MatterThe structures of differenttypes of atoms and howthey join together deter-mine all the properties ofmatter that you canobserve.

SECTION 1AtomsMain Idea Matter is madeup of tiny particles calledatoms.

SECTION 2Combinations of AtomsMain Idea Compoundsand mixtures are formedfrom combinations ofatoms.

SECTION 3Properties of MatterMain Idea The physicalproperties of a substanceare the characteristics thatcan be observed withoutchanging the substanceinto a new substance. Matter, Matter Everywhere!

Everything in this scene is matter, which can exist as solid, liquid,or gas. You can see solids and liquids, but not gas. Only one thing occurs naturally on Earth in all three forms. Can youguess what it is?

What is matter made of and how can it take such varied forms?Write what you know now in your Science Journal, and compare it with what you learn afteryou read the chapter.

Science Journal

John Coletti/Index Stock

3333

Start-Up Activities

Change the State of WaterOn Earth, water is unique because it is foundas a solid, liquid, or gas. Water is invisible asa gas, but you know it is there when fogforms over a lake or a puddle of water driesup. The following lab will help you visualizehow matter can change states.

1. Pour 500 mL of water into a 1,000-mLglass beaker.

2. Mark the level of water in the beaker withthe bottom edge of a piece of tape.

3. Place the beaker on a hot plate.

4. With the help of an adult, heat the wateruntil it boils for 5 min. Let the water cool.

5. With the help of an adult, compare thelevel of the water to the bottom edge ofthe tape.

6. Think Critically Did the amount ofwater in the beaker change? In yourScience Journal, explain what happenedto the water.

Matter Make the followingFoldable to help you understandthe vocabulary terms in thischapter.

Fold a vertical sheet of notebookpaper from side toside.

Cut along every third line of only thetop layer to form tabs.

Label each tab with vocabulary words.

Build Vocabulary As you read the chapter, listthe vocabulary words on the tabs. As you learnthe definitions, write them under the tab for eachvocabulary word.

STEP 3

STEP 2

STEP 1

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

0

34 A CHAPTER 2 Matter

Apply It! Pick a paragraphfrom another section of this chapter and dia-gram the main ideas as you did above.

Learn It! Main ideas are the most important ideas in aparagraph, section, or chapter. Supporting details are facts or examplesthat explain the main idea. Understanding the main idea allows you tograsp the whole picture.

Picture It! Read the following paragraph. Draw a graphicorganizer like the one below to show the main idea and supporting details.

On Earth, matter occurs in four physicalstates. These four states are solid, liquid, gas, and plasma. You might have had solid toast andliquid milk or juice for breakfast this morning.You breathe air, which is a gas. A lightning boltduring a storm is an example of matter in itsplasma state.

—from page 47

Main Idea

Supporting Details Supporting Details Supporting Details

34 B

The main idea is often the first

sentence in a paragraph but

not always.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.

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

1 Matter is anything that has mass and takes up space.

2 Everything that exists is matter (including heat,light, and ideas).

3 Liquids and gases are not matter.

4 Electrons are atomic particles with a negativecharge that exist outside the atomic nucleus.

5 Atoms are the same as molecules.

6 If the ends of a pair of magnets have oppositepoles, the two ends will repel each other.

7 The components of a mixture can be separated byphysical means.

8 In solids, the individual particles vibrate, but theydon’t switch positions with each other.

9 Anything that melts, freezes, or boils has water in it.

10 Gases are less dense than solids because the spac-ing between the particles is greater.

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

The Building Blocks of MatterWhat do the objects you see, the air you breathe, and the

food you eat have in common? They are matter. Matter is any-thing that has mass and takes up space. Heat and light are notmatter, because they have no mass and do not take up space.Glance around the room. If all the objects you see are matter,why do they look so different from one another?

Atoms Matter, in its various forms, surrounds you. You can’tsee all matter as clearly as you see water, which is a transparentliquid, or rocks, which are colorful solids. You can’t see air, forexample, because air is colorless gases. The forms or propertiesof one type of matter differ from those of another type becausematter is made up of tiny particles called atoms. The structuresof different types of atoms and how they join together deter-mine all the properties of matter that you can observe. Figure 1illustrates how small objects, like atoms, can be put together in different ways.

This figure shows only two types of atoms represented by thetwo colors. In reality, there are over 90 types of atoms havingdifferent sizes, making great variety possible.

■ Identify the states of matter.■ Describe the internal structure

of an atom.■ Compare isotopes of an element.

Nearly everything around you—air,water, food, and clothes—is madeof atoms.

Review Vocabularymass: amount of matter in anobject

New Vocabulary

• matter • atomic

• atom number

• element • mass

• proton number

• neutron • isotope

• electron

Atoms

Figure 1 Like atoms, the same fewblocks can combine in many ways. Infer How could this model help explainthe variety of matter?

34 CHAPTER 2 Matter

SECTION 1 Atoms 35

Searching forElementsProcedure1. Obtain a copy of the

periodic table of the elements and familiarizeyourself with the elements.

2. Search your house for itemsmade of various elements.

3. Use a highlighter to high-light the elements you dis-cover on your copy of theperiodic table.

Analysis1. Were certain types of ele-

ments more common?2. Infer why you did not

find many of the elements.

The Structure of Matter Matter is joined together muchlike the blocks shown in Figure 1. The building blocks of matterare atoms. The types of atoms in matter and how they attach toeach other give matter its properties.

Elements When atoms combine, they form many differenttypes of matter. Your body contains several types of atoms com-bined in different ways. These atoms form the proteins, DNA,tissues, and other matter that make you the person you are.Most other objects that you see also are made of several differ-ent types of atoms. However, some substances are made of onlyone type of atom. Elements are substances that are made of onlyone type of atom and cannot be broken down into simpler sub-stances by normal chemical or physical means.

Elements combine to make a variety of items you depend onevery day. They also combine to make up the minerals that com-pose Earth’s crust. Minerals usually are combinations of atomsthat occur in nature as solid crystals and are usually found as mix-tures in ores. Some minerals, however, are made up of only oneelement. These minerals, which include copper and silver, arecalled native elements. Table 1 shows some common elementsand their uses. A table of the elements, called the periodic table ofthe elements, is included on the inside back cover of this book.

Table 1 Some Common Uses of Elements

Element Phosphorus Silver Copper Carbon

Native state Phosphorus Silver Copper Graphiteof the element

Uses of the Fertilizer Tableware Wire Ski waxelement

(tl)Stephan Frisch/Stock Boston, (tcl)Dane S. Johnson/Visuals Unlimited, (tcr)Ken Lucas/Visuals Unlimited, (tr)Mark A. Schneider/Photo Researchers, (bl)Aaron Haupt, (bcl)Amanita Pictures, (bcr)Charles D. Winters/Photo Researchers, (br)Aaron Haupt

36 CHAPTER 2 Matter

Modeling the AtomHow can you study things that are too small to be seen with

the unaided eye? When something is too large or too small toobserve directly, models can be used. The model airplane,shown in Figure 2, is a small version of a larger object. A modelalso can describe tiny objects, such as atoms, that otherwise aredifficult or impossible to see.

The History of the Atomic Model More than 2,300 yearsago, the Greek philosopher Democritus (dih MAH kruh tuss)proposed that matter is composed of small particles. He calledthese particles atoms and said that different types of matter werecomposed of different types of atoms. More than 2,000 yearslater, John Dalton expanded on these ideas. He theorized that allatoms of an element contain the same type of atom.

Protons and Neutrons In the early 1900s, additional workled to the development of the current model of the atom, shownin Figure 3. Three basic particles make up an atom—protons,neutrons (NOO trahnz), and electrons. Protons are particlesthat have a positive electric charge. Neutrons have no electriccharge. Both particles are located in the nucleus—the center ofan atom. With no negative charge to balance the positive chargeof the protons, the charge of the nucleus is positive.

Electrons Particles with a negative charge are called electrons, and they exist outside of the nucleus. In 1913, NielsBohr, a Danish scientist, proposed that an atom’s electrons travelin orbitlike paths around the nucleus. He also proposed thatelectrons in an atom have energy that depends on their distancefrom the nucleus. Electrons in paths that are closer to thenucleus have lower energy, and electrons farther from thenucleus have higher energy.

The Current Atomic Model Over the next several decades,research showed that electrons can be grouped into energy levels,each holding only a specific number of electrons. Also, electronsdo not travel in orbitlike paths. Instead, scientists use a modelthat resembles a cloud surrounding the nucleus. Electrons can beanywhere within the cloud, but evidence suggests that they arelocated near the nucleus most of the time. To understand howthis might work, imagine a beehive. The hive represents thenucleus of an atom. The bees swarming around the hive are likeelectrons moving around the nucleus. As they swarm, you can’tpredict their exact location, but they usually stay close to the hive.

Figure 2 This model airplane isa small-scale version of a largeobject.

High-speedelectrons(�charge)

Protons(�charge)

Nucleus

Neutrons(no charge)

Figure 3 This model of a heliumatom shows two protons and twoneutrons in the nucleus, and twoelectrons in the electron cloud.

John Evans

SECTION 1 Atoms 37

Counting Atomic ParticlesYou now know where protons, neutrons, and electrons are

located, but how many of each are in an atom? The number ofprotons in an atom depends on the element. All atoms of thesame element have the same number of protons. For example,all iron atoms—whether in train tracks or breakfast cereal—contain 26 protons, and all atoms with 26 protons are ironatoms. The number of protons in an atom is equal to the atomic number of the element. This number can be foundabove the element symbol on the periodic table that is printedin the back of this book. Notice that as you go from left to righton the periodic table, the atomic number of the elementincreases by one.

How many electrons? In a neutral atom, the number ofprotons is equal to the number of electrons. This makes theoverall charge of the atom zero. Therefore, for a neutral atom:

Atoms of an element can lose or gain electrons and still bethe same element. When this happens, the atom is no longerneutral. Atoms with fewer electrons than protons have a positivecharge, and atoms with more electrons than protons have anegative charge.

How many neutrons? Unlike protons, atoms of the sameelement can have different numbers of neutrons. The number ofneutrons in an atom isn’t found on the periodic table. Instead,you need to be given the atom’s mass number. The mass numberof an atom is equal to the number of protons plusthe number of neutrons. The number of neu-trons is determined by subtracting the atomicnumber from the mass number. For example, ifthe mass number of nitrogen is 14, subtracting itsatomic number, seven, tells you that nitrogen hasseven neutrons. In Figure 4, the number of neu-trons can be determined by counting the bluespheres and the number of protons by countingorange spheres. Atoms of the same element thathave different numbers of neutrons are calledisotopes. Table 2 lists useful isotopes of some elements.

How are isotopes of the sameelement different?

Atomic number � number of protons � number of electrons

��

���

�

Nucleus

Electron cloud

Figure 4 This radioactive carbon atom is found in organicmaterial. Determine this atom’s mass number.

Isotopes Some isotopes ofelements are radioactive.Physicians can introducethese isotopes into apatient’s circulatory sys-tem. The low-level radia-tion they emit allows theisotopes to be tracked asthey move throughout thepatient’s body. Explain howthis would be helpful indiagnosing a disease.

38 CHAPTER 2 Matter

Uses of Isotopes Scientists have found uses for isotopes thatbenefit humans. For example, medical doctors use radioactiveisotopes to treat certain types of cancer, such as prostate cancer.Geologists use isotopes to date some rocks and fossils.

Table 2 Some Useful Isotopes

Isotope Number of Number of Number of Atomic Mass Protons Neutrons Electrons Number Number

Hydrogen-1 1 0 1 1 1

Hydrogen-2 1 1 1 1 2

Hydrogen-3 1 2 1 1 3

Carbon-12 6 6 6 6 12

Carbon-14 6 8 6 6 14

Self Check1. Explain how the air you breathe fits the definition

of matter.

2. Explain why it is helpful to have a model of an atom.

3. Determine the charge of an atom that has five protonsand five electons.

4. Explain how isotopes can be used to benefit humans.

5. Think Critically Oxygen-16 and oxygen-17 are isotopesof oxygen. The numbers 16 and 17 represent their massnumbers, respectively. If the element oxygen has anatomic number of 8, how many protons and neutronsare in these two isotopes?

SummaryThe Building Blocks of Matter

• Matter has mass and takes up space.

• Matter is made of particles called atoms.

• Elements are substances that are made ofonly one type of atom.

Modeling the Atom

• The current model of an atom includes protons, neutrons, and electrons.

• Protons and neutrons are found in thenucleus. Protons have a positive charge andneutrons are neutral. Electrons are locatedaround the nucleus and have a negativecharge.

Counting Atomic Particles

• The atomic number of an element equals thenumber of protons in an atom.

• The mass number of an element equals thenumber of protons plus the number of neutrons in an atom.

• Atoms of the same element having differentnumbers of neutrons are called isotopes.

6. Use Numbers If a sodium atom has 11 protons and 12 neutrons, what is its mass number?

7. Simple Equations The mass number of a nitrogenatom is 14. Find its atomic number in the periodictable shown on the inside back cover of this book.Then determine the number of neutrons in its nucleus.

earth.msscience.com/self_check_quiz

SECTION 2 Combinations of Atoms 39

Interactions of AtomsWhen you take a shower, eat your lunch, or do your home-

work on the computer, you probably don’t think about ele-ments. But everything you touch, eat, or use is made from them.Elements are all around you and in you.

There are about 90 naturally occurring elements on Earth.When you think about the variety of matter in the universe, youmight find it difficult to believe that most of it consists of com-binations of these same elements. How could so few elementsproduce so many different things? This happens because ele-ments can combine in countless ways. For example, the sameoxygen atoms that you breathe also might be found in manyother objects, as shown in Figure 5. As you can see, each combi-nation of atoms is unique. How do these combinations formand what holds them together?

Combinations of Atoms

■ Describe ways atoms combine to form compounds.

■ List differences betweencompounds and mixtures.

On Earth, most matter exists ascompounds or mixtures.

Review Vocabularyforce: a push or a pull

New Vocabulary

• compound

• molecule

• ion

• mixture

• heterogeneous mixture

• homogeneous mixture

• solution

Solid limestone has oxygen within its structure.

This canistercontains pureoxygen gas.

Oxygen also is present in the juices of theseapples.

Figure 5 Oxygen is a common element foundin many different solids, liquids, and gases.Infer How can the same element, made from thesame type of atoms, be found in so many differentmaterials?

(l)Herbert Kehrer/OKAPIA/Photo Researchers, (r)Bruce Hands/Getty Images, (c)Doug Martin

40 CHAPTER 2 Matter

Compounds When the atoms of more than one element combine, they form a compound. A compound contains atoms of more than one type ofelement that are chemically bonded together. Water,shown in Figure 6, is a compound in which two hydro-gen atoms are bonded to each oxygen atom. Tablesalt—sodium chloride—is a compound consisting ofsodium atoms bonded to chlorine atoms. Compoundsare represented by chemical formulas that show theratios and types of atoms in the compound. For exam-ple, the chemical formula for sodium chloride is NaCl.The formula for water is H2O.

What atoms form the compound water?

The properties of compounds often are very different fromthe properties of the elements that combine to form them.Sodium is a soft, silvery metal, and chlorine is a greenish, poi-sonous gas, but the compound they form is the white, crystallinetable salt you use to season food. Under normal conditions onEarth, the hydrogen and oxygen that form water are gases. Watercan be solid ice, liquid water, or gas. Which form do you think ismost common for water at Earth’s south pole?

Chemical Properties A property that describes a change thatoccurs when one substance reacts with another is called a chem-ical property. For example, one chemical property of water is thatit changes to hydrogen gas and oxygen gas when an electric cur-rent passes through it. The chemical properties of a substancedepend on what elements are in that substance and how they arearranged. Iron atoms in the mineral biotite will react with waterand oxygen to form iron oxide, or rust, but iron mixed withchromium and nickel in stainless steel resists rusting.

BondingThe forces that hold the atoms together in compounds are

called chemical bonds. These bonds form when atoms share orexchange electrons. However, only those electrons having thehighest energies in the electron cloud can form bonds. As youread in the last section, these are found farthest from thenucleus. An atom can have only eight electrons in this highestenergy level. If more electrons exist, they must form a new,higher energy level. If an atom has exactly eight electrons in itsoutermost level, it is unlikely to form bonds. If an atom hasfewer than eight electrons in its outermost level, it is unstableand is more likely to combine with other atoms.

H

HO

Figure 6 The water you drink isa compound consisting of hydro-gen and oxygen atoms.Identify how hydrogen and oxy-gen are united to form water.

Topic: Periodic TableVisit for Weblinks to information about theperiodic table and chemicalbonding.

Activity Research five elementsthat you are unfamiliar with andmake a table showing their names,atomic number, properties, andhow they are used.

earth.msscience.com

Kenji Kerins

SECTION 2 Combinations of Atoms 41

Covalent Bonds Atoms can combine toform compounds in two different ways. Oneway is by sharing the electrons in their outer-most energy levels. The type of bond thatforms by sharing outer electrons is a covalentbond. A group of atoms connected by cova-lent bonds is called a molecule. For example,two atoms of hydrogen can share electronswith one atom of oxygen to form a moleculeof water, as shown in Figure 7. Each of thehydrogen atoms has one electron in its out-ermost level, and the oxygen has six electronsin its outermost level. This arrangementcauses hydrogen and oxygen atoms to bondtogether. Each of the hydrogen atomsbecomes stable by sharing one electron with the oxygen atom,and the oxygen atom becomes stable by sharing two electronswith the two hydrogen atoms.

Ionic Bonds In addition to sharing electrons, atoms alsocombine if they become positively or negatively charged. Thistype of bond is called an ionic bond. Atoms can be neutral, orunder certain conditions, atoms can lose or gain electrons.When an atom loses electrons, it has more protons than elec-trons, so the atom is positively charged. When an atom gainselectrons, it has more electrons than protons, so the atom is neg-atively charged. Electrically charged atoms are called ions.

Ions are attracted to each other when they have oppositecharges. This is similar to the way magnets behave. If the ends ofa pair of magnets have the same type of pole, they repel eachother. Conversely, if the ends have opposite poles, they attractone another. Ions formelectrically neutral com-pounds when they join. Themineral halite, commonlyused as table salt, forms inthis way. A sodium (Na)atom loses an outer electronand becomes a positivelycharged ion. As shown inFigure 8, if the sodium ioncomes close to a negativelycharged chlorine (Cl) ion,they attract each other andform the salt you use onfrench fries or popcorn.

H H

O

Energy levels

Cl

Sodium ion (�) Chlorine ion (�)

Na

Figure 7 A molecule of waterconsists of two atoms of hydrogenthat share outer electrons with oneatom of oxygen.

Figure 8 Table salt forms whena sodium ion and a chlorine ion areattracted to one another.Draw Conclusions What kind ofbond holds ions together?

42 CHAPTER 2 Matter

Metallic Bonds Metallic bonds are found inmetals such as copper, gold, aluminum, and sil-ver. In this type of bond, electrons are free tomove from one positively charged ion toanother. This free movement of electrons isresponsible for key characteristics of metals.The movement of electrons, or conductivity,allows metals like copper, shown in Figure 9, topass an electric current easily.

Hydrogen Bonds Some bonds, called hydro-gen bonds, can form without the interactions ofelectrons. The arrangement of hydrogen andoxygen atoms in water molecules causes themto be polar molecules. A polar molecule has apositive end and a negative end. This happensbecause the atoms do not share electronsequally. When hydrogen and oxygen atomsform a molecule with covalent bonds, thehydrogen atoms produce an area of partial pos-itive charge and the oxygen atom produces anarea of partial negative charge. The positive endof one molecule is attracted to the negative end

of another molecule, as shown in Figure 10, and a weak hydro-gen bond is formed. The different parts of the water moleculeare slightly charged, but as a whole, the molecule has no charge.This type of bond is easily broken, indicating that the chargesare weak.

Hydrogen bonds are responsible for several properties ofwater, some of which are unique. Cohesion is the attractionbetween water molecules that allows them to form raindropsand to form beads on flat surfaces. Hydrogen bonds cause waterto exist as a liquid, rather than a gas, at room temperature. Aswater freezes, hydrogen bonds force water molecules apart, intoa structure that is less dense than liquid water.

Figure 9 This machine is mak-ing cable from spools of wire.Electrons move freely along thiswire, passing from one copper ionto another.Identify What type of bond holdscopper atoms together?

More �

More �

HH

H

HH

H

H

HH

H

H

HO

O

OO

OO

H

HO

H

HO

Figure 10 The ends of polar mole-cules, such as water, have opposite partialcharges. This allows molecules to be held together by hydrogen bonds.

Ken Whitmore/Getty Images

SECTION 2 Combinations of Atoms 43

MixturesSometimes compounds and elements mix together but do

not combine chemically. A mixture is composed of two or moresubstances that are not chemically combined. There are two dif-ferent types of mixtures—heterogeneous and homogeneous.The components of a heterogeneous mixture are not mixedevenly and each component retains its own properties. Maybeyou’ve seen a rock like the one in Figure 11. Several differentminerals are mixed together, but if you were to examine theminerals separately, you would find that they have the sameproperties and appearance as they have in the rock.

The components of a homogeneous mixture are evenlymixed throughout. You can’t see the individual components.Another name for a homogeneous mixture is a solution. Theproperties of the components of this type of mixture often aredifferent from the properties of the mixture. Ocean water is anexample of a liquid solution that consists of salts mixed with liquid water.

What is a solution?

Separating MixturesThe components of a mixture can be separated by physical

means. For example, you can sit at your desk and pick out theseparate items in your backpack, or you can let the water evap-orate from a saltwater mixture and the salt will remain.

Separating the components of a mixture is a relatively easytask compared to separating those of a compound. The sub-stances in a compound cannot be separated by physical means.An existing compound can be changed to one or more new sub-stances by chemically breaking down the original compound.For example, a drop of dilute hydrochloric acid (HCl) can beplaced on calcium carbonate (CaCO3) and carbon dioxide(CO2) is released. Can you think of an example of a substancethat could be chemically broken down?

Figure 11 This rockcontains a variety ofmineral compoundsthat, together, form amixture.

Classifying Forms of MatterProcedure1. Make a chart with the

columns Mixtures,Compounds, and Elements.

2. Classify each of these itemsinto the proper column onyour chart: air, sand,hydrogen, muddy water,sugar, ice, sugar water,water, salt, oxygen, copper.

3. Make a solution using twoor more of the items listedabove.

Analysis1. How does a solution

differ from other typesof mixtures?

2. How does an element dif-fer from a compound?

Mark Steinmetz

44 CHAPTER 2 Matter

Self Check1. Explain how atoms or ions combine to form

compounds.

2. Classify sweetened tea as a solution or a compound.

3. Infer Why do metals transmit electricity so well?

4. Identify What does the formula tell you about a chemical compound?

5. Think Critically How can you determine whether saltwater is a solution or a compound?

SummaryInteractions of Atoms

• A compound contains atoms of more than onetype of element that are chemically bonded.

Bonding

• Atoms share electrons in covalent bonds.

• Atoms lose or gain electrons in ionic bonds.

• In metallic bonds electrons move freely fromone metal ion to another.

• Hydrogen bonds can form between polar molecules.

Mixtures

• A combination of two or more substances thatare not chemically combined is a mixture.

• Components of a heterogeneous mixture arenot mixed evenly.

• Components of a homogeneous mixture orsolution are evenly mixed.

6. Infer You have seen how the Na� ion attracts theCl� ion forming the compound sodium chloride, NaCl.What compound would form from Ca�2 and Cl�?

7. Design How would you separate a mixture of sugarand sand? Devise an experiment to do this. Discussyour procedure with your teacher. Perform the experiment and write the results.

Figure 12 The ocean is a mix-ture of many different forms ofmatter. The ocean water itself is asolution, a homogeneous mixture.

Exploring MatterAir, sweetened tea, salt water,

and the contents of your back-pack are examples of mixtures.The combination of rocks, fish,and coral shown in Figure 12also is a mixture. In each case,the materials within the mixtureare not chemically combined.The individual components aremade of compounds or ele-ments. The atoms in these com-pounds lost their individualproperties when they combined.

Seashells and coral reefs contain calciumcarbonate, which has the formula CaCO3.

Properties of CaCO3 differ greatly from those of its elements,calcium, carbon, and oxygen. For example, calcium is a soft, sil-very metal, oxygen is a gas, and carbon can be a black solid. Incontrast, calcium carbonate is hard and white. For example, italso is found in limestone and marble.

earth.msscience.com/self_check_quizStuart Westmorland/Danita Delimont Agent

How would you describe some of the objects in your classroom? Perhaps your desktop isabout one-half the size of a door. Measuringphysical properties in a laboratory experimentwill help you make better observations.

Real-World QuestionHow are physical properties of objects measured?

Goals■ Measure various physical properties in SI.■ Determine sources of error.

Materialstriple beam balance rock sample100-mL graduated cylinder stringmetersticks (2) globenon-mercury thermometers (3) waterstick or dowel

Safety Precautions

WARNING: Never “shake down” lab thermometers.

Procedure1. Go to every station and determine the

measurement requested. Record yourobservations in a data table and list sources of error.a. Use a balance to determine the mass, to

the nearest 0.1 g, of the rock sample.b. Use a graduated cylinder to measure the

water volume to the nearest 0.5 mL.c. Use three thermometers to determine

the average temperature, to the nearest0.5°C, at a selected location in the room.

d. Use a meterstick to measure the length, tothe nearest 0.1 cm, of the stick or dowel.

e. Use a meterstick and string to measurethe circumference of the globe. Beaccurate to the nearest 0.1 cm.

Conclude and Apply1. Compare your results with those provided

by your teacher.

2. Calculate your percentage of error in eachcase. Use this formula.

% error � � 100

3. Being within five to seven percent of the correct value is considered good. Ifyour error exceeds ten percent, what could you do to improve your results and reduce error?

your val. � teacher’s val.���

teacher’s val.

Scales of Measurement

Compare your conclusions with those ofother students in your class. For more help,refer to the Science Skill Handbook.

Measurement and Error

Sample at Value of CausesStation Measurement of Error

a. mass � ___ g

b. volume � ___ mL

c. (location) average temp. � ___ °C

d. length� ___ cm

e. circumference� ___ cm

LAB 45

Do not

write

in this

book.

46 CHAPTER 2 Matter

Physical Properties of MatterIn addition to the chemical properties of matter that you

have already investigated in this chapter, matter also has otherproperties that can be described. You might describe a pair ofblue jeans as soft, blue, and about 80 cm long. A sandwich couldhave two slices of bread, lettuce, tomato, cheese, and turkey.These descriptions can be made without altering the sandwichor the blue jeans in any way. The properties that you canobserve without changing a substance into a new substance arephysical properties.

One physical property that you will use to describe matter isdensity. Density is a measure of the mass of an object divided byits volume. Generally, this measurement is given in grams percubic centimeter (g/cm3). For example, the average density ofliquid water is about 1 g/cm3. So 1 cm3 of pure water has a massof about 1 g.

An object that’s more dense than water will sink in water. Onthe other hand, an object that’s not as dense as water will floatin water. When oil spills occur on the ocean, as shown in Figure 13,the oil floats on the surface of the water and washes up onbeaches. Because the oil floats, even a small spill can spread outand cover large areas.

Properties of Matter

Figure 13 Oil spills on the oceanspread across the surface of thewater. Infer How does the density of oilcompare to the density of water?

■ Describe the physical propertiesof matter.

■ Identify what causes matter tochange state.

■ List the four states of matter.

You can recognize many substancesby their physical properties.

Review Vocabularyenergy: the ability to causechange

New Vocabulary

• density

John S. Lough/Visuals Unlimited

States of MatterOn Earth, matter occurs in four physical states. These four

states are solid, liquid, gas, and plasma. You might have had solidtoast and liquid milk or juice for breakfast this morning. Youbreathe air, which is a gas. A lightning bolt during a storm is anexample of matter in its plasma state. What are the differencesamong these four states of matter?

Solids The reason some matter is solid is that its particles arein fixed positions relative to each other. The individual particlesvibrate, but they don’t switch positions with each other. Solidshave a definite shape and take up a definite volume.

Suppose you have a puzzle that is completely assembled. Thepieces are connected so one piece cannot switch positions withanother piece. However, the pieces can move a little, but stayattached to one another. The puzzle pieces in this model repre-sent particles of a substance in a solid state. Such particles arestrongly attracted to each other and resist being separated.

Solve One-Step Equations

1. You discover a gold bar while exploring an old shipwreck. It measures 10 cm � 5 cm �2 cm. It has a mass of 1,930 g. Find the density of gold.

2. A bar of soap measures 8 cm � 5 cm � 2 cm. Its mass is 90 g. Calculate its density.Predict whether this soap will float.

For more practice, visit earth.msscience.com/math_practice

CALCULATING DENSITY You want to find the density of a small cube of an unknown material. It measures 1 cm � 1 cm � 2 cm. It has a mass of 8 g.

SolutionThis is what you know:

This is what you need tofind out:

This is the procedureyou need to use:

Check your answer:

● mass: m � 8 g● volume: v � 1 cm � 1 cm � 2 cm � 2 cm3

● d � m/v

density: d

● substitute: d � 8 g/2 cm3

● Divide to solve for d: d � 4 g/cm3

● The density is 4 g/cm3

Multiply by the volume. You should get the given mass.

SECTION 3 Properties of Matter 47

Liquids Particles in a liquid are attracted to each other, but arenot in fixed positions as they are in the solid shown in Figure 15.This is because liquid particles have more energy than solid par-ticles. This energy allows them to move around and changepositions with each other.

When you eat breakfast, you might have several liquids at thetable such as syrup, juice, and milk. These are substances in theliquid state, even though one flows more freely than the othersat room temperature. The particles in a liquid can change posi-tions to fit the shape of the container they are held in. You canpour any liquid into any container, and it will flow until itmatches the shape of its new container.

Gases The particles that make up gases have enough energy toovercome any attractions between them. This allows them tomove freely and independently. Unlike liquids and solids, gasesspread out and fill the container in which they are placed. Airfresheners work in a similar way. If an air freshener is placed ina corner, it isn’t long before the particles from the air freshenerhave spread throughout the room. Look at the hot-air balloonshown in Figure 15C. The particles in the balloon are evenlyspaced throughout the balloon. The balloon floats in the sky,because the hot air inside the balloon is less dense than thecolder air around it.

How do air fresheners work?

Plasma Although it is probablyunfamiliar to most people, plasma isthe most common state of matter inthe universe. This state is associatedwith high temperatures. Can youname something that is in theplasma state? Stars like the Sun,shown in Figure 14, are composed ofmatter in the plasma state. Plasmaalso exists in Jupiter’s magnetic field.On Earth, plasma is found in light-ning bolts, as shown in Figure 15D.Plasma is composed of ions and elec-trons. It forms when high tempera-tures cause some of the electronsnormally found in an atom’s electroncloud to escape and move outside ofthe electron cloud.

Figure 14 The Sun is anexample of a plasma.

Topic: States of Matter Visit forWeb links to information aboutthe four states of matter.

Activity Search for informationon a family of elements called thehalogens. Use the informationyou find to write a “WantedPoster” on one halogen. Includeitems such as physical descrip-tion, distinguishing characteris-tics, and known associates.

earth.msscience.com

48 CHAPTER 2 MatterCORBIS

NGS TITLE

Figure 15

VISUALIZING STATES OF MATTER

M502-d06C-M

SS02ben

Matter on Earth exists naturally in four different states—solid, liquid, gas, andplasma—as shown here. The state of

a sample of matter depends upon the amount ofenergy its atoms or molecules possess. The moreenergy that matter contains, the more freely itsatoms or molecules move, because they are ableto overcome the attractive forces that tend tohold them together.

GAS In air and other gases,atoms or molecules have sufficientenergy to separate from each othercompletely and move in all directions.

C

LIQUID The atoms or moleculesin a liquid such as water haveenough energy to overcome someattractive forces and move over andaround one another.

B

SOLID In a solid such as galena, thetightly packed atoms or molecules lackthe energy to move out of position.

A

PLASMA Electrically charged particles in lightning are free moving.

D

S02

SECTION 3 Properties of Matter 49(tl)Breck P. Kent/Earth Scenes, (tr)Storm Pirate Productions/Artville/PictureQuest, (bl)CORBIS/PictureQuest, (br)E.R. Degginger/Earth Scenes

50 CHAPTER 2 Matter

Changing the State of Matter

Matter is changed from a liquid to a solidat its freezing point and from a liquid to a gasat its boiling point. You may know the freezingand boiling points of water. Water begins tochange from a liquid to a solid at its freezingpoint of 0°C. It boils at 100°C. Water is theonly substance that occurs naturally on Earthas a solid, liquid, and gas. Other substancesdon’t naturally occur in these three states onEarth because of the limited temperaturerange Earth experiences. For example, temper-

atures on Earth do not get cold enough for solid carbon dioxideto exist naturally. However, it can be manufactured.

The attraction between particles of a substance and theirrate of movement are factors that determine the state of matter.When thermal energy is added to ice, the rate of movement ofits molecules increases. This allows the molecules to move morefreely and causes the ice to melt. As Figure 16 shows, even solidmetal can melt when enough thermal energy is added.

Changes in state also occur because of increases or decreasesin pressure. For example, decreasing pressure lowers the boilingpoints of liquids. At high elevations, water boils at a lower tem-perature because the air pressure has decreased. Also, manysolids melt at lower temperatures when pressure is decreased.Intense pressure keeps material in Earth’s mantle in a solid orsemi-solid state even though the temperature is high. A decreasein pressure can cause some material to melt and form magma.However, extreme changes in pressure usually are required toalter the melting points of solids by only a few degrees.

Changes in Physical PropertiesChemical properties of matter don’t change when the matter

changes state, but some of its physical properties change. Forexample, the density of water changes as water changes state. Icefloats in liquid water, as seen in Figure 17, because it is less densethan liquid water. This is unique, because most materials aredenser in their solid state than in their liquid state.

Why does ice float in water?

Some physical properties of substances don’t change whenthey change state. For example, water is colorless and transpar-ent in each of its states.

Figure 16 A solid metal can bechanged to a liquid by adding ther-mal energy to its molecules. Describe what is happening to themolecules during this change.

Figure 17 If ice were moredense than water, lakes wouldfreeze solid from the bottom up.Infer What effect might this haveon the fish?

(t)Paul Chesley/Getty Images, (b)David Muench/CORBIS

SECTION 3 Properties of Matter 51

Self Check1. List the four states of matter in order from lowest to

highest particle movement.

2. Explain how temperature can bring about changes inthe state of matter.

3. Explain why an ice cube will melt if compressed, eventhough the temperature remains the same.

4. Think Critically Suppose you blow up a balloon andthen place it in a freezer. Later, you find that the balloon has shrunk and has bits of ice in it. Explain.

SummaryPhysical Properties of Matter

• Density is the mass of an object divided by itsvolume.

States of Matter

• Solids have a definite shape and volume.

• Liquids take the shape of their containers.

• Gases spread out and fill their containers.

• Plasma occurs at high temperatures and hassuch high energy that some electrons mayescape their electron clouds.

Changing the State of Matter

• Both temperature and pressure can causechanges in the state of matter.

Changes in Physical Properties

• Chemical properties do not change whenmatter changes state, but physical propertiescan change.

5. Classify Assign each of the following items to one ofthe four states of matter and describe their character-istics: groundwater, lightning, lava, snow, textbook,ice cap, notebook, apple juice, eraser, glass, cotton,helium, iron oxide, lake, limestone, and water vapor.

6. Infer You have probably noticed that some liquids,such as honey and molasses, flow slowly at room temperature. How does heating affect flow rate?

Matter on Mars Matter in one state often can be

changed to another state by adding orremoving thermal energy. Changes inthermal energy might explain whyMars appears to have had considerablewater on its surface in the past but nowhas little or no water on its surface.Recent images of Mars reveal that theremight still be some groundwater thatoccasionally reaches the surface, asshown in Figure 18. But what couldexplain the huge water-carved channelsthat formed long ago? Much of the liq-uid water on Mars might have changedstate as the planet cooled to its current temperature. Scientistsbelieve that some of Mars’s liquid water soaked into theground and froze, forming permafrost. Some of the watermight have frozen to form the polar ice caps. Even more of thewater might have evaporated into the atmosphere and escapedto space.

Figure 18 Groundwater mightreach the surface of Mars along theedge of this large channel.

earth.msscience.com/self_check_quizNASA/JPL/Malin Space Science Systems

Design Your OwnDesign Your Own

DETERMINING DENSITYReal-World Question

Which has a greater density—a rock or a piece of wood? Is cork moredense than clay? Density is the ratio of an object’s mass to its volume.

Form a HypothesisState a hypothesis about what process you can use to measure andcompare the densities of several materials.

Test Your HypothesisMake a Plan1. As a group, agree upon and write the hypothesis statement.

2. As a group, list the steps that you need to take to test your hypoth-esis. Be specific, describing exactly what you will do at each step.List your materials.

3. Working as a group, use the equation: density � mass/volume.Devise a method of determining the mass and volume of eachmaterial to be tested.

4. Design a data table in your Science Journal so that it is ready touse as your group collects data.

52 CHAPTER 2 Matter

Goals■ List some ways that

the density of an objectcan be measured.

■ Design an experimentthat compares the densities of severalmaterials.

Possible Materialspantriple-beam balance 100-mL beaker 250-mL graduated

cylinder waterchalkpiece of quartzpiece of claysmall wooden blocksmall metal blocksmall corkrockruler

Safety Precautions

WARNING: Be wary ofsharp edges on some of thematerials and take care notto break the beaker orgraduated cylinder. Washhands thoroughly withsoap and water when finished.

(t)StudiOhio, (b)Matt Meadows

5. Read over your entire experiment to make sure that all steps are in a logicalorder.

6. Should you run the process more than once for any of the materials?

7. Identify any constants, variables, and controls of the experiment.

Follow Your Plan1. Make sure your teacher approves your plan before you start.

2. Carry out the experiment as planned.

3. While the experiment is going on, write any observations that you make andcomplete the data table in your Science Journal.

Analyze Your Data1. Observe Do you observe anything about the way objects with greater

density feel compared with objects of lower density?

2. Predict Which of those objects you measured directly would float inwater? Which would sink?

3. Predict how your volume measurements might be affected by using a tool to push a floating object under water. Explain how this errormight increase or decrease the density you obtained.

Conclude and Apply1. Form Hypotheses Based on your results, would you hypothesize

that a cork is more dense, the same density, or less dense thanwater?

2. Draw Conclusions Without measuring the density of an object that floats, conclude how you know that it has a density of less than 1.0 g/cm3.

3. Predict Would the density of the clay beaffected if you were to break it into smallerpieces?

4. Explain why ships float, even though they aremade mostly of steel that has a density muchgreater than that of water.

LAB 53

Write an informational pamphlet ondifferent methods for determining thedensity of objects. Include equations and a step-by-step procedure.

(t)Tim Courlas, (b)Royalty-Free/CORBIS

. . . The diameter of an atom isabout 100,000 times as great asthe diameter of its nucleus. Supposethat when you sit in a chair, you representthe nucleus of an atom. The nearest electronin your atom would be about 120 kmaway—nearly half the distance across the Florida peninsula.

54 CHAPTER 2 Matter

. . . The melting point ofcesium is 28.4°C. It wouldmelt in your hand if you heldit. You would not want to holdcesium, though, because itwould react strongly with yourskin. In fact, the metal mighteven catch fire.

Other elements 1.5%

Oxygen46.6%

Silicon27.7%

Potassium 2.6%Sodium 2.8%

Magnesium 2.1%

Calcium 3.6%

Iron 5.0%

Aluminum 8.1%

. . . More than ninety elementsoccur naturally. However, about 98 percent of Earth’s crust consists ofonly the eight elements shown here.

Looking at the circlegraph, which is the third most abundant element inEarth’s crust?

Find Out About ItVisit to find out more about atoms and isotopes. What

is a radioactive isotope of an element? How are isotopes used in science?earth.msscience.com/science_stats

. . . Uranium has the greatestmass of the abundant naturalelements. One atom of uranium has amass number that is more than 235 timesgreater than the mass number of onehydrogen atom, the element with the leastmass. However, the diameter of a uraniumatom is only about three times the size ofa hydrogen atom, similar to the differencebetween a baseball and a volleyball.

Amazing AtomsDid you know . . .

(t)KS Studios, (b)StudiOhio

Copy and complete the following concept map. Use the terms: liquids, plasma, matter, and solids.

Atoms

1. Matter is anything that has mass and takesup space.

2. The nucleus of an atom contains protonswith a positive charge and neutrons withno charge. Electrons, which have a negativecharge, surround the nucleus.

3. Isotopes are atoms of the same element thathave different numbers of neutrons.

Combinations of Atoms

1. Atoms join to form compounds and mol-ecules. A compound is a substance made of two or more elements. The chemical and physical properties of a compound dif-fer from those of the elements of which it iscomposed.

2. A mixture is a substance in which the components are not chemically combined.

Properties of Matter

1. Physical properties can be observed andmeasured without causing a chemicalchange in a substance. Chemical propertiescan be observed only when one substancereacts with another substance.

2. Atoms or molecules in a solid are in fixedpositions relative to one another. In a liq-uid, the atoms or molecules are closetogether but are freer to change positions.Atoms or molecules in a gas move freely tofill any container.

3. Because of Earth’s narrow temperaturerange, water is the only substance knownthat occurs naturally as a solid, liquid,and gas.

4. One physical property that is used todescribe matter is density. Density is a ratioof the mass of an object to its volume. Amaterial that is less dense will float in amaterial that is more dense.

defined

can form

Gases

Has mass and takes up

space

CHAPTER STUDY GUIDE 55earth.msscience.com/interactive_tutor(l)Doug Martin, (r)Matt Meadows

Explain the difference between the vocabularywords in each of the following sets.

1. atom—element

2. mass number—atomic number

3. solution—heterogeneous mixture

4. matter—compound—element

5. heterogeneous mixture—homogeneousmixture

6. proton—neutron—electron

7. isotope—atom

8. atom—ion

9. mixture—compound

10. neutron—mass number

Choose the word or phrase that best answers thequestion.

11. Which of the following contains only onetype of atom?A) compound C) elementB) mixture D) solution

12. Which of the following has a positiveelectric charge?A) electron C) neutronB) proton D) atom

13. In an atom, what forms a cloud aroundthe nucleus?A) electrons C) neutronsB) protons D) positive ions

14. A carbon atom has a mass number of 12.How many protons and how many neutrons does it have?A) 6, 6 C) 6, 12B) 12, 12 D) 12, 6

15. On Earth, oxygen usually exists as which of the following?A) solid C) liquidB) gas D) plasma

Use the illustration below to answer question 16.

16. In the section of the periodic table shownabove, which element has 24 protons?A) titanium C) chromiumB) manganese D) vanadium

17. An isotope known as iodine-131 has 53 protons. How many neutrons does it have?A) 78 C) 68B) 53 D) 184

18. Which of the following are electricallycharged?A) molecule C) isotopeB) solution D) ion

19. Which of the following is not a physicalproperty of water?A) transparentB) colorlessC) higher density in the liquid state than

in the solid stateD) changes to hydrogen and oxygen when

electricity passes through it

Scandium21Sc

44.956

Titanium22Ti

47.88

Vanadium23V

50.942

Chromium24Cr

51.996

Manganese25Mn

54.938

56 CHAPTER REVIEW

atom p. 34atomic number p. 37compound p. 40density p. 46electron p. 36element p. 35heterogeneous mixture

p. 43homogeneous mixture

p. 43

ion p. 41isotope p. 37mass number p. 37matter p. 34mixture p. 43molecule p. 41neutron p. 36proton p. 36solution p. 43

earth.msscience.com/vocabulary_puzzlemaker

20. Infer If an atom has no electric charge,what can be said about the number ofprotons and electrons it contains?

21. Identify Carbon has six protons and nitro-gen has seven protons. Which has thegreatest number of neutrons—carbon-13,carbon-14, or nitrogen-14?

22. Explain Would isotopes of the same ele-ment have the same number of electrons?

23. Infer If a sodium atom loses an electronand becomes a sodium ion with a chargeof 1�, what would happen if a calciumatom loses two electrons?

24. Predict You are told that an unknown liquid has a density of 0.79 g/cm3 and willnot mix evenly with water. Predict whatwill happen if you pour some of this liquid into a glass of water, stir, and waitfive minutes.

Use the table below to answer question 25.

25. Make and Use Graphs Use the table above tomake a line graph. For each isotope, plotthe mass number along the y-axisand the atomic number along the x-axis.What is the relationship between massnumber and atomic number?

26. Classify Use the periodic table of the elements, located on the inside backcover, to classify the following substancesas elements or compounds: iron, alu-minum, carbon dioxide, gold, water,and sugar.

Atomic Number v. Mass Number

Element Atomic Number Mass Number

Fluorine 9 19

Lithium 3 7

Carbon 6 12

Nitrogen 7 14

Beryllium 4 9

Boron 5 11

CHAPTER REVIEW 57

27. Will it float? You have a heavy piece of woodthat measures 2 cm � 10 cm � 5 cm. You findits mass is 89 g. Will this piece of wood float?

Use the graph below to answer question 28.

28. Interpret Graphs Many elements occur in nature as mixtures of several isotopes. Thegraph above shows the distribution in nature of three isotopes of an element. Assuming thatthe most abundant isotope has an equal num-ber of protons and neutrons, use the periodictable on the inside back cover of this book to identify this element and name its three isotopes.

earth.msscience.com/chapter_review

Percent of Three Isotopes of an Unknown Element

20

30

10

0

40

90

50

70

60

Mass number

Perc

ent

24 25 26

80

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

Use the figure below to answer question 1.

1. Which of the following terms best describesthe snack shown above?A. heterogeneous mixtureB. homogeneous mixtureC. solutionD. compound

2. Which of the following has a negative charge?A. electron C. nucleusB. proton D. neutron

3. In which type of bond do atoms share electrons?A. metallic C. ionicB. hydrogen D. covalent

4. Which state of matter consists of ions andelectrons?A. solid C. gasB. plasma D. liquid

5. Which particle orbits an atom’s nucleus?A. isotope C. protonB. neutron D. electron

6. Which of the following terms best describesseawater?A. solution C. isotopeB. ion D. element

7. Which of the events described below is anexample of a change of state?A. river water flowing into an oceanB. air being heated in a hot air balloon to

make it riseC. ice being crushed for snow conesD. a puddle of water evaporating after

a rain

8. Which of the following particles alwaysare present in equal number in a neutralatom?A. protons, neutronsB. electrons, neutronsC. protons, electronsD. electrons, ions

9. In which state of matter do atoms vibratebut remain in fixed positions?A. solid C. plasmaB. gas D. liquid

This block was taken from the periodic table. Use theillustration below to answer questions 10–12.

10. What is the chemical symbol for carbon?A. C C. SB. H D. Sn

11. In which state does pure carbon exist atroom temperature?A. gas C. solidB. liquid D. plasma

12. What is carbon’s atomic number?A. 10 C. 12.011B. 13 D. 6

Carbon

6

C12.011

58 STANDARDIZED TEST PRACTICE

Instructions Listen carefully to the instructions from theteacher and read the directions and each question carefully.

Ed Young/CORBIS

STANDARDIZED TEST PRACTICE 59

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

13. What is an atom?

14. How is an element different from a compound?

15. How do homogeneous mixtures differfrom heterogeneous mixtures?

16. Why does ice float in liquid water?

17. What liquid formed channels on the sur-face of Mars long ago? What property ofliquids made this possible?

Use the table below to answer questions 18–21.

18. How much more dense is platinum thangold, in grams per cubic centimeter?

19. What is the mass in grams of one cubiccentimeter of pure gold? Hint: density �mass � volume

20. How many cubic centimeters of space are taken up by 10.5 g of silver? Howmany are taken up by the same mass of gold?

21. An aluminum lid has a mass of 6.5 g. Ithas a volume of 2.4 cm3. Calculate thedensity of aluminum in grams per cubiccentimeter.

Record your answers on a sheet of paper.

Use the illustration below to answer question 22.

22. A balloon contains helium gas. How arethe helium atoms distributed in the bal-loon? Do the atoms move? If so, how?Copy the sketch above on your paper and draw the helium atoms inside it.

23. Compare and contrast protons, neutrons,and electrons.

24. What is an isotope? Why are some iso-topes useful to society?

25. What is the difference between chemicalproperties and physical properties? Listone example of each type.

26. How is atomic number different frommass number?

27. Explain what happens to water moleculeswhen ice melts.

28. Compare the covalent, ionic, metallic, andhydrogen bonds. Explain how these bondsform and describe their properties.

29. Explain, using examples, how the proper-ties of compounds differ from those ofatoms that combine to form them.

30. How does the current atomic modeldescribe the movement and location ofelectrons?

Density of Some Metals

Metal Density (g/cm3)

copper 8.9

silver 10.5

lead 11.3

gold 19.3

platinum 21.5

aluminum 2.7

earth.msscience.com/standardized_test