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.)

L2

L2

Reading Focus

1

Section 5.2

Print• Laboratory Manual, Investigation 5A • Guided 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• iText, Section 5.2• Presentation Pro CD-ROM, Section 5.2• Go Online, NSTA SciLinks, Periodic law

Section Resources

The Periodic Table 131

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

UunUuu 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

L2

L1

2

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.

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.

The Periodic Table 131

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.

L1

Section 5.2 (continued)

The Periodic Table 133

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.

L2

L2

The Periodic Table 133

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 elementÕs 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 iso-topes 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.

L2

Section 5.2 (continued)

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.

The Periodic Table 135

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.

Class Time 20 minutes

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.

L2

The Periodic Table 135

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.

L1

L2

Section 5.2 (continued)

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?

The Periodic Table 137

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.

L3

L2

The Periodic Table 137

Answer to . . .

Transition metals

138 Chapter 5

Section 5.2 Assessment

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 iText, use it to review key concepts in Section 5.2.

L1

L2

3

L2

Section 5.2 (continued)

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