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34 Chapter 2
2.1 Matter
Reading StrategyComparing and Contrasting Copy thegraphic organizer. As you read, complete theorganizer to compare and contrast protons,neutrons, and electrons.
Key ConceptsWhat is an element?
What particles make upatoms?
What are isotopes?
What are compounds andwhy do they form?
How do chemical bondsdiffer?
Vocabulary◆ element◆ atomic number◆ energy level◆ isotope◆ mass number◆ compound◆ chemical bond◆ ion◆ ionic bond◆ covalent bond◆ metallic bond
You and everything else in the universe are made of matter. Matter isanything that has volume and mass. On Earth, matter usually exists inone of three states—solid, liquid, or gas. A solid is a type of matter thathas a definite shape and a definite volume. Rocks and minerals are solids.A liquid is matter that has a definite volume, but not a definite shape.Earth’s oceans, rivers, and lakes are liquids. A gas is matter that has nei-ther a definite shape nor a definite volume. Most of Earth’s atmosphereiscomposedof the gases nitrogen and oxygen.Though matter can be clas-sified by its physical state: solid, liquid, or gas, it is more useful to look atits chemical composition and structure. Each of Earth’s nearly 4000 min-erals is a unique substance. The building blocks of minerals are elements.
Elements and the Periodic TableThe names of many elements are probably very familiar to you. Manycommon metals are elements, such as copper, iron, silver, and gold.
An element is a substance that cannot be broken down into sim-pler substances by chemical or physical means. There are more than112 known elements, and new elements continue to be discovered. Ofthese, 92 occur naturally, the others are produced in laboratories.
The elements have been organized by their properties in a docu-ment called the periodic table, which is shown in Figure 1 on pages 36and 37. You see from the table that the name of each element is repre-sented by a symbol consisting of one, two, or three letters. Symbolsprovide a shorthand way of representing an element. Each element is
Protons Electrons Neutrons
Differences
Similarities
For: Links on the periodic table
Visit: www.SciLinks.org
Web Code: cjn-1021
34 Chapter 2
FOCUS
Section Objectives2.1 Explain how elements are
related to minerals.2.2 Identify the kinds of particles
that make up atoms.2.3 Explain the differences
between ions and isotopes.2.4 Explain what compounds are
and describe why they form.2.5 Compare and contrast the
three major types of chemicalbonds.
Build VocabularyConcept Map Have students constructa concept map using the terms chemicalbond, ionic bond, covalent bond, andmetallic bond. The main concept(chemical bond) should be at the top.Tell students to place the terms in ovalsand list the characteristics of each typeof bond underneath the oval. For eachtype of bond, students should includesome examples and their properties.
Reading StrategyDifferences: Electron is much lessmassive than proton and neutron;electron is negatively charged, protonis positively charged, neutron is notcharged.Similarities: All are subatomicparticles.
INSTRUCT
Elements and thePeriodic TableBuild Reading LiteracyRefer to p. 392D in Chapter 14, whichprovides guidelines for this strategy.
Preview Have students preview thesection (pp. 34–43), focusing theirattention on headings, visuals, andboldfaced material. Ask: Based on yourpreview, which figure in the sectiondo you think contains the mostinformation? (Figure 1 on pp. 36–37)Based on your preview, name threeclasses of elements. (metals, nonmetals,and metalloids)Visual, Verbal
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2
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Reading Focus
1
Section 2.1
Download a worksheet on theperiodic table for students tocomplete, and find additionalteacher support from NSTA SciLinks.
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Minerals 35
also known by its atomic number, which is shown above each symbolon the table. Look at the block for sulfur, element 16, and gold, ele-ment 79. Sulfur and gold are minerals made of one element. Mostelements are not stable enough to exist in pure form in nature. Thus,most minerals are combinations of elements.
The rows in the periodic table are called periods. Thenumber of elements in a period varies. Period 1, for example,contains only two elements. These elements are hydrogen(H) and helium (He). Period 2 contains the elements lithium(Li) through neon (Ne). Periods 4 and 5 each contain 18 ele-ments while Period 6 includes 32 elements.
The columns in the periodic table are called groups. Notethat there are 18 groups in the periodic table shown on pages36 and 37. Elements within a group have similar properties.
Of the known elements, only eight make up most ofEarth’s continental crust. These eight elements are listed inTable 1. Notice that six of the eight elements in Table 1 are clas-sified as metals. Metals have specific properties such as theability to be shaped and drawn into wire. Metals are also goodconductors of heat and electricity. They combine in thousandsof ways to form compounds, the building blocks of most Earthmaterials. To understand how elements form compounds weneed to review their building blocks which are atoms.
AtomsAs you might already know, all elements are made of atoms. Anatom is the smallest particle of matter that contains the characteris-tics of an element.
The central region of an atom is called the nucleus. The nucleuscontains protons and neutrons. Protons are dense particles with pos-itive electrical charges. Neutrons are equally dense particles that haveno electrical charge. Electrons, which are small particles with little massand negative electrical charges, surround an atom’s nucleus.
Protons and Neutrons A proton has about the same mass asa neutron. Hydrogen atoms have only a single proton in their nuclei.Other atoms contain more than 100 protons. The number of protonsin the nucleus of an atom is called the atomic number. All atoms withsix protons, for example, are carbon atoms. The atomic number ofcarbon is 6. Likewise, every atom with eight protons is an oxygen atom.The atomic number of oxygen is 8.
Atoms have the same number of protons and electrons. Carbonatoms have six protons and therefore six electrons. Oxygen atoms haveeight protons in their nuclei and have eight electrons surrounding thenucleus.
Element Approximate Percentageby Weight
Oxygen (O) 46.6
Silicon (Si) 27.7
Aluminum (Al) 8.1
Iron (Fe) 5.0
Calcium (Ca) 3.6
Sodium (Na) 2.8
Potassium (K) 2.6
Magnesium (Mg) 2.1
All others 1.7
Table 1 Relative Abundance ofthe Most Common Elements in
Earth’s Continental Crust
Source: Data from Brian Mason.
Build Math SkillsUsing Tables and Graphs Havestudents convert Table 1 into a circlegraph. Ask: Why would a circle graphbe a good alternative way to showthe information in Table 1? (A circlegraph shows the parts that make up awhole, just as the elements listed in thetable make up a whole—100 percent ofthe elements in the continental crust.)Suggest that students first estimate thesize of each wedge of the circle graphand draw the graph accordingly. Thenhave them precisely draw the graph byfirst multiplying each percent by 360°to find the central angle of each wedge.They can then use a protractor to draweach central angle on a circle. Studentscan compare their estimates with theirprecise graphs. Some students may wishto create their graphs using software.Ask: What advantage does a circlegraph have over a table of percent-ages? (The sizes of the wedges of thegraph often make it easier to comparedifferent quantities.)Visual, Logical
AtomsIntegrate BiologyCell Nucleus Students may know thatmost cells in living organisms also havea structure called a nucleus. Informstudents that the cell’s nucleus containsthe cell’s genetic, or hereditary, material.Ask: How are an atom’s nucleus anda cell’s nucleus similar? (They are bothcentral structures of a basic unit.) Howare the two nuclei different? (The cellnucleus controls the activities of the cell.The atomic nucleus does not have asimilar function.)Logical
Although the text says that all matteris made of atoms, this is not strictlytrue everywhere in the universe. Forexample, the solar wind produced bythe sun consists of a stream of protonsand electrons. Also, in a neutron star,enormous pressure forces electrons andprotons in the atoms in a star to combinewith each other, leaving only a verydense ball of neutrons.Logical
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Minerals 35
Customize for English Language Learners
To help students understand the idea of energylevels, have them work in pairs to think ofeveryday situations that involve different levels.Examples might include dresser drawers,shelves in a bookshelf, and bleachers ins agym. Ask students how these analogies are
different from energy levels in atoms. (Energylevels are not physical objects and are not evenlyspaced.) If you have a bookshelf in the class,have students place marbles on different levelsto represent electrons.
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36 Chapter 2
103
LrLrLawrencium
(262)
3
LiLithium6.941
1
HHydrogen
1.0079
11A
19
KPotassium
39.098
37
RbRubidium
85.468
4
BeBeryllium9.0122
12
MgMagnesium
24.305
11
NaSodium22.990
20
CaCalcium
40.08
38
SrStrontium
87.62
56
BaBarium137.33
88
RaRadium
(226)
71
LuLutetium
174.97
72
HfHafnium178.49
73
TaTantalum
180.95
74
WTungsten
183.85
75
ReRhenium186.21
76
OsOsmium
190.2
104
RfRfRutherfordium
(261)
105
DbDbDubnium
(262)
106
SgSgSeaborgium
(263)
107
BhBhBohrium
(264)
108
HsHsHassium
(265)
109
MtMtMeitnerium
(268)
39
YYttrium88.906
40
ZrZirconium
91.22
41
NbNiobium92.906
42
MoMolybdenum
95.94
43
TcTcTechnetium
(98)
44
RuRuthenium
101.07
45
RhRhodium
102.91
21
ScScandium
44.956
22
TiTitanium
47.90
23
VVanadium
50.941
24
CrChromium
51.996
25
MnManganese
54.938
26
FeIron
55.847
27
CoCobalt58.933
55
CsCesium132.91
87
FrFrancium
(223)
22A
33B
44B
55B
66B
77B
8 9
57
LaLanthanum
138.91
Lanthanide Series
Actinide Series89
Ac Actinium
(227)
90
ThThorium232.04
92
UUranium238.03
93
NpNpNeptunium
(237)
94
PuPuPlutonium
(244)
91
PaProtactinium
231.04
58
CeCerium140.12
60
NdNeodymium
144.24
61
PmPmPromethium
(145)
62
SmSamarium
150.4
77
IrIridium192.22
59
PrPraseodymium
140.91
8B
Met
als
Met
alloid
s
Nonmet
als
Solid
Liquid
Gas
Not foundin nature
C
BrBr
H
Li
Hg
TcTc
B
Periodic Table of the Elements
Figure 1
Metals—elements that aregood conductors of heat andelectric current
Nonmetals—elements that are poor conductors of heat and electric current
Metalloids—elements withproperties that are somewhatsimilar to metals and nonmetals
36 Chapter 2
Use VisualsFigure 1 Use this figure to discusshow information is shown on a periodictable. Ask: What are the boldfacedsingle or double letters, such as H andLi ? (symbols for each element) What isthe number above each symbol? (theelement’s atomic number) What is thenumber below each symbol? (theelement’s atomic mass) What do thecolors of the boxes indicate? (Theyshow whether an element is a metal,transition metal, nonmetal, noble gas,lanthanide, or actinide.)Visual, Logical
Build Science SkillsUsing Tables and Graphs Use thedata in Figure 1 to show the advantageof arranging elements by atomic numberinstead of atomic mass. Make a largegraph with atomic number on thehorizontal axis and atomic mass on thevertical axis for elements 1 through 20.Draw straight lines between the points.Ask: What does the graph show aboutthe general relationship betweenatomic number and atomic mass?(As the atomic number increases, so doesthe atomic mass.) Are there any pointson the graph that do not follow thepattern? (Yes, the atomic mass ofelement 18, argon, is greater than theatomic mass of element 19, potassium.)Point out that arranging the elementsstrictly by increasing atomic mass wouldresult in some elements with unlikeproperties being grouped together.Visual, Logical
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Section 2.1 (continued)
Although plutonium is classified as a syntheticelement, traces of plutonium isotopes Pu-238and Pu-239 appear at low concentrations (aboutone part per 1011) in pitchblende, a uraniumore. In 1971, Darlene Hoffman, a scientist at
Los Alamos National Laboratory, discoveredtraces of Pu-244 in Precambrian rocks. Becausethis isotope has a half-life of about 82 millionyears, it probably existed when Earth formed.
Facts and Figures
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Minerals 37
6
CCarbon12.011
28
NiNickel58.71
29
CuCopper63.546
30
ZnZinc
65.38
31
GaGallium69.72
32
GeGermanium
72.59
33
As Arsenic74.922
34
SeSelenium
78.96
35
BrBromine79.904
36
KrKrypton
83.80
51
Sb Antimony
121.75
52
TeTellurium
127.60
54
XeXenon131.30
81
TlThallium204.37
82
PbLead207.2
83
BiBismuth208.98
84
PoPolonium
(209)
85
At Astatine
(210)
86
RnRadon(222)
50
SnTin
118.69
13
Al Aluminum
26.982
14
SiSilicon28.086
15
PPhosphorus
30.974
16
SSulfur32.06
17
ClChlorine35.453
18
Ar Argon39.948
5
BBoron10.81
6
CCarbon12.011
7
NNitrogen14.007
8
OOxygen15.999
9
FFluorine18.998
10
NeNeon
20.179
2
HeHelium4.0026
46
PdPalladium
106.4
47
AgSilver107.87
48
CdCadmium
112.41
78
PtPlatinum195.09
110
UunUunUnunnilium
(269)
111
UuuUuuUnununium
(272)
112
UubUubUnunbium
(277)
* * *114
UuqUuqUnunquadium
*
79
AuGold
196.97
80
HgMercury200.59
63
EuEuropium
151.96
*Name not officially assigned.
64
GdGadolinium
157.25
65
TbTerbium158.93
66
DyDysprosium
162.50
67
HoHolmium
164.93
68
ErErbium167.26
69
TmThulium168.93
70
YbYtterbium
173.04
95
AmAm Americium
(243)
96
CmCmCurium(247)
97
BkBkBerkelium
(247)
98
CfCfCalifornium
(251)
99
EsEsEinsteinium
(252)
100
FmFmFermium
(257)
101
MdMdMendelevium
(258)
102
NoNoNobelium
(259)
10 111B
122B
13 3A
144A
155A
166A
177A
18 8A
Atomic number
Element symbol
Atomic massElement name
49
InIndium114.82
53
IIodine126.90
IntegrateLanguage ArtsElements 110, 111, 112, and 114 havenot been named yet. Scientists canpropose names for new elements, butthe International Union of Pure andApplied Chemistry has final approval.Until new elements receive officialnames, chemists refer to them by theirLatin-based atomic numbers. Forexample, element 114 is calledununquadium, Latin for one-one-four.Increase students’ familiarity with theperiodic table by discussing some of thestrategies used to name elements(scientists, geographic locations,mythological characters).Verbal, Portfolio
Build Science SkillsComparing and Contrasting Forthis activity, use a periodic table that isseveral years old to display or distributeto students. You might use one from anolder textbook. To illustrate the dynamicnature of science, have studentscompare Figure 1 to the older periodictable. Ask: What differences do younotice between the two periodictables? (Depending on when the oldertable was printed, the number of elementsmay vary and some elements in Period 7may not have assigned names. Somevalues for atomic mass are likely to vary.)Make a list of responses on the board.Then ask: How will the periodic tablechange in the future? (Unnamedelements will be assigned official namesand more elements may be discovered.)Visual, Verbal
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38 Chapter 2
Electrons An electron is the smallestof the three fundamental particles in anatom. An electron has a mass of about1/1836 the mass of a proton or a neu-tron. Electrons move about the nucleusso rapidly that they create a sphere-shaped negative zone. You can picturemoving electrons by imagining a cloudof negative charges surrounding thenucleus, as shown in Figure 2.
Electrons are located in regionscalled energy levels. Each energy level
contains a certain number of electrons. Interactions among elec-trons in the outermost energy levels explains how atoms formcompounds, as you will find out later in the chapter.
IsotopesAtoms of the same element always have the same number of protons.For example, every carbon atom has 6 protons. Carbon is elementnumber 6 on the periodic table. But the number of neutrons for atomsof the same element can vary. Atoms with the same number ofprotons but different numbers of neutrons are isotopes of an ele-ment. Isotopes of the same element are labeled using a conventioncalled the mass number and with the element’s name or symbol. Themass number of an atom is the total mass of the atom (protons plusneutrons) expressed in atomic mass units. The proton and the neu-tron each have a mass that is slightly larger than the atomic mass unit.Recall that the mass of an electron is so small that the number of elec-trons has no effect on the mass number of an atom.
Carbon has 15 different isotopes. Models for three of these areshown in Figure 3. Carbon-12 makes up almost 99 percent of allcarbon on Earth. Carbon-12 has 6 protons and 6 neutrons. Carbon-13makes up much of the remaining naturally occurring carbon atomson Earth. Carbon-13 has 6 protons and 7 neutrons.Though only tracesof carbon-14 are found in nature, the presence of this isotope is oftenused to determine the age of once-living things. Carbon-14 has6 protons and 8 neutrons
The nuclei of most atoms are stable. However, many elements haveatoms whose nuclei are unstable. Such atoms disintegrate through aprocess called radioactive decay. Radioactive decay occurs because theforces that hold the nucleus together are not strong enough.
How are electrons, protons, and neutronsalike and how are they different?
Q Are the minerals in thischapter the same as those indietary supplements?
A Not ordinarily. Most mineralsfound in dietary supplementsare compounds made in thelaboratory. These dietary min-erals often contain elementsthat are metals, such as calcium,potassium, magnesium, andiron. From the geologist’s pointof view, a mineral must be a nat-urally occurring crystalline solid.
Third energy-level
Secondenergy-level
First energy-levelNucleus(neutrons
and protons)
Figure 2 Model of an AtomThe electrons that move about anatom’s nucleus occupy distinctregions called energy levels.
38 Chapter 2
Use VisualsFigure 2 Use this diagram to show amodel of the atom. Explain to studentsthat each energy level contains a certainnumber of electrons.Visual
Build Math SkillsCalculating An electron has a mass of9.11 � 10�28 g. Have students calculatea more exact ratio between the mass ofa proton and the mass of an electron.If necessary, review the idea of a ratio:a dimensionless number used tocompare two values. (The mass of aproton is 1.674 � 10�24 g. 1.674 �10�24 g/9.11 � 10-28 g � 1838) Theratio is actually 1836:1. The error is dueto rounding.Logical
Build Science SkillsUsing Models Havestudents build modelsof atoms similar toFigure 2 using materialsfound at home or in the classroom.Models do not have to be exactly toscale but should show the relationshipsamong the particles clearly.Visual, Logical
IsotopesBuild Science SkillsCalculating Oxygen-18 has a massnumber of 18 and 10 neutrons in itsnucleus. Oxygen-17 has a mass numberof 17 and 9 neutrons in its nucleus.Ask: What is the atomic number ofoxygen? (8)Logical
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Section 2.1 (continued)
Carbon-14 can be used to find the ages of someobjects. Carbon-14 is formed continuously bynatural processes in the atmosphere. Carbon inthe atmosphere reacts with oxygen to formcarbon dioxide. Plants take in carbon dioxideduring photosynthesis, the process by whichthey use energy in sunlight to make food.Initially, the ratio of carbon-14 to carbon-12 isthe same in plants as it is in the atmosphere. Thesame is true for an animal that eats a plant. Aftera plant or animal dies, though, it no longer takesin carbon. The carbon-14 gradually undergoes
radioactive decay to form nitrogen-14 with ahalf-life of 5730 years. The age of an objectcontaining plant or animal material can bedetermined by comparing the ratio of carbon-14 to carbon-12 in the object to the ratio ofthese isotopes in the atmosphere. If the ratio ofcarbon-14 to carbon-12 in the object is one-quarter the ratio of carbon-14 to carbon-12 inthe atmosphere, for example, then two half-lives, or 11,460 years, have passed since theplant or animal was alive.
Facts and Figures
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Minerals 39
During radioactive decay, unstable atoms radiate energy and par-ticles. Some of this energy powers the movements of Earth’s crust andupper mantle. The rates at which unstable atoms decay are measur-able. Therefore certain radioactive atoms can be used to determine theages of fossils, rocks, and minerals.
Why Atoms BondMost elements exist combined with other elements to form substanceswith properties that are different from the elements themselves.Sodium is often found combined with the element chlorine as the min-eral halite. Lead ore is really the mineral galena, which is the element,lead, combined with the element, sulfur. Chemical combinations ofthe atoms of elements are called compounds. A compound is asubstance that consists of two or more elements that are chemicallycombined in specific proportions. Compounds form when atoms aremore stable (exist at a lower energy state) in a combined form. Thechemical process, called bonding, centers around the electron arrange-ments of atoms. Thus, when atoms combine with others to formcompounds, they gain, lose, or share electrons.
Scientists have discovered that the most stable elements are foundon the right side of the periodic table in Group 8A (18). These ele-ments have a very low reactivity and exist in nature as single atoms.Scientists explain why atoms form compounds by considering how anatom undergoes changes to its electron structure to be more like atomsin Group 8A.
What are isotopes?
Carbon-12stable
Carbon-13stable
Carbon-14unstable (radioactive)
Proton Neutron
Figure 3 Nuclei ofIsotopes of CarbonCarbon has many isotopes.Of these, three occur in nature. Comparing andContrasting How are thenuclei of these isotopesthe same, and how dothey differ?
Isotopes and NumbersPurpose Students will observe therelationships among number of protons,number of neutrons, atomic number,and mass number for different isotopes.
Materials overhead projector, red andgreen gummy candies
Procedure Explain that the greencandies represent neutrons and the redcandies represent protons. Model acarbon-12 nucleus by placing a group of6 red candies and 6 green candies onthe overhead. Ask students to count thenumber of candies (particles) todetermine the mass number of thecarbon atom (12). Then ask studentswhat the atomic number is for carbon(6). Then remove a red candy (proton)and ask if the atom is still carbon (no).Replace the red candy and add a greencandy (neutron). Ask students if theatom is still carbon (yes). Then ask:How is this atom different from theoriginal one? (The atom has a differentisotope, carbon-13.) Show students theappropriate notation to representisotopes: element name with massnumber or element symbol with massnumber and atomic number.
carbon-13 or 136C
Expected Outcome Students shouldgain a familiarity with mass numbers,atomic numbers, and isotopes.Visual
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Minerals 39
Answer to . . .
Figure 3 The isotopes all have thesame number of protons, and thus, thesame atomic number, but each has adifferent number of neutrons.
They all are subatomicparticles that make up
atoms. Protons have positive electricalcharges, neutrons have no charge, andelectrons have negative charges.Protons and neutrons are found in anatom’s nucleus. Electrons move aboutthe nucleus.
Isotopes are atoms ofthe same element with
the same number of protons butdifferent numbers of neutrons.
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40 Chapter 2
Look at Figure 4. It shows the shorthand way of representing thenumber of electrons in the outer energy level. Recall that electronsmove about the nucleus of an atom in a region called an electroncloud. Within this cloud, only a certain number of electrons canoccupy each energy level. For example, a maximum of two electronscan occupy the first energy level. From Figure 4, you see that helium(He) is shown with two electrons. A maximum of eight electrons canbe found in the second energy level. You also see from the figure thatneon (Ne) is shown with eight electrons. When an atom’s outer-most energy level does not contain the maximum number ofelectrons, the atom is likely to form a chemical bond with one ormore other atoms. Chemical bonds can be thought of as the forcesthat hold atoms together in a compound. The principal types of chem-ical bonds are ionic bonds, covalent bonds, or metallic bonds.
Types of Chemical BondsIonic Bonds An atom that gains electrons becomes negativelycharged. This happens because the atom now has more electrons thanprotons. An atom that loses electrons becomes positively charged. Thishappens because the atom now has more protons than electrons. Anatom that has an electrical charge because of a gain or loss of one ormore electrons is called an ion. Oppositely charged ions attract eachother to form crystalline compounds. Ionic bonds form betweenpositive and negative ions.
Group1 2 13 14 15 16 17 18
Electron Dot Diagrams for Some Representative Elements
H
Li
Na
K
Be
Mg
Ca
B
Al
Ga
C
Si
Ge
N
P
As
O
S
Se
F
Cl
Br
He
Ne
Ar
Kr
Figure 4 In an electron dotdiagram, each dot representsan electron in the atom’s outerenergy level. These electronsare sometimes called valenceelectrons. Observing How manyelectrons do sodium andchlorine have in their outerenergy levels?
40 Chapter 2
Build Science SkillsPredicting Emphasize that, except forhydrogen and helium, the dots in anelectron dot diagram do not representall of the electrons in an atom, just thevalence electrons.
Have students look at Figure 4. Ask themto predict the electron dot diagramsfor rubidium, strontium, indium, tin,antimony, tellurium, iodine, and xenon.(These elements—Rb, Sr, In, Sn, Sb, Te, I,and Xe—have the same valence electronconfigurations as the elements directlyabove them in the periodic table.)Logical, Visual
Types ofChemical Bonds
Many students think that atoms becomepositively charged as a result of gainingprotons. Challenge this misconceptionby explaining that electrons are the onlysubatomic particles that can be removedfrom or added to an atom during achemical reaction. Remind students thatprotons are bound into the nuclei ofatoms and cannot be removed or addedduring chemical reactions.Logical
Integrate ChemistryIonic Compounds and ConductionWhy are solid ionic compounds poorconductors of electricity whereas meltedionic compounds are good conductors?Tell students that for an electric currentto flow through a substance, chargedparticles must be able to move from oneplace to another. In a solid ionic crystal,the ions are fixed in a lattice. Ask: Whycan’t ionic solids conduct electricity?(Since the ions are in fixed positions, theycannot conduct current.) What happensif the solid is melted? (The ions arefreed from the lattice.) Why is themelted solid a good conductor ofelectricity? (The ions can move aroundand conduct a current.)Logical
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Section 2.1 (continued)
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Some common compounds on Earth have both a chemical nameand a mineral name. For example, table salt has a chemical name,sodium chloride, and a mineral name, halite. Salt forms when sodium(Na) reacts with chlorine (Cl) as shown in Figure 5A. Sodium is veryunstable and reactive. Sodium atoms lose one electron and becomepositive ions. Chlorine atoms gain one electron and become negativeions. These oppositely charged ions are attracted to each other andform the compound called sodium chloride.
The properties of a compound are different from the properties ofthe elements in the compound. Sodium is a soft, silvery metal thatreacts vigorously with water. If you held it in your hand, sodium couldburn your skin. Chlorine is a green poisonous gas. Chemically com-bined these atoms produce table salt, the familiar crystalline solid thatis essential to health.
What happens when two or more atoms react?
Na� Cl�
Na Cl+ Na+ Cl –
Figure 5 A When sodium metal comes in contact withchlorine gas, a violent reaction occurs. B Sodium atomstransfer one electron to the outer energy levels of chlorineatoms. Both ions now have filled outer energy levels C Thepositive and negative ions formed attract each other to forma crystalline solid with a rigid structure.
Formation of Sodium Chloride
B
C
Minerals 41
A
Use VisualsFigure 5 Use this diagram to explainhow an ionic compound forms. Ask:What happens to the sodium atomwhen it loses an electron? (It becomesa positive ion.) What happens to achlorine atom when it gains anelectron? (It becomes a negative ion.)What happens to the two ions? (Theyare attracted to each other and form acompound.)Visual, Logical
Integrate HealthSodium and Chlorine in the BodySodium chloride, or table salt, is anessential nutrient for human beings. Tellstudents that sodium and chlorine bothhelp maintain the acid-base balance inthe body. Sodium is also involved inmaintaining the water balance of thebody and in nerve function. Chlorine isneeded for the formation of gastric juicefor digestion of food. The averageAmerican gets about 20 times therequired intake of sodium.Logical
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Minerals 41
Answer to . . .
Figure 4 Sodium has one electron inits outer energy level (valence electron)and chlorine has seven.
Electrons are gained,lost, or shared when
two or more atoms react to form acompound.
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Compounds that contain ionic bonds are called ionic com-pounds. Figure 6 shows calcium fluoride, a common ioniccompound. Our model for ionic bonding suggests that one cal-cium atom transfers two electrons from its outermost energylevel to two atoms of fluorine. This transfer gives all atoms theright numbers of electrons in their outer energy levels. Thecompound that forms is known as the mineral fluorite.
Ionic compounds are rigid solids with high melting andboiling points. These compounds are poor conductors ofelectricity in their solid states. When melted, however, manyionic compounds are good conductors of electricity. Mostionic compounds consist of elements from groups 1 and 2 onthe periodic table reacting with elements from groups 16 and17 of the table.
Covalent Bonds Covalent bonds form when atomsshare electrons. Compounds with covalent bonds are calledcovalent compounds. Figure 7 shows silicon dioxide, one ofthe most common covalent compounds on Earth. Silicondioxide forms when one silicon atom and two oxygen atomsshare electrons in their outermost energy levels. Silicon diox-ide is also known as the mineral quartz.
The bonding in covalent compounds results in propertiesthat differ from those of ionic compounds. Unlike ioniccompounds, many covalent compounds have low meltingand boiling points. For example, water, a covalent com-pound, boils at 100°C at standard pressure. Sodium chloride,an ionic compound, boils at 1413°C at standard pressure.Covalent compounds also are poor conductors of electric-ity, even when melted.
The smallest particle of a covalent compoundthat shows the properties of that compound is a mol-ecule. A molecule is a neutral group of atoms joinedby one or more covalent bonds. Water, for example,consists of molecules. These molecules are made oftwo hydrogen atoms covalently-bonded to oneoxygen atom. The many gases that make up Earth’satmosphere, including hydrogen, oxygen, nitrogen,and carbon dioxide, also consist of molecules.
How do ionic bonds form, and what aresome properties of ionic compounds?
H OH
H2O
42 Chapter 2
CaF
Ca2+
F
F
F+
–
–B
A
B
A
Figure 6 Ionic Compound A Fluorite is anionic compound that forms when calciumreacts with fluorine. B The dots shown withthe element’s symbol represent the electronsin the outermost levels of the ions. Explaining Explain what happens to theelectrons in calcium atoms and fluorineatoms when fluorite forms.
Figure 7 Covalent Compounds A Quartz is acovalent compound that forms when silicon andoxygen atoms bond. B Water consists of moleculesformed when hydrogen and oxygen share electrons.
42 Chapter 2
Build Reading LiteracyRefer to p. 502 in Chapter 18, whichprovides guidelines for this strategy.
Visualize Tell students that forming amental image of concepts they arelearning helps them remember newconcepts. After students have readabout ionic, covalent, and metallicbonds, have them visualize models foreach type of bond. Then encouragestudents to draw diagrams thatdemonstrate the differences amongthese three types of bonds.Visual
Comparing BondsPurpose Students observe differencesin the properties of substances withdifferent bonds.
Materials rock salt, chalk, copper wire,hammer, goggles
Procedure Take students outside to anopen area. Allow them to examine thesamples of rock salt, chalk, and copperwire. Have students stand back a safedistance. Put on goggles, then placeeach sample on a hard surface and hit itwith a hammer. Invite students toobserve how each sample looks afterbeing pounded with the hammer.
Expected Outcome The rock salt andchalk shatter because they are ionic andcovalent substances, respectively. Thecopper wire changes shape instead ofshattering because metals are malleable.Visual
Many students do not differentiateamong atoms, molecules, and ions intheir perceptions of particles. Challengethis misconception by having studentsmake drawings to represent an atom, amolecule, and an ion. Students shoulddraw a single sphere for an atom, atleast two spheres joined in some way fora molecule, and one sphere with eithera plus or a minus sign for an ion.Visual
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Section 2.1 (continued)
Unlike ionic and covalent compounds, metalsare malleable and ductile. Instead, metal ionsare held together in a “sea of electrons”referred to as the metallic bond. When a
piece of metal is deformed, the ions move tonew positions. The piece of metal does notbreak because the ions are still held attractedto the electrons.
Facts and Figures
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Section 2.1 Assessment
Reviewing Concepts1. What is an element?
2. What kinds of particles make up atoms?
3. What are isotopes?
4. What are compounds and why do theyform?
5. Contrast ionic, covalent, and metallicbonds.
Critical Thinking6. Comparing and Contrasting Compare
and contrast solids, liquids, and gases.
7. Applying Concepts What elements inTable 1 are metals?
8. Applying Concepts A magnesium atomneeds two electrons to fill its outermostenergy level. A chlorine atom needs one
electron to fill its outermost shell. Ifmagnesium reacts with chlorine, what type ofbond will most likely form? Explain.
9. Applying Concepts Which elements in theperiodic table might combine with oxygen toform compounds similar to magnesiumdioxide (MgO2)?
10. The isotopes of carbon have from 2 to 16neutrons. Use this information to make atable that shows the 15 isotopes of carbonand the atomic number and mass numberof each.
Metallic Bonds Metals are malleable,which means that they can be easily shaped.You’ve observed this property when youwrapped aluminum foil around food or crushedan aluminum can. Metals are also ductile, mean-ing that they can be drawn into thin wireswithout breaking. The wiring in your school orhome is probably made of the metal copper.Metals are excellent conductors of electricity.
Metallic bonds form when electronsare shared by metal ions. Figure 8 shows amodel for this kind of bond. The sharing of anelectron pool gives metals their characteristicproperties. Using the model you can see howan electrical current is easily carried throughthe pool of electrons. Later in this chapter, youwill learn about some metals that are classifiedas minerals.
Minerals 43
+– + + + +
+++++
+ + + ++
+++++
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–
–
–
–
––
–
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–
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–
–
–
–
–
–
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–
–
Figure 8 Metallic Bonds A Metals form bondswith one another by sharing electrons. B Suchbonds give metals, such as this copper, theircharacteristic properties. Metals can be easilyformed and shaped.
A
B
ASSESSEvaluateUnderstandingHave students describe why substancesform ionic, covalent, and metallicbonds.
ReteachUse Figures 5 and 6 to review theformation of ions and ionic bonds. Besure students understand that the ionicbond is the electrostatic attractionbetween ions of opposite charge. Ioniccompounds do not exist as discrete pairsof ions, but as aggregates of ions.
Solutions10. The atomic number, which is thenumber of protons in an element, isthe same for each isotope of carbon.The mass number varies from 8(6 protons � 2 neutrons) to 24(6 protons � 18 neutrons).
L1
L2
3
Minerals 43
4. A compound is a substance that consistsof two or more elements. Compounds formas the result of changes in the arrangementof electrons in the outermost shells of thebonded atoms.5. Ionic bonds are those that form whenelectrons are transferred. Covalent bondsinvolve the sharing of electrons. Metallicbonds exist when electrons are shared bymetallic ions.6. All are forms of matter, and thus all aremade of atoms. A solid has a definite shapeand definite volume. A liquid has a definite
Section 2.1 Assessment
1. An element is a class of matter that con-tains only one type of atom. An element can-not be broken down, chemically or physically,into a simpler substance with the sameproperties.2. Protons and neutrons are found in anatom’s nucleus, while electrons move aboutthis central core.3. Isotopes are atoms of the same elementthat have the same number of protons butdifferent numbers of neutrons.
volume, but not a definite shape. A gashas neither a definite volume nor a definiteshape.7. aluminum, iron, calcium, sodium,potassium, magnesium8. An ionic bond forms because magnesiumwill give up or transfer its two electrons totwo chlorine ions.9. Elements in groups 1 and 2 have similarproperties to those of magnesium and oftencombine with oxygen to form compounds.
Answer to . . .
Figure 6 Calcium transfers its twoelectrons to two fluorine atoms,forming two fluoride ions.
Ionic bonds form whenelectrons are transferred
from one atom to another. Ioniccompounds are rigid solids with highmelting and boiling points and arepoor conductors of electricity in theirsolid states. When melted, many ioniccompounds are good conductors ofelectricity.
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