atoms, elements, and - somerset academy · atoms, elements, and all types of matter— the periodic...

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Atoms, Elements, andthe Periodic TableAll types of matter—

elements, compounds, and mixtures—are made of atoms.

SECTION 1Structure of MatterMain Idea Atoms containprotons and neutrons in atiny nucleus and electrons ina cloud around the nucleus.

SECTION 2The Simplest MatterMain Idea An element ismade of atoms that have thesame number of protons.

SECTION 3Compounds and MixturesMain Idea Compoundscontain different types ofatoms bonded together.Mixtures contain differentsubstances mixed together.

What a fun ride!The pilot gives the propane burner a long, loud blast that will heatthe air in the balloon, making you soar higher. During your ride,you might start thinking about what is keeping you airborne. Inthis chapter, as you learn about atoms and elements, you will beable to understand more about matter.

Make a list of three questions that you think of when you look atthe picture. Science Journal

(bkgd.)Russell Dohrman/Index Stock

Atoms, Elements, and thePeriodic Table Make the fol-lowing Foldable to help you

identify the main ideas about atoms, elements,compounds, and mixtures.

Draw a mark at themidpoint of a sheetof paper along theside edge. Thenfold the top andbottom edges in totouch the midpoint.

Fold in half fromside to side.

Open and cutalong the insidefold lines to formfour tabs.

Label each tab asshown.

Read and Write As you read the chapter, listseveral everyday examples of atoms, elements,compounds, and mixtures on the back of theappropriate tab.

STEP 4

STEP 3

STEP 2

STEP 1

Observe Matter You’ve just finished playing basketball.You’re hot and thirsty. You reach for yourbottle of water and take a drink. Releasingyour grip, you notice that the bottle is nearlyempty. Is the bottle really almost empty?According to the dictionary, empty means“containing nothing.” When you have fin-ished all the water in the bottle, will it beempty or full?

1. Wad up a drypaper towel ortissue and tapeit to the insideof a plastic cupas shown.

2. Fill a bowl or sink with water. Turn thecup upside down and slowly push thecup straight down into the water as faras you can.

3. Slowly raise the cup straight up and outof the water. Remove the paper towelor tissue paper and examine it.

4. Think Critically In your Science Journal,describe the lab and its results. Explainwhat you think happened. Was anythingin the cup besides the paper? If so, whatwas it?

Start-Up Activities

Preview this chapter’s contentand activities at red.msscience.com

Atoms Elements

Compounds Mixtures

9797(bkgd.)Russell Dohrman/Index Stock, (inset)Morrison Photography

http://www.glencoe.com

98 A CHAPTER 4 Atoms, Elements, and the Periodic Table

Apply It! Make a vocabularybookmark with a strip of paper. As you read,keep track of words you do not know or wantto learn more about.

Learn It! What should you do if you find a word you don’tknow or understand? Here are some suggested strategies:

Practice It! Look at the word charge in the followingpassage. See how context clues can help you understand its meaning.

1. Use context clues (from the sentence or the paragraph) to helpyou define it.

2. Look for prefixes, suffixes, or root words that you already know.3. Write it down and ask for help with the meaning.4. Guess at its meaning.5. Look it up in the glossary or a dictionary.

Thomson knew that like charges repel eachother and opposite charges attract each other.When he saw that the [cathode] rays traveledtoward a positively charged plate, he concludedthat the cathode rays were made up of nega-tively charged particles. These invisible, nega-tively charged particles are called . electrons

Context ClueLike charges repeleach other andopposite chargesattract each other.

Context Clue. . . cathode rayswere made up ofnegatively chargedparticles.

Context ClueNegatively chargedparticles are calledelectrons.

—from page 102

98 B

Before You Read Statement After You ReadA or D A or D

1 Matter cannot be created or destroyed.

2 The model of the atom has remained mostlyunchanged since the idea of atoms was firstproposed.

3 Atoms contain mostly empty space.

4 All atoms contain at least one neutron.

5 Two atoms of the same element might containdifferent numbers of neutrons.

6 If you are given the element name, you candetermine the mass number of an atom.

7 A mixture is a type of substance.

8 Substances that contain the same elements willhave the same chemical and physical properties.

9 Both compounds and mixtures contain morethan one type of element.

Print out a worksheetof this page at red.msscience.com

Read a paragraph containing

a vocabulary term from

beginning to end. Then,

go back to determine the

meaning of the term.Use this to focus on the main ideas as you read the chapter.

Before you read the chapter, respond to the statements

below on your worksheet or on a numbered sheet of paper.

• Write an A if you agree with the statement.

• Write a D if you disagree with the statement.

After you read the chapter, look back to this page to see if you’ve

changed your mind about any of the statements.

• If any of your answers changed, explain why.

• Change any false statements into true statements.

• Use your revised statements as a study guide.


98 CHAPTER 4 Atoms, Elements, and the Periodic Table

What is matter?Is a glass with some water in it half empty or half full?

Actually, neither is correct. The glass is completely full—half fullof water and half full of air. What is air? Air is a mixture of sev-eral gases, including nitrogen and oxygen, which are kinds ofmatter. Matter is anything that has mass and takes up space. So,even though you can’t see it or hold it in your hand, air is mat-ter. What about all the things you can see, taste, smell, andtouch? Most are made of matter, too. Look at the things picturedin Figure 1 and determine which of them are matter.

What isn’t matter?You can see the words on this page because of the light from

the Sun or from a fixture in the room. Does light have mass ortake up space? What about the warmth from the Sun or the heatfrom the heater in your classroom? Light and heat do not takeup space, and they have no mass. Therefore, they are not formsof matter. Emotions, thoughts, and ideas are not matter either.Does this information change your mind about the items in Figure 1?

Why is air matter, but light is not?

■ Describe characteristics of matter.■ Identify what makes up matter.■ Identify the parts of an atom.■ Compare the models that are

used for atoms.

Matter makes up almost everythingwe see—and much of what wecan’t see.

Review Vocabularydensity: the mass of an objectdivided by its volume

New Vocabulary

• matter

• atom

• law of conservation of matter

• electron

• nucleus

• proton

• neutron

Structure of Matter

Figure 1 A rainbow is formedwhen light filters through the rain-drops, a plant grows from a seed inthe ground, and a statue is sculptedfrom bronze.Identify which are matter.

(l)Gary C. Will/Visuals Unlimited, (c)Mark Burnett/Stock Boston, (r)CORBIS

What makes up matter?Suppose you cut a chunk of wood into smaller and smaller

pieces. Do the pieces seem to be made of the same matter as thelarge chunk you started with? If you could cut a small enoughpiece, would it still have the same properties as the first chunk?Would you reach a point where the last cut resulted in a piecethat no longer resembled the first chunk? Is there a limit to howsmall a piece can be? For centuries, people have asked questionslike these and wondered what matter is made of.

An Early Idea Democritus, who lived from about 460 B.C. to 370 B.C., was a Greek philosopher who thought the universe wasmade of empty space and tiny bits of stuff. He believed that thebits of stuff were so small they could no longer be divided intosmaller pieces. He called these tiny pieces atoms. The term atomcomes from a Greek word that means “cannot be divided.” Todayan atom is defined as a small particle that makes up most typesof matter. Figure 2 shows the difference between Democritus’sideas and those of other early scientists and philosophers.Democritus thought that different types of atoms existed forevery type of matter and that the atom’s identity explained thecharacteristics of each type of matter. Democritus’s ideas aboutatoms were a first step toward understanding matter. However,his ideas were not accepted for over 2,000 years. It wasn’t untilthe early 1800s that scientists built upon the concept of atoms toform the current atomic theory of matter.

SECTION 1 Structure of Matter 99

Figure 2 Early Beliefs About the Composition of Matter

Many Indian Kashyapa, an

Many GreekDemocritus Aristotle

Chinese Philosophers

Indian Philosophers (380 B.C.) (330 B.C.)

Philosophers (1,000 B.C.)

Philosopher (500–300 B.C.)

(300 B.C.)

(1,000 B.C.)

• Ether—an • Five elements • Earth • Tiny individual • Empty space • Metal invisible broken down • Water particles he could not exist • Earth substance into smaller • Air called atomos • Earth • Water that filled units called • Fire • Empty space • Water • Air the heavens parmanu through which • Air • Fire • Earth • Parmanu of atoms move • Fire • Water earth • Each substance • Air elements are composed of • Fire heavier than one type of air elements atomos

Atomism Historiansnote that Leucippusdeveloped the idea ofthe atom around 440 B.C.He and his student,Democritus, refined theidea of the atom yearslater. Their concept of theatom was based on fivemajor points: (1) all mat-ter is made of atoms,(2) there are emptyspaces between atoms,(3) atoms are completesolids, (4) atoms do nothave internal structure,and (5) atoms are differ-ent in size, shape, andweight.


Lavoisier’s Contribution Lavoisier (la VWAH see ay), aFrench chemist who lived about 2,000 years after Democritus,also was curious about matter—especially when it changedform. Before Lavoisier, people thought matter could appear anddisappear because of the changes they saw as matter burned orrusted. You might have thought that matter can disappear ifyou’ve ever watched wood burn in a fireplace or at a bonfire.Lavoisier showed that wood and the oxygen it combines withduring burning have the same mass as the ash, water, carbondioxide, and other gases that are produced, as shown in Figure 3.In a similar way, an iron bar, oxygen, and water have the samemass as the rust that forms when they interact. From Lavoisier’swork came the law of conservation of matter, which states thatmatter is not created or destroyed—it only changes form.

Models of the AtomModels are often used for things that are too small or too

large to be observed or that are too difficult to be understoodeasily. One way to make a model is to make a smaller version ofsomething large. If you wanted to design a new sailboat, wouldyou build a full-sized boat and hope it would float? It would bemore efficient, less expensive, and safer to build and test asmaller version first. Then, if it didn’t float, you could changeyour design and build another model. You could keep tryinguntil the model worked.

In the case of atoms, scientists use large models to explainsomething that is too small to be looked at. These models of theatom were used to explain data or facts that were gatheredexperimentally. As a result, these models are also theories.

Figure 3 When woodburns, matter is not lost.The total mass of the woodand the oxygen it com-bines with during a fireequals the total mass ofthe ash, water vapor, car-bon dioxide, and othergases produced.Infer When you burnwood in a fireplace, what isthe source of oxygen?

wood � oxygen � ash � gases � water vapor

Investigating theUnseenProcedure1. Your teacher will give you

a sealed shoe box thatcontains one or moreitems.

2. Try to find out how manyand what kinds of itemsare inside the box. Youcannot look inside the box.The only observations youcan make are by handlingthe box.

Analysis1. How many items do you

infer are in the box? Sketchthe apparent shapes of theitems and identify them ifyou can.

2. Compare your procedurewith how scientists per-form experiments andmake models to find outmore about the atom.

Mark Burnett


Dalton’s Atomic Model In the early 1800s, an Englishschoolteacher and chemist named John Dalton studied theexperiments of Lavoisier and others. Dalton thought he coulddesign an atomic model that explained the results of those ex-periments. Dalton’s atomic model was a set of ideas—not aphysical object. Dalton believed that matter was made of atomsthat were too small to be seen by the human eye. He alsothought that each type of matter was made of only one kind ofatom. For example, gold atoms make up a gold nugget and givea gold ring its shiny appearance. Likewise, iron atoms make upan iron bar and give it unique properties, and so on. Becausepredictions using Dalton’s model were supported by data, themodel became known as the atomic theory of matter.

Sizes of Atoms Atoms are so small it would take about 1 million of them lined up in a row to equal the thickness ofa human hair. For another example of how small atoms are, lookat Figure 4. Imagine you are holding an orange in your hand. Ifyou wanted to be able to see the individual atoms on the orange’s surface, the size of the orange would have to be increased to the size of Earth. Then,imagine the Earth-sized orange coveredwith billions and billions of marbles.Each marble would represent one of theatoms on the skin of the orange. No mat-ter what kind of model you use to pictureit, the result is the same—an atom is anextremely small particle of matter.

Figure 4 If this orange were aslarge as Earth, each of its atomswould be marble-sized.

(l)Mark Burnett, (r)NASA


Discovering the Electron One of the many pioneers in thedevelopment of today’s atomic model was J.J. Thomson, anEnglish scientist. He conducted experiments using a cathode raytube, which is a glass tube sealed at both ends out of which mostof the air has been pumped. Thomson’s tube had a metal plateat each end. The plates were connected to a high-voltage electri-cal source that gave one of the plates—the anode—a positivecharge and the other plate—the cathode—a negative charge.During his experiments, Thomson observed rays that traveledfrom the cathode to the anode. These cathode rays were bent bya magnet, as seen in Figure 5, showing that they were made upof particles that had mass and charge. Thomson knew that likecharges repel each other and opposite charges attract each other.When he saw that the rays traveled toward a positively chargedplate, he concluded that the cathode rays were made up of neg-atively charged particles. These invisible, negatively charged par-ticles are called electrons.

Why were the cathode rays in Thomson’scathode ray tube bent by a magnet?

Try to imagine Thomson’s excitement at this discovery. Hehad shown that atoms are not too tiny to divide after all. Rather,they are made up of even smaller subatomic particles. Other sci-entists soon built upon Thomson’s results and found that theelectron had a small mass. In fact, an electron is 1/1,837 themass of the lightest atom, the hydrogen atom. In 1906,Thomson received the Nobel Prize in Physics for his work on thediscovery of the electron.

Matter that has an equal amount of positive and negativecharge is said to be neutral—it has no net charge. Because mostmatter is neutral, Thomson pictured the atom as a ball of posi-tive charge with electrons embedded in it. It was later deter-mined that neutral atoms contained an equal number ofpositive and negative charges.

Figure 5 In Thomson’s experi-ment, the magnet caused the cath-ode rays inside the tube to bend.Describe what you think wouldhappen to the cathode rays if themagnet were removed.

Metal electrode(cathode)

Vacuum pump

Magnet

Metal electrode(anode)

Topic: Subatomic ParticlesVisit for Weblinks to information about particlesthat make up atoms.

Activity Can any of the particlesbe divided further? Display yourdata in a table.

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Van Bucher/Photo Researchers



Thomson’s Model Thomson’s model, shown inFigure 6, can be compared to chocolate chips spreadthroughout a ball of cookie dough. However, themodel did not provide all the answers to the questionsthat puzzled scientists about atoms.

Rutherford—The Nucleus Scientists still hadquestions about how the atom was arranged andabout the presence of positively charged particles. Inabout 1910, a team of scientists led by ErnestRutherford worked on these questions. In their exper-iment, they bombarded an extremely thin piece ofgold foil with alpha particles. Alpha particles are tiny,high-energy, positively charged particles that he pre-dicted would pass through the foil. Most of the particles passedstraight through the foil as if it were not there at all. However,other particles changed direction, and some even bounced back.Rutherford thought the result was so remarkable that he latersaid, “It was almost as incredible as if you had fired a 15-inchshell at a piece of tissue paper, and it came back and hit you.”

Positive Center Rutherford concluded that because so manyof the alpha particles passed straight through the gold foil, theatoms must be made of mostly empty space. However, becausesome of the positively charged alpha particles bounced offsomething, the gold atoms must contain some positivelycharged object concentrated in the midst of this empty space.Rutherford called the positively charged, central part of theatom the nucleus (NEW klee us). He named the positivelycharged particles in the nucleus protons. He also suggested thatelectrons were scattered in the mostly empty space around thenucleus, as shown in Figure 7.

Figure 7 Rutherford concluded that the atommust be mostly empty space in which electronstravel in random paths around the nucleus. He alsothought the nucleus of the atom must be small andpositively charged.Identify where most of the mass of an atom is con-centrated.

Negativelycharged electron

Ball of positive charge

“Empty space”containing electrons

Positively chargednucleus

Randomelectronpaths

Figure 6 Thomson’s modelshows the atom as electronsembedded in a ball of positivecharge.Explain how Thomson knew atomscontained positive and negativecharges.

Nucleus ofprotons andneutrons

Electron paths atdifferent energy levels


Discovering the Neutron Rutherford had been puzzled byone observation from his experiments with nuclei. After the col-lisions, the nuclei seemed to be heavier. Where did this extramass come from? James Chadwick, a student of Rutherford’s,answered this question. The alpha particles themselves were notheavier. The atoms that had been bombarded had given off newparticles. Chadwick experimented with these new particles andfound that, unlike electrons, the paths of these particles were notaffected by an electric field. To explain his observations, he saidthat these particles came from the nucleus and had no charge.Chadwick called these uncharged particles neutrons (NEWtrahnz). His proton-neutron model of the atomic nucleus is stillaccepted today.

Improving the Atomic ModelEarly in the twentieth century, a scientist named Niels Bohr

found evidence that electrons in atoms are arranged accordingto energy levels. The lowest energy level is closest to the nucleusand can hold only two electrons. Higher energy levels are fartherfrom the nucleus and can contain more electrons. To explainthese energy levels, some scientists thought that the electronsmight orbit an atom’s nucleus in paths that are specific distancesfrom the nucleus, as shown in Figure 8. This is similar to howthe planets orbit the Sun.

The Modern Atomic Model As a result of continuing research, scientists now realize that because electrons have characteristics that are similar to waves and particles, theirenergy levels are not defined, planet-like orbits around thenucleus. Rather, it seems most likely that electrons move in whatis called the atom’s electron cloud, as shown in Figure 9.

Figure 8 This simplified Bohrmodel shows a nucleus of protonsand neutrons and electron pathsbased on energy levels.

Physicists and ChemistsPhysicists generally studythe physical atom. Thephysical atom includes theinner components of anatom such as protons andneutrons, the forces thathold or change their posi-tions in space and the bulkproperties of elements suchas melting point. Chemists,on the other hand, studythe chemical atom. Thechemical atom refers to themanner in which differentelements relate to eachother and the new sub-stances formed by theirunion.

Self Check1. List five examples of matter and five examples that are

not matter. Explain your answers.

2. Describe and name the parts of the atom.

3. Explain why the word atom was an appropriate termfor Democritus’s idea.

4. Think Critically When neutrons were discovered, werethese neutrons created in the experiment? How doesLavoisier’s work help answer this question?

5. Explain the law of conservation of matter using yourown examples.

6. Think Critically How is the electron cloud model differ-ent from Bohr’s atomic model?

SummaryWhat is matter?

• Matter is anything that has mass and takes upspace.

• Matter is composed of atoms.

Models of the Atom

• Democritus introduced the idea of an atom.Lavoisier showed matter is neither creatednor destroyed, just changed.

• Dalton’s ideas led to the atomic theory ofmatter.

• Thomson discovered the electron.

• Rutherford discovered protons exist in thenucleus.

• Chadwick discovered the neutron.

Improving the Atomic Model

• Niels Bohr suggested electrons move inenergy levels.

• More recent physicists introduced the ideaof the electron cloud and were able to breakdown protons and neutrons into smallerparticles called quarks.

7. Classify each scientist and his contribution accordingto the type of discovery each person made. Explainwhy you grouped certain scientists together.

8. Evaluate Others’ Data and Conclusions Analyze,review, and critique the strengths and weaknesses ofThomson’s “cookie dough” theory using the results of Rutherford’s gold foil experiment.


The Electron Cloud The electron cloud is a sphericalcloud of varying density surrounding the nucleus. Thevarying density shows where an electron is more or lesslikely to be. Atoms with electrons in higher energy levelshave electron clouds of different shapes that also showwhere those electrons are likely to be. Generally, the elec-tron cloud has a radius 10,000 times that of the nucleus.

Further Research By the 1930s, it was recognized thatmatter was made up of atoms, which were, in turn, made upof protons, neutrons, and electrons. But scientists, calledphysicists, continued to study the basic parts of this atom.Today, they have succeeded in breaking down protonsand neutrons into even smaller particles called quarks.These particles can combine to make other kinds of tinyparticles, too. The six types of quarks are up, down, strange,charmed, top, and bottom. Quarks have fractional electriccharges of �2/3 or �1/3, unlike the �1 charge of a protonor the �1 charge of an electron. Research will continue asnew discoveries are made about the structure of matter.

Nucleus

Electron cloud

Figure 9 This model of the atom showsthe electrons moving around the nucleus ina region called an electron cloud. The darkcloud of color represents the area where theelectron is more likely to be found.Infer What does the intensity of color nearthe nucleus suggest?

red.msscience.com/self_check_quiz


The ElementsHave you watched television today? TV sets are common, yet

each one is a complex system. The outer case is made mostly ofplastic, and the screen is made of glass. Many of the parts thatconduct electricity are metals or combinations of metals. Otherparts in the interior of the set contain materials that barely con-duct electricity. All of the different materials have one thing incommon: they are made up of even simpler materials. In fact, ifyou had the proper equipment, you could separate the plastics,glass, and metals into these simpler materials.

One Kind of Atom Eventually, though, you would separatethe materials into groups of atoms. At that point, you wouldhave a collection of elements. An element is matter made ofonly one kind of atom. At least 110 elements are known and atleast 90 of them occur naturally on Earth. These elements makeup gases in the air, minerals in rocks, and liquids such as water.Examples of naturally occurring elements include the oxygenand nitrogen in the air you breathe and the metals gold, silver,aluminum, and iron. The other elements are known as syntheticelements. These elements have been made in nuclear reactionsby scientists with machines called particle accelerators, like theone shown in Figure 10. Some synthetic elements have impor-tant uses in medical testing and are found in smoke detectorsand heart pacemaker batteries.

■ Describe the relationshipbetween elements and theperiodic table.

■ Explain the meaning of atomicmass and atomic number.

■ Identify what makes an isotope.■ Contrast metals, metalloids, and

nonmetals.

Everything on Earth is made of theelements that are listed on theperiodic table.

Review Vocabularymass: a measure of the amountof matter an object has

New Vocabulary

• element • atomic mass

• atomic • metalnumber • nonmetal

• isotope • metalloid

• mass number

The Simplest Matter

106

Figure 10 The Tevatron has a circum-ference of 6.3 km—a distance thatallows particles to accelerate to highspeeds. These high-speed collisionscan create synthetic elements.

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The Periodic TableSuppose you go to a library, like the one shown in

Figure 11, to look up information for a school assignment.How would you find the information? You could look ran-domly on shelves as you walk up and down rows of books,but the chances of finding your book would be slim. Toavoid such haphazard searching, some libraries use theDewey Decimal Classification System to categorize andorganize their volumes and to help you find books quicklyand efficiently.

Charting the Elements Chemists have created a chartcalled the periodic table of the elements to help themorganize and display the elements. Figure 12 shows howscientists changed their model of the periodic table overtime.

On the inside back cover of this book, you will find a mod-ern version of the periodic table. Each element is represented bya chemical symbol that contains one to three letters. The sym-bols are a form of chemical shorthand that chemists use to savetime and space—on the periodic table as well as in written for-mulas. The symbols are an important part of an internationalsystem that is understood by scientists everywhere.

The elements are organized on the periodic table by theirproperties. There are rows and columns that represent relation-ships between the elements. The rows in the table are calledperiods. The elements in a row have the same number of energylevels. The columns are called groups. The elements in eachgroup have similar properties related to their structure. Theyalso tend to form similar bonds.

Figure 11 When you look forinformation in the library, a sys-tem of organization called theDewey Decimal ClassificationSystem helps you find a bookquickly and efficiently.

Dewey Decimal Classification System

000 Computers, information and general reference

100 Philosophy and psychology

200 Religion

300 Social sciences

400 Languages

500 Science

600 Technology

700 Arts and recreation

800 Literature

900 History and geography

Topic: New ElementsVisit for Weblinks to information about newelements.

Activity Research physical prop-erties of two synthetic elements.

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SECTION 2 The Simplest Matter 107Tom Stewart/The Stock Market/CORBIS


Figure 12

VISUALIZING THE PERIODIC TABLE


The familiar periodic tablethat adorns many scienceclassrooms is based on a

number of earlier efforts to iden-tify and classify the elements. Inthe 1790s, one of the first lists ofelements and their compoundswas compiled by French chemistAntoine-Laurent Lavoisier, who is shown in the background picture with his wife and assis-tant, Marie Anne.Three othertables are shown here.

John Dalton (Britain, 1803)used symbols to representelements. His table alsoassigned masses to eachelement.

An early alchemist put togetherthis table of elements and com-pounds. Some of the symbolshave their origin in astrology.

Dmitri Mendeleev (Rus-sia, 1869) arranged the63 elements known to exist at that time intogroups based on theirchemical properties andatomic weights. He leftgaps for elements he predicted were yet to be discovered.

(br)New York Public Library, General Research Division, Astor, Lenox, and Tilden Foundations, (others)Bettmann/CORBIS

SECTION 2 The Simplest Matter 109

Identifying CharacteristicsEach element is different and has unique properties. These

differences can be described in part by looking at the relation-ships between the atomic particles in each element. The periodictable contains numbers that describe these relationships.

Number of Protons and Neutrons Look up the elementchlorine on the periodic table found on the inside back cover ofyour book. Cl is the symbol for chlorine, as shown in Figure 13,but what are the two numbers? The top number is the element’satomic number. It tells you the number of protons in thenucleus of each atom of that element. Every atom of chlorine,for example, has 17 protons in its nucleus.

What are the atomic numbers for Cs, Ne, Pb, and U?

Isotopes Although the number of protons changes from ele-ment to element, every atom of the same element has the samenumber of protons. However, the number of neutrons can varyeven for one element. For example, some chlorine atoms have 18 neutrons in their nucleus while others have 20. These twotypes of chlorine atoms are chlorine-35 and chlorine-37. Theyare called isotopes (I suh tohps), which are atoms of the sameelement that have different numbers of neutrons.

You can tell someone exactly which isotope you are referringto by using its mass number. An atom’s mass number is thenumber of protons plus the number of neutrons it contains. Thenumbers 35 and 37, which were used to refer to chlorine, aremass numbers. Hydrogen has three isotopes with mass numbersof 1, 2, and 3. They are shown in Figure 14. Each hydrogen atomalways has one proton, but in each isotope the number of neu-trons is different.

Figure 13 The periodic tableblock for chlorine shows its sym-bol, atomic number, and atomicmass.Determine if chlorine atoms aremore or less massive than carbonatoms.

Figure 14 Three isotopes ofhydrogen are known to exist. Theyhave zero, one, and two neutronsin addition to their one proton.Protium, with only the one proton,is the most abundant isotope.

Chlorine17Cl

35.453

DeuteriumProtium Tritium

1 Proton0 Neutrons

1 Proton2 Neutrons

1 Proton1 Neutron


Atomic Mass The atomic mass is the weighted averagemass of the isotopes of an element. The atomic mass is thenumber found below the element symbol in Figure 13. Theunit that scientists use for atomic mass is called the atomicmass unit, which is given the symbol u. It is defined as 1/12the mass of a carbon-12 atom.

The calculation of atomic mass takes into account thedifferent isotopes of the element. Chlorine’s atomic mass of35.45 u could be confusing because there aren’t any chlorineatoms that have that exact mass. About 76 percent of chlo-rine atoms are chlorine-35 and about 24 percent are chlo-rine-37, as shown in Figure 15. The weighted average massof all chlorine atoms is 35.45 u.

Classification of ElementsElements fall into three general categories—metals, metal-

loids (ME tuh loydz), and nonmetals. The elements in each cat-egory have similar properties.

Metals generally have a shiny or metallic luster and are goodconductors of heat and electricity. All metals, except mercury, aresolids at room temperature. Metals are malleable (MAL yuh bul),which means they can be bent and pounded into various shapes.The beautiful form of the shell-shaped basin in Figure 16 is aresult of this characteristic. Metals are also ductile, which meansthey can be drawn into wires without breaking. If you look at theperiodic table, you can see that most of the elements are metals.

Figure 15 If you have 1,000atoms of chlorine, about 758 willbe chlorine-35 and have a mass of34.97 u each. About 242 will bechlorine-37 and have a mass of36.97 u each. The total mass of the1,000 atoms is 35,454 u, so theaverage mass of one chlorine atomis about 35.45 u.

Figure 16 The artisan is chas-ing, or chiseling, the malleablemetal into the desired form.

24.2%Cl–37

75.8%Cl–35

Circle Graph Showing Abundance of Chlorine Isotopes

Average atomic mass � 35.45 u

Emmanuel Scorcelletti/Liaison Agency/Getty Images

Self Check1. Explain some of the uses of metals based on their

properties.

2. Describe the difference between atomic number andatomic mass.

3. Define the term isotope. Explain how two isotopes ofan element are different.

4. Identify the isotopes of hydrogen.

5. Think Critically Describe how to find the atomic num-ber for the element oxygen. Explain what this informa-tion tells you about oxygen.

SummaryThe Elements

• An element is matter made of only one typeof atom.

• Some elements occur naturally on Earth.Synthetic elements are made in nuclearreactions in particle accelerators.

• Elements are divided into three categoriesbased on certain properties.

The Periodic Table

• The periodic table arranges and displays allknown elements in an orderly way.

• Each element has a chemical symbol.

Identifying Characteristics

• Each element has a unique number ofprotons, called the atomic mass number.

• Isotopes of an element are important whendetermining the atomic mass of an element.

6. Simple Equation An atom of niobium has a massnumber of 93. How many neutrons are in the nucleusof this atom? An atom of phosphorus has 15 protonsand 15 neutrons in the nucleus. What is the mass number of this isotope?

Other Elements Nonmetals are elementsthat are usually dull in appearance. Most arepoor conductors of heat and electricity. Manyare gases at room temperature, and bromine isa liquid. The solid nonmetals are generallybrittle, meaning they cannot change shapeeasily without breaking. The nonmetals areessential to the chemicals of life. More than 97percent of your body is made up of variousnonmetals, as shown in Figure 17. You can seethat, except for hydrogen, the nonmetals arefound on the right side of the periodic table.

Metalloids are elements that have charac-teristics of metals and nonmetals. On theperiodic table, metalloids are found betweenthe metals and nonmetals. All metalloids aresolids at room temperature. Some metalloidsare shiny and many are conductors, but they are not as good atconducting heat and electricity as metals are. Some metalloids,such as silicon, are used to make the electronic circuits in com-puters, televisions, and other electronic devices.

What is a metalloid?

Figure 17 You are made up ofmostly nonmetals.

SECTION 2 The Simplest Matter 111

Oxygen 65%

Other elements 2.3%

Hydrogen 9.5%Nitrogen 3.2%Calcium 1.5%

Carbon 18.5%

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The periodic table organizes the elements, butwhat do they look like? What are they used for?In this lab, you’ll examine some elements andshare your findings with your classmates.

Real-World QuestionWhat are some of the characteristics and purposes of the chemical elements?

Goals■ Classify the chemical elements.■ Organize the elements into the groups and

periods of the periodic table.

Materialscolored markers large bulletin boardlarge index cards 81/2-in � 14-in paper Merck Index thumbtacksencyclopedia *pushpins*other reference

materials *Alternate materials

Safety Precaution

WARNING: Use care when handling sharp objects.

Procedure1. Select the assigned number of elements

from the list provided by your teacher.

2. Design an index card for each of yourselected elements. On each card, mark theelement’s atomic number in the upper left-hand corner and write its symbol and namein the upper right-hand corner.

3. Research each of the elements and writeseveral sentences on the card about itsappearance, its other properties, and its uses.

4. Classify each of your elements as a metal, ametalloid, or a nonmetal based upon itsproperties.

5. Write the appropriate classification on eachof your cards using the colored marker cho-sen by your teacher.

6. Work with your classmates to make a largeperiodic table. Use thumbtacks to attachyour cards to a bulletin board in their properpositions on the periodic table.

7. Draw your own periodic table. Place theelements’ symbols and atomic numbers inthe proper locations on your table.

Conclude and Apply1. Interpret the class data and classify the ele-

ments into the categories metal, metalloid,and nonmetal. Highlight each category in adifferent color on your periodic table.

2. Predict the properties of a yet-undiscoveredelement located directly under francium onthe periodic table.


Elements and thePeriodic Table

Doug Martin

SubstancesScientists classify matter in several ways that depend on

what it is made of and how it behaves. For example, matter that has the same composition and properties throughout is called a substance. Elements, such as a bar of gold or a sheetof aluminum, are substances. When different elements combine,other substances are formed.

Compounds What do you call the colorless liquid that flowsfrom the kitchen faucet? You probably call it water, but maybeyou’ve seen it written H2O. The elements hydrogen and oxygenexist as separate, colorless gases. However, these two elementscan combine, as shown in Figure 18, to form the compoundwater, which is different from the elements that make it up. Acompound is a substance whose smallest unit is made up ofatoms of more than one element bonded together.

Compounds often have properties that are different from theelements that make them up. Water is distinctly different fromthe elements that make it up. It is also different from anothercompound made from the same elements. Have you everused hydrogen peroxide (H2O2) to disinfect a cut? Thiscompound is a different combination of hydrogen andoxygen and has different properties from those of water.

Water is a nonirritating liquid that is used for bathing,drinking, cooking, and much more. In contrast, hydrogenperoxide carries warnings on its labels such as KeepHydrogen Peroxide Out of the Eyes. Although it is useful insolutions for cleaning contact lenses, it is not safe for youreyes as it comes from the bottle.

Compounds andMixtures

Figure 18 A space shuttle is powered by the reaction betweenliquid hydrogen and liquid oxygen. The reaction produces a largeamount of energy and the compound water.Explain why a car that burns hydrogen rather than gasoline wouldbe friendly to the environment.

■ Identify the characteristics of acompound.

■ Compare and contrast differenttypes of mixtures.

The food you eat, the materials youuse, and all matter can be classifiedby compounds or mixtures.

Review Vocabularyformula: shows which elementsand how many atoms of eachmake up a compound

New Vocabulary

• substance • mixture

• compound

SECTION 3 Compounds and Mixtures 113

NA

SA

Comparing CompoundsProcedure

1. Collect the following substances—granularsugar, rubbing alcohol,and salad oil.

2. Observe the color, appear-ance, and state of eachsubstance. Note the thickness or texture ofeach substance.

3. Stir a spoonful of each substance into separateglasses of hot tap waterand observe.

Analysis1. Compare the different prop-

erties of the substances.2. The formulas of the three

substances are made of onlycarbon, hydrogen, and oxy-gen. Infer how they canhave different properties.


Compounds Have Formulas What’s the difference betweenwater and hydrogen peroxide? H2O is the chemical formula forwater, and H2O2 is the formula for hydrogen peroxide. Theformula tells you which elements make up a compound aswell as how many atoms of each element are present. Look atFigure 19. The subscript number written below and to the rightof each element’s symbol tells you how many atoms of that ele-ment exist in one unit of that compound. For example, hydro-gen peroxide has two atoms of hydrogen and two atoms ofoxygen. Water is made up of two atoms of hydrogen and oneatom of oxygen.

Carbon dioxide, CO2, is another common compound.Carbon dioxide is made up of one atom of carbon and twoatoms of oxygen. Carbon and oxygen also can form the com-pound carbon monoxide, CO, which is a gas that is poisonousto all warm-blooded animals. As you can see, no subscript isused when only one atom of an element is present. A given com-pound always is made of the same elements in the same propor-tion. For example, water always has two hydrogen atoms forevery oxygen atom, no matter what the source of the water is.No matter what quantity of the compound you have, the for-mula of the compound always remains the same. If you have 12 atoms of hydrogen and six atoms of oxygen, the compoundis still written H2O, but you have six molecules of H2O (6 H2O),not H12O6. The formula of a compound communicates its iden-tity and makeup to any scientist in the world.

Propane has three carbon and eight hydrogenatoms. What is its chemical formula?

Figure 19 The elementshydrogen and oxygen can formtwo compounds—water andhydrogen peroxide. Note thedifferences in their structure.

H2O2

Hydrogenatoms

Oxygen atoms

O

H

H

O

H2O

Oxygen atom

Hydrogen atoms

O

HH

Mark Burnett

MixturesWhen two or more substances (elements or

compounds) come together but don’t combine tomake a new substance, a mixture results. Unlikecompounds, the proportions of the substances in amixture can be changed without changing the iden-tity of the mixture. For example, if you put somesand into a bucket of water, you have a mixture ofsand and water. If you add more sand or morewater, it’s still a mixture of sand and water. Its iden-tity has not changed. Air is another mixture. Air is amixture of nitrogen, oxygen, and other gases, whichcan vary at different times and places. Whateverthe proportion of gases, it is still air. Even your bloodis a mixture that can be separated, as shown inFigure 20, by a machine called a centrifuge.

How do the proportions of amixture relate to its identity?


What’s the best way to desalt ocean water?

Methods for Desalting Ocean Water

Process Amount of Water a Unit

Special Needs Number of People

Can Desalt in a Day (m3) Needed to Operate

Distillation 1,000 to 200,000 lots of energy to boil the water many

Electrodialysis 10 to 4,000 stable source of electricity 1 to 2 persons

Identifying the Problem The table above compares desalting

methods. In distillation, the ocean wateris heated. Pure water boils off and iscollected, and the salt is left behind.Electrodialysis uses an electric currentto pull salt particles out of water.

Solving the Problem 1. What method(s) might you use

to desalt the water for a largepopulation where energy isplentiful?

2. What method(s) would you chooseto use in a single home?

You can’t drink ocean water becauseit contains salt and other suspended

materials. Or can you? In many areasof the world where drinking water isin short supply, methods for getting

the salt out of salt water are beingused to meet the demand for freshwater. Use your problem-solvingskills to find the best method to usein a particular area.

Plasma

Platelets and white blood cells

Red blood cells

Figure 20 The layersin this blood sampleinclude plasma,platelets, whiteblood cells, andred blood cells.

Klaus Guldbrandsen/Science Photo Library/Photo Researchers


Your blood is a mixture made up of ele-ments and compounds. It contains white

blood cells, red blood cells, water, and a number of dissolved sub-stances. The different parts of blood can be separated and usedby doctors in different ways. The proportions of the substancesin your blood change daily, but the mixture does not change itsidentity.

Separating Mixtures Sometimes you can use a liquid to separate a mixture of solids. For example, if you add water toa mixture of sugar and sand, only the sugar dissolves in thewater. The sand then can be separated from the sugar and waterby pouring the mixture through a filter. Heating the remainingsolution will separate the water from the sugar.

At other times, separating a mixture of solids of differentsizes might be as easy as pouring them through successivelysmaller sieves or filters. A mixture of marbles, pebbles, and sandcould be separated in this way.

Figure 21 Mixtures are part of your everyday life.

Topic: MixturesVisit for Weblinks to information aboutseparating mixtures.

Activity Describe the differencebetween mixtures and compounds.

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Self Check1. List three examples of compounds and three examples

of mixtures. Explain your choices.

2. Determine A container contains a mixture of sand,salt, and pebbles. How can each substance be separatedfrom the others?

3. Think Critically Explain whether your breakfast wasa compound, a homogeneous mixture, or a heteroge-neous mixture.

SummarySubstances

• A substance can be either an element or acompound.

• A compound contains more than one kind ofelement bonded together.

• A chemical formula shows which elements andhow many atoms of each make up a compound.

Mixtures

• A mixture contains substances that are notchemically bonded together.

• There are many ways to separate mixtures,based on their physical properties.

• Homogeneous mixtures are those that are thesame throughout. These types of mixtures canbe solids, liquids, or gases.

• Heterogeneous mixtures have larger partsthat are different from each other.

4. Compare and contrast compounds and mixturesbased on what you have learned from this section.

5. Use a Database Use a computerized card catalog ordatabase to find information about one element fromthe periodic table. Include information about theproperties and uses of the mixtures and/or compounds in which the element is frequently found.

Homogeneous orHeterogeneous Mix-tures, such as the onesshown in Figure 21, canbe classified as homoge-neous or heterogeneous.Homogeneous means “thesame throughout.” Youcan’t see the different partsin this type of mixture. Infact, you might not always

know that homogeneous mixtures are mixtures because you can’ttell by looking. Which mixtures in Figure 21 are homogeneous?No matter how closely you look, you can’t see the individual partsthat make up air or the parts of the mixture called brass in the lampshown. Homogeneous mixtures can be solids, liquids, or gases.

A heterogeneous mixture has larger parts that are differentfrom each other. You can see the different parts of a heteroge-neous mixture, such as sand and water. How many heteroge-neous mixtures are in Figure 21? A pepperoni and mushroompizza is a tasty kind of heterogeneous mixture. Other examplesof this kind of mixture include tacos, vegetable soup, a toy boxfull of toys, or a toolbox full of nuts and bolts.

Rocks and MineralsScientists called geologistsstudy rocks and minerals. A mineral is composed of apure substance. Rocks aremixtures and can bedescribed as being homo-geneous or heterogeneous.Research to learn moreabout rocks and mineralsand note some examples ofhomogeneous and hetero-geneous rocks in yourScience Journal.

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Real-World QuestionYou will encounter many com-pounds that look alike. For exam-ple, a laboratory stockroom is filledwith white powders. It is importantto know what each is. In a kitchen,cornstarch, baking powder, andpowdered sugar are compoundsthat look alike. To avoid mistakingone for another, you can learn howto identify them. Different com-pounds can be identified by usingchemical tests. For example, somecompounds react with certain liq-uids to produce gases. Other com-binations produce distinctive colors. Some compounds have highmelting points. Others have low melting points. How can the com-pounds in an unknown mixture be identified by experimentation?

Goals■ Test for the presence

of certain compounds.■ Decide which of these

compounds are presentin an unknown mixture.

Materialstest tubes (4)cornstarchpowdered sugarbaking sodamystery mixturesmall scoops (3)dropper bottles (2)iodine solutionwhite vinegarhot plate250-mL beakerwater (125 mL)test-tube holdersmall pie pan

Safety Precautions

WARNING: Use cautionwhen handling hot objects.Substances could stain orburn clothing. Be sure topoint the test tube awayfrom your face and yourclassmates while heating.

Mystery Msxture

118 CHAPTER 4 Atoms, Elements, and the Periodic Table(t)Mark Burnett, (b)Michael Newman/PhotoEdit, Inc.

Procedure1. Copy the data table into your Science Journal. Record your results carefully for

each of the following steps.

2. Place a small scoopful of cornstarch on the pie pan. Do the same for the sugarand baking soda making separate piles. Add a drop of vinegar to each. Washand dry the pan after you record your observations.

3. Again, place a small scoopful of cornstarch, sugar, and baking soda on the piepan. Add a drop of iodine solution to each one. Wash and dry the pan after yourecord your observations.

4. Again place a small scoopful ofeach compound in a separate testtube. Hold the test tube with thetest-tube holder and with an ovenmitt. Gently heat the test tube in abeaker of boiling water on a hotplate.

5. Follow steps 2 through 4 to testyour mystery mixture for eachcompound.

Analyze Your DataIdentify from your data table which compound(s) you have.

Conclude and Apply1. Describe how you decided which substances were in your unknown mixture.

2. Explain how you would be able to tell if all three compounds were not in yourmystery substance.

3. Draw a Conclusion What would you conclude if you tested baking powderfrom your kitchen and found that it fizzed with vinegar, turned blue withiodine, and did not melt when heated?

Make a different data table to display yourresults in a new way. For more help, referto the Science Skill Handbook.

LAB 119

Identifying Presence of Compounds

Substance Fizzes Turns Blue Melts to Be with with When Tested Vinegar Iodine Heated

Cornstarch

Sugar

Baking soda

Mystery mix

Do not write in this book.

The world’s earliestscientists were peo-ple who were curi-

ous about the world aroundthem and who tried to develop

explanations for the things theyobserved. This type of observation and inquiryflourished in ancient cultures such as those foundin India and China. Read on to see how the ancientIndians and Chinese defined matter.

Indian IdeasTo Indians living about 3,000 years ago,

the world was made up of five elements: fire,air, earth, water, and ether,

which they thought of as anunseen substance that filledthe heavens. Building upon

this concept, the early Indianphilosopher Kashyapa (kah SHI

ah pah) proposed that the five ele-ments could be broken down into smaller

units called parmanu (par MAH new). Parmanuwere similar to atoms in that they were too smallto be seen but still retained the properties of theoriginal element. Kashyapa also believed thateach type of parmanu had unique physical andchemical properties.

Parmanu of earth elements, for instance, wereheavier than parmanu of air elements. The differ-ent properties of the parmanu determined thecharacteristics of a substance. Kashyapa’sideas about matter are similar to thoseof the Greek philosopher Democritus,who lived centuries after Kashyapa.

Chinese IdeasThe ancient Chinese also broke

matter down into five elements: fire,wood, metal, earth, and water. Unlikethe early Indians, however, the Chinesebelieved that the elements constantlychanged form. For example, wood can be burnedand thus changes to fire. Fire eventually diesdown and becomes ashes, or earth. Earth givesforth metals from the ground. Dew or water col-lects on these metals, and the water then nurturesplants that grow into trees, or wood.

This cycle of constant change was explainedin the fourth century B.C. by the philoso-pher Tsou Yen. Yen, who is knownas the founder of Chinese scien-tific thought, wrote that allchanges that took place innature were linked tochanges in the five elements.

SCIENCEAND

HISTORYSCIENCE

CAN CHANGE THE COURSE OF HISTORY!

air

earth

Research Write a brief paragraph that compares and contraststhe ancient Indian and Chinese views of matter. How are theydifferent? Similar? Which is closer to the modern view of matter?Explain.

For more information, visitred.msscience.com/time

fire

metal

water Two cultures observed the world around them differently

metal

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Copy and complete the following concept map.

Structure of Matter

1. Matter is anything that occupies space andhas mass.

2. Matter is made up of atoms.

3. Atoms are made of smaller parts calledprotons, neutrons, and electrons.

4. Many models of atoms have been createdas scientists try to discover and define theatom’s internal structure. Today’s model hasa central nucleus with the protons and neu-trons, and an electron cloud surrounding it.

The Simplest Matter

1. Elements are the building blocks of matter.

2. An element’s atomic number tells how manyprotons its atoms contain, and its atomicmass tells the average mass of its atoms.

3. Isotopes are two or more atoms of the sameelement that have different numbers ofneutrons.

Compounds and Mixtures

1. Compounds are substances that are producedwhen elements combine. Compounds con-tain specific proportions of the elementsthat make them up.

2. Mixtures are combinations of compoundsand elements that have not formed newsubstances. Their proportions can change.

CHAPTER STUDY GUIDE 121red.msscience.com/interactive_tutor

which is a substance made of two or more

which are materials that cannot be broken

down and are made of

whichare composed of

whichcan be either

can bea

can bea

Matter

Compound

Homogeneous

Protons


Fill in the blanks with the correct vocabularyword or words.

1. The __________ is the particle in the nucleus of the atom that carries a positivecharge and is counted to identify the atomicnumber.

2. The new substance formed whenelements combine chemically is a(n)__________.

3. Anything that has mass and takes up spaceis __________.

4. The particles in the atom that account formost of the mass of the atom are protonsand __________.

5. Elements that are shiny, malleable, ductile,good conductors of heat and electricity, andmake up most of the periodic table are__________.

Choose the word or phrase that best answers thequestion.

6. What is a solution an example of?A) elementB) heterogeneous mixtureC) compoundD) homogeneous mixture

7. The nucleus of one atom contains 12 pro-tons and 12 neutrons, while the nucleusof another atom contains 12 protons and16 neutrons. What are the atoms?A) chromium atoms B) two different elements C) two isotopes of an elementD) negatively charged

8. What is a compound?A) a mixture of chemicals and elementsB) a combination of two or more elementsC) anything that has mass and occupies

spaceD) the building block of matter

9. What does the atom consist of?A) electrons, protons, and alpha particlesB) neutrons and protonsC) electrons, protons, and neutronsD) elements, protons, and electrons

10. In an atom, where is an electron located?A) in the nucleus with the protonB) on the periodic table of the elementsC) with the neutron D) in a cloudlike formation surrounding

the nucleus

11. How is matter defined?A) the negative charge in an atomB) anything that has mass and occupies

spaceC) the mass of the nucleusD) sound, light, and energy

12. What are two atoms that have the samenumber of protons called?A) metalsB) nonmetalsC) isotopesD) metalloids

13. Which is a heterogeneous mixture?A) air C) a saladB) brass D) apple juice

122 CHAPTER REVIEW

atom p. 99atomic mass p. 110atomic number p. 109compound p. 113electron p. 102element p. 106isotope p. 109law of conservation

of matter p. 100mass number p. 109

matter p. 98metal p. 110metalloid p. 111mixture p. 115neutron p. 104nonmetal p. 111nucleus p. 103proton p. 103substance p. 113

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CHAPTER REVIEW 123

Use the illustration below to answer questions 14and 15.

14. Using the figure above, krypton has A) an atomic number of 84.B) an atomic number of 36.C) an atomic mass of 36.D) an atomic mass of 72.

15. From the figure, the element krypton is A) a solid. C) a mixture.B) a liquid. D) a gas.

16. Analyze Information A chemical formula iswritten to indicate the makeup of a com-pound. What is the ratio of sulfur atomsto oxygen atoms in SO2?

17. Determine which element contains sevenprotons.

18. Describe Using the periodic table, what arethe atomic numbers for carbon, sodium,and nickel?

19. Explain how cobalt-60 and cobalt-59 can bethe same element but have different massnumbers.

20. Analyze Information What did Rutherford’sgold foil experiment tell scientists aboutatomic structure?

21. Predict Suppose Rutherford had bom-barded aluminum foil with alpha particlesinstead of the gold foil he used in his

experiment. What observations do youpredict Rutherford would have made?Explain your prediction.

22. Draw Conclusions You are shown a liquidthat looks the same throughout. You’retold that it contains more than one typeof element and that the proportion ofeach varies throughout the liquid. Is thisan element, a compound, or a mixture?

Use the illustrations below to answer question 23.

23. Interpret Scientific Illustrations Look at the twocarbon atoms above. Explain whether ornot the atoms are isotopes.

24. Explain how the atomic mass of an elementis determined.

25. Newspaper Article As a newspaper reporter inthe year 1896, you have heard about the dis-covery of the electron. Research and write anarticle about the scientist and the discovery.

�

�

�

�

�

��

�

�

��

�

Krypton36Kr

83.80

26. Atomic Mass Krypton has six naturally occurringisotopes with atomic masses of 78, 80, 82, 83,84, and 86. Make a table of the number of pro-tons, electrons, and neutrons in each isotope.

27. Atomic Ratio A researcher is analyzing twodifferent compounds, sulfuric acid (H2SO4) andhydrogen peroxide (H2O2). What is the ratioof hydrogen to oxygen in sulfuric acid? What isthe ratio of hydrogen to oxygen in hydrogenperoxide?

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Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

1. Which of the scientists below introducedthe idea that matter is made up of tiny,individual bits called atoms?A. Arrhenius C. ChadwickB. Avogadro D. Democritus

Use the illustration below to answer questions 2 and 3.

2. The periodic table block shown above listsproperties of the element chlorine. Whatdoes the number 35.453 mean?A. the number of neutrons and in every

chlorine atomB. the number of neutrons and protons in

every chlorine atomC. the average number of neutrons in a

chlorine atomD. the average number of neutrons and

protons in a chlorine atom

3. According to the periodic table block, howmany electrons does an uncharged atom ofchlorine have?A. 17 C. 35B. 18 D. 36

4. Which of the following scientists envi-sioned the atom as a ball of positive chargewith electrons embedded in it, much likechocolate chips spread through cookiedough?A. Crookes C. ThomsonB. Dalton D. Rutherford

Use the illustration below to answer questions 5 and 6.

5. Which of the following correctly identifiesthe three atoms shown in the illustrationabove?A. hydrogen, lithium, sodiumB. hydrogen, helium, lithiumC. hydrogen, helium, heliumD. hydrogen, hydrogen, hydrogen

6. What is the mass number for each of theatoms shown in the illustration?A. 0, 1, 2B. 1, 1, 1C. 1, 2, 2D. 1, 2, 3

7. Which of the following are found close tothe right side of the periodic table?A. metals C. nonmetalsB. lanthanides D. metalloids

8. Which of the following is a characteristicthat is typical of a solid, nonmetal element?A. shinyB. brittleC. good heat conductorD. good electrical conductor

1 Proton1 Neutron

1 Proton0 Neutrons

1 Proton2 Neutrons

Chlorine17Cl

35.453

Full Understanding Read each question carefully for fullunderstanding.

124 STANDARDIZED TEST PRACTICE

Record your answers on the answer sheetprovided by your teacher or on a sheet of paper.

9. Are electrons more likely to be in anenergy level close to the nucleus or faraway from the nucleus? Why?

10. How many naturally-occurring elementsare listed on the periodic table?

11. Is the human body made of mostly metal,nonmetals, or metalloids?

12. A molecule of hydrogen peroxide is com-posed of two atoms of hydrogen and twoatoms of oxygen. What is the formula forsix molecules of hydrogen peroxide?

13. What is the modern-day name forcathode rays?

Use the illustration below to answer questions 14

and 15.

14. The illustration above shows atoms of anelement and molecules of a compoundthat are combined without making a newcompound. What term describes a combi-nation such as this?

15. If the illustration showed only the elementor only the compound, what term woulddescribe it?

Record your answers on a sheet of paper.

16. Describe Dalton’s ideas about the compo-sition of matter, including the relationshipbetween atoms and elements.

Use the illustration below to answer questions 17

and 18.

17. The illustration above shows Rutherford’sgold foil experiment. Describe the setupshown. What result did Rutherford expectfrom his experiment?

18. What is the significance of the particlesthat reflected back from the gold foil?How did Rutherford explain his results?

19. Describe three possible methods for sepa-rating mixtures. Give an example for eachmethod.

20. What are the rows and columns on theperiodic table called? How are elements inthe rows similar, and how are elements inthe columns similar?

21. Describe how Thomson was able to showthat cathode rays were streams of parti-cles, not light.

22. Describe how the mass numbers, oratomic masses, listed on the periodic tablefor the elements are calculated.

Source of positivelycharged particles

Positively chargedparticle beam

Detector screen

Most of the particles pass

through the foil with

little or no deflection.

A few of the particlesricochet back toward

the source.

Gold foil

STANDARDIZED TEST PRACTICE 125red.msscience.com/standardized_test


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