Chapter2.AtomsandElements
StudentObjectives
2.1ImagingandMovingIndividualAtoms


Describescanningtunnelingmicroscopy(STM)andhowatomsareimagedonsurfaces.
Defineatomandelement.
2.2EarlyIdeasabouttheBuildingBlocksofMatter


Describetheearliestdefinitionsofatomsandmatter(Greeks).
Knowthatgreateremphasisonobservationandthedevelopmentofthescientificmethodledtothe
scientificrevolution.
2.3ModernAtomicTheoryandtheLawsThatLedtoIt




Stateandunderstandthelawofconservationofmass(alsofromSection1.2).
Stateandunderstandthelawofdefiniteproportions.
Stateandunderstandthelawofmultipleproportions.
KnowthefourpostulatesofDalton’satomictheory.
2.4TheDiscoveryoftheElectron


DescribeJ.J.Thomson’sexperimentswiththecathoderaytubeandunderstandhowtheyprovide
evidencefortheelectron.
DescribeRobertMillikan’soil‐dropexperimentandunderstandhowitenablesmeasurementofthe
chargeofanelectron.
2.5TheStructureoftheAtom


Defineradioactivity,nucleus,proton,andneutron.
UnderstandThomson'splum‐puddingmodelandhowErnestRutherford’sgold‐foilexperiment
refuteditbygivingevidenceforanuclearstructureoftheatom.
2.6SubatomicParticles:Protons,Neutrons,andElectronsinAtoms

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Defineatomicmassunit,atomicnumber,andchemicalsymbol.
Recognizechemicalsymbolsandatomicnumbersontheperiodictable.
Defineisotope,massnumber,andnaturalabundance.
Determinethenumberofprotonsandneutronsinanisotopeusingthechemicalsymbolandthe
massnumber.
Defineion,anion,andcation.
Understandhowionsareformedfromelements.
16
Chapter2.AtomsandElements
2.7FindingPatterns:ThePeriodicLawandthePeriodicTable

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
Definetheperiodiclaw.
Knowthatelementswithsimilarpropertiesareplacedintocolumns(calledgroups)intheperiodic
table.
Defineanddistinguishbetweenmetals,nonmetals,andmetalloids.
Identifymain‐groupandtransitionelementsontheperiodictable.
Knowthegeneralpropertiesofelementsinsomespecificgroups:noblegases,alkalimetals,alkaline
earthmetals,andhalogens.
Knowandunderstandtherationaleforelementsthatformionswithpredictablecharges.
2.8AtomicMass:TheAverageMassofanElement’sAtoms


Calculateatomicmassfromisotopemassesandnaturalabundances.
Definemassspectrometryandunderstandhowitcanbeusedtomeasuremassandrelative
abundance.
2.9MolarMass:CountingAtomsbyWeighingThem




Understandtherelationshipbetweenmassandcountofobjectssuchasatoms.
DefinemoleandAvogadro’snumber.
Calculateandinterconvertbetweennumberofmolesandatoms.
Calculateandinterconvertbetweennumberofmolesandmass.
SectionSummaries
LectureOutline


Terms,Concepts,Relationships,Skills
Figures,Tables,andSolvedExamples
TeachingTips


SuggestionsandExamples
MisconceptionsandPitfalls
17
Chapter2.AtomsandElements
LectureOutline
Terms,Concepts,Relationships,Skills 2.1ImagingandMovingIndividualAtoms
 Descriptionofscanningtunnelingmicroscopy(STM)
 Introductiontomacroscopicandmicroscopic
perspectives.
 Definitionsofatomandelement.
2.2EarlyIdeasabouttheBuildingBlocksofMatter
 Historyofchemistryfromantiquity(~450bc)
 Scientificrevolution(1400s‐1600s)
2.3ModernAtomicTheoryandtheLawsThatLedtoIt
 Lawofconservationofmass
o Matterisneithercreatednordestroyed.
o Atomsatthestartofareactionmayrecombineto
formdifferentcompounds,butallatomsare
accountedforattheend.
o Massofreactants=massofproducts.
 Lawofdefiniteproportions
o Differentsamplesofthesamecompoundhave
thesameproportionsofconstituentelements
independentofsamplesourceorsize.
 Lawofmultipleproportions
 JohnDalton’satomictheory
18
Figures,Tables,andSolvedExamples



Introfigure:tipofanSTM
movingacrossasurface
Figure2.1ScanningTunneling
Microscopy
Figure2.2ImagingAtoms

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unnumberedfigure:modelsand
photosofNaandCl 2 forming
NaCl
Example2.1LawofDefinite
Proportions
unnumberedfigure:modelsof
COandCO 2 illustratingthelawof
multipleproportions
Example2.2LawofMultiple
Proportions
ChemistryinYourDay:Atoms
andHumans
Chapter2.AtomsandElements
TeachingTips
SuggestionsandExamples
2.1ImagingandMovingIndividualAtoms
 OtherSTMimagescanbefoundreadilyontheInternet.
 Itisusefultoreiteratetheanalogiesaboutsize;theone
usedinthechaptercomparesanatomtoagrainofsand
andagrainofsandtoalargemountainrange.
2.2EarlyIdeasabouttheBuildingBlocksofMatter
 Theviewofmatterasmadeupofsmall,indestructible
particleswasignoredbecausemorepopularphilosophers
likeAristotleandSocrateshaddifferentviews.
 LeucippusandDemocritusmayhavebeenprovencorrect,
buttheyhadnomoreevidencefortheirideasthan
Aristotledid.
 Observationsanddataledscientiststoquestionmodels;
thescientificmethodpromotestheuseofacycleofsuch
inquiry.
2.3ModernAtomicTheoryandtheLawsThatLedtoIt
 Thatmatteriscomposedofatomsgrewfromexperiments
andobservations.
 ConceptualConnection2.1TheLawofConservationof
Mass
 Investigatingthelawofdefiniteproportionsrequires
preparingordecomposingasetofpuresamplesofa
compoundlikewater.
 Investigatingthelawofmultipleproportionsrequires
preparingordecomposingsetsofpuresamplesfrom
relatedcompoundslikeNO,NO 2 ,andN 2 O 5 .
 ConceptualConnection2.2TheLawsofDefiniteand
MultipleProportions
19
MisconceptionsandPitfalls

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
STMisnotactuallyshowing
imagesofatomslikeonemight
imagineseeingwithalight
microscope.
Atomsarenotcoloredspheres;
theimagesusecolorto
distinguishdifferentatoms.
Theoriesarenotautomatically
acceptedandmaybeunpopular
forlongperiodsoftime.
Philosophyandreligioncanbe
supportedbyarguments;
sciencerequiresthattheoriesbe
testableandthereforefalsifiable.
Measurementstoestablishearly
atomictheorieswereperformed
atthemacroscopiclevel.The
scientistsobservedproperties
forwhichtheycouldcollectdata
(e.g.,massorvolume).
Chapter2.AtomsandElements
LectureOutline
Terms,Concepts,Relationships,Skills 2.4TheDiscoveryoftheElectron
 Thomson’scathode‐raytubeexperiments
o Highvoltageproducedastreamof
particlesthattraveledinstraightlines.
o Eachparticlepossessedanegative
charge.
o Thomsonmeasuredthecharge‐to‐
massratiooftheelectron.
 Millikan’soil‐dropexperiments
o Oildropletsreceivedchargefrom
ionizingradiation.
o Chargeddropletsweresuspendedin
anelectricfield.
o Themassandchargeofeachoildrop
wasusedtocalculatethemassand
chargeofasingleelectron.
2.5TheStructureoftheAtom
 Thomson’splum‐puddingmodel:negatively
chargedelectronsinaseaofpositivecharge
 Radioactivity
o Alphadecayprovidesthealpha
particlesforRutherford’sexperiment.
 Rutherford’sexperiment
o Alphaparticlesdirectedatathingold
filmdeflectinalldirections,including
backatthealphasource.
o Onlyaconcentratedpositivecharge
couldcausethealphaparticlesto
bounceback.
 Rutherford’snucleartheory
o mostmassandallpositivecharge
containedinasmallnucleus
o mostofatombyvolumeisempty
space
o protons:positivelychargedparticles
o neutralparticleswithsubstantial
massalsoinnucleus
20
Figures,Tables,andSolvedExamples

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
Figure2.3CathodeRayTube
unnumberedfigure:propertiesofelectrical
charge
Figure2.4Thomson’sMeasurementofthe
Charge‐to‐MassRatiooftheElectron
Figure2.5Millikan’sMeasurementofthe
Electron'sCharge
unnumberedfigure:plum‐puddingmodel
Figure2.6Rutherford’sGoldFoilExperiment
Figure2.7TheNuclearAtom
unnumberedfigure:scaffoldingandempty
space
Chapter2.AtomsandElements
TeachingTips
SuggestionsandExamples
2.4TheDiscoveryoftheElectron
 Reviewtheattraction,repulsion,andadditivityofcharges.
 Discussthephysicsofelectricfieldsgeneratedbymetal
plates.
 Ademonstrationofacathoderaytubewillhelpstudents
betterunderstandThomson’sexperiments.
 DemonstratehowMillikan’scalculationworksandwhyhe
coulddeterminethechargeofasingleelectron.
2.5TheStructureoftheAtom
 Itmaybeusefultogiveabriefdescriptionof
radioactivity.Rutherford’sexperimentmakesmoresense
ifoneknowssomepropertiesofthealphaparticleand
fromwhereitcomes.
 Thomsonidentifiedelectronsandsurmisedtheexistence
ofpositivechargenecessarytoformaneutralatom.The
plum‐puddingmodelisthesimplestwaytoaccountfor
theobservations.
 Thefigureaboutscaffoldingsupportsdiscussionaboutan
atombeingmostlyemptyspacebutstillhavingrigidity
andstrengthinthemacroscopicview.Thisisanother
exampleofapparentdifferencesbetweenthemicroscopic
andmacroscopicproperties.
21
MisconceptionsandPitfalls


Millikandidnotmeasurethe
chargeofasingleelectron;he
measuredthechargeofa
numberofelectronsand
deducedthechargeofasingle
electron.
Studentsoftendon’tunderstand
thesourceofalphaparticlesin
Rutherford’sexperiments.
Chapter2.AtomsandElements
LectureOutline
Terms,Concepts,Relationships,Skills 2.6SubatomicParticles:Protons,Neutrons,and
ElectronsinAtoms
 Propertiesofsubatomicparticles
o atomicmassunits(amu)
 proton,neutron:~1amu
 electron:~0.006amu
o charge
 relativevalue:1forelectron,
+1forproton
 absolutevalue:1.61019C
 Atomicnumber(numberofprotons):
definingcharacteristicofanelement
 Isotope:sameelement,differentmass
(differentnumberofneutrons)
 Ion:atomwithnonzerocharge
o anion:negativelycharged(more
electrons)
o cation:positivelycharged(fewer
electrons)
2.7FindingPatterns:ThePeriodicLawandthe
PeriodicTable
 Periodiclawandtheperiodictable
o generallyarrangedbyascendingmass
o recurring,periodicproperties;
elementswithsimilarproperties
arrangedintocolumns:groups(or
families)
 Majordivisionsoftheperiodictable
o metals,nonmetals,metalloids
o main‐groupelements,transition
elements
 Groups(families)
o noblegases(group8A)
o alkalimetals(group1A)
o alkalineearthmetals(group2A)
o halogens(group7A)
 Ionswithpredictablecharges:basedon
stabilityofnoble‐gaselectroncount
o group1A:1+
o group2A:2+
o group3A:3+
o group5A:3
o group6A:2
o group7A:1
22
Figures,Tables,andSolvedExamples
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

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unnumberedfigure:baseball
Table2.1SubatomicParticles
unnumberedfigure:lightningandcharge
imbalance
Figure2.8HowElementsDiffer
Figure2.9ThePeriodicTable
unnumberedfigure:portraitofMarieCurie
Example2.3AtomicNumbers,Mass
Numbers,andIsotopeSymbols
ChemistryinYourDay:WhereDidElements
ComeFrom?
unnumberedfigure:discoveryofthe
elements
Figure2.10RecurringProperties
Figure2.11MakingaPeriodicTable
unnumberedfigure:stampfeaturingDmitri
Mendeleev
Figure2.12Metals,Nonmetals,and
Metalloids
Figure2.13ThePeriodicTable:Main‐Group
andTransitionElements
unnumberedfigure:thealkalimetals
unnumberedfigure:thehalogens
Figure2.14ElementsThatFormIonswith
PredictableCharges
Example2.4PredictingtheChargeofIons
ChemistryandMedicine:TheElementsof
Life
Figure2.15ElementalCompositionof
Humans(byMass)
Chapter2.AtomsandElements
TeachingTips
SuggestionsandExamples
2.6SubatomicParticles:Protons,Neutrons,andElectronsinAtoms
 Theanalogyofthebaseballandagrainofricetoaprotonand an
electronismeanttoillustratethedifferenceinmassbutnotsize.
 Electricalchargecanbedemonstratedwithstaticelectricity.
Twoballoonschargedwithwoolorhumanhairwillrepeleach
other.
 Namesofelementscomefromvarioussources.TomLehrer’s
“ElementSong”canbefoundontheInternet.
 Isotopicabundancesareinvariantintypicallab‐sizedsamples
becauseofsuchlargenumbersofatoms.
 ConceptualConnection2.5TheNuclearAtom,Isotopes,andIons
 Thehistoryofchemistryinvolvesconsiderableculturaland
genderdiversity.ExamplesincludebothLavoisiers(French),
Dalton(English),Thomson(English),MarieCurie
(Polish/French),Mendeleev(Russian),Millikan(American),
RobertBoyle(Irish),AmedeoAvogadro(Italian).
 TheChemistryinYourDayboxgivesabroaddescriptionofthe
originofatoms.
2.7FindingPatterns:ThePeriodicLawandthePeriodicTable
 Otherdisplaysoftheperiodictablecanbefoundinjournals
(Schwartz,J.Chem.Educ.2006,83,849;Moore,J.Chem.Educ.
2003,80,847;Bouma,J.Chem.Educ.1989,66,741),books,and
ontheInternet.
 Periodictablesarearrangedaccordingtotheperiodiclawbut
cancomparemanyfeatures,e.g.phasesofmatter,sizesofatoms,
andcommonions.Thesearepresentedasaseriesoffiguresin
thetext.
 ChemistryandMedicine:TheElementsofLifeprovidesan
opportunitytorelatethetopicstoeverydaylife.Someofthe
otherelementsinthefigureandtablerepresenttraceminerals
thatarepartofgoodnutrition.Theperiodiclawaccountsfor
whysomearenecessaryandothersaretoxic.
23
MisconceptionsandPitfalls



Studentssometimes
confusethemassnumber
asbeingequaltothe
numberofneutrons,not
thenumberofneutrons
plusthenumberof
protons.
Studentslogically(but
mistakenly)presumethat
themassofanisotopeis
equaltothesumofthe
massesoftheprotonsand
neutronsinthatisotope.
Theperiodictableis
betteratpredicting
microscopicproperties,
thoughmacroscopic
propertiesarealsooften
illustrated.
Chapter2.AtomsandElements
LectureOutline
Terms,Concepts,Relationships,Skills 2.8AtomicMass:TheAverageMassofan
Element’sAtoms
 Averageatomicmassisbasedon
naturalabundanceandisotopicmasses.
 Massspectrometry
o atomsconvertedtoionsand
deflectedbymagneticfieldsto
separatebymass
o outputdata:relativemassvs.
relativeabundance
2.9MolarMass:CountingAtomsbyWeighing
Them
 MoleconceptandAvogadro’snumber
 Convertingbetweenmolesandnumber
ofatoms
 Convertingbetweenmassandnumber
ofmoles
Figures,Tables,andSolvedExamples




unnumberedfigure:periodictableboxforCl
Example2.5AtomicMass
Figure2.16TheMassSpectrometer
Figure2.17TheMassSpectrumofChlorine

unnumberedfigure:penniescontaining~1molof
Cu
unnumberedfigure:1tbspofwatercontains~1
molofwater
Example2.6ConvertingbetweenNumberof
MolesandNumberofAtoms
unnumberedfigure:relativesizesofAl,C,He
unnumberedfigure:balancewithmarblesand
peas
Example2.7ConvertingbetweenMassand
Amount(NumberofMoles)
Example2.8TheMoleConcept–Converting
betweenMassandNumberofAtoms
Example2.9TheMoleConcept







24
Chapter2.AtomsandElements
TeachingTips
SuggestionsandExamples
2.8AtomicMass:TheAverageMassofanElement'sAtoms
 Themassesofisotopesmustbereconciledwithan
elementhavingonlywholenumberquantitiesofprotons
andneutrons;thevaluesshouldbenearlyintegralsince
themassofelectronsissosmall.
 Massspectrometryisaneffectivewaytodemonstrate
wherevaluesofnaturalabundanceareobtained.
2.9MolarMass:CountingAtomsbyWeighingThem
 Reviewthestrategyforsolvingnumericalproblems:sort,
strategize,solve,check.
 Estimatinganswersisanimportantskill;thenumberof
atomswillbeverylarge(i.e.somelargepoweroften)
evenfromasmallmassorsmallnumberofmoles.
 ConceptualConnection2.7Avogadro’sNumber
 ConceptualConnection2.8TheMole
25
MisconceptionsandPitfalls



Studentsaretemptedto
calculateaverageatomicmassby
addingtogetherisotopicmasses
anddividingbythenumberof
isotopes.
Atomicmassontheperiodic
tableisusuallynotintegraleven
thoughelementshaveonly
wholenumbersofprotonsand
neutrons.
Manystudentsareintimidated
byestimatinganswersin
calculationsinvolvingpowersof
ten.
Chapter2.AtomsandElements
Additional Problem for Converting between
Number of Moles and Number of Atoms
(Example 2.6)
Calculate the number of moles of iron in a sample that
has 3.83 x 1023 atoms of iron.
Sort
Given 3.83 x 1023 Fe atoms
You are given a number of iron atoms and
asked to find the amount of iron in moles.
Find mol Fe
Strategize
Conceptual Plan
Convert between number of atoms and
number of moles using Avogadro’s number.
atoms

mol
1 mol Fe
6.022  1023 Fe atoms
Relationships Used
6.022 x 1023 = 1 mol (Avogadro’s number)
Solve
Follow the conceptual plan. Begin with 3.83 x
1023 Fe atoms and multiply by the ratio that
equates moles and Avogadro’s number.
Check
Solution
3.83  10 23 Fe atoms 
1 mol Fe
= 0.636 mol Fe
6.022  10 23 Fe atoms
The sample was smaller than Avogadro’s number so the
answer should be a fraction of a mole. The value of the
sample has 3 significant figures, and the answer is
provided in that form.
26
Chapter2.AtomsandElements
Calculate the number of grams of silver in an
American Silver Eagle coin that contains
Additional Problem for Converting between
Mass and Number of Moles (Example 2.7)
0.288 moles of silver.
Sort
Given 0.288 mol Ag
You are given the amount of silver in moles and
asked to find the mass of silver.
Find g Ag
Strategize
Conceptual Plan
Convert amount (in moles) to mass using the molar
mass of the element.
mol Ag

g Ag
107.87 g Ag
1 mol Ag
Relationships Used
107.87 g Ag = 1 mol Ag
Solve
Solution
Follow the conceptual plan to solve the problem.
Start with 0.288 mol, the given number, and multiply
by the molar mass of silver.
0.288 mol Ag 
107.87 g Ag
= 31.07 g Ag
1 mol Ag
31.07 g = 31.1 g Ag
The magnitude of the answer makes sense since
we started with an amount smaller than a mole.
The molar amount and answer both have 3
significant figures.
Check
27
Chapter2.AtomsandElements
Additional Problem for the Mole Concept—
Converting between Mass and Number of
Atoms (Example 2.8)
What mass of iron (in grams) contains 1.20  1022
atoms of Fe? A paperclip contains about that number
of iron atoms.
Sort
Given 1.20  1022 Fe atoms
You are given a number of iron atoms and asked
to find the mass of Fe.
Find g Fe
Strategize
Conceptual Plan
Convert the number of Fe atoms to moles using
Avogadro’s number. Then convert moles Fe into
grams of iron using the molar mass of Fe.
Fe atoms

mol Fe
1 mol Fe
6.022  10 23 Fe atoms

g Fe
55.85 g Fe
1 mol Fe
Relationships Used
6.022  1023 = 1 mol (Avogadro’s number)
55.85 g Fe = 1 mol Fe
Solve
Follow the conceptual plan to solve the problem.
Begin with 1.20 x 1022 atoms of Fe, multiply by
the ratio derived from Avogadro’s number, and
finally multiply by the atomic mass of Fe.
Check
Solution
1.20  1022 Fe atoms 
1 mol Fe
55.85 g Fe

23
6.022  10 Fe atoms 1 mol Fe
= 1.11 g Fe
The units and magnitude of the answer make sense.
The sample is smaller than a mole. The number of
atoms and mass both have 3 significant figures.
28
Chapter2.AtomsandElements
Additional Problem for the Mole Concept
(Example 2.9)
An iron sphere contains 8.55  1022 iron atoms.
What is the radius of the sphere in centimeters?
The density of iron is 7.87 g/cm3.
Sort
Given 8.55  1022 Fe atoms
d = 7.87 g/cm3
You are given the number of iron atoms in a sphere
and the density of iron. You are asked to find the
radius of the sphere.
Find radius (r) of a sphere
Strategize
Conceptual Plan
The critical parts of this problem are density, which
relates mass to volume, and the mole, which relates
number of atoms to mass:
Fe atoms
(cm3)

mol Fe
55.85 g Fe
1 mol Fe
1 mol Fe
6.022  10 23 Fe atoms
(1) Convert from the number of atoms to the
number of moles using Avogadro’s number;
V (cm3)
(2) Convert from the number of moles to the
number of grams using the molar mass of iron;

V =
(3) Convert from mass to volume using the density
of iron;

g Fe

V
1 cm3
7.87 g Fe
r (cm)
4
 r3
3
Relationships Used
6.022 x 1023 = 1 mol (Avogadro’s number)
(4) Find the radius using the formula for the volume
of a sphere.
55.85 g Fe = 1 mol Fe
d (density of Fe) = 7.87 g/cm3
V = 4/3 r3 [volume of a sphere with
a radius of r]
Solve
Solution
Follow the conceptual plan to solve the problem.
Begin with 8.55 x 1022 Fe atoms and convert to
moles, then to grams and finally to a volume in cm3.
Solve for the radius using the rearranged equation.
8.55  1022 atoms 
55.85 g Fe
1 mol Fe

23
6.022  10 atoms
1 mol Fe

r =
3
3V
=
4
3
1 cm3
= 1.00757 cm3
7.87 g Fe
3  1.00757 cm3
= 0.622 cm
4
The units (cm) are correct and the magnitude of the
answer makes sense compared with previous
problems.
Check
29