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Atoms and thePeriodic Table

Atoms and thePeriodic Table

C H A P T E R 4

1 Atomic StructureWhat Are Atoms?What’s in an Atom?Models of the Atom

2 A Guided Tour of the Periodic Table

Organization of the Periodic Table

Some Atoms Form IonsHow Do the Structures

of Atoms Differ?

3 Families of ElementsHow Are Elements

Classified?MetalsNonmetals

4 Using Moles to Count AtomsCounting ThingsCalculating with Moles

Chapter Preview

102 Copyright © by Holt, Rinehart and Winston. All rights reserved.

Background Have you ever wondered why most metals shine?Metals shine because they are made of elements that reflectlight. Another property of metals is that they do not shatter.Metals bend as they are pressed into thin, flat sheets during thecoin-making process. All metals share some similarities, but eachmetal has its own unique chemical and physical properties.

The unique building shown on the opposite page is theGuggenheim Museum in Bilboa, Spain. This art museum is cov-ered in panels made of titanium. Titanium is a strong, durablemetallic element that can be used for a variety of purposes.

Metals, like everything around us, are made of trillions of tiny units that are too small to see. These units are called atoms.Atoms determine the properties of all substances. For example,gold atoms make gold softer and shinier than silver, which ismade of silver atoms. Pennies get their color from the copperatoms they are coated with. In this chapter, you will learn whatdetermines an atom’s properties, why atoms are considered thesmallest units of elements, and how elements are classified.

Activity 1 What metals do you see during a typical day? Describetheir uses and their properties.

Activity 2 Describe several different ways to classify the metalsshown on the opposite page.

Pre-Reading Questions1. How are the atoms of all elements alike?2. How does the periodic table help us learn

about atoms and elements?3. Which elements does your body contain?

103

ACTIVITYACTIVITYFocusFocus

Atoms determine theproperties of objects.For example, metalatoms give gold itsshine and the ability to be worked into different shapes.

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Atomic Structure> Explain Dalton’s atomic theory, and describe why it was

more successful than Democritus’s theory.> State the charge, mass, and location of each part of an

atom according to the modern model of the atom.> Compare and contrast Bohr’s model with the modern

model of the atom.

Atoms are everywhere. They make up the air you are breath-ing, the chair you are sitting in, and the clothes you are

wearing. This book, including this page you are reading, is alsomade of atoms.

What Are Atoms?Atoms are tiny units that determine the properties of all matter.The aluminum cans shown in Figure 1 are lightweight and easyto crush because of the properties of the atoms that make up thealuminum.

Our understanding of atoms required many centuriesIn the fourth century BCE, the Greek philosopher Democritussuggested that the universe was made of invisible units calledatoms. The word atom is derived from the Greek word meaning“unable to be divided.” He believed movements of atoms causedthe changes in matter that he observed.

Although Democritus’s theory of atoms explained someobservations, Democritus was unable to provide the evidenceneeded to convince people that atoms really existed. Throughoutthe centuries that followed, some people supported Democritus’s

theory. But other theories were also proposed. As thescience of chemistry was developing in the 1700s,

more emphasis was put on making careful andrepeated measurements in scientific experiments.As a result, more-reliable data were collected andused to favor one theory over another.

O B J E C T I V E S

SECTION

1

K E Y T E R M S

nucleusprotonneutron electronorbitalvalence electron

▲

Disc One, Module 2:Models of the AtomUse the Interactive Tutor to learn moreabout this topic.

Figure 1The atoms in aluminum, seenhere as an image from a scanningtunneling electron microscope,give these aluminum cans theirproperties.

AluminumAtoms

Copyright © by Holt, Rinehart and Winston. All rights reserved.

John Dalton developed an atomic theoryIn 1808, an English schoolteacher named John Dalton proposedhis own atomic theory. Dalton’s theory was developed with a sci-entific basis, and some parts of his theory still hold true today.Like Democritus, Dalton proposed that atoms could not bedivided. Today, we know that atoms are actually made up of evensmaller particles! According to Dalton, all atoms of a given ele-ment were exactly alike. Dalton also stated that atoms of differ-ent elements could join to form compounds. Today, Dalton’stheory is considered the foundation for modern atomic theory.

Atoms are the building blocks of moleculesAn atom is the smallest part of an element that still has the el-ement’s properties. Imagine dividing a coin made of pure copperuntil the pieces were too small for you to see. If you were able tocontinue dividing these pieces, you would be left with the sim-plest units of the coin—copper atoms. All the copper atomswould be alike. Each copper atom would have the same chemi-cal properties as the coin you started with.

You have learned that atoms can join. Figure 2 shows atomsjoined together to form molecules of water. The water we see isactually made of a very large number of water molecules.Whether it gushes downstream in a riverbed or is bottled for usto drink, water is always the same: each molecule is made of twohydrogen atoms and one oxygen atom.

A T O M S A N D T H E P E R I O D I C T A B L E 105

Figure 2Each molecule of water is made

of two hydrogen atoms and oneoxygen atom.

B

Hydrogen atoms

Oxygenatom

The water that we see, no matter whatits source, is made of many molecules. A

Moleculesof water

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What’s in an Atom?Less than 100 years after Dalton published his atomic theory, sci-entists determined that atoms consisted of still smaller particlesand could be broken down even further. While we now know thatatoms are made up of many different subatomic particles, weneed to study only three of these particles to understand thechemistry of most substances.

Atoms are made of protons, neutrons, and electronsAt the center of each atom is a small, dense with apositive electric charge. The nucleus is made of and

These two subatomic particles are almost identical insize and mass, but protons have a positive electric charge whileneutrons have no electric charge at all. Moving around outsidethe nucleus is a cloud of very tiny negatively charged subatomicparticles with very little mass. These particles are called

To get an idea of how far from the nucleus an elec-tron can be, see Figure 3. If the nucleus of an atom were the sizeof a marble, the whole atom would be the size of a football sta-dium! A helium atom, shown in Figure 4, has one more protonand one more electron than a hydrogen atom has. The number ofprotons and electrons an atom has is unique for each element.

Unreacted atoms have no overall chargeYou might be surprised to learn that atoms are not charged eventhough they are made of charged protons and electrons. Atomsdo not have a charge because they have an equal number of pro-tons and electrons whose charges exactly cancel. A helium atomhas two protons and two electrons. The atom is neutral becausethe positive charge of the two protons exactly cancels the nega-tive charge of the two electrons.

electrons.

neutrons.protons

nucleus

Charge of two protons: +2Charge of two neutrons: 0Charge of two electrons: −2Total charge of a helium atom: 0

Proton +1 1.67 × 10−27 In the nucleus

Neutron 0 1.67 × 10−27 In the nucleus

Electron −1 9.11 × 10−31 Moving aroundoutside the nucleus

Subatomic Particles

Particle Charge Mass (kg) Location in the atom

106 C H A P T E R 4

2e–

Nucleus ProtonNeutron

Helium Atom

nucleus an atom’s centralregion which is made up ofprotons and neutrons

proton a subatomic particlethat has a positive charge andthat is found in the nucleus ofan atom

neutron a subatomic particlethat has no charge and thatis found in the nucleus of anatom

electron a subatomic parti-cle that has a negative charge

▲▲

▲▲

Figure 3If the nucleus of an atom werethe size of a marble, the wholeatom would be the size of a foot-ball stadium

Figure 4A helium atom is made of twoprotons, two neutrons, and twoelectrons (2e–).



Models of the AtomDemocritus in the fourth century BCE and later Dalton, in thenineteenth century, thought that the atom could not be split. Thattheory had to be modified when it was discovered that atoms aremade of protons, neutrons, and electrons. Like most scientificmodels and theories, the model of the atom has been revisedmany times to explain such new discoveries.

Bohr’s model compares electrons to planetsIn 1913, the Danish scientist Niels Bohr suggested that electronsin an atom move in set paths around the nucleus much likethe planets orbit the sun in our solar system. In Bohr’s model,each electron has a certain energy that is determined by itspath around the nucleus. This path defines the electron’s energylevel. Electrons can only be in certain energy levels. They mustgain energy to move to a higher energy level or lose energy tomove to a lower energy level.

One way to imagine Bohr’s model is to compare an atom tothe stairless building shown in Figure 5. Imagine that the nucleusis in a very deep basement and that the electronic energy levelsbegin on the first floor. Electrons can be on any floor of the build-ing but not between floors. Electrons gain energy by riding up inthe elevator and lose energy by riding down in the elevator.Bohr’s description of energy levels is still considered accuratetoday.

Electrons act more like wavesBy 1925, Bohr’s model of the atomno longer explained electron behav-ior. So a new model was proposedthat no longer assumed that elec-trons orbited the nucleus along defi-nite paths like planets orbiting thesun. In this modern model of theatom, it is believed that electronsbehave more like waves on a vibrat-ing string than like particles.

Basement

1st energy level

Nucleus

2nd energy level

3rd energy level

4th energy level

8e–

18e–

2e–

Remember that protons have apositive charge and neutronsare neutral.

V

Figure 5The energy levels of an atomare like the floors of the build-ing shown here. The energydifference between energylevels decreases as the energylevel increases.

Electronscannot bebetweenfloors.


An electron’s exact location cannot be determinedImagine the moving blades of a fan, like theone shown in Figure 6. If you were asked whereany one of the blades was located at a certaininstant, you would not be able to give an exactanswer. It is very difficult to know the exactlocation of any of the blades because they aremoving so quickly. All you know for sure is thateach blade could be anywhere within theblurred area you see as the blades turn.

It is impossible to determine both the exactlocation of an electron in an atom and the elec-tron’s speed and direction. The best scientistscan do is calculate the chance of finding anelectron in a certain place within an atom. Oneway to visually show the likelihood of findingan electron in a given location is by shading.The darker the shading, the better the chance offinding an electron at that location. The wholeshaded region is called an electron cloud.

Electrons exist in energy levelsWithin the atom, electrons with different amounts of energy existin different energy levels. There are many possible energy levelsthat an electron can occupy. The number of filled energy levels anatom has depends on the number of electrons. The first energylevel holds two electrons, and the second energy level holds eight.So, a lithium atom, with three electrons, has two electrons in itsfirst energy level and one in the second. Figure 7 shows how thefirst four energy levels are filled.

108 C H A P T E R 4

2e�

8e�

18e�

32e� Energy level 4

Energy level 1

Energy level 2Energy level 3

Figure 6The exact location of any of theblades of this fan is difficult todetermine. The exact locationof an electron is impossible todetermine.

Figure 7Electrons can be foundin different energy levels.Each energy level holdsa certain number ofelectrons.


Electrons are found in orbitals within energy levelsThe regions in an atom where electrons are likely to be found arecalled Within each energy level, electrons occupyorbitals that have the lowest energy. The four different kinds oforbitals are the s, p, d, and f orbitals. The simplest kind of orbitalis an s orbital. An s orbital can have only one possible orientationin space because it has a shape like a sphere, as shown in Figure 8.An s orbital has the lowest energy and can hold two electrons.

A p orbital, on the other hand, is dumbbell shaped and can beoriented three different ways in space, as shown in Figure 9. Theaxes on the graphs are drawn to help you picture how theseorbitals look in three dimensions. Imagine the y-axis being flaton the page. Imagine the dotted lines on the x- and z-axes goinginto the page, and the darker lines coming out of the page. A porbital has more energy than an s orbital has. Because each porbital can hold two electrons, the three p orbitals can hold atotal of six electrons.

The d and f orbitals are much more complex. There are fivepossible d orbitals and seven possible f orbitals. An f orbital hasthe greatest energy. Although all these orbitals are very differentin shape, each can hold a maximum of two electrons.

orbitals.


y

z

x

y

z

x

y

z

x

y

z

x

QuickQuickQuick ACTIVITYACTIVITY

A scientific model is a simplified representationbased on limited knowledge that describes how anobject looks or functions. In this activity, you willconstruct your own model.

1. Obtain from your teacher a can that is coveredby a sock and sealed with tape. An unknownobject is inside the can.

2. Without unsealing the container, try to determinethe characteristics of the object inside by exam-ining it through the sock. What is the object’smass? What is its size, shape, and texture?Record all of your observations in a data table.

3. Remove the taped sock so that you can touchthe object without looking at it. Record theseobservations as well.

4. Use the data you have collected to draw amodel of the unknown object.

5. Finally remove the object to see what it is. Compare and contrast the model you madewith the object it is meant to represent.

Constructing a Model

Figure 9Each of these p orbitals can hold amaximum of two electrons, so allthree together can hold a total ofsix electrons.

orbital a region in an atomwhere there is a high prob-ability of finding electrons

▲

Figure 8An s orbital is shaped like asphere, so it has only one possibleorientation in space. An s orbitalcan hold a maximum of twoelectrons.


Every atom has between one and eight valence electronsAn electron in the outermost energy level of an atom is calleda Valence electrons determine an atom’schemical properties and its ability to form bonds. The single elec-tron of a hydrogen atom is a valence electron because it is theonly electron the atom has. The glowing red sign shown in Figure10 is made of neon atoms. In a neon atom, which has 10 elec-trons, 2 electrons fill the lowest energy level. Its valence elec-trons, then, are the 8 electrons that are farther away from thenucleus in the atom’s second (and outermost) energy level.

valence electron.

110 C H A P T E R 4

S E C T I O N 1 R E V I E W

1. Summarize the main ideas of Dalton’s atomic theory.

2. Explain why Dalton’s theory was more successful thanDemocritus’s theory.

3. List the charge, mass, and location of each of the three sub-atomic particles found within atoms.

4. Predict how many valence electrons a nitrogen atom has.

5. Explain why oxygen atoms are neutral.

6. Compare an atom’s structure to a ladder. What parts of theladder correspond to the energy levels of the atom? Identifyone way a real ladder is not a good model for the atom.

7. Explain how the path of an electron differs in Bohr’s modeland in the modern model of the atom.

8. Critical Thinking In the early 1900s, two associates of NewZealander Ernest Rutherford bombarded thin sheets of goldwith positively charged subatomic particles. They foundthat most particles passed right through the sheets butsome bounced back as if they had hit something solid.Based on their results, what do you think an atom is madeof? What part of the atom caused the particles to bounceback? (Hint: Positive charges repel other positive charges.)

S U M M A R Y

> Elements are made of verysmall units called atoms.

> The nucleus of an atom ismade of positively chargedprotons and unchargedneutrons.

> Negatively charged elec-trons surround the nucleus.

> Atoms have an equal num-ber of protons and electrons.

> In Bohr’s model of theatom, electrons orbit thenucleus in set paths.

> In the modern atomicmodel, electrons are foundin orbitals within eachenergy level.

> Electrons in the outermostenergy level are calledvalence electrons.

(Valence electrons)

Neon Atom

8e–

2e–

valence electron an elec-tron that is found in the outer-most shell of an atom andthat determines the atom’schemical properties

▲

Figure 10The neon atoms of this sign haveeight valence electrons. The signlights up because atoms first gainenergy and then release thisenergy in the form of light.


> Relate the organization of the periodic table to the arrangement of electrons within an atom.

> Explain why some atoms gain or lose electrons to form ions.> Determine how many protons, neutrons, and electrons an atom

has, given its symbol, atomic number, and mass number.> Describe how the abundance of isotopes affects an element’s

average atomic mass.

A Guided Tour of the Periodic Table

When you are in a store, are your favorite items placed ran-domly on the shelves? Usually similar items are grouped

together, as shown in Figure 11, so that you can find what you needquickly. The periodic table organizes the elements in a similar way.

Organization of the Periodic TableThe periodic table groups similar elements together. This organi-zation makes it easier to predict the properties of an elementbased on where it is in the periodic table. In the periodic tableshown in Figure 12, elements are represented by their symbolsand are arranged in a certain order. The order is based on thenumber of protons an atom of that element has in its nucleus.

A hydrogen atom has one proton, so hydrogen is the first el-ement listed in the periodic table. A helium atom has two protonsand is the second element listed. Elements are listed in this orderin the periodic table because the states that whenelements are arranged this way, similarities in their propertieswill occur in a regular pattern.

periodic law

O B J E C T I V E S

SECTION

2

K E Y T E R M S

periodic lawperiodgroupionatomic numbermass numberisotopeatomic mass unit (amu)average atomic mass

▲

Figure 11In many stores, similar items aregrouped so that they are easier to find.

periodic law the law thatstates that the repeatingchemical and physical proper-ties of elements change peri-odically with the atomicnumbers of the elements

▲

Copyright © by Holt, Rinehart and Winston.All rights reserved.

Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9

Group 1 Group 2

1

2

3

4

5

6

7

Perio

d

6C

Carbon12.0107

Atomic number

Symbol

Name

Average atomic mass

† Estimated from currently availableIUPAC data.

* The systematic names and symbols for elements greater than 109 will be used until the approval of trivial names by IUPAC.

H1

Hydrogen1.007 94

Key:3

Lithium6.941

4

BerylliumLi Be

11

Sodium

12

Magnesium24.3050

Na Mg

58

Cerium140.116

59

Praseodymium140.907 65

60

Neodymium144.24

61

Promethium(145)

62

Samarium150.36

Ce Pr Nd Pm Sm

90

Thorium232.0381

91

Protactinium231.035 88

92

Uranium238.0289

93

Neptunium(237)

94

Plutonium(244)

Th Pa U Np Pu

19

Potassium39.0983

20

Calcium40.078

21

Scandium44.955 910

22

Titanium47.867

23

Vanadium50.9415

24

Chromium51.9961

25

Manganese54.938 049

26

Iron55.845

27

Cobalt58.933 200

VK Ca Sc Ti Cr Mn Fe Co

37

Rubidium85.4678

38

Strontium87.62

39

Yttrium88.905 85

40

Zirconium91.224

41

Niobium92.906 38

42

Molybdenum95.94

43T

Technetium (98)

44

Ruthenium101.07

45

Rhodium102.905 50

Rb Sr Y Zr Nb Mo c Ru Rh

87

Francium(223)

88

Radium(226)

89

Actinium(227)

104

Rutherfordium(261)

105

Dubnium(262)

106

Seaborgium(263)

107

Bohrium(264)

108

Hassium(265)

109

Meitnerium(268)†

Fr Ra Ac Rf Db Sg Bh Hs Mt

55

Cesium132.905 45

56

Barium137.327

57

Lanthanum138.9055

72

Hafnium178.49

73

Tantalum180.9479

74

Tungsten183.84

75

Rhenium186.207

76 77

Osmium190.23

Iridium192.217

Cs Ba La Hf T W Re IrOsa

9.012 182

22.989 770

Figure 12The Periodic Table of the Elements

112 C H A P T E R 4

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28Ni

Nickel58.6934

29Cu

Copper63.546

30ZnZinc65.39

31Ga

Gallium69.723

32Ge

Germanium72.61

33As

Arsenic74.921 60

34Se

Selenium78.96

35Br

Bromine79.904

36Kr

Krypton83.80

13Al

Aluminum26.981 538

14Si

Silicon28.0855

15P

Phosphorus30.973 761

16S

Sulfur32.066

17Cl

Chlorine35.4527

18Ar

Argon39.948

5B

Boron10.811

6C

Carbon12.0107

7N

Nitrogen14.006 74

8O

Oxygen15.9994

9F

Fluorine18.998 4032

10NeNeon20.1797

2He

Helium4.002 602

46Pd

Palladium106.42

47AgSilver

107.8682

48Cd

Cadmium112.411

49In

Indium114.818

50SnTin

118.710

51Sb

Antimony121.760

52Te

Tellurium127.60

53I

Iodine126.904 47

54Xe

Xenon131.29

110Uun*

Ununnilium(269)†

111Uuu*

Unununium(272)†

112Uub*

Ununbium(277)†

114Uuq*

Ununquadium(285)†

78Pt

Platinum195.078

79AuGold

196.966 55

80Hg

Mercury200.59

81Tl

Thallium204.3833

82PbLead207.2

83Bi

Bismuth208.980 38

84Po

Polonium(209)

85At

Astatine(210)

86Rn

Radon(222)

63Eu

Europium151.964

64Gd

Gadolinium157.25

65Tb

Terbium158.925 34

66Dy

Dysprosium162.50

67

Holmium164.930 32

68

Erbium167.26

69

Thulium168.934 21

70

Ytterbium173.04

71

Lutetium174.967

Ho Er Tm Yb Lu

95Am

Americium(243)

96CmCurium

(247)

97Bk

Berkelium(247)

98Cf

Californium(251)

99

Einsteinium(252)

100

Fermium(257)

101

Mendelevium(258)

102

Nobelium(259)

103

Lawrencium(262)

Es Fm Md No Lr

A team at Lawrence Berkeley National Laboratories reported the discovery of elements 116 and 118 in June 1999. The same team retracted the discovery in July 2001. The discovery of element 114 has been reported but not confirmed.

Group 13 Group 14 Group 15 Group 16 Group 17

Group 18

Group 10 Group 11 Group 12

The atomic masses listed in this table reflect the precision of current measurements. (Values listed in parentheses are those of the element’s most stable or most common isotope.) In calculations throughout the text, however, atomic masses have been rounded to two places to the right of the decimal.

Metals

Alkali metals

Alkaline-earth metals

Transition metals

Other metals

Nonmetals

Hydrogen

Semiconductors (also known as metalloids) Other nonmetals

Halogens

Noble gases

A T O M S A N D T H E P E R I O D I C T A B L E 113Copyright © by Holt, Rinehart and Winston. All rights reserved.

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114 C H A P T E R 4

period a horizontal row ofelements in the periodic table

group (family) a verticalcolumn of elements in theperiodic table

▲▲

The periodic table helps determine electron arrangementHorizontal rows in the periodic table are called Just as thenumber of protons an atom has increases by one as you move fromleft to right across a period, so does its number of electrons. You candetermine how an atom’s electrons are arranged if you knowwhere the corresponding element is located in the periodic table.

Hydrogen and helium are both located in Period 1 of the peri-odic table. Figure 13 shows that a hydrogen atom has one elec-tron in an s orbital, while a helium atom has one more electron,for a total of two. Lithium is located in Period 2. The electronarrangement for lithium is just like that for a helium atom,except that lithium has a third electron in an s orbital in the sec-ond energy level, as follows:

Energy level Orbital Number of electrons1 s 22 s 1

As you continue to move to the right in Period 2, you can seethat a carbon atom has electrons in s orbitals and p orbitals. Thelocations of the six electrons in a carbon atom are as follows:

Energy level Orbital Number of electrons1 s 22 s 22 p 2

A nitrogen atom has three electrons in p orbitals, an oxygenatom has four, and a fluorine atom has five. Figure 13 shows thata neon atom has six electrons in p orbitals. Each orbital can holdtwo electrons, so all three p orbitals are filled.

Elements in the same grouphave similar propertiesValence electrons determinethe chemical properties ofatoms. Atoms of elements inthe same or column,have the same number ofvalence electrons, so these el-ements have similar proper-ties. Remember that theseelements are not exactly alike,though, because atoms ofthese elements have differentnumbers of protons in theirnuclei and different numbersof electrons in their filledinner energy levels.

group,

periods.

1

2

3

4

5

6

7

6

7

1e- in an s orbital

2e- filling an s orbital

s orbitals filled,1e- in a p orbital

s orbitals filled,2e- in p orbitals

C

HeH He

Li Be

s orbitals filled, 6e- filling three p orbitals

B O FN Nes orbitalsp orbitals

d orbitalsf orbitals

Figure 13The electronic arrangement ofatoms becomes increasingly morecomplex as you move further rightacross a period and further downa group of the periodic table.


Some Atoms Form IonsAtoms of Group 1 elements are reactive becausetheir outermost energy levels contain only one elec-tron. Atoms that do not have filled outer s and porbitals may undergo a process called ionization.That is, they may gain or lose valence electrons sothat they have a full outermost s and/or p orbital. Ifan atom gains or loses electrons, it no longer has thesame number of electrons as it does protons. Because thecharges do not cancel completely as they did before, the thatforms has a net electric charge, as shown for the lithium ion inFigure 14. Sodium chloride, or table salt, shown in Figure 15 ismade of sodium and chloride ions.

A lithium atom loses one electron to form a 1+ charged ionLithium is located in Group 1 of the periodic table. It is so reac-tive that it even reacts with the water vapor in the air. An electronis easily removed from a lithium atom, as shown in Figure 14. Theatomic structure of lithium explains its reactivity. A lithium atomhas three electrons. Two of these electrons occupy the first energylevel in the s orbital, but only one electron occupies the secondenergy level. This single valence electron makes lithium veryreactive. Removing this electron forms a positive ion, or cation.

A lithium ion, written as Li+, is much less reactive than alithium atom because it has a full outer s orbital. Atoms of otherGroup 1 elements also have one valence electron. They are alsoreactive and behave similarly to lithium.

A fluorine atom gains one electron to form a 1– charged ionLike lithium, fluorine is also very reactive. However, instead oflosing an electron to become less reactive, an atom of the elementfluorine gains one electron to form an ion with a 1– charge.Fluorine is located in Group 17 of the periodic table, and eachatom has nine electrons. Two of these electrons occupy the firstenergy level, and seven valence electrons occupy the secondenergy level. A fluorine atom needs only one more electron to havea full outermost energy level. An atom of fluo-rine easily gains this electron to form a nega-tive ion, or anion, as shown in Figure 16.

Ions of fluorine are called fluoride ionsand are written as F–. Because atoms of otherGroup 17 elements also have seven valenceelectrons, they are also reactive and behavesimilarly to fluorine.

ion


Figure 14The valence electron of a reactivelithium atom may be removed toform a lithium ion, Li+, with a 1+charge.

ion an atom or group of atomsthat has lost or gained one ormore electrons and has a neg-ative or positive charge

▲

Figure 16A fluorine atom easily gains onevalence electron to form a fluorideion, F–, with a 1– charge.

Lithium atom Lithium ion

Electron lost

+

Fluorine atom

Electron gained

Fluoride ion

–

+1e-

-1e-

Figure 15Table salt is made of sodium andchloride ions.


How Do the Structures of Atoms Differ?As you have seen with lithium and fluorine, atoms of different el-ements have their own unique structures. Because these atomshave different structures, they have different properties. An atomof hydrogen found in a molecule of swimming-pool water hasproperties very different from an atom of uranium in nuclear fuel.

Atomic number equals the number of protonsThe Z, tells you how many protons are in anatom. Remember that atoms are always neutral because theyhave an equal number of protons and electrons. Therefore, theatomic number also equals the number of electrons the atomhas. Each element has a different atomic number. For example,the simplest atom, hydrogen, has just one proton and one elec-tron, so for hydrogen, Z � 1. The largest naturally occurringatom, uranium, has 92 protons and 92 electrons, so Z � 92 foruranium. The atomic number for a given element never changes.

Mass number equals the total number of subatomic particles in the nucleusThe A, of an atom equals the number of protonsplus the number of neutrons. A fluorine atom has 9 protons and10 neutrons, so A = 19 for fluorine. Oxygen has 8 protons and 8neutrons, so A = 16 for oxygen. This mass number includes onlythe number of protons and neutrons (and not electrons) becauseprotons and neutrons provide most of the atom’s mass. Althoughatoms of an element always have the same atomic number, theycan have different mass numbers. Figure 17 shows which sub-atomic particles in the nucleus of an atom contribute to theatomic number and which contribute to the mass number.

mass number,

atomic number,

116 C H A P T E R 4

Mass number, A =number of protons + number of neutrons

Atomic number, Z =number of protons

Nucleus

Figure 17 Atoms of the same element havethe same number of protons andtherefore have the same atomicnumber. But they may have differ-ent mass numbers, depending onhow many neutrons each atom has.

atomic number the num-ber of protons in the nucleusof an atom

mass number the sum ofthe numbers of protons and neutrons in the nucleus of an atom

▲▲

Disc One, Module 3:Periodic PropertiesUse the Interactive Tutor to learn moreabout these topics.


Isotopes of an element have different numbers of neutronsNeutrons can be added to an atom without affecting the numberof protons and electrons the atom is made of. Many elementshave only one stable form, while other elements have different“versions” of their atoms. Each version has the same number ofprotons and electrons as all other versions but a different num-ber of neutrons. These different versions, or vary inmass but are all atoms of the same element because they eachhave the same number of protons.

The three isotopes of hydrogen, shown in Figure 18, have thesame chemical properties because each is made of one protonand one electron. The most common hydrogen isotope, protium,has only a proton in its nucleus. A second isotope of hydrogenhas a proton and a neutron. The mass number, A, of this secondisotope is two, and the isotope is twice as massive. In fact, thisisotope is sometimes called “heavy hydrogen.” It is also known asdeuterium, or hydrogen-2. A third isotope has a proton and twoneutrons in its nucleus. This third isotope, tritium, has a massnumber of three.

Some isotopes are more common than othersHydrogen is present on both the sun and on Earth. In bothplaces, protium (the hydrogen isotope without neutrons in itsnucleus) is found most often. Only a very small fraction of theless common isotope of hydrogen, deuterium, is found on thesun and on Earth, as shown in Figure 19. Tritium is an unstableisotope that decays over time, so it is found least often.

isotopes,


Isotopes of Hydrogen

ProtiumA = 1

DeuteriumA = 2

TritiumA = 3

Figure 18Protium has only a proton in its nucleus. Deuteriumhas both a proton and a neutron in its nucleus, whiletritium has a proton and two neutrons.

isotope an atom that has the same number of protonsas other atoms of the sameelement do but that has a dif-ferent number of neutrons

▲

Figure 19Hydrogen makes up less than

1% of Earth’s crust. Only 1 out ofevery 6000 of these hydrogenatoms is a deuterium isotope.

A

Seventy-five percent of themass of the sun is hydrogen, withprotium isotopes outnumberingdeuterium isotopes 50 000 to 1.

B


Cl3517

Mass number

Atomic number

Mass number

Atomic number

17 protons17 electrons Cl37

1717 protons17 electrons

37 − 17 = 20 neutrons35 − 17 = 18 neutrons

Calculating the number of neutrons in an atomAtomic numbers and mass numbers may be included along withthe symbol of an element to represent different isotopes. The twoisotopes of chlorine are represented this way in Figure 20. If youknow the atomic number and mass number of an atom, you cancalculate the number of neutrons it has. Uranium has several isotopes. The isotope that is used in nuclearreactors is uranium-235, or 235

92U. Like all uranium atoms, it hasan atomic number of 92, so it must have 92 protons and 92 elec-trons. It has a mass number of 235, which means its number ofprotons and neutrons together is 235. The number of neutronsmust be 143.

The mass of an atomThe mass of a single atom is very small. A single fluorine atomhas a mass less than one trillionth of a billionth of a gram.Because it is very hard to work with such tiny masses, atomicmasses are usually expressed in atomic mass units. An

is equal to one-twelfth of the mass of a carbon-12 atom. This isotope of carbon has six protons and six neutrons,so individual protons and neutrons must each have a mass ofabout 1.0 amu because electrons contribute very little mass.

Often, the atomic mass listed for an element in the periodictable is an average atomic mass for the element as it is found innature. The for an element is a weightedaverage, so the more commonly found isotopes have a greatereffect on the average than rare isotopes.

Figure 21 shows how the natural abundance of chlorine’s twoisotopes affects chlorine’s average atomic mass. The averageatomic mass of chlorine is 35.45 amu. This mass is much closerto 35 amu than to 37 amu. That’s because the atoms of chlorinewith masses of nearly 35 amu are found more often and thereforecontribute more to chlorine’s average atomic mass than chlorineatoms with masses of nearly 37 amu.

average atomic mass

mass unit (amu)atomic

118 C H A P T E R 4

atomic mass unit (amu)a unit of mass that describesthe mass of an atom or mole-cule; it is exactly one-twelfthof the mass of a carbon atomwith mass number 12

average atomic massthe weighted average of themasses of all naturally occur-ring isotopes of an element

▲▲

Figure 20One isotope of chlorinehas 18 neutrons, whilethe other isotope has 20 neutrons.

Mass number (A): 235Atomic number (Z): − 92Number of neutrons: 143

QuickACTIVITYACTIVITYQuickQuickQuick

IsotopesCalculate the number of neutrons there are in the fol-lowing isotopes. (Use the periodic table to find theatomic numbers.)

1. carbon-14 2. nitrogen-153. sulfur-354. calcium-45 5. iodine-131




1. Explain how you can determine the number of protons,electrons, and neutrons an atom has from an atom’s massnumber and its atomic number.

2. Calculate how many neutrons a phosphorus-32 atom has.

3. Name the elements represented by the following symbols:a. Li d. Br g. Nab. Mg e. He h. Fec. Cu f. S i. K

4. Compare the number of valence electrons an oxygen, O, atomhas with the number of valence electrons a selenium, Se, atomhas. Are oxygen and selenium in the same period or group?

5. Explain why some atoms gain or lose electrons to form ions.

6. Predict which isotope of nitrogen is more commonly found,nitrogen-14 or nitrogen-15. (Hint: What is the averageatomic mass listed for nitrogen in the periodic table?)

7. Describe why the elements in the periodic table arearranged in order of increasing atomic number.

8. Critical Thinking Before 1937, all naturally occurring el-ements had been discovered, but no one had found anytrace of element 43. Chemists were still able to predict the chemical properties of this element (now called tech-netium), which is widely used today for diagnosing medicalproblems. How were these predictions possible? Which elements would you expect to be similar to technetium?

S U M M A R Y

> Elements are arranged inorder of increasing atomicnumber so that elementswith similar properties arein the same column, orgroup.

> Elements in the same grouphave the same number ofvalence electrons.

> Reactive atoms may gain or lose valence electrons to form ions.

> An atom’s atomic numberis its number of protons.

> An atom’s mass number is its total number of pro-tons and neutrons in thenucleus.

> Isotopes of an elementhave different numbers of neutrons, and thereforehave different masses.

> An element’s average atomic mass is a weightedaverage of the masses of its naturally occurring isotopes.

Figure 21The average atomic mass of chlorine is closer to 35amu than it is to 37 amubecause 35Cl isotopes arefound more often than 37Cl isotopes.

Cl17

Chlorine

35.4527(76%)

35Cl

37Cl

(24%)

Average atomic mass

Note: Calculations using the values from the pie chart donot give a result of exactly 35.45 amu because of rounding.


www.scilinks.orgTopic: Element FamiliesSciLinks code: HK4046

Families of Elements

> Locate alkali metals, alkaline-earth metals, and transitionmetals in the periodic table.

> Locate semiconductors, halogens, and noble gases in theperiodic table.

> Relate an element’s chemical properties to the electronarrangement of its atoms.

O B J E C T I V E S

SECTION

3

120 C H A P T E R 4

K E Y T E R M S

metalnonmetalsemiconductoralkali metalalkaline-earth metaltransition metalhalogennoble gas

▲

Figure 22Just like the members of this

family, elements in the periodic table

share certain similarities.B

A

Li

V

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

Rf

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Re

Bh

IrOs

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Fe

Ru

Hs

Co

Rh

Mt

H

Tc

Es Fm Md No Lr

Ho Er Tm Yb Lu

Pt

Uun*Uuu*

Au Hg Tl Pb Bi Po At Rn

Uub* Uuq* Uuh* Uuo*

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ni Cu Zn Ga Ge As Se Br Kr

Al Si P S Cl Ar

B C N O F Ne

He

Pd Ag Cd In Sn Sb Te I Xe

3

11

19

37

55

87

58

90

59

91

60

92

61

93

62

94

4

12

20

38

56

88

21

39

57

89

22

40

72

104

23

41

73

105

24

42

74

106

25

43

75

107

26

44

76 77

108

27

45

109

1

63

95

64

96

65

97

66

98

67

99

68

100

69

101

70

102

71

103

28 29 30 31 32 33 34 35 36

13 14 15 16 17 18

5 6 7 8 9 10

2

46 47 48 49 50 51 52 53 54

78

110 111

79 80 81 82 83 84 85 86

112 114 116 118

3

Note: Sometimes the boxed elements toward the right side of the periodic table are classified as a separate group and called semiconductors or metalloids.

4 5 6 7 8 9

1

1

2

3

4

5

6

7

2 13 14 15 16 17

18

10 11 12

MetalsNonmetals

A B

You may have wondered why groups in the periodic table aresometimes called families. Consider your own family. Though

each member is unique, you all share certain similarities. Allmembers of the family shown in Figure 22A, for example, have asimilar appearance. Members of a family in the periodic tablehave many chemical and physical properties in common becausethey have the same number of valence electrons.

How Are Elements Classified?Think of each element as a member of a family that is also relatedto other elements nearby. Elements are classified as metals ornonmetals, as shown in Figure 22B. This classification groups el-ements that have similar physical and chemical properties.


Elements are classified into three groupsAs you can see in Figure 22B, most elements are Mostmetals are shiny solids that can be stretched and shaped. Theyare also good conductors of heat and electricity. All except for hydrogen, are found on the right side of the periodictable. Nonmetals may be solids, liquids, or gases. Solid non-metals are typically dull and brittle and are poor conductors ofheat and electricity. But some elements that are classified as non-metals can conduct under certain conditions. These elements aresometimes considered to be their own group and are called

or metalloids.

MetalsMany elements are classified as metals. To further classify metals,similar metals are grouped together. There are four differentkinds of metals. Two groups of metals are located on the left sideof the periodic table. Other metals, like aluminum, tin, and lead,are located toward the right side of the periodic table. Most metals,though, are located in the middle of the periodic table.

The alkali metals are very reactiveSodium is found in Group 1 of the periodictable, as shown in Figure 23A. Like other

it is soft and shiny and reactsviolently with water. Sodium must be storedin oil, as in Figure 23B, to prevent it fromreacting with moisture in the air.

An atom of an alkali metal is very reac-tive because it has one valence electron thatcan easily be removed to form a positive ion.You have already seen in Section 2 howlithium, another alkali metal, forms positiveions with a 1+ charge. Similarly, the valenceelectron of a sodium atom can be removedto form the positive sodium ion Na+.

Because alkali metals such as sodiumare so reactive, they are not found in natureas elements. Instead, they combine withother elements to form compounds. Forexample, the salt you use to season yourfood is actually the compound sodium chlo-ride, NaCl.

alkali metals

semiconductors

nonmetals,

metals.


19

KPotassium39.0983

11

NaSodium

22.989 770

3

LiLithium6.941

37

RbRubidium85.4678

55

CsCesium

132.905 45

87

FrFrancium

(223)

metal an element that isshiny and conducts heat and electricity well

nonmetal an element thatconducts heat and electricitypoorly

semiconductor an elementor compound that conductselectric current better than aninsulator but not as well as aconductor does

alkali metal one of the elements of Group 1 of theperiodic table

▲▲

▲▲

Figure 23The alkali metals are located on

the left edge of the periodic table.A

The alkali metal sodium must bestored in oil. Otherwise, it will reactviolently with moisture and oxygenin the air.

B

Alkali Metals

Group 1


Alkaline-earth metals are found in limestone and in the human bodyCalcium is in Group 2 of the periodic table, as shown in Figure 24A,and is an Atoms of alkaline-earth metals,such as calcium, have two valence electrons. Alkaline-earth met-als are less reactive than alkali metals, but they may still react toform positive ions with a 2+ charge. When the valence electronsof a calcium atom are removed, a calcium ion, Ca2+, forms.Alkaline-earth metals like calcium also combine with other el-ements to form compounds.

Calcium compounds make up the hard shells of many seaanimals. When the animals die, their shells settle to form largedeposits that eventually become limestone or marble, both ofwhich are very strong materials used in construction. Coral isone example of a limestone structure. The “skeletons” of millionsof tiny animals combine to form sturdy coral reefs that many fishrely on for protection, as shown in Figure 24B. Your bones andteeth also get their strength from calcium compounds.

Magnesium is another alkaline-earth metal that has proper-ties similar to calcium. Magnesium is the lightest of all structuralmetals and is used to build some airplanes. Magnesium, as Mg2+,activates many of the enzymes that speed up processes in thehuman body. Magnesium also combines with other elements toform many useful compounds. Two magnesium compounds arecommonly used medicines—milk of magnesia and Epsom salts.

alkaline-earth metal.

122 C H A P T E R 4

alkaline-earth metal oneof the elements of Group 2 ofthe periodic table

▲

20

CaCalcium40.078

12

MgMagnesium

24.3050

4

BeBeryllium9.012 182

38

SrStrontium

87.62

56

BaBarium137.327

88

RaRadium(226)

Figure 24The alkaline-earth

metals make up thesecond column ofelements from theleft edge of the peri-odic table.

A Fish can escape their predators byhiding among the hard projections oflimestone coral reefs that are made ofcalcium compounds.

B

Alkaline-earth Metals

Group 2

Quick ACTIVITYACTIVITYQuickQuickQuick

Elements in Your Food1. For 1 day, make a list

of the ingredients in all the foods and drinks you consume.

2. Identify which ingredi-ents on your list arecompounds.

3. For each compound onyour list, try to figure out what elements it is made of.


Gold, silver and platinum are transition metalsGold is a valuable Figure 25A shows that thetransition metals are located in Groups 3–12 of the periodictable. Unlike most other transition metals, gold is not found combined with other elements as an ore but as the free metal.

Transition metals, like gold, are much less reactive thansodium or calcium, but they can lose electrons to form positiveions too. There are two possible cations that a gold atom canform. If an atom of gold loses only one electron, it forms Au+. Ifthe atom loses three electrons, it forms Au3+. Some transitionmetals can form as many as four differently charged cationsbecause of their complex arrangement of electrons.

All metals, including transition metals, conduct heat and elec-tricity. Most metals can also be stretched and shaped into flatsheets, or pulled into wire. Because gold, silver, and platinum arethe shiniest metals, they are often molded into different kinds ofjewelry, as shown in Figure 25B.

There are many other useful transition metals. Copper isoften used for electrical wiring or plumbing. Light bulb filamentsare made of tungsten. Iron, cobalt, copper, and manganese playvital roles in your body chemistry. Mercury, shown in Figure 26,is the only metal that is a liquid at room temperature. It is oftenused in thermometers because it flows quickly and easily withoutsticking to glass.

transition metal.


Figure 26Mercury is an unusual metalbecause it is a liquid at roomtemperature. Continued expo-sure to this volatile metal canharm you because if you breathein the vapor, it accumulates inyour body.

transition metal one ofthe elements of Groups 3–12of the periodic table

▲

Figure 25The transition metals are located in

the middle of the periodic table.A

The properties of transition metals gradually transition, orshift, from being more similar toGroup 2 elements to being moresimilar to Group 13 elements asyou move from left to rightacross a period.

V

The transition metals platinum, gold, andsilver are often shaped to make jewelry.B

Transition Metals


Technetium and promethium are synthetic elementsTechnetium and promethium are both man-made elements. Theyare also both radioactive, which means the nuclei of their atomsare continually decaying to produce different elements. There areseveral different isotopes of technetium. The most stable isotopeis technetium-99, which has 56 neutrons. Technetium-99 can beused to diagnose cancer as well as other medical problems in softtissues of the body, as shown in Figure 27.

When looking at the periodic table, you might have wonderedwhy part of the last two periods of the transition metals areplaced toward the bottom. This keeps the periodic table narrowso that similar elements elsewhere in the table still line up.Promethium is one element located in this bottom-most section.Its most useful isotope is promethium-147, which has 86 neu-trons. Promethium-147 is an ingredient in some “glow-in-the-dark” paints.

All elements with atomic numbers greater than 92 are alsoman-made and are similar to technetium and promethium. Forexample, americium, another element in the bottom-most sectionof the periodic table, is also radioactive. Tiny amounts of americ-ium-241 are found in most household smoke detectors. Althougheven small amounts of radioactive material can affect you, amer-icum-241 is safe when contained inside your smoke detector.

124 C H A P T E R 4

Figure 27With the help of the radioactiveisotope technetium-99, doctorsare able to confirm that thispatient has a healthy brain.

Why do some metals cost more than others?

Abundance in PriceMetal Earth’s crust (%) ($/kg)

Aluminum (Al) 8.2 1.55

Chromium (Cr) 0.01 0.06

Copper (Cu) 0.0060 2.44

Gold (Au) 0.000 0004 11 666.53

Iron (Fe) 5.6 0.03

Silver (Ag) 0.000 007 154.97

Tin (Sn) 0.0002 6.22

Zinc (Zn) 0.007 1.29

1. The table at right gives the abundance of somemetals in Earth’s crust. List the metals in orderfrom most to least abundant.

2. List the metals in order of price, from the cheap-est to the most expensive

Analysis1. If the price of a metal depends on its abun-

dance, you would expect the order to be thesame on both lists. How well do the two listsmatch? Mention any exceptions.

2. The order of reactivity of these metals, frommost reactive to least reactive, is aluminum,zinc, chromium, iron, tin, copper, silver, andgold. Use this information to explain any excep-tions you noticed in item 3.

3. Create a spreadsheet that can be usedto calculate how many grams of eachmetal you could buy with $100.

COMPUTERS K I L L


NonmetalsExcept for hydrogen, nonmetals are found onthe right side of the periodic table. They includesome elements in Groups 13–16 and all the el-ements in Groups 17 and 18.

Carbon is found in three different forms andcan also form many compoundsCarbon and other nonmetals are found on theright side of the periodic table, as shown inFigure 28A. Although carbon in its pure state isusually found as graphite (pencil “lead”) or dia-mond, the existence of fullerenes, a third form,was confirmed in 1990. The most famousfullerene consists of a cluster of 60 carbonatoms, as shown in Figure 28B.

Carbon can also combine with other el-ements to form millions of carbon-containingcompounds. Carbon compounds are found inboth living and nonliving things. Glucose,C6H12O6, is a sugar in your blood. A type ofchlorophyll, C55H72O5N4Mg, is found in allgreen plants. Many gasolines contain isooctane,C8H18, while rubber tires are made of large mol-ecules with many repeating C5H8 units.

Nonmetals and their compounds are plentiful on Earth Oxygen, nitrogen, and sulfur are other common nonmetals. Eachmay form compounds or gain electrons to form the negative ionsoxide, O2–, sulfide, S2–, and nitride, N3–. The most plentiful gasesin the air are the nonmetals nitrogen and oxygen. Although sul-fur itself is an odorless yellow solid, many sulfur compounds, like those in rotten eggs and skunk spray, are known for their terrible smell.


Figure 28Most nonmetals are located on the right

side of the periodic table.A

Connection toARCHITECTUREARCHITECTUREARCHITECTUREARCHITECTUREARCHITECTUREARCHITECTURE

The discoverers of the first andmost famous fullerene named

the molecule buckminsterfullerene. Itsstructure resembles a geodesic dome, akind of structure designed by American engineerand inventor R. Buckminster Fuller. A geodesicdome encloses the most space using the fewestmaterials. Any strains caused by the ground shiftingor strong winds have little affect on a geodesicdome. That’s because the strains are spread evenlythroughout the entire structure. These sturdy struc-tures have been used successfully as radar towersin Antarctica in winds as strong as 90 m/s (200mi/h) for over 25 years. Geodesic domes providethe framework for some sports arenas, theaters,greenhouses, and even some homes.

Making the Connection1. How does the shape of a geodesic dome differ

from a more typical building?

2. Explain why energy savings are greater in thiskind of structure than in a boxlike building thatencloses the same amount of space.

The way carbon atoms are connected in themost recently discovered form of carbon re-sembles the familiar pattern of a soccer ball.

B

Nonmetals


Chlorine is a halogen that protects you from harmful bacteriaChlorine and other are located in Group 17 of theperiodic table, as shown in Figure 29A. You have probably noticedthe strong smell of chlorine in swimming pools. Chlorine iswidely used to kill bacteria in pools, like the one shown in Figure 29B, as well as in drinking-water supplies.

Like fluorine atoms, which you learned about in Section 2,chlorine atoms are very reactive. As a result, chlorine forms com-pounds. For example, the chlorine in most swimming pools isadded in the form of the compound calcium hypochlorite,Ca(OCl)2. Elemental chlorine is a poisonous yellowish green gasmade of pairs of joined chlorine atoms. Chlorine gas has thechemical formula Cl2. A chlorine atom may also gain an electronto form a negative chloride ion, Cl�. The attractions between Na+

ions and Cl� ions form table salt, NaCl.Fluorine, bromine, and iodine are other Group 17 elements.

Fluorine is a poisonous yellowish gas, bromine is a dark red liquid, and iodine is a dark purple solid. Atoms of each of theseelements can also form compounds by gaining an electron tobecome negative ions. A compound containing the negative ionfluoride, F�, is used in some toothpastes and added to somewater supplies to help prevent tooth decay. Adding a compoundcontaining iodine as the negative ion iodide, I�, to table saltmakes “iodized” salt. You need this ion in your diet for your thy-roid gland to function properly.

halogens

126 C H A P T E R 4

EARTH SCIENCEEighty-one elementshave been detected insea water. Magnesiumand bromine are two

such elements. To recover anelement from a sample of seawater, you must evaporatesome of the water from thesample. Sodium chloride thencrystallizes and the liquid thatremains becomes more con-centrated in bromide, magne-sium, and other ions than theoriginal sea water was, makingtheir recovery easier.

35

BrBromine79.904

17

ClChlorine35.4527

9

FFluorine

18.998 4032

53

IIodine

126.904 47

85

AtAstatine(210)

Figure 29The halogens are

in the second columnfrom the right of the periodic table.

A Chlorine keeps pool water bacteria-free for swimmers to enjoy.B

Halogens

Group 17

halogen one of the elementsof Group 17 of the periodictable

▲


The noble gases are inertNeon is one of the that makeup Group 18 of the periodic table, as shownin Figure 30A. It is responsible for the brightreddish orange light of “neon” signs. Figure 30B shows how mixing neon withanother substance, such as mercury, canchange the color of a sign.

The noble gases are different from mostelements that are gases because they existas single atoms instead of as molecules.Like other members of Group 18, neon isinert, or unreactive, because its s and porbitals are full of electrons. For this rea-son, neon and other noble gases do not gainor lose electrons to form ions. They alsodon’t join with other atoms to form com-pounds under normal conditions.

Helium and argon are other commonnoble gases. Helium is less dense than airand is used to give lift to blimps and bal-loons. Argon is used to fill light bulbsbecause its lack of reactivity prevents fila-ments from burning.

Semiconductors are intermediate conductors of heat and electricityFigure 31 shows that the elements sometimes referred to as semi-conductors or metalloids are clustered toward the right side ofthe periodic table. Only six elements—boron, silicon, germa-nium, arsenic, antimony, and tellurium—are semiconductors.Although these elements are classified as nonmetals, each onealso has some properties of metals. And as their name implies,semiconductors are able to conduct heat and electricity undercertain conditions.

Boron is an extremely hard element. It is often added to steelto increase steel’s hardness and strength at high temperatures.Compounds of boron are often used to make heat-resistant glass.Arsenic is a shiny solid that tarnishes when exposed to air.Antimony is a bluish white, brittle solid that also shines like ametal. Some compounds of antimony are used as fire retardants.Tellurium is a silvery white solid whose ability to conductincreases slightly with exposure to light.

noble gases


noble gas an unreactive element of Group 18 of theperiodic table

▲

Figure 31Semiconductors are locatedtoward the right side of the periodic table.

18

ArArgon39.948

10

NeNeon

20.1797

2

HeHelium

4.002 602

36

KrKrypton83.80

54

XeXenon131.29

86

RnRadon(222)

Figure 30The noble gases are located on the

right edge of the periodic table.A

A neon sign is usually reddishorange, but adding a few drops of mer-cury makes the light a bright blue.

B

Group 18

Semiconductors

Noble Gases


Silicon is the most familiar semiconductorSilicon atoms, usually in the form of compounds, account for 28% of the mass of Earth’s crust. Sand is made of the most com-mon silicon compound, called silicon dioxide, SiO2. Small chipsmade of silicon, like those shown in Figure 32, are used in theinternal parts of computers.

Silicon is also an important component of other semiconduc-tor devices such as transistors, LED display screens, and solarcells. Impurities such as boron, aluminum, phosphorus, andarsenic are added to the silicon to increase its ability to conductelectricity. These impurities are usually added only to the surfaceof the chip. This process can be used to make chips of differentconductive abilities. This wide range of possible semiconductordevices has led to great advances in electronic technology.

128 C H A P T E R 4


1. Classify the following elements as alkali, alkaline-earth, ortransition metals based on their positions in the periodic table:a. iron, Fe c. strontium, Srb. potassium, K d. platinum, Pt

2. Predict whether cesium forms Cs� or Cs2� ions.

3. Describe why chemists might sometimes store reactivechemicals in argon, Ar. To which family does argon belong?

4. Determine whether the following substances are likely to bemetals or nonmetals:a. a shiny substance used to make flexible bed springsb. a yellow powder from underground minesc. a gas that does not reactd. a conducting material used within flexible wires

5. Describe why atoms of bromine, Br, are so reactive. Towhich family does bromine belong?

6. Predict the charge of a beryllium ion.

7. Identify which element is more reactive: lithium, Li, or barium, Ba.

8. Creative Thinking Imagine you are a scientistwho has just discovered a new element. Youhave confirmed that the element is a metal but areunsure whether it is an alkali metal, an alkaline-earth metal,or a transition metal. Write a paragraph describing theadditional tests you can do to further classify this metal.

S U M M A R Y

> Metals are shiny solids thatconduct heat and electricity.

> Alkali metals, located inGroup 1 of the periodictable, are very reactive.

> Alkaline-earth metals,located in Group 2, are lessreactive than alkali metals.

> Transition metals, located inGroups 3–12, are not veryreactive.

> Nonmetals usually do notconduct heat or electricitywell.

> Nonmetals include the inertnoble gases in Group 18,the reactive halogens inGroup 17, and some el-ements in Groups 13–16.

> Semiconductors are non-metals that are intermedi-ate conductors of heat andelectricity.

Figure 32Silicon chips are the basic buildingblocks of computers.

WRITINGS K I L L


> Explain the relationship between a mole of a substanceand Avogadro’s constant.

> Find the molar mass of an element by using the periodictable.

> Solve problems converting the amount of an element inmoles to its mass in grams, and vice versa.

Using Moles to Count Atoms

Counting objects is one of the very first things children learnto do. Counting is easy when the objects being counted are

not too small and there are not too many of them. But can youimagine counting the grains of sand along a stretch of beach orthe stars in the night-time sky?

Counting ThingsWhen people count out large numbers of small things, they oftensimplify the job by using counting units. For example, when youorder popcorn at a movie theater, the salesperson does not countout the individual popcorn kernels to give you. Instead, youspecify the size of container you want, and that determines howmuch popcorn you get. So the “counting unit” for popcorn is thesize of the container: small, medium, or large.

There are many different counting unitsThe counting units for popcorn are only an approximation andare not exact. Everyone who orders a large popcorn will not get exactly the same number of popcorn kernels. Many otheritems, however, require more-exact counting units, as shown inFigure 33. For example, you cannot buy just one egg at the gro-cery store. Eggs are packaged by the dozen. Copy shops buypaper in reams, or 500-sheet bundles.

An object’s mass may sometimes be used to “count” it. Forexample, if a candy shopkeeper knows that 10 gumballs have amass of 21.4 g, then the shopkeeper can assume that there are 50 gumballs on the scale when the mass is 107 g (21.4 g � 5).

O B J E C T I V E S

SECTION

4


K E Y T E R M S

moleAvogadro’s constantmolar massconversion factor

▲

Figure 33Eggs are counted by the dozen,and paper is counted by the ream.


The mole is useful for counting small particlesBecause chemists often deal with large numbers of small parti-cles, they use a large counting unit—the abbreviated mol.A mole is a collection of a very large number of particles.

About 602 213 670 000 000 000 000 000!

This number is usually written as 6.022 � 1023/mol and isreferred to as The constant is named inhonor of the Italian scientist Amedeo Avogadro. Avogadro’s con-stant is defined as the number of particles, 6.022 � 1023, inexactly 1 mol of a pure substance.

One mole of gumballs is 6.022 � 1023 gumballs. One mole ofpopcorn is 6.022 � 1023 kernels of popcorn. This amount of pop-corn would cover the United States and form a pile about 500 km(310 mi) high! It is unlikely that you will ever come in contactwith this much gum or popcorn, so it does not make sense to usemoles to count either of these items. The mole is useful, however,for counting atoms.

You might wonder why 6.022 � 1023 represents the numberof particles in 1 mol. The mole has been defined as the numberof atoms in 12.00 grams of carbon-12. Experiments have shownthat 6.022 � 1023 is the number of carbon-12 atoms in 12.00 g of carbon-12. One mole of carbon consists of 6.022 � 1023 car-bon atoms, with an average atomic mass of 12.01 amu.

Moles and grams are relatedThe mass in grams of 1 mol of a substance is called its

For example, 1 mol of carbon-12 atoms has amolar mass of 12.00 g. But a mole of an element will usuallyinclude atoms of several isotopes. So the molar mass of an el-ement in grams is the same as its average atomic mass in amu,which is listed in the periodic table. The average atomic mass forcarbon is 12.01 amu. One mole of carbon, then, has a mass of12.01 g. Figure 34 demonstrates this idea for magnesium.

molar mass.

Avogadro’s constant.

mole,

130 C H A P T E R 4

mole the SI base unit usedto measure the amount of asubstance whose number ofparticles is the same as thenumber of atoms of carbon in12 g of carbon-12

Avogadro’s constantequals 6.022 � 1023/mol; thenumber of particles in 1 mol

molar mass the mass ingrams of 1 mol of a substance

▲▲

▲

Figure 34One mole of magnesium (6.022 � 1023 Mg atoms) has a mass of 24.30 g. Note that thebalance is only accurate to one-tenth of a gram, so it reads 24.3 g.

Did you know that Avogadronever knew his own constant?Count Amedeo Avogadro(1776–1856) was a lawyerwho became inter-ested in math-ematics andphysics.Avogadro’s constant wasactually deter-mined by JosephLoschmidt, a German physi-cist in 1865, nine years afterAvogadro’s death.

Mg12

Magnesium

24.3050


www.scilinks.orgTopic: Avogadro’s

ConstantSciLinks code: HK4013

Calculating with MolesBecause the amount of a substance and its mass are related, it isoften useful to convert moles to grams, and vice versa. You canuse to relate units.

Using conversion factorsHow did the shopkeeper mentioned on the previous page knowthe mass of 50 gumballs? He multiplied by a conversion factor to determine the number of gumballs on the scale from theircombined mass. Multiplying by a conversion factor is like multi-plying by 1 because both parts of the conversion factor arealways equal.

The shopkeeper knows that exactly 10 gumballs have a com-bined mass of 21.4 g. This relationship can be written as twoequivalent conversion factors, both of which are shown below.

The shopkeeper can use one of these conversion factors todetermine the mass of 50 gumballs because mass increases in apredictable way as more gumballs are added to the scale, as youcan see from Figure 35.

21.4 g��10 gumballs

10 gumballs��

21.4 g

conversion factors


64.2

42.8

21.4

10 30Number of gumballs

Mas

s (g

)

20 400

85.6

0

conversion factor a ratiothat is derived from the equal-ity of two different units andthat can be used to convertfrom one unit to another

▲

Figure 35There is a direct relationshipbetween the number ofgumballs and their mass.Ten gumballs have a mass of21.4 g, 20 gumballs have amass of 42.8 g, and 30 gum-balls have a mass of 64.2 g.

A B C

C

B

A


132 C H A P T E R 4

Math SkillsMath SkillsConversion Factors What is the mass of exactly 50 gumballs?

List the given and unknown values.Given: mass of 10 gumballs = 21.4 gUnknown: mass of 50 gumballs = ? g

Write down the conversion factor that converts number of gumballs to mass.

The conversion factor you choose should have the unityou are solving for (g) in the numerator and the unit youwant to cancel (number of gumballs) in the denominator.

Multiply the number of gumballs by this conversion factor, and solve.

50 gumballs × = 107 g21.4 g

��10 gumballs

3

21.4 g��10 gumballs

2

1

Conversion Factors1. What is the mass of exactly 150 gumballs?2. If you want 50 eggs, how many dozens must you buy? How many

extra eggs do you have to take?3. If a football player is tackled 1.7 ft short of the end zone, how

many more yards does the team need to get a touchdown?

PracticePractice

A

Relating amount to massJust as in the gumball example, there is also a rela-tionship between the amount of an element in molesand its mass in grams. This relationship is graphed foriron nails in Figure 36. Because the amount of ironand the mass of iron are directly related, the graph isa straight line.

An element’s molar mass can be used as if it werea conversion factor. Depending on which conversionfactor you use, you can solve for either the amount ofthe element or its mass.

167.4

111.6

55.8

1.000 3.000Amount of iron (mol Fe)

Mas

s of

iron

(g

Fe)

2.000 4.0000

223.2

0

A B C

C

B

A

Figure 36There is a direct relationshipbetween the amount of an element and its mass.


Converting moles to gramsConverting between the amount of an element in moles and itsmass in grams is outlined in Figure 37. For example, you candetermine the mass of 5.50 mol of iron by using Figure 37 as aguide. First you must find iron in the periodic table. Its averageatomic mass is 55.85 amu. This means iron’s molar mass is 55.85 g/mol Fe. Now you can set up the problem using the molarmass as if it were a conversion factor, as shown in the sampleproblem below.


Math SkillsMath Skills

Converting Amount to MassWhat is the mass in grams of each of the following?1. 2.50 mol of sulfur, S 3. 0.50 mol of carbon, C2. 1.80 mol of calcium, Ca 4. 3.20 mol of copper, Cu

Amount (mol) Mass (g)

molar mass of element1 mol of element

=+

molar mass of element1 mol of element= +

PracticeHINT

Notice how iron’s molar mass,55.85 g/mol Fe, includes units(g/mol) and a chemical symbol(Fe). The units specify that thismass applies to 1 mol of sub-stance. The symbol for iron,Fe, clearly indicates the sub-stance. Remember to alwaysinclude units in your answersand make clear the substanceto which these units apply.Otherwise, your answer hasno meaning.

Figure 37The molar mass of an elementallows you to convert between the amount of the element and its mass.

PracticePractice

Converting Amount to Mass Determine the mass in grams of5.50 mol of iron.

List the given and unknown values.Given: amount of iron � 5.50 mol Fe

molar mass of iron � 55.85 g/mol FeUnknown: mass of iron � ? g Fe

Write down the conversion factor that converts moles to grams.

The conversion factor you choose should have whatyou are trying to find (grams of Fe) in the numeratorand what you want to cancel (moles of Fe) in the denominator.

�515.

m85

olgFFee

�

Multiply the amount of iron by this conversion factor, and solve.

5.50 mol Fe � �515.

m85

olgFFee

� � 307 g Fe

3

2

1


134 C H A P T E R 4


1. Define Avogadro’s constant. Describe how Avogadro’s con-stant relates to a mole of a substance.

2. Determine the molar mass of the following elements:a. manganese, Mn c. arsenic, Asb. cadmium, Cd d. strontium, Sr

3. List the two equivalent conversion factors for the molarmass of silver, Ag.

4. Explain why a graph showing the relationship between theamount of a particular element and the element’s mass is a straight line.

5. Critical Thinking Which has more atoms: 3.0 g of iron, Fe,or 2.0 g of sulfur, S?

6. What is the mass in grams of 0.48 mol of platinum, Pt?

7. How many moles are present in 620 g of mercury, Hg?

8. How many moles are present in 11 g of silicon, Si?

9. How many moles are present in 205 g of helium, He?

S U M M A R Y

> One mole of a substancehas as many particles asthere are atoms in exactly12.00 g of carbon-12.

> Avogadro’s constant,6.022 � 1023/mol, is equalto the number of particlesin 1 mol.

> Molar mass is the mass in grams of 1 mol of a substance.

> An element’s molar mass ingrams is equal to its aver-age atomic mass in amu.

> An element’s molar masscan be used to convertfrom amount to mass, andvice versa.


PracticeHINT

Once you have learned how toconvert mass to amount, youshould use this sample problemto check your answers to thepractice on the previous page.


Converting Mass to Amount Determine the amount of ironpresent in 352 g of iron.

List the given and unknown values.Given: mass of iron = 352 g Fe

molar mass of iron = 55.85 g/mol FeUnknown: amount of iron = ? mol Fe

Write down the conversion factor that converts grams to moles.

The conversion factor you choose should have whatyou are trying to find (moles of Fe) in the numeratorand what you want to cancel (grams of Fe) in the denominator.

�515.

m85

olgFFee

�

Multiply the mass of iron by this conversion factor, and solve.

352 g Fe × �515.

m85

olgFFee

� = 6.30 mol Fe

3

2

1


M A T H S K I L L S 135

Conversion FactorsA chemical reaction requires 5.00 mol of sulfur as a reactant. What is the mass of this sulfur in grams?

List all given and unknown values.

Given: amount of sulfur, 5.00 mol Smolar mass of sulfur, 32.07 g/mol S

Unknown: mass of sulfur (g)

Write the conversion factor for moles to grams.

The conversion factor you choose should have the unit you are solving for (g S) in the numerator and the unit you want to cancel (mol S) in the denominator.

Multiply the number of moles by this conversion factor, and solve.

5.00 mol � � 160.4 g S

Therefore, 160.4 grams of sulfur are needed for the reaction.

Using the example above, calculate the following:

1. If 4.00 mol of copper are needed as a reactant, what is the copper’s mass in grams?

2. A combustion reaction requires 352 g of oxygen. What is the amount of oxygen inmoles?

3. If 622 g of lead are required for a reaction, what is the amount of the lead in moles?

32.07 g S��1 mol S

3

32.07 g S��1 mol S

2

1

Math SkillsMath SkillsMath Skills

Molar Masses

Copper 63.55 g/mol

Oxygen 16.00 g/mol

Sulfur 32.07 g/mol

Lead 207.2 g/mol

PracticePractice


6. The organization of the periodic table isbased ona. the number of protons in an atom.b. the mass number of an atom.c. the number of neutrons in an atom.d. the average atomic mass of an element.

7. The majority of elements in the periodictable area. nonmetals. c. synthetic.b. conductors. d. noble gases.

8. Elements with some properties of metalsand some properties of nonmetals areknown asa. alkali metals. c. halogens.b. semiconductors. d. noble gases.

9. An atom of which of the following elements is unlikely to form a positivelycharged ion?a. potassium, K c. barium, Bab. selenium, Se d. silver, Ag

10. Atoms of Group 18 elements are inertbecausea. they combine to form molecules.b. they have no valence electrons.c. they have filled inner energy levels.d. they have filled outermost energy levels.

11. Which of the following statements aboutkrypton is not true?a. Its molar mass is 83.80 g/mol Kr.b. Its atomic number is 36.c. One mole of krypton atoms has a mass of

41.90 g.d. It is a noble gas.

Chapter HighlightsBefore you begin, review the summaries of thekey ideas of each section, found at the end ofeach section. The key vocabulary terms arelisted on the first page of each section.

1. Which of Dalton’s statements about theatom was later proven false?a. Atoms cannot be subdivided.b. Atoms are tiny.c. Atoms of different elements are not

identical.d. Atoms join to form molecules.

2. Which statement is not true of Bohr’s modelof the atom?a. The nucleus can be compared to the sun.b. Electrons orbit the nucleus.c. An electron’s path is not known exactly.d. Electrons exist in energy levels.

3. According to the modern model of the atom, a. moving electrons form an electron cloud.b. electrons and protons circle neutrons.c. neutrons have a positive charge.d. the number of protons an atom has

varies.

4. If an atom has a mass of 11 amu and con-tains five electrons, its atomic numbermust bea. 55. c. 6.b. 16. d. 5.

5. Which statement about atoms of elements inthe same group of the periodic table is true?a. They have the same number of protons.b. They have the same mass number.c. They have similar chemical properties.d. They have the same number of total

electrons.

UNDERSTANDING CONCEPTSUNDERSTANDING CONCEPTS

136 C H A P T E R 4

R E V I E WC H A P T E R 4

www.scilinks.orgTopic: Metals/Nonmetals SciLinks code: HK4086


12. How many protons and neutrons does a silicon, Si, atom have, and where are each of these subatomic particles located? Howmany electrons does a silicon atom have?

13. Identify the particles that make up an atom.How do these particles relate to the identityof an atom?

14. Draw two different types of orbitals, statetheir names, and describe how they arefilled.

15. Describe the process of ionization, and givetwo different examples of elements thatundergo this process.

16. Explain why different atoms of the sameelement always have the same atomic number but can have different mass numbers. What are these different atomscalled?

17. Distinguish between the following:a. an atom and a moleculeb. an atom and an ionc. a cation and an anion

18. List several familiar transition metals andtheir uses.

19. How is the periodic law demonstrated withthe halogens?

20. Explain why semiconductors, or metalloids,deserve their name.

21. Distinguish between alkali metals andalkaline-earth metals, and give severalexamples of how they are used.

22. State Avogadro’s constant and explain itsrelationship to the mole.

23. What does an element’s molar mass tell youabout the element?

24. Graphing Use a graphing calcula-tor, a computer spreadsheet, or a graphing program to plot theatomic number on the x-axis and the aver-age atomic mass in amu on the y-axis forthe transition metals in Period 4 of the peri-odic table (from scandium to zinc). Do younotice a break in the trend near cobalt?Explain why elements with larger atomicnumbers do not necessarily have largeratomic masses.

25. Converting Mass to Amount For an experi-ment you have been asked to do, you need1.5 g of iron. How many moles of iron doyou need?

26. Converting Mass to Amount James is hold-ing a balloon that contains 0.54 g of heliumgas. What amount of helium is this?

27. Converting Amount to Mass A pure goldbar is made of 19.55 mol of gold. What isthe mass of the bar in grams?

28. Converting Amount to Mass Robyn recy-cled 15.1 mol of aluminum last month.What mass of aluminum in grams did she recycle?

29. Creative Thinking Some forces push twoatoms apart while other forces pull themtogether. Describe how the subatomic parti-cles in each atom interact to produce theseforces.

30. Applying Knowledge Explain why magne-sium forms ions with the formula Mg2+, notMg+ or Mg-.


USING VOC ABULARYUSING VOC ABULARY

THINKING CR ITIC ALLYTHINKING CR ITIC ALLY

BUILDING MATH SKILLSBUILDING MATH SKILLS

COMPUTERS K I L L


39. Problem Solving What would happen topoisonous chlorine gas if the followingalterations were made to the chlorine?

a. A proton is added to each atom.b. An electron is added to each atom.c. A neutron is added to each atom.

40. Locating Information Some “neon” signscontain substances other than neon to pro-duce different colors. Design your ownlighted sign, and find out which substancesyou could use to produce the colors youwant your sign to be.

41. Making Decisions Suppose you have only1.9 g of sulfur for an experiment and youmust do three trials using 0.030 mol of Seach time. Do you have enough sulfur?

42. Communicating Effectively The study ofthe nucleus produced a new field of medi-cine called nuclear medicine. Pretend youare writing an article for a hospital news-letter. Describe how radioactive substancescalled tracers are sometimes used to detectand treat diseases.

43. Working Cooperatively With a group ofyour classmates, make a list of 10 elementsand their average atomic masses. Calculatethe amount in moles for 6.0 g of each element. Rank your elements from the element with the greatest amount to the element with the least amount in a 6.0 gsample. Do you notice a trend in theamounts as atomic number increases?Explain why or why not.

44. Applying Knowledge You read a science fic-tion story about an alien race of silicon-based life-forms. Use information from theperiodic table to hypothesize why the authorchose silicon over other elements. (Hint:Life on Earth is carbon based.)

31. Evaluating Data The figure below showsrelative ionic radii for positive and negativeions of elements in Period 2 of the periodictable. Explain the trend in ion size as youmove from left to right across the periodictable. Why do the negative ions have largerradii than the positive ions?

32. Making Comparisons Although carbon andlead are in the same group, some of theirproperties are very different. Propose a rea-son for this. (Hint: Look at the periodictable to locate each element and find outhow each is classified.)

33. Problem Solving How does halving theamount of a sample of an element affect thesample’s mass?

34. Understanding Systems When an atom losesan electron, what is the atom’s charge? Whatdo you think happens to the size of the atom?

35. Applying Knowledge What property do thenoble gases share? How does this propertyrelate to the electron configuration of thenoble gases?

36. Applying Knowledge Write the chemicalsymbols for helium, carbon, gold, lead,sodium, potassium, and copper.

37. Critical Thinking Why is it difficult to meas-ure the size of an atom?

38. Critical Thinking Particle accelerators aredevices that speed up charged particles in order to smash the particles together.Sometimes the result of the collision is anew nucleus. How can scientists determinewhether the nucleus formed is that of a newelement or that of a new isotope of a knownelement?

138 C H A P T E R 4

R E V I E WC H A P T E R 4

Li+ Be2+ N3– O2– F–

0.60 0.31 1.71 1.40 1.36 DEVELOPING LI FE/WORK SKILLSDEVELOPING LI FE/WORK SKILLS


45. Connection to Health You can keep yourbones healthy by eating 1200–1500 mg of calcium a day. Use the table below tomake a list of the foods you might eat in a day to satisfy your body’s need for cal-cium. How does your typical diet comparewith this?

Item, serving size Calcium (mg)

Plain lowfat yogurt, 1 cup 415

Ricotta cheese, 1/2 cup 337

Skim milk, 1 cup 302

Cheddar cheese, 1 ounce 213

Cooked spinach, 1/2 cup 106

Vanilla ice cream, 1/2 cup 88

46. Concept Mapping Copy the unfinished concept map below onto a sheet of paper.Complete the map by writing the correctword or phrase in the lettered boxes.

47. Connection to Physics Research the originsof the elements. The big bang theory suggeststhat the universe began with an enormousexplosion. What was formed as a result ofthe big bang? Describe the matter that waspresent after the explosion. How much timepassed before the elements as we knowthem were formed?

48. Connection to Earth Science The isotopecarbon-14 is used in radiocarbon- dating of animal and plant fossils. Scientists useother isotopes to tell the ages of rocks andmeteorites. Do some research and find outwhich isotopes are used to date rocks andmeteorites.


neutronsa.

nucleusb.

f.element

g.c.

e.d.

which isclassified into

in an atomis called the

and determineswhere an

is locatedin the

The number of

and

of an atomis the

which is differentfor each

in the

and

Art Credits: Fig. 2, Kristy Sprott; Fig. 4, Kristy Sprott; Fig. 5, Uhl Studios, Inc.; Fig. 8, J/B WoolseyAssociates; Fig. 10, Kristy Sprott; Fig. 12-17, Kristy Sprott; Fig. 19-21, Kristy Sprott; Fig. 24-25, Kristy Sprott; Fig. 27-31, Kristy Sprott; Fig. 32, Leslie Kell; Fig. 36, Leslie Kell; “Thinking Critically” (molecules), Kristy Sprott.

Photo Credits: Chapter Opener image of Guggenheim museum in Bilbao, Spain by Rafa RivasAFP/CORBIS; liquid gold by Torpham/The Image Works; Fig. 1(microscopic), Courtesy JEOL; Fig. 1(cans), Victoria Smith/HRW; Fig 2.(man), Ron Chapple/Getty Images/FPG International; Fig. 2(waterfall), Bill Bachman/Masterfile; Fig. 3(stadium), Douglas Peebles/CORBIS; Fig. 3(marble),CORBIS Images/HRW; Fig. 6, Steven Begleiter/Index Stock; “Quick Activity,” Sam Dudgeon/HRW;Fig. 10, SuperStock; Fig. 11, Peter Van Steen/HRW; Fig. 15, Rhonda Sidney/The Image Works; Fig. 19A, Tom Van Sant/Geosphere Project, Santa Monica/Science Photo Library/Photo Researchers,Inc.; Fig. 19B, NASA/Corbis Stock Market; Fig. 22, Mimi Cotter/International Stock Photography; Fig. 23(l), E. R. Degginger/Color-Pic, Inc.; Fig. 23(r), Jerry Mason/SPL/Photo Researchers, Inc.; Fig. 24, Jeff Hunter/Getty Images/The Image Bank; Fig. 25, Peter Van Steen/HRW; Fig. 26, Russ Lappa/Science Source/Photo Researchers, Inc.; Fig. 27, Oullette/Theroux/Publiphoto/PhotoResearchers, Inc.; ‘Connection to Architecture,” Dilip Methta/Contact Press Images/Picture Quest;Fig. 29, Scott Barrow/International Stock Photography; Fig. 30, Rob Boudreau/Getty Images/Stone;Fig. 32, Digital Image copyright 2004, Eyewire; Fig. 33, Sam Dudgeon/HRW; “Did You Know,”BETTMANN/CORBIS; Figs. 34, 35, 36, Sam Dudgeon/HRW; “Design Your Own Lab,” Peter VanSteen/HRW.

INTEGR ATING CONCEPTSINTEGR ATING CONCEPTS

www.scilinks.orgTopic: Origin of Elements SciLinks code: HK4097


Comparing the PhysicalProperties of Elements

� Procedure

Identifying Metal Elements1. In this lab, you will identify samples of unknown

metals by comparing the data you collect with refer-ence information listed in the table at right. Use atleast two of the physical properties listed in the tableto identify each metal.

Deciding Which Physical Properties You WillAnalyze

2. Density is the mass per unit volume of a substance. Ifthe metal is box-shaped, you can measure its length,width, and height, and then use these measurementsto calculate the metal’s volume. If the shape of themetal is irregular, you can add the metal to a knownvolume of water and determine what volume ofwater is displaced.

3. Relative hardness indicates how easy it is to scratch a metal. A metal with a higher value can scratch ametal with a lower value, but not vice versa.

4. Relative heat conductivity indicates how quickly a metalheats or cools. A metal with a value of 100 will heator cool twice as quickly as a metal with a value of 50.

5. If a magnet placed near a metal attracts the metal,then the metal has been magnetized by the magnet.

Designing Your Experiment6. With your lab partner(s), decide how you will use the

materials provided to identify each metal you aregiven. There is more than one way to measure someof the physical properties that are listed, so you mightnot use all of the materials that are provided.

7. In your lab report, list each step you will perform inyour experiment.

8. Have your teacher approve your plan before you carryout your experiment.

How can you distinguish metal elementsby analyzing their physical properties?

> Hypothesizewhich physical properties can helpyou distinguish between differentmetals.

> Identify unknown metals by comparing the data you collect with reference information.

balancebeakers (several)graduated cylinderhot plateicemagnetmetal samples, unidentified (several)metric rulerstopwatchwaterwax

USING SCIENTIFIC METHODS

Introduction

Objectives

Materials

140 C H A P T E R 4 Copyright © by Holt, Rinehart and Winston. All rights reserved.


Performing Your Experiment9. After your teacher approves your plan, carry out your experiment. Keep in mind

that the more careful your measurements are, the easier it will be for you toidentify the unknown metals.

10. Record all the data you collect and any observations you make in your lab report.

� Analysis1. Make a table listing the physical properties

you compared and the data you collectedfor each of the unknown metals.

2. Which metals were you given? Explain thereasoning you used to identify each metal.

3. Which physical properties were the easiestfor you to measure and compare? Whichwere the hardest? Explain why.

4. What would happen if you tried to scratchaluminum foil with zinc?

5. Explain why it would be difficult to distinguish between iron and nickel unless you calculate each metal’s density.

6. Suppose you find a metal fastener anddetermine that its density is 7 g/mL. Whatare two ways you could determinewhether the unknown metal is tin or zinc?

� Conclusions7. Suppose someone gives you an alloy that is made of both zinc and nickel. In

general, how do you think the physical properties of the alloy would compare with those of each individual metal?

Aluminum (Al) 2.7 28 100 no

Iron (Fe) 7.9 50 34 yes

Nickel (Ni) 8.9 67 38 yes

Tin (Sn) 7.3 19 28 no

Tungsten (W) 19.3 100 73 no

Zinc (Zn) 7.1 28 49 no

Density Relative Relative heat MagnetizedMetal (g/mL) hardness conductivity by magnet?

Physical Properties of Some Metals


chapter 4 atoms and the periodic table - grygla public … · atoms and the periodic table chapter...

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