5.1 organizing the elements -...

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 Strategy Identifying 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 in his table.

5.1.2 Explain how the predictionsMendeleev made and thediscovery of new elementsdemonstrated the usefulness of 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 elements to 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 paragraphs on page 126. Ask, Based on yoursequence, what happened afterLavoisier grouped the knownelements into four categories?(Scientists looked for different ways to 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

FYI In Section 5.1, the term mass is used 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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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.

0124_hsps09te_Ch05.qxp 4/18/07 11:01 AM Page 127

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 Compare the process you used to construct your tableto the process Mendeleev used to make histable. Describe similarities and differences.

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128 Chapter 5

Making a Model of 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.


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

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

ASSESSEvaluate UnderstandingAssign 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 elements into 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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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 can be 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.


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.


5.2 The Modern Periodic Table

Reading Strategy Previewing Copy the table below. Beforeyou read, write two questions about theperiodic table on pages 132 and 133. As youread, write answers to your questions.

Key ConceptsHow is the modernperiodic table organized?

What does the atomicmass of an elementdepend on?

What categories are usedto classify elements on theperiodic table?

How do properties varyacross a period in theperiodic table?

Vocabulary◆ period◆ group◆ periodic law◆ atomic mass unit

(amu)◆ metals◆ transition metals ◆ nonmetals◆ metalloids

Figure 5 shows a synthesizer keyboard with labels for the notes thatcorrespond to the white keys. If you strike the key labeled middle Cand then play the white keys in order from left to right, you will hearthe familiar do-re-mi-fa-sol-la-ti scale. The next white note is a C thatis an octave above middle C. An octave is the interval between any twonotes with the same name. (The prefix octa- means “eight.”) Becausethe scale repeats at regular eight-note intervals, the scale is an exampleof a periodic pattern.

The sounds of musical notes that are separated by an octave arerelated, but they are not identical. In a similar way, elements in thesame column of the periodic table are related because their propertiesrepeat at regular intervals. But elements in different rows are not iden-tical. You can use the modern periodic table of elements to classifyelements and to compare their properties.

Question

Questions About the Periodic Table

a. ?

c. ?

b. ?

d. ?

Answer

A B C D E F G A B C D E F G A B C D E F G

MiddleG

130 Chapter 5

Figure 5 On this synthesizerkeyboard, there is a repeatingpattern of notes. The eight-noteinterval between any two noteswith the same name is an octave.Observing How many octavesare visible on the keyboard?

130 Chapter 5

FOCUS

Objectives5.2.1 Describe the arrangement

of elements in the modernperiodic table.

5.2.2 Explain how the atomic massof an element is determinedand how atomic mass units are defined.

5.2.3 Identify general properties of metals, nonmetals, andmetalloids.

5.2.4 Describe how properties ofelements change across aperiod in the periodic table.

Build Vocabulary

Vocabulary Knowledge Rating Chart Have students construct a chart with fourcolumns labeled Term, Can Define or UseIt, Heard or Seen It, and Don’t Know.Have students copy the terms period,group, periodic law, atomic mass unit,metals, transition metals, nonmetals, andmetalloids into column 1 and rate theirterm knowledge by putting a check inone of the other columns. Ask how manystudents actually know each term. Havethem share their knowledge. Ask focusedquestions to help students predict textcontent based on the term, thus enablingthem to have a purpose for reading. Afterstudents have read the section, have themrate their knowledge again.

Reading Strategya. and b. Students might ask themeaning of the term atomic mass, whytwo series of elements are placed belowthe main body of the table, why thereare two numbering systems for thecolumns, or why Period 7 is incomplete.(Student answers will vary depending onquestions asked.)

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Reading Focus

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Section 5.2

Print• Laboratory Manual, Investigation 5A • Reading and Study Workbook With

Math Support, Section 5.2 and Math Skill: Calculating Average Atomic Mass

• Transparencies, Section 5.2

Technology• Probeware Lab Manual, Lab 2• Interactive Textbook, Section 5.2• Presentation Pro CD-ROM, Section 5.2• Go Online, NSTA SciLinks, Periodic law

Section Resources


The Periodic LawMendeleev developed his periodic table before the discovery of pro-tons. He did not know that all atoms of an element have the samenumber of protons. He did not know that atoms of two different ele-ments could not have the same number of protons. In the modernperiodic table, elements are arranged by increasing atomic number(number of protons). Figure 6 shows one way the known elementscan be arranged in order by increasing atomic number.

Periods Each row in the table of elements in Figure 6 is a period.Period 1 has 2 elements. Periods 2 and 3 have 8 elements. Periods 4and 5 have 18 elements. Period 6 has 32 elements. The number of ele-ments per period varies because the number of available orbitalsincreases from energy level to energy level.

To understand the structure of the table, think about what hap-pens as the atomic number increases. The first energy level has onlyone orbital. The one electron in a hydrogen atom and the two elec-trons in a helium atom can fit in this orbital. But one of the threeelectrons in a lithium atom must be in the second energy level. That iswhy lithium is the first element in Period 2. Sodium, the first elementin Period 3, has one electron in its third energy level. Potassium, thefirst element in Period 4, has one electron in its fourth energy level.This pattern applies to all the elements in the first column on the table.

Groups Each column on the periodic table is called a group. Theelements within a group have similar properties. Properties ofelements repeat in a predictable way when atomic numbers are usedto arrange elements into groups. The elements in a group have sim-ilar electron configurations. An element’s electron configurationdetermines its chemical properties. Therefore, members of a group inthe periodic table have similar chemical properties. This pattern ofrepeating properties is the periodic law.

Look at Figure 7 on pages 132 and 133. There are 18 groups in thisperiodic table. Some elements from Periods 6 and 7 have been placedbelow Period 7 so that the table is more compact.

For: Links on periodic law

Visit: www.SciLinks.org

Web Code: ccn-1052

Li

H

K

Rb

Be

MgNa

Ca

Sr

Ba

Ra

Cs

Fr Ac Th U Np PuPa Lr

Lu Hf Ta W Re Os

Rf Db Sg Bh Hs Mt

Y Zr Nb Mo Tc Ru Rh

Sc Ti V Cr Mn Fe Co

IrLa Ce Nd Pm SmPr Eu Gd Tb Dy Ho Er Tm Yb

Am Cm Bk Cf Es Fm Md No

Ni Cu Zn Ga Ge As Se Br Kr

Sb Te Xe

Tl Pb Bi Po At Rn

Sn

Al Si P S Cl Ar

B C N O F Ne

He

Pd Ag Cd

Pt

Ds Rg Uub UuqUuq

Au Hg

In I

1

2

3

4

5

6

7

Figure 6 This diagram shows oneway to display a periodic table ofthe elements. There are 7 rows, orperiods, in the table. There are32 columns, or groups, in the table. Comparing and ContrastingCompare the numbers of elementsin periods 1, 3, and 5.

INSTRUCT

The Periodic LawBuild Reading LiteracyPreview Refer to page 36D in Chapter 2, which provides the guide-lines for using a preview strategy.

Have students preview the section (pp. 130–138), focusing their attentionon headings, visuals, and boldfacedmaterial. Ask, Based on your preview,which figure in the section containsthe most information? (Figure 7 on pp. 132–133) Based on your preview,name three classes of elements.(Metals, nonmetals, and metalloids)Visual, Verbal

Build Science SkillsUsing Tables and Graphs Use thedata in Figure 7 to show the advantageof arranging elements by atomic numberinstead of atomic mass. Make a largegraph with atomic number on thehorizontal axis and atomic mass on thevertical axis for elements 1 through 20.Draw straight lines between the points.Ask, What does the graph show aboutthe general relationship betweenatomic number and atomic mass? (Asthe atomic number increases, so does theatomic mass.) Are there any points onthe graph that do not follow the pat-tern? (Yes, the atomic mass of element 18,argon, is greater than the atomic mass ofelement 19, potassium.) Point out thatarranging the elements strictly byincreasing atomic mass would result insome elements with unlike propertiesbeing grouped together. Visual, Logical

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Customize for English Language Learners

Simplify the PresentationTailor your teaching presentation of the sectioncontent to the less proficient English skills ofyour students. Do this by speaking directly andsimplifying the words and sentence structuresused to explain the material. For example, splita cause-and-effect sentence into two sentenceslabeled Cause and Effect. Use visual aids. For

example, use the keyboard in Figure 5 toexplain the interval of an octave. Use bodylanguage when appropriate to emphasizeimportant words. For example, use a horiz-ontal gesture when discussing periods androws. Use a vertical gesture when describinggroups and columns.

F G

Download a worksheet on theperiodic law for students tocomplete, and find additionalteacher support from NSTA SciLinks.

Answer to . . .

Figure 5 3 octaves

Figure 6 There are 2 elements inPeriod 1, 8 in Period 3, and 18 inPeriod 5.


PPLS


132 Chapter 5

Periodic Table of the ElementsFigure 7 In a modern periodictable of the elements, elementsare arranged in order ofincreasing atomic number.

132 Chapter 5

Use VisualsFigure 7 Begin by having studentscompare the layouts in Figures 6 and 7.Ask, What is the major difference inthe layouts? (Some elements fromPeriods 6 and 7 have been placed belowthe table.) How are the layouts alike?(Elements are arranged in order by atomicnumber. Elements with similar propertiesare in the same group and propertiesrepeat in a predictable way from period toperiod.) Return to Figure 7 when atomicmasses are discussed on p. 134, andwhen ways to classify elements on theperiodic table are introduced on p. 135.(The table shows two classificationsystems: the 1–18 numbering systemapproved by the International Union of Pure and Applied Chemistry (IUPAC),and a system in which two sets ofgroups numbered 1–8 are distinguishedby A and B labels. Unless students ask,you may want to let students wonderabout the A and B classification system,which will be addressed in the introduc-tion to Section 5.3.)Visual, Logical

FYI Placement of the lanthanides andactinides below the main body of thetable also serves to emphasize thesimilarities among these elementsrelated to their electron configurations.

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DDssDarmstadtium

RRggRoentgenium


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Visit: PHSchool.com

Web Code: ccp-1052

Integrate Language ArtsElements 110, 111, 112, and 114 havenot been named yet. Scientists can pro-pose names for new elements, but theInternational Union of Pure and AppliedChemistry has final approval. Until newelements receive official names, chemistsrefer to them by their Latin-based atomicnumbers. For example, element 114 iscalled ununquadium, Latin for one-one-four. Increase students’ familiarity withthe periodic table by having themidentify some of the strategies used toname elements (scientists, geographiclocations, mythological characters).Verbal, Portfolio

Build Science SkillsComparing and Contrasting For thisactivity, use a periodic table displayed inthe classroom, or make copies of aperiodic table that is a few years old todistribute to students. To illustrate thedynamic nature of science, have studentscompare Figure 7 to the older periodictable. Ask, What differences do younotice between the two periodictables? (Depending on when the oldertable was printed, the number of elementsmay vary and some elements in Period 7may not have assigned names. Somevalues for atomic mass are likely to vary. A periodic table may include electronconfigurations for each element.) Make alist of responses on the board. Then ask,How will the periodic table change inthe future? (Unnamed elements will beassigned official names and more elementsmay be discovered.)Visual, Verbal, Group

FYI Although plutonium is classified as asynthetic element, traces of plutoniumisotopes Pu-238 and Pu-239 appear atlow concentrations (about one part per1011) in pitchblende, a uranium ore. In1971, Darlene Hoffman, a scientist at LosAlamos National Laboratory, discoveredtraces of Pu-244 in Precambrian rocks.Because this isotope has a half-life ofabout 82 million years, it probablyexisted when Earth formed.

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IPLS

For: Activity on the periodic tableVisit: PHSchool.comWeb Code: ccp-1052

Students can learn more about theelements by interacting with aclickable periodic table online.


134 Chapter 5

Atomic MassThere are four pieces of information for each element in Figure 7: thename of the element, its symbol, its atomic number and its atomicmass. Atomic mass is a value that depends on the distributionof an element’s isotopes in nature and the masses of those isotopes.You will use atomic masses when you study chemical reactions inChapter 7.

Atomic Mass Units The mass of an atom in grams is extremelysmall and not very useful because the samples of matter that scientistswork with contain trillions of atoms. In order to have a convenientway to compare the masses of atoms, scientists chose one isotope toserve as a standard. Recall that each isotope of an element has a dif-ferent number of neutrons in the nuclei of its atoms. So the atoms oftwo isotopes have different masses.

Scientists assigned 12 atomic mass units to the carbon-12 atom,which has 6 protons and 6 neutrons. An atomic mass unit (amu) isdefined as one twelfth the mass of a carbon-12 atom.

Isotopes of Chlorine In nature, most elements exist as a mixtureof two or more isotopes. Figure 8 shows that the element chlorine has thesymbol Cl, atomic number 17, and an atomic mass of 35.453 atomicmass units. (The unit for atomic mass is not listed in the periodic table,but it is understood to be the amu.) Where does the number 35.453come from? There are two natural isotopes of chlorine, chlorine-35 andchlorine-37. An atom of chlorine-35 has 17 protons and 18 neutrons. Anatom of chlorine-37 has 17 protons and 20 neutrons. So the mass of anatom of chlorine-37 is greater than the mass of an atom of chlorine-35.

Weighted Averages Your teacher may use a weighted averageto determine your grade. In a weighted average, some values are moreimportant than other values. For example, test scores may count moreheavily toward your final grade than grades on quizzes or grades onhomework assignments.

Figure 9 lists the atomic masses for two naturallyoccurring chlorine isotopes. If you add the atomic massesof the isotopes and divide by 2, you get 35.967, not 35.453.The value of the atomic mass for chlorine in the periodictable is a weighted average. The isotope that occurs innature about 75% of the time (chlorine-35) contributesthree times as much to the average as the isotope thatoccurs in nature about 25% of the time (chlorine-37).

What is an atomic mass unit?

Isotope

Chlorine-35

Chlorine-37

Percentage

75.78%

24.22%

Atomic Mass

34.969

36.966

Distribution of ChlorineIsotopes in Nature

17

ClChlorine35.453

Atomic number

Element symbol

Atomic massElement name

Figure 8 This box provides fourpieces of information about theelement chlorine: its symbol, itsname, its atomic number, and itsatomic mass.

Figure 9 This table shows the distribution andatomic masses for the two natural isotopes ofchlorine. Using Tables Which isotope occurs more often in nature?

134 Chapter 5

Atomic Mass

Students may not realize that all atoms ofan element are isotopes. In other words,students may think that there is one“regular” atom and several variationscalled isotopes. Explain that a sample ofan element found in nature contains amixture of the different isotopes of thatelement. The symbols on the periodictable represent “average” atoms ofelements. In fact, atoms with the atomicmasses listed on the table do not exist.For example, there are no carbon atomswith an atomic mass of 12.011 amu. Thisvalue is a weighted average of the atomicmasses of stable carbon isotopes. Thevalue is close to the assigned value forcarbon-12 because about 99% of acarbon sample is carbon-12 atoms.Verbal, Logical

FYI An atomic mass given in parentheses in Figure 7 is the mass number of thelongest-lived isotope of an element thathas no stable isotopes and for which theabundance of isotopes in nature showsgreat variability (or a complete absencein the case of technetium or prometh-ium). Technetium and promethium havebeen detected in the spectra of stars.

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Atomic Mass Units From the mid-1800s to1960, oxygen was the standard for atomicmasses. (Oxygen was likely chosen because itforms compounds with many elements.) Afterthe discovery of isotopes, physicists andchemists began to use different standards.Physicists assigned the value 16.000 amuexclusively to oxygen-16. Other oxygenisotopes had different values. Chemistscontinued to use 16.000 amu as the average

for all oxygen atoms. Although the differencesbetween the standards were small, the situ-ation was potentially confusing.

In 1961, chemists and physicists agreed ona unified standard based on the carbon-12isotope, which is assigned a value of 12.000amu. (Although the SI abbreviation for atomicmass unit was changed to u for unified whenscientists adopted the unified atomic massunit, the amu notation is still widely used.)

Facts and Figures

Classes of ElementsThe periodic table in Figure 7 presents three different ways to classifyelements. First, elements are classified as solids, liquids, or gases, basedon their states at room temperature. The symbols for solids are black.The symbols for liquids are purple. The symbols for gases are red.

Second, elements are divided into those that occur naturally andthose that do not. All but two elements with atomic numbers 1through 92 occur on Earth. Elements with atomic numbers of 93 andhigher do not occur naturally. The symbols for these elements arewhite. In Chapter 10, you will find out how elements that do not occurin nature are produced.

The third classification system puts elements into categories basedon their general properties. Elements are classified as metals,nonmetals, and metalloids. In the periodic table, metals are located onthe left, nonmetals are on the right, and metalloids are in between.

Metals The majority of the elements on the periodic table are clas-sified as metals. In Figure 7, they are represented by blue boxes. Metalsare elements that are good conductors of electric current and heat.Except for mercury, metals are solids at room temperature. Mostmetals are malleable. Many metals are ductile; that is, they can bedrawn into thin wires.

Some metals are extremely reactive and some do not react easily.One way to demonstrate this difference is to compare the behavior ofgold and the behavior of magnesium when these metals are exposedto the oxygen in air. Gold remains shiny because it does not react withthe oxygen. Magnesium reacts with the oxygen and quickly dulls.Figure 10A shows one magnesium coil that is dull and one that is shiny.Figure 10B shows one use for a metal with a shiny surface.

Defining a Metal

Procedure 1. Use forceps to put a piece of

magnesium into a test tubein a test tube rack. Using agraduated cylinder, add5 mL of hydrochloric acidto the test tube. CAUTION Wear plasticgloves because the acid canburn skin or clothing. Recordyour observations.

2. Repeat Step 1 with sulfur,aluminum, and silicon.

Analyze and Conclude1. Classifying Based on their

locations in the periodictable, classify the fourelements as metals,metalloids, or nonmetals.

2. Comparing andContrasting Comparethe behavior of the metalswith the acid to thebehavior of the otherelements with the acid.

3. Forming OperationalDefinitions Use yourobservations to write adefinition of a metal.

Figure 10 Magnesium and aluminum are typicalmetals. A When magnesium reacts with oxygen, a dull layer forms on its surface. The layer can beremoved to reveal magnesium’s shiny surface.B Many telescope mirrors are coated withaluminum to produce a surface that reflectslight extremely well.


A

B

Classes of Elements

Defining a Metal

ObjectiveAfter completing this activity, studentswill be able to • use a chemical property to distinguish

metals.

Skills Focus Forming OperationalDefinitions

Prep Time 20 minutes

Materials forceps; magnesium; testtubes; test-tube rack; graduated cylinder;20 mL 2 M HCl; small pieces of sulfur,aluminum, and silicon

Advance Prep Prepare 1 L of 2 M HCl:add 200 mL of 10 M HCl to a 1-Lvolumetric flask containing 750 mL ofwater and swirl gently to mix. Add waterto bring the volume to 1 L. CAUTIONWear safety goggles, a lab apron, andneoprene gloves. Use concentrated HCl ina fume hood or other well-ventilated area.Never add water to acid.Polish the magnesium lightly with steelwool to remove any magnesium oxide.


Safety Remind students to use care inadding the acid and to rinse any acid offskin or clothing with water. CAUTION Thereaction of Mg in HCl will make the test tubehot. Keep spill-control materials (bakingsoda or citric acid) nearby to clean upspills. Repeat as necessary to remove allacid contamination. Elemental sulfur mayemit H2S when dispersed in HCl. Test thesulfur beforehand in a fume hood or otherwell-ventilated area. Supply silicon aschips, not in powdered form, which isflammable. Neutralize the acid solutionswith baking soda and wash them downthe drain with excess water.

Teaching Tips• Caution students not to get fingerprints

on the Mg and Al samples.• The complete reaction of Al and HCl

will require more than 45 minutes.However, the results after 15 minuteswill indicate how the materials react.

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Expected OutcomeElement ObservationMagnesium Bubbles, test tube becomes hot,

reaction complete in about 30 seconds, final solution clear.

Sulfur No visible reaction

Aluminum Slight bubbling in 5 minutes, testtube becomes warm after about 15 minutes, final mixture slightlycloudy with powdery gray precipitate.

Silicon No visible reaction

Analyze and Conclude1. Aluminum and magnesium are metals.Sulfur is a nonmetal and silicon is a metalloid.2. Only the metals react with the acid. 3. A metal is a substance that reacts with HCl. Logical

Answer to . . .

Figure 9 Chlorine-35

One-twelfth the mass ofa carbon-12 atom


The metals in groups 3 through 12 are called transition metals.Transition metals are elements that form a bridge between the ele-ments on the left and right sides of the table. Transition elements, suchas copper and silver, were among the first elements discovered. Oneproperty of many transition metals is their ability to form compoundswith distinctive colors. The How It Works box on page 137 describes theuse of transition elements in the production of colored glass.

Some transition elements have more properties in common thanelements in other groups. This is especially true of ele-

ments in the lanthanide and actinide series. Theseelements are so similar that chemists in the 1800shad difficulty separating them when they werefound mixed together in nature. A compound

of erbium and oxygen was used to tint the lensesshown in Figure 11.

Nonmetals In Figure 7, nonmetals are represented by yellowboxes. As their name implies, nonmetals generally have propertiesopposite to those of metals. Nonmetals are elements that are poor con-ductors of heat and electric current. Because nonmetals have lowboiling points, many nonmetals are gases at room temperature. In fact,all the gases in the periodic table are nonmetals. The nonmetals that aresolids at room temperature tend to be brittle. If they are hit with ahammer, they shatter or crumble.

Nonmetals vary as much in their chemical properties as they do intheir physical properties. Some nonmetals are extremely reactive, somehardly react at all, and some fall somewhere in between. Fluorine inGroup 17 is the most reactive nonmetal. It even forms compoundswith some gases in Group 18, which are the least reactive elements inthe table. The toothpaste in Figure 12 contains a compound of thenonmetal fluorine and the metal sodium. This compound helps toprotect your teeth against decay.

Metalloids In the periodic table in Figure 7, metalloids are repre-sented by green boxes. Metalloids are elements with properties that fallbetween those of metals and nonmetals. For example, metals are goodconductors of electric current and nonmetals are poor conductors ofelectric current. A metalloid’s ability to conduct electric current varieswith temperature. Pure silicon (Si) and germanium (Ge) are good insu-lators at low temperatures and good conductors at high temperatures.

Which type of metals tend to form compounds withdistinctive colors?

Figure 11 A compound oferbium (Er) and oxygen is usedto tint glass pink.

Figure 12 Toothpaste containsa compound that helps toprotect teeth from tooth decay.The compound is formed fromthe nonmetal fluorine and themetal sodium.

136 Chapter 5

136 Chapter 5

Integrate HealthPeople who work under fluorescentlights or spend a lot of time viewing a computer screen sometimes choosepink lenses. Athletes participating inhigh-speed winter sports often use pinklenses because they help to increasecontrast and depth perception whenthe available light is limited. Gray lensesare very common; they reduce theamount of light without changing itscolor. Have students research situationsin which lenses with colors other thanpink are used.Verbal, Portfolio

Build Reading LiteracySummarize Refer to page 598D inChapter 20, which provides theguidelines for summarizing.

Have students write a summary of thetext on pp. 135–136. Summaries shouldinclude information about each of thevocabulary terms on these pages. Ask,Based on your summary, which classof elements has properties that fallbetween the properties of two otherclasses of elements? (Metalloids)Verbal, Portfolio

FYI The important role metalloids play assemiconductors is addressed in Chapter 6.

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Fluoride in Toothpaste According to FDAregulations, toothpaste can contain sodiumfluoride, sodium monofluorophosphate, orstannous fluoride at concentrations of 850 to1150 ppm total fluorine. A package of tooth-paste sold commercially cannot contain morethan 276 mg of fluorine. Because too muchfluoride can have adverse affects on health,

people should rinse away excess toothpaste.There must be a warning on toothpastepackages to keep the product out of the reachof children under 6 years of age. Youngchildren need to be supervised when theybrush their teeth until they have learned howto minimize ingestion of the toothpaste.

Facts and Figures

Making Glass

Colored glassMetallic elements are mixed withthe raw ingredients to producecolored glass. Iron or chromiumis added for green, copper orgold for red, and cobalt for blue.

Cooling the glassThe glass is cooled

slowly in a temperature-controlled oven to keepit from cracking.

Hot glass is placed in the mold.

Rollers

Lime (calciumoxide)

Sand(silicon

dioxide)

Soda ash (sodiumcarbonate)

Glasscutter

Oven

Melted tin Floating the glasson liquid tin produces a glass

surface that is as smooth as thesurface of the liquid tin.

Furnace

Making bottlesMass-produced glassbottles are made byadding hot glass toa mold and shapingthe glass with air athigh pressure. Air blown

through the airtube forces theliquid glass toassume the shapeof the bottle mold.

Airtube

Mold sealed

Adding the raw ingredients Sand, lime, andsoda ash are poured into the furnace and heated

to 1500°C (2730°F). Recycled waste glass, called cullet,is also added, to reduce the cost of raw materials.

Heating in the furnace The furnaceheats the ingredients, producing liquid

glass at 1100°C (2010°F). Rollers move the hotand molten glass to the next stage.

Liquid glass The glass is floatedover a bath of melted tin. The glass

emerges at 600°C (1110°F) as a continuoussheet with the same thickness throughout.

Cuttingthe glass

A diamond-tipped cutter isused to cut thecooled glass.

Cullet(wasteglass)

For more than 4500 years, people have made glass fromsand. The float-glass process shown below is used to makelarge sheets of glass for windows, while molds are usedto make glass bottles. Interpreting Diagrams How is airused in making glass bottles?


Air pushes the glass to thebottom of the mold, where the

neck of the bottle will form.

Making GlassFloat-glass plants are among the largestbuildings in the world. Giant bins holdthe raw materials for making glass. Hugeroof ventilators and stacks release theintense heat needed to produce theliquid glass. The glassmaking operationis continuous, with the fires burningconstantly. Often a glass plant willproduce various tints of glass that areused in different applications.

Interpreting Diagrams Air at highpressure is used to force the liquid glassto take the shape of the mold. Visual, Verbal

For EnrichmentInterested students can research andreport on the work of glassblowers andcompare their techniques for shapingglass with the molding process that isdescribed on p. 137. Have students usethe library to find books, magazinearticles, and videos to help in theirresearch. Verbal, Portfolio

FYI Tell students that showing the rawingredients of glass as four equalsegments of a pie is not meant to reflecttheir actual percentages in the mixture.Adding soda ash saves energy becausesodium carbonate lowers the meltingtemperature of the mixture. Runningthe glass over rollers instead of themolten tin produces an uneven surface.

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Answer to . . .

Transition metals


138 Chapter 5


Reviewing Concepts1. What determines the order of the elements

in the modern periodic table?

2. Describe the periodic law.

3. What two factors determine the atomicmass of an element?

4. Name three categories that are used toclassify the elements in the periodic table.

5. What major change occurs as you movefrom left to right across the periodic table?

Critical Thinking6. Formulating Hypotheses The atomic mass

of iodine (I) is less than the atomic mass oftellurium (Te). But an iodine atom has onemore proton than a tellurium atom. Explainhow this situation is possible.

7. Applying Concepts Explain how you knowthat no new element with an atomic numberless than 100 will be discovered.

8. Comparing and Contrasting Compare thereactions with water of the elements sodiumand magnesium.

Variation Across a Period The properties within a period change in a similar way from left to rightacross the table, except for Period 1. Across a period from left toright, the elements become less metallic and more nonmetallic intheir properties. The most reactive metals are on the left side of thetable. The most reactive nonmetals are on the right in Group 17. ThePeriod 3 elements shown in Figure 13 provide an example of this trend.

There are three metals, a metalloid, and four nonmetals in Period 3.If you were unwise enough to hold a piece of sodium in your hand, itwould react quickly and violently with the water on your moist skin.But magnesium will not react with water unless the water is hot.Aluminum does not react with water, but it does react with oxygen.

Silicon is the least reactive element in Period 3 (except for argon).Under ordinary conditions, phosphorus and sulfur do not react withwater, but they do react with oxygen. They also react with chlorine,which is a highly reactive nonmetal. Chlorine must be handled with asmuch care as sodium. Argon hardly reacts at all.

Explanatory Paragraph The word isotopecomes from the Greek words isos, meaning“equal,” and topos, meaning “place.” Writea paragraph explaining how the isotopeschlorine-35 and chlorine-37 occupy thesame place in the periodic table.

Figure 13 From left to rightacross Period 3, there are threemetals (Na, Mg, and Al), onemetalloid (Si), and four nonmetals(P, S, Cl, and Ar). Many light bulbsare filled with argon gas. Observing Which other elementin Period 3 is a gas?

Aluminum SulfurSodium Magnesium Chlorine ArgonPhosphorusSilicon

Variation Across a Period

Period 3 PropertiesPurpose Students observe differencesin electrical conductivity among threePeriod 3 elements.

Materials 6-volt battery, flashlight bulbwith holder, 3 pieces of insulated wirewith the ends stripped, 2.5-cm aluminumstrip, small silicon chip, 2.5-cm piece of sulfur

Advance Prep Use the battery,flashlight bulb with holder, and thewires to make an open circuit.

Procedure Touch the free ends of thetwo wires to each end of the aluminumstrip. Have students observe the bulb.Repeat for silicon and sulfur.

Expected Outcome The material usedto complete the circuit determines thebrightness of the light. For aluminum,the bulb is bright; for silicon, the bulb isdim; for sulfur, the bulb does not light.Students should conclude that thePeriod 3 elements become less metallicfrom left to right across the period.Visual, Logical

ASSESSEvaluate UnderstandingAsk students to identify the generalproperties of metals, nonmetals, andmetalloids.

ReteachUse Figure 13 to illustrate how theproperties of elements change from left toright across a period in the periodic table.

Student answers should reflect the factthat all the isotopes of an atom occupythe same place on the periodic table,despite their different mass numbers.

If your class subscribes to the Interactive Textbook, use it toreview key concepts in Section 5.2.

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Section 5.2 Assessment 6. Answers may include that the telluriumisotopes that are most abundant have manyneutrons in their nuclei or that all telluriumatoms have more neutrons than iodine atoms. 7. The atomic number of an elementcorresponds to the number of protons in theelement’s atoms. The atomic number must bea whole number. All the places between 1 and100 are already filled with existing elements. 8. Sodium reacts quickly and violently withwater at room temperature. Magnesium willnot react unless the water is hot.

1. In the modern periodic table, elements arearranged by increasing atomic number.2. Properties of elements repeat in apredictable way when atomic numbers areused to arrange elements into groups. 3. Atomic mass is a value that depends on thedistribution of an element’s isotopes in natureand the masses of those isotopes.4. Metals, nonmetals, and metalloids5. The elements become less metallic andmore nonmetallic in their properties.

Answer to . . .

Figure 13 Chlorine

138 Chapter 5

5.3 Representative Groups

Reading Strategy Monitoring Your Understanding Copythe table below. As you read, record animportant fact about each element listed.

Key ConceptsWhy do the elementsin a group have similarproperties?

What are some propertiesof the A groups in theperiodic table?

Vocabulary◆ valence electron◆ alkali metals◆ alkaline earth

metals◆ halogens◆ noble gases

Why is hydrogen located on the left side of the periodic table withthe active metals? It is a nonmetal gas that seems to have more incommon with the nonmetals in Group 17. Hydrogen’s location isrelated to its electron configuration, not its properties.

Valence ElectronsDid you wonder why there are two numbering schemes on the periodictable in Figure 7? When the A groups are numbered from 1 through 8,they provide a useful reminder about the electron configurations ofthe elements in those groups. The number of an A group matches thenumber of valence electrons in an electron configuration for an ele-ment in that group. A valence electron is an electron that is in thehighest occupied energy level of an atom. These electrons play a keyrole in chemical reactions. Properties vary across a period because thenumber of valence electrons increases from left to right.

Elements in a group have similarproperties because they have the samenumber of valence electrons. These pro-perties will not be identical because thevalence electrons are in different energylevels. Valence electrons explain the loca-tion of hydrogen. Because hydrogen has asingle valence electron, it is grouped withother elements, such as lithium, that haveonly one valence electron.

Figure 14 Because hydrogen isflammable, it can be used as afuel in automobiles like this one.An engine that burns hydrogenhas a key advantage over anengine that burns gasoline. Only water is produced whenhydrogen burns.

a. ?

b. ?

c. ?

Element Important Fact

Magnesium

Aluminum

Chlorine

139

FOCUS

Objectives5.3.1 Relate the number of valence

electrons to groups in theperiodic table and to propertiesof elements in those groups.

5.3.2 Predict the reactivity of someelements based on theirlocations within a group.

5.3.3 Identify some properties ofcommon A group elements.

Build VocabularyConcept Map Have students constructa concept map with eight branches andtitle it Groups in the Periodic Table. Asstudents read, they can add the namesof groups to each branch, the group’snumber of valence electrons, elementsin the group, and some properties ofthese elements.

Reading StrategyPossible answers: a. Magnesium plays akey role in the production of sugar inplants. Mixtures of magnesium andother metals can be as strong as steel,but much lighter. b. Aluminum is themost abundant metal in Earth’s crust.Much less energy is needed to purifyrecycled aluminum than to extractaluminum from bauxite. c. Chlorine is a highly reactive, nonmetal gas that isused to kill bacteria in water.

INSTRUCT

Valence ElectronsIntegrate Space ScienceHydrogen exhibits metallic propertiesunder extreme conditions. Scientistshave theorized for decades that metallichydrogen exists in the core of planetssuch as Jupiter. Interior pressure onJupiter is millions of times greater thanthe pressure at the surface of Earth. Atthis pressure, electrons flow easilybetween hydrogen molecules. Havestudents do research and write aparagraph that compares and contraststhe cores of Jupiter and Earth, accordingto the current state of scientificknowledge. Verbal, Portfolio

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Reading Focus

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Print• Laboratory Manual, Investigation 5B• Reading and Study Workbook With

Math Support, Section 5.3 • Transparencies, Section 5.3

Technology• Interactive Textbook, Section 5.3• Presentation Pro CD-ROM, Section 5.3• Go Online, Science News, Elements

Section Resources

Section 5.3

PPLS


140 Chapter 5

The Alkali MetalsThe elements in Group 1A are called alkali metals. These metals havea single valence electron and are extremely reactive. Because they areso reactive, alkali metals are found in nature only in compounds. Themost familiar of these compounds is table salt—a compound ofsodium and chlorine (sodium chloride). Sodium chloride can beobtained through the evaporation of seawater or from large saltdeposits on the surface of Earth or underground.

Not all the elements in a group are equally reactive. Sodium is morereactive than lithium, potassium is more reactive than sodium, andrubidium is more reactive than potassium. The reactivity of alkalimetals increases from the top of Group 1A to the bottom.

Sodium is about as hard as cold butter and can be cut with a sharpknife, as shown in Figure 15A. Sodium melts at about 98°C and has alower density than water. A piece of sodium may be able to float onwater, but Figure 15B shows that it won’t be there for long. The sodiumreacts violently with water and releases enough energy to ignite thehydrogen gas that is produced. Sodium and potassium are storedunder oil to keep them from reacting with the oxygen and water vaporin air. Cesium is so reactive that it reacts with water at temperatures aslow as –115°C. Cesium is usually stored in a sealed glass tube contain-ing argon gas.

How many valence electrons does an alkalimetal have?

For: Articles on elements

Visit: PHSchool.com

Web Code: cce-1053

3

LiLithium

19

KPotassium

37

RbRubidium

11

NaSodium

55

CsCesium

87

FrFrancium

Group 1A

A

B

Figure 15 The element sodium is an alkalimetal A Unlike most metals, sodium is softenough to cut with a knife. B When sodiumreacts with water, enough energy is releasedto ignite the hydrogen that is produced.Predicting What happens when potassiumcomes in contact with water?

140 Chapter 5

The Alkali MetalsUse VisualsFigure 15 Ask students to study thetwo photos and the column of elementsin Figure 15. Ask, What properties ofsodium are shown in the photos?(Sodium is a soft solid at room tempera-ture with a metallic luster when firstexposed to air. Sodium is extremelyreactive and it reacts violently with waterto form hydrogen gas.) Point out tostudents that the reactivity of the alkalimetals increases from the top of thegroup to the bottom. Ask, Which alkalimetals are less reactive than cesiumbut more reactive than lithium?(Sodium, potassium, and rubidium)Visual, Logical

Build Science SkillsCommunicating Results Explain tostudents that Robert Bunsen and GustavKirchoff discovered cesium in 1840 andrubidium in 1841 by burning the sub-stances and observing the color of theflames. Have students research the originof the terms cesium and rubidium. Havestudents explain why these names areappropriate. (Cesium comes from the Latinword caesium, which means “heavenlyblue.” Rubidium comes from the Latinword rubidus, which means “dark red.”The names describe the colors of lightemitted when the elements are burned.)Logical

FYI Francium has been described as themost unstable element among the first103 elements. Its longest-lived isotope,francium-223, has a half-life of only 22minutes. The estimate is that there isonly about one ounce of francium onEarth at any moment.

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Science News provides studentswith current information onelements.

Customize for English Language Learners

Compare/Contrast ChartAfter students have read about Groups 1A and2A, create a chart on the board with the titleAlkali Metals vs. Alkaline Earth Metals. Separatethe chart into two columns labeled Similarities

and Differences. Ask for student responses to help you fill in the chart. After all correctanswers have been recorded, keep the chartdisplayed as a reference for students.


The Alkaline Earth MetalsThe elements in Group 2A are called alkaline earth metals. All alka-line earth metals have two valence electrons. Metals in Group 2A areharder than metals in Group 1A. The melting point of magnesium is650°C, which is much higher than the melting point of sodium—98°C.

Differences in reactivity among the alkaline earth metals areshown by the ways they react with water. Calcium, strontium, andbarium react easily with cold water. Magnesium will react with hotwater, but no change appears to occur when beryllium is added towater. Magnesium and calcium have essential biological functions andthey provide materials used in construction and transportation.

Magnesium Magnesium plays a key role in the process that usessunlight to produce sugar in plants like the one in Figure 16. The com-pound at the center of this process is chlorophyll (KLAWR uh fil), andat the center of chlorophyll is magnesium. A mixture of magnesiumand other metals can be as strong as steel, but much lighter. Reducingoverall mass without sacrificing strength is an important considera-tion in transportation. The frames of bicycles and backpacks oftencontain magnesium.

Calcium Your body needs calcium to keep your bones and teethstrong. Calcium carbonate—a compound of calcium, carbon, andoxygen—is the main ingredient in chalk, limestone, coral, and thepearl in Figure 16. Your toothpaste may contain the compoundcalcium carbonate because this hard substance can polish yourteeth. The plaster cast in Figure 16 contains calcium sulfate,which is a compound of calcium, sulfur, and oxygen.

4

BeBeryllium

12

MgMagnesium

20

CaCalcium

38

SrStrontium

56

BaBarium

88

RaRadium

Group 2A

Figure 16 Chlorophyll molecules in spinachcontain magnesium. An oyster shell and apearl are both made from calciumcarbonate. A plaster cast contains thecompound calcium sulfate.

Plaster cast

Oyster shell with pearl

Spinach plant

The Alkaline Earth Metals

FYIThe mineral gypsum is heated toproduce a white powdery substancecalled plaster of Paris. When water isadded to plaster of Paris, heat is releasedas the plaster quickly hardens. Duringthe process, the plaster expands byabout 0.3–0.6%. A plaster cast is oftenreplaced by a sturdier, more lightweightfiberglass cast after the swelling aroundan injury subsides.

Egyptians used plaster to join blocksof stone in pyramids. Romans madeplaster casts of Greek statues. In the1700s, wooden houses in Paris wereoften covered in plaster to protectagainst fire. This measure was taken inresponse to the destruction of Londonby fire in 1666.


Answer to . . .

Figure 15 When potassium reactswith water, enough energy is releasedto ignite the hydrogen that is produced.

An alkali metal has onevalence electron.


The Boron Family Group 3A contains the metalloid boron, the well-known metal aluminum, and three less familiarmetals (gallium, indium, and thallium). All theseelements have three valence electrons.

Aluminum is the most abundant metalin Earth’s crust. It is often found combined withoxygen in a mineral called bauxite (BAWKS eyet).Aluminum is less reactive than sodium and mag-nesium. It is strong, lightweight, malleable, and agood conductor of electric current.

More than 10 percent of the aluminum pro-duced is used as packaging. Some aluminum isused in window screens, window frames, and gut-ters. Parts of cars and airplanes are also made fromaluminum. People are encouraged to recycle alu-minum because the energy needed to purifyrecycled aluminum is only about 5 percent of theenergy needed to extract aluminum from bauxite.

A compound of boron, silicon, and oxygen isused to make a type of glass that does not shattereasily when it undergoes a rapid change in tem-perature. Glass that contains boron is used tomake laboratory glassware, such as the flasks inFigure 17. It is also used in cookware that can godirectly from the oven to the refrigerator.

The Carbon Family Group 4A contains a nonmetal (carbon), twometalloids (silicon and germanium), and twometals (tin and lead). Each of these elements hasfour valence electrons. Notice that the metallicnature of the elements increases from top tobottom within the group. In keeping with thistrend, germanium is a better conductor of electriccurrent than silicon.

Life on Earth would not exist without carbon.Except for water, most of the compounds in

your body contain carbon. Reactions that occurin the cells of your body are controlled by carboncompounds. Carbon and its compounds are dis-cussed in Chapter 9, Carbon Chemistry.

Silicon is the second most abundant elementin Earth’s crust. It is found as silicon dioxide inquartz rocks, sand, and glass. The clay used to pro-duce the pottery in Figure 18 contains siliconcompounds called silicates. Silicon carbide, acompound of silicon and carbon, is extremelyhard. Saw blades tipped with silicon carbide lastmany times longer than ordinary steel blades.

Which Group 3A element isa nonmetal?

31

GaGallium

81

TlThallium

13

Al Aluminum

5

BBoron

49

InIndium

Figure 17 These students are using flasksmade from glass that contains boron. Thistype of glass does not shatter as easily asglass without boron.

32

GeGermanium

82

PbLead

50

SnTin

14

SiSilicon

6

CCarbon

Figure 18 The clay used to make thispottery contains compounds calledsilicates. These compounds always containsilicon and oxygen. They usually containaluminum and often contain otherelements such as iron.

Group 3A

Group 4A

142 Chapter 5

142 Chapter 5

The Boron FamilyUse Community ResourcesInvite a representative from a communityrecycling program or a commercialrecycler to speak to your class about theimportance of recycling materials such asaluminum. Have students ask questionsabout the kinds of materials that arerecycled and how the recycling processis different for each of them. They mayalso ask how recycling has changed overthe past 10 years and what changes areexpected in the future. Interpersonal, Portfolio

The Carbon FamilyIntegrate MathTell students that silicon dioxide is themost abundant substance in Earth’scrust. It is, of course, a compound of theelements silicon and oxygen. Point outto students that only eight elementsmake up 98.5% of Earth’s crust: oxygen(46.6%), silicon (27.7%), aluminum(8.1%), iron (5.0%), calcium (3.6%),sodium (2.8%), potassium (2.6%), andmagnesium (2.1%). Have students workin pairs to create a circle graph thatshows this data. Remind students thatthey may need to combine some ele-ments under a category labeled Other.If students need help constructing acircle graph, you may want to referthem to the Math Skills in the Skillsand Reference Handbook at the end of the student text.Visual, Logical

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The Nitrogen FamilyGroup 5A contains two nonmetals (nitrogen andphosphorus), two metalloids (arsenic and anti-mony), and one metal (bismuth). Like the groupson either side of it, Group 5A includes elementswith a wide range of physical properties. Nitrogenis a nonmetal gas, phosphorus is a solid nonmetal,and bismuth is a dense metal. Despite their dif-ferences, all the elements in Group 5A have fivevalence electrons. Nitrogen and phosphorus arethe most important elements in Group 5A.

When air is cooled, the oxygen condensesbefore the nitrogen because nitrogen has a lowerboiling point than oxygen. Much of the nitrogenobtained from air is used to produce fertilizers,like the three shown in Figure 19. Besidesnitrogen, fertilizers often contain phosphorus.Your body uses compounds containing nitrogenand phosphorus to control reactions and releaseenergy from food.

Phosphorus exists as an element in severalforms with different properties. White phospho-rus is so reactive that it bursts into flame when itis in contact with oxygen. Red phosphorus is lessreactive and is used to make matches ignite.

The Oxygen FamilyGroup 6A has three nonmetals (oxygen, sulfur,and selenium), and two metalloids (tellurium andpolonium). All the elements in Group 6A have sixvalence electrons.

Oxygen is the most abundant element inEarth’s crust. Complex forms of life need oxygento stay alive because oxygen is used to release theenergy stored in food. Oxygen can be stored as aliquid under pressure in oxygen tanks. There mustbe no sparks or flames near an oxygen tankbecause materials that are flammable burn easilyin pure oxygen.

Ozone is another form of the element oxygen.At ground level, ozone can irritate your eyes andlungs. At upper levels of the atmosphere, ozoneabsorbs harmful radiation emitted by the sun.

Sulfur was one of the first elements to be dis-covered because it is found in large naturaldeposits like the one in Figure 20. The main useof sulfur is in the production of sulfuric acid, acompound of sulfur, hydrogen, and oxygen. Moresulfuric acid is produced in the United States thanany other chemical. About 65 percent of the sul-furic acid produced is used to make fertilizers.

34

SeSelenium

52

TeTellurium

84

PoPolonium

16

SSulfur

8

OOxygen

33

As Arsenic

51

Sb Antimony

83

BiBismuth

15

PPhosphorus

7

NNitrogen

Figure 20 Sulfur is often found innature in its elemental form—notcombined with other elements.Inferring What does this informationtell you about the reactivity of sulfur?

Figure 19 The composition of a fertilizervaries with its intended use. The numberson the bags of fertilizer are, from left toright, the relative amounts of nitrogen,phosphorus, and potassium.Analyzing Data Which type of fertilizercontains the most phosphorus?

Group 5A

Group 6A

The Nitrogen FamilyBuild Reading LiteracyIdentify Main Idea/Details Refer topage 98D in Chapter 4, which providesthe guidelines for identifying main ideasand details.

Guide students in applying this strategyto the text on page 143. Tell students to look for the main idea of eachparagraph and then list one or twosupporting details. If the paragraph hasno topic sentence, have students list twoimportant facts from the paragraph. Verbal, Portfolio

FYIOf the 18 elements essential for plantgrowth, nitrogen, phosphorus, andpotassium are most likely to be lacking.The numbers on the fertilizer packagesshown in Figure 19 represent percent N,percent P2O5, and percent K2O. (In thepast, oxides were often used as stan-dards for chemical comparisons.)Nitrogen and phosphorus are oftenpresent as nitrates and phosphates.

The Oxygen Family

Students may think that the air theybreathe is pure oxygen. Challenge thismisconception by reminding studentsthat air is a mixture of gases. Air is 78% nitrogen and 21% oxygen. Havestudents research what gases make up the remaining 1% of air. (Answersshould include carbon dioxide, watervapor, argon, and other noble gases.)Logical

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Answer to . . .

Figure 19 Tomato food

Figure 20 Sulfur is not highlyreactive under ordinary conditions.

Carbon

Phosphorus The element phosphorus has 10 forms, which are usually grouped as white,red, and black phosphorus for simplicity. Thewhite phosphorus forms are the least stable.

In 1680, Robert Boyle demonstrated thatphosphorus ignited by friction could be usedto light wooden splints that had been dippedin sulfur. There are two types of matches. In astrike-anywhere match, all of the required

ingredients (often phosphorus sulfide andpotassium chlorate) are in the match head. In a safety match, the ingredients are dividedbetween the match head and a rough strikingsurface on the side of the matchbox. A safetymatch can be lit only when the tip is drawnacross the striking surface, which containsphosphorus sulfide.

Facts and Figures


144 Chapter 5

The HalogensThe elements in Group 7A are called halogens. Each halogen has sevenvalence electrons. Figure 21 shows the range of physical propertiesamong the halogens. Fluorine and chlorine are gases, bromine is aliquid that evaporates quickly, and iodine is a solid that sublimes.

Despite their physical differences, the halogens have similarchemical properties. They are highly reactive nonmetals, with fluo-rine being the most reactive and chlorine a close second. Halogensreact easily with most metals. Figure 21 shows what happens whenheated steel wool is plunged into chlorine.

Recall that a fluorine compound is used to prevent tooth decay. Ifyou use pans with a nonstick coating to make omelets or muffins, youhave seen another use of a fluorine compound. Have you ever noticeda sharp smell when adding bleach to a load of clothes? The smell comesfrom a small amount of chlorine gas that is released from a chlorinecompound in the bleach. Chlorine is also used to kill bacteria in drink-ing water and swimming pools. The woman in Figure 21 is testing thelevel of chlorine in a swimming pool.

Your body needs iodine to keep your thyroid gland working prop-erly. This gland controls the speed at which reactions occur in yourbody. Seafood is a good source of iodine. At a time when fresh fish wasnot available in all parts of the United States, people began to addiodine compounds to table salt. Salt that contains such compounds iscalled iodized salt.

35

BrBromine

85

At Astatine

17

ClChlorine

9

FFluorine

53

IIodine

Group 7A

Chlorine Bromine Iodine

Figure 21 At room temperature, chlorine is a gas, bromine is aliquid, and iodine is a solid. Halogens react easily with metals, suchas the iron in steel wool. At a swimming pool, the chlorine contentmust be tested frequently. Applying Concepts What processcauses iodine vapor to collect in a flask of solid iodine?

Chlorine reacting with steel wool

144 Chapter 5

The HalogensBuild Reading LiteracyKWL Refer to page 124D in thischapter, which provides the guidelinesfor KWL (Know/Want to Know/Learned).

Teach this independent study skill as awhole-class exercise. 1. Draw a three-column KWL chart on the board forstudents to copy. 2. Have studentscomplete the Know column with facts,examples, and other information thatthey already know about the Group 7Aelements (the halogens). 3. Tell studentsto complete the Want to Know columnwith questions about the halogens. 4. Have students read p. 144 to learnmore about the halogens. As they read,have them note answers to their ques-tions in the Learned column, along withother facts, examples, and details theylearned. 5. Have students draw anInformation I Expect to Use box belowtheir KWL chart. Have them review theinformation in the Learned column and categorize the useful information in the box. Verbal

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Halogens The name astatine comes from the Greek astatos, meaning “unstable.”Astatine is a radioactive element whose moststable isotope, At-210, has a half-life of only8.1 h. Astatine is the most metallic of thehalogens. It is usually classified as a metalloid,but is sometimes regarded as a nonmetal.

Because of its rarity and instability, astatine hasno practical uses.

Both bromine and iodine are volatile. Iodinecomes from the Greek ioeides, meaning “violetcolored.” It is named for the color of iodinevapor, not the color of its solid crystals, whichare dark gray.

Facts and Figures


Reviewing Concepts1. Explain why elements in a group have

similar properties.

2. What is the relationship between an alkalimetal’s location in Group 1A and its reactivity?

3. What element exists in almost everycompound in your body?

4. Which Group 5A elements are foundin fertilizer?

5. Which group of elements is the least reactive?

6. Why is hydrogen located in a group withreactive metals?

7. What biological function requires magnesium?

8. Why is aluminum recycled?

9. What is the main use of sulfur?

10. Why is chlorine added to drinking water?

Critical Thinking 11. Comparing and Contrasting In which

class of elements is there a greater range ofproperties, the metals or the nonmetals? Givean example to support your answer.

12. Making Generalizations What happens tothe reactivity of nonmetals within a groupfrom the top of the group to the bottom?

The Noble Gases The elements in Group 8A are called noble gases. Helium hastwo valence electrons. Each of the other noble gases has eightvalence electrons. The noble gases are colorless and odor-less and extremely unreactive. In Chapter 6, you will study therelationship between the electron configurations of the noblegases and their low reactivity.

It is not easy to discover a colorless, odorless gas. It is evenharder if the gas rarely reacts. Scientists discovered argon whenthey noticed that the density of nitrogen collected from air didnot match the density of nitrogen formed during chemicalchanges. In time, the scientists figured out that the “impurity” inatmospheric nitrogen was an unknown element.

An element that does not react easily with other elementscan be very useful. For example, during one stage in the processof making computer chips, pure silicon is heated in a furnace at1480�C. At this temperature, silicon reacts with both oxygen andnitrogen. So the heating must take place in an argon atmosphere.

Some light bulbs are filled with argon because the glowingfilament in the bulb will not react with argon as it would reactwith oxygen. Using argon increases the number of hours the bulbcan be lit before it burns out. All the noble gases except radonare used in “neon” lights like those shown in Figure 22.


Using Physical Properties In Section 2.2,three ways to use physical properties arediscussed. Find one example in Section 5.3that illustrates each use. If necessary, rereadpages 48 and 50.

36

KrKrypton

54

XeXenon

86

RnRadon

18

Ar Argon

10

NeNeon

2

HeHelium

Figure 22 When electric current passesthrough noble gases, they emit differentcolors. Helium emits pink, neon emitsorange-red, argon emits lavender, kryptonemits white, and xenon emits blue.

Group 8AThe Noble GasesBuild Science SkillsInferring Hold up an incandescentlight bulb and tell students that thefilament in the light bulb is made oftungsten, which emits light when it isheated to a high temperature. Explainthat a light bulb with a tungstenfilament contains small amounts ofgases, such as argon, that do not reacteasily. Ask, Why isn’t air used in thelight bulb? (The heated filament wouldburn in air, which contains oxygen.)Visual, Logical

ASSESSEvaluate UnderstandingWrite the names of A group elementsdiscussed in Section 3.3 on separateindex cards. Distribute one card to eachpair of students and have them add thefollowing information to the card: chem-ical symbol, atomic number, groupnumber and group name, number ofvalence electrons, physical state at roomtemperature, class of element (metal,nonmetal, or metalloid), and one or twoproperties of the element.

ReteachUse the segments of the periodic tablethat appear throughout the section toreview each A group. Emphasize howthe metallic properties of elementsincrease from top to bottom within agroup and how the number of valenceelectrons changes from left to rightacross the periodic table.

Examples of Identifying Materials:Distinguish halogens by their states andcolors at room temperature.

Examples of Choosing Materials: Using hard calcium carbonate to polishteeth; using argon to increase the life of a light bulb.

Examples of Separating Materials:Sodium chloride from seawater byevaporation; nitrogen from oxygenbased on their boiling points.

If your class subscribes tothe Interactive Textbook, use it toreview key concepts in Section 5.3.

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8. The energy needed to purify recycled alum-inum is only about 5% of the energy needed to extract aluminum from bauxite.9. To produce sulfuric acid10. Chlorine is added to drinking water to kill bacteria.11. Accept all answers that are supported byreasonable arguments. Students may choosenonmetals and say that they display a greaterrange of physical properties and reactivity. 12. The reactivity of nonmetals decreases fromthe top to the bottom of a group.


1. They have similar properties because theyhave the same number of valence electrons.2. The reactivity of alkali metals increases fromthe top of Group 1A to the bottom.3. Carbon4. Nitrogen and phosphorus5. The noble gases (Group 8A)6. Hydrogen is placed with other elementsthat have a single valence electron. 7. The process that uses sunlight to producesugar in plants

Answer to . . .

Figure 21 Sublimation



Eating a variety of foods helps to ensure that allthe elements needed by your body are available.The required elements can be classified as major,lesser, or trace elements. An element is classifiedbased on its percentage by mass in the body.

The six major elements are hydrogen,oxygen, carbon, nitrogen, phosphorus, andcalcium. These six major elements account foralmost 99 percent of your body mass. Nearlyevery compound in your body contains carbonand hydrogen, and many contain oxygen too.The compounds that control all the chemicalchanges that take place in cells contain nitrogen.Calcium is essential for healthy bones and teeth.Phosphorus is found in your DNA and in themolecules that transfer energy within cells.

The lesser elements are iron, potassium,zinc, sodium, sulfur, chlorine, and magnesium.For each lesser element, there is a recommendedamount that needs to be taken in daily. Theseamounts vary from 15 milligrams for zinc to400 milligrams for magnesium. Lesser elementshelp your body build tissues and maintain othercell processes. For example, nerves and musclesrequire magnesium to function properly.

The trace elements are vanadium, chromium,molybdenum, manganese, cobalt, copper, boron,tin, silicon, selenium, fluorine, and iodine. Thequantities required are tiny, but trace elementsperform important functions. For example, redblood cells would not mature without cobalt.

Elemental Friends and FoesSome elements are essential for your health, and some areextremely harmful. You need to obtain the right amountsof the twenty-five essential elements through a balanceddiet, and to reduce your exposure to the harmful elements.

Essential Elements of the Human Body

Major elements (approximately 98.6 percent of total)

Lesser elements (approximately 1.4 percent of total)

Trace elements (less than 0.01 percent of total)

Nonessential elements

Se

Si P S Cl

C N O F

Sn I50

Tin

53

Iodine

34

Selenium

14

Silicon

15

Phosphorus

16

Sulfur

17

Chlorine

6

Carbon

7

Nitrogen

8

Oxygen

9

Fluorine

H

Na Mg

K Ca V Cr Mn Fe Co Cu Zn

Mo42

Molybdenum

24

Chromium

25

Manganese

26

Iron

27

Cobalt

29

Copper

30

Zinc

23

Vanadium

20

Calcium

19

Potassium

11

Sodium

12

Magnesium

1

Hydrogen

146 Chapter 5

B5

Boron

146 Chapter 5

Elemental Friends and FoesBackgroundAll packaged and processed food sold in the United States displays a label with nutritional information. The label is designed to be easy to read and toenable consumers to quickly find theinformation they need to makeappropriate food choices.

The label contains a Daily Valuepercentage (%DV) for calorie-containingnutrients such as fats and carbohydrates,as well as for cholesterol, vitamins, andminerals. For vitamins and minerals, the%DV is based on the Reference DailyIntake (RDI) values established by theU.S. Food and Drug Administration.

On current food labeling, the %DV forvitamins and minerals is the percentageof RDI available in a single serving. Forexample, the RDI for magnesium is 400milligrams. If a single serving of a certainbrand of cereal contains 40 milligrams ofmagnesium, the %DV for magnesium islisted as 10%.

It is likely that the number of elementsclassified as essential will grow alongwith advancements in understanding of nutrition and the human body. Forexample, nickel is an essential element in some species, but has not yet beendetermined to be essential in humans.

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Essential elementsThe 25 elements essential to the human bodyare generally ingested as part of compoundsfound in food. The roles and functions of afew of these elements are shown here.

OxygenThis is the most abundantelement in your body.

The most importantfunction of oxygen is tohelp release the energystored in foods. Youabsorb oxygen fromthe air you breathe.

O8

Oxygen

VanadiumVanadium can help controlblood sugar levels. It alsoplays an important role in

the formation ofbones and teeth.

Vanadium can befound in blackpeppercorns.

V23

Vanadium

IodineIodine isrequired

in small amountsfor the productionof thyroxine by thethyroid gland. Thyroxinecontrols the rate of all chemical processes in the body. Fresh fish is a good source of iodine.

I53

Iodine

HydrogenHydrogen is found infoods and in water,

which accounts for morethan 60 percent of bodymass. Chemical reactionsin cells take place in water.

H1

Hydrogen

CarbonCarbon is thesecond most

common element inthe human body. It isessential to life, because it ispresent in almost every compoundin the body. If a food containscarbohydrates, proteins, or fats,it contains carbon compounds.

C6

Carbon

PotassiumPotassium is essential to muscle and nerve

function, and helps keepthe body’s fluids inbalance. It also stimulatesthe kidneys to removebody wastes. Potassiumcan be found in fruitand dairy products.

K19

Potassium

IronIron is a veryimportant trace

element because it ispart of hemoglobin.This compound transportsoxygen through the bloodto every cell in the body.Meat, fish, and leafy greenvegetables, such as spinach,are good sources of iron.

Fe26

Iron

RED SNAPPER

WATER

BLACK PEPPERCORNS

PASTA

CHEESES

GRAPES

SPINACH


Build Science Skills

Drawing Conclusions

Purpose Students identify elements whose compounds are used to fortify foods.

Materials empty containers of fortifiedfood products such as milk, juice, salt,and bread


Procedure Explain that sometimescompounds of essential elements areadded to foods so that people will havea sufficient amount of these elements in their diets. Tell students that to fortifymeans to enrich or increase the nutrientvalue of food. Pass the empty containersaround. Have students look at the labels.Ask, Which essential elements havebeen added to the foods? (Answersmay include calcium, iron, and iodine.)Why are these elements essential?(Students’ answers should includeinformation from pp. 146 and 147.)

Expected Outcome Students discoverthat compounds of calcium, iron, andiodine are likely to be added when food is fortified.Logical, Visual

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Some elements should be avoided completely.These foes include metals, such as lead andmercury, and the metalloid arsenic. Harmfulelements may enter the body in water, air, orfood. Inside the body, nonessential elementsmay compete with essential elements anddisrupt cell functions. Large amounts ofharmful elements can stress the body’s normalmethods for eliminating toxins. Harmfulelements can build up in body tissues.

For decades lead was used in paint and ingasoline to improve engine performance. Theseproducts are now lead free. The use of mercuryin thermometers has been reduced and arseniccompounds are no longer used in pesticides.

Many trace elements are only helpful ifingested in the small recommended amounts.Larger quantities of most trace elements canbe harmful, as can larger-than-requiredamounts of lesser elements, such as sodium.

LeadToo much lead inthe bloodstream

can lead to organdamage and learningdifficulties, especially inyoung children. For thisreason, the use of lead-based paint was bannedin 1978. Children maystill be a risk if they livein an older house withlayers of peeling paint.

ArsenicArsenic has been known as apoison for centuries, yet

compounds of arsenic were usedto treat some diseases before thediscovery of penicillin. Arseniccompounds are no longer used toprotect crops from insect pests or topreserve wood. Drinking water canabsorb arsenic as it flows over rocks.But the amount of arsenic in drinkingwater is limited by law to less than50 micrograms in each liter of water.

Arsenicpesticide

MercuryMercury is used in numerous

industrial processes,but it is toxic andcan damage thebrain and nervoussystem. For thisreason it should behandled with greatcare. It is particularlyimportant to avoidinhaling mercury vapor.

148 Chapter 5

Harmful Elements

82

PbLead

80

HgMercury

33

AsArsenic

148 Chapter 5

Build Science SkillsMaking Judgments Assign as aresearch topic one of the harmfulelements—mercury, lead, or arsenic—to each student. Have students use theInternet or the library to find two or threerecent newspaper or magazine articlesrelated to the harmful effects of exposureto the element. Ask students to write aparagraph summarizing each article, and then write a paragraph explainingwhether or not they think that moresteps should be taken to protect peoplefrom exposure to the element.

Have a class discussion or debate inwhich students present their researchfindings and their viewpoints. Ask, Whatare the harmful effects of the elementyou researched? (Sample answer:Exposure to lead can damage the centralnervous system, kidneys, and digestivesystem.) What precautions for the useof this element are currently in place?(Sample answer: Lead is no longer allowedas a gasoline additive; regulations prohibitrenting an apartment or house with peel-ing and flaking lead paint to families withyoung children; and lead levels in drinkingwater have been reduced.) Are theseprecautions sufficient? Explain youranswer. (Sample answer: Yes, becausethese regulations have helped significantlyreduce the number of children sufferingfrom lead exposure. According to theCenters for Disease Control, this numberdecreased about 80% between the late1970s and mid-1990s. An EPA documentdated December 2002 reports that in1978 nearly three to four million childrenwere affected. In the 1990s, the numberdeclined to about 890,000.)Interpersonal, Group

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(continued)

■ Choose a trace element other than vanadium,selenium, or iodine. Find out which foods aregood sources of the element.Write a paragraph explaininghow your diet meets or couldbe adjusted to meet yourneed for this element.

■ Take a Discovery Channel Video Field Trip by watching “You Are WhatYou Eat.”

Going Further

ZincThis trace element can befound in almost every cell of

your body. Among other things, ithelps to support a healthy immunesystem. Beef is a good source ofzinc, but no more than 40 milli-grams of zinc should be takendaily. Too much zinc can causeanemia by reducing iron uptake.

SodiumIt is hard to avoid sodium inyour diet because table salt

contains a sodium compound(sodium chloride). Everybodyneeds some sodium each day tomaintain water balance and nervefunction. But too much sodium(more than 3 grams daily) cancause high blood pressure.

SeleniumThis trace element helps to maintain ahealthy immune system. Brazil nuts are a

good source of selenium, as are fruits andvegetables. While selenium supplements maybe useful for some people, no more than 400 micrograms should be taken daily. Toomuch selenium can cause nerve damage.

BEEF

Video Field Trip

BRAZIL NUTS

TABLE SALT

Too much of a good thingMany of the elementsfound in your body areneeded in only very smallamounts. Too much canoften be harmful. The Food and DrugAdministration providesguidelines on the safe dailyquantities to take throughfood or supplements.


34

SeSelenium

30

ZnZinc

11

NaSodium

Integrate HealthA person’s diet must contain somesodium compounds so that importantfunctions such as maintenance ofappropriate water levels within cells andtransmission of nerve impulses will occur.However, the level of sodium compoundsin food (especially in processed foods) isso high that most people’s intake ofsodium compounds exceeds requiredlevels. Have students research thepossible adverse health effects of anexcess of sodium in the body.Verbal

Going FurtherChromium: black pepper, broccoli,asparagus, mushrooms, liver, raisins,nuts, brewer’s yeast; molybdenum:legumes, leafy vegetables, grains;manganese: nuts, oatmeal, ginger, rice; cobalt: meat, dairy products, greenleafy vegetables; silicon: whole grains,liver, red meat. (Tin exists in sufficientquantities in water, food, and air.)Verbal, Portfolio

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After students have viewed the Video Field Trip, ask them the following questions: How did someancient civilizations preserve their dead? (Byembalming, or using preservatives) What are twotypes of information that scientists discover by examining mummies? (Student answers mayinclude age, gender, diet, and cause of death.) Whatevidence led forensic scientists to suspectTutankhamen, also known as King Tut, might

not have died from natural causes? (X-raysshowed bone damage to his skull probably caused by a blow to his head.) List features that scientistsfound in the bones of mummies in Chile.(Student answers may include bone deformationaround the ear, bones with significant nitrogendeposits, and strong and healthy teeth.) What doforensic scientists suspect to be the causes ofthe features found in these mummies? (Fishing in cold waters could have caused the growth aroundthe ears. Nitrogen deposits in their bones could havebeen caused by a diet rich in seafood. A diet of fishcould explain the strong, healthy teeth.)

Video Field Trip

You Are What You Eat


5.1 organizing the elements -...

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