleev’sstrategy for arranging the elementsinto rows and columns to form aperiodic table.

The paragraph should include informa-tion on how Mendeleev organized histable, why he left gaps in the table, thepredictions he made based on the table,and how the discovery of galliumdemonstrated the usefulness of the table.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 5.1

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The Periodic Table 129

5. In order to place elements with similarproperties in the same column, Mendeleevneeded to leave spaces for undiscoveredelements.6. The scientist tests whether the model canbe used to make accurate predictions.7. With only 17 known elements to work with,the scientist would not have had enough data.8. Mendeleev based his predictions on theproperties of nearby elements and otherelements in the same column.

Section 5.1 Assessment

1. Mendeleev arranged the elements in rows inorder of increasing mass so that elements withsimilar properties were in the same column.2. The close match between Mendeleev’spredictions and the actual properties of newelements showed how useful his periodic tablecould be.3. Mendeleev provided an organizing principlethat worked for all of the known elements.4. In solitaire, cards are arranged intocategories called suits and ordered by value.

Answer to . . .

Figure 4 The melting point ofgallium is slightly higher than roomtemperature.

Mendeleev placedbromine in Group VII

because bromine and chlorine havesimilar properties.