2OO7AP@CHEMTSTRY FREE-RESPONSE OUESTIONS (Form B)
First
Ionization Energy
(kJ mol-t)
Second
Ionization Energy
(kJ mol-l)
Third
Ionization Energy
(kJ mol-l)
Element 1
t,251
2,300
3,820
Element2
496
4,560
6,910
Element3
738
1,450
7,730
Element4
1,000
2,250
3,360
6. The table aboveshowsthe first threeionization energiesfor atomsof four elementsfrom the third period of the
periodictable.The elementsare numberedrandomly.Use the information in the table to answerthe following
questions.
(a) Which elementis most metallicin character?
Explainyour reasoning.
(b) Identifyelement3. Explainyour reasoning.
(c) Write the completeelectronconfigurationfor an atom of element3.
(d) What is the expectedoxidationstatefor the mostcommonion of element2 ?
(e) What is the chemicalsymbolfor element2 ?
(0 A neutralatom of which of the four elementshasthe smallestradius?
STOP
ENDOF EXAM
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-12-
AP@CHEMISTRY
2007SCORING GUIDELINES (Form B)
Question 6
FirstIonization
Energy
(kJmol-r)
I t{l
Element 1
Element2
Element3
Element4
496
738
1.000
SecondIonization
Energy
(kJ mol-l)
Third Ionization
Energy
(kJ mol-1)
2,300
4,560
1,450
2.250
3,820
6,910
7,730
3.360
The tableaboveshowsthe first threeionizationenergiesfor atomsof four elementsfrom the third periodof the
periodictable.The elementsarenumberedrandomly.Use the informationin the tableto answerthe following
questions.
(a) Which elementis mostmetallicin character?
Explainyour reasoning.
Element2. It hasthe lowestfirst-ionizationenergy.Metallic
elementsloseelectron(s)when they becomeions,andelement
2 requiresthe leastamountof energyto removean electron.
One point is earnedfor
the identification.
One point is earnedfor
thejustification,
(b) Identifyelement3. Explain your reasoning.
Magnesium.Element3 haslow first and secondionizationenergies
relativeto the third ionizationenergy,indicatingthatthe elementhas
two valenceelectrons,which is true for magnesium.
(Thethird ionizationof element3 is dramaticallyhigher,indicating
the removalof an electronfrom a noblesascore.)
One point is earnedfor
the identification.
One point is earnedfor
thejustification.
(c) Write the completeelectronconfigurationfor an atom of element3.
ls2 zs22p6 3s2
Onepoint is earnedfor the correctelectronconfiguration.
(d) What is the expectedoxidationstatefor the mostcommonion of element2?
l+
One point is earnedfor the correctoxidation state.
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AP. CHEMISTRY
2007SCORINGGUIDELII\ES (Form B)
Question 6 (continued)
(e) Whatis thechemicalsymbolfor element2?
Na
One point is eamedfor the correct symbol.
(f) A neutralatom of which of the four elementshasthe smallestradius?
Element I
One point is eamed for the correct
identification of the element.
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2OOI AP@ CHEMISTRY
FREE.RESPONSE
OI'ESTIONS
6. Answer the following questions,which pertain to binary compounds.
(a) In the box provided below, draw a completeLewis electron-dotdiagramfor the IF3 molecule.
(b) On the basisof the Lewis electron-dotdiagramthat you drew in part (a), predict the moleculargeometryof
the IF3 molecule.
(c) In the SO, molecule,both of the bondsbetweensulfur and oxygen havethe samelength.Explain this
observation,supportingyour explanationby drawing in the box below a kwis electron-dotdiagram(or
diagrams)for the SO2 molecule.
(d) On the basisof your Lewis electron-dotdiagram(s)in part (c), identify the hybridization of the sulfur atom
in the SO" molecule.
The reactionbetween SO2(S) and O2(s) to form SO3(S)is representedbelow.
zSo2G)+oz(s) t' 2Sor(s)
The reactionis exothermic.The reactionis slow at25oC;however,a catalystwill causethe reactionto proceed
faster.
(e) Using the axesprovided on the next page,draw the completepotential-energydiagramfor both the
catalyzedand uncatalyzedreactions. Clearly label the curve that representsthe catalyzedreaction.
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-12-
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AP@CHEMISTRY
2OO7
SCORINGGUIDELINES
Ouestion 6
Answerthefollowingquestions,
whichpertainto binarycompounds.
(a) In theboxprovidedbelow,drawa completeLewiselectron-dot
diagramfor theIF3 molecule.
.E.
' .:.
.:' l.
'.1'r'.{'
One point is earnedfor a correctLewis diagram(can be done with dots or lines).
(b) On the basisof the Lewis electron-dotdiagramthat you drew in part (a), predict the moleculargeometryof
the IF" molecule.
One point is eamedfor the moleculargeometryconsistentwith the Lewis diagram
T-shaped
in part(a).
I
(c) In the SOr molecule,both of the bondsbetweensulfur andoxygenhavethe samelength.Explainthis
observation,supportingyour explanationby drawing in the box below a Lewis electron-dotdiagram(or
diagrams)for the SO2 molecule.
.s 'ci.:'i.q:
(
. .-";.
:Q. .g'
One point is earnedfor a correctdiagram(canbe done with dots or lines).
One point is earnedfor someindication or discussionof resonance(but the point is not earnedfor a
descriptionof resonanceas a dynamic process).
OR
One point is earnedfor a correct diagram
(canbe donewith dots or lines).
The bondsare the samelength becausethey are both I
double bonds.
One point is earnedfor statingthat both bonds
aredoublebonds.
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APECHEMISTRY
2OO7SCORINGGUIDELINES
Ouestion 6 (continued)
(d) On the basisof your Lewis electron-dotdiagram(s)in part (c), identify the hybridization of the sulfur
atomin the SO, molecule.
One point is earnedfor hybridization consistentwith part (c).
sp2
The reactionbetween SO2(S) and O2(S) to form SOr(S) is representedbelow.
zSo2(s)+oz(g) p 2 Sor(s)
The reactionis exothermic.The reactionis slow at25"C: however,a catalystwill causethe reactionto
proceedfaster.
(e) Using the axesprovided below, draw the completepotential-energydiagramfor both the catalyzedand
uncatalyzedreactions.Clearly label the curve that representsthe catalyzedreaction.
>r
po
4)
f r'l
.9l
ReactionFrogress
One point is earnedfor an uncatalyzedreactioncurve that must show that Eo> 0 and Al1 < 0.
One point is earnedf.ora catalyzedreactioncurve that must show Eo < uncatalyzedEo ,
must be clearly labeled,and must begin and end at the sameenergiesas the uncatalyzedcurve.
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2006 AP@ CTIEI\IITSTRY
OUESTIONS
E.REE-RESPONSE
(Fotln
B)
AnswerEITHER Question7 OR Question8 below.Only oneof thesetwo questionswill be graded.If you startboth
questions,
be sureto crossout the questionyou do not want graded.The SectionII scoreweightingfor the question
you chooseis 15 percent.
7. Account for eachof the following observationsin termsof atomic theory and/orquantumtheory.
(a) Atomic size decreasesfrom Na to Cl in the periodic table.
(b) Boroncommonlyforms moleculesof the type BXr. Thesemoleculeshavea trigonalplanarstructure.
(c) The first ionizationenergyof K is lessthanthat of Na.
(d) Eachelementdisplaysa uniquegas-phase
emissionspectrum.
owing.
each of
ed with an
ith you
,LA
iner w
, the
(c) S
(d)
rjections
ng soda
n
rednessand itching
made
relievedby applyinga
Includea chemicalequationwith your answer.
id sodi
STOP
ENDOF EXAM
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t2
AP@CHEMTSTRY
( For mB)
2 0 0 6S C ORINGGUIDELINES
Ouestion 7
7. Accountfor eachof the following observations
in termsof atomictheoryand/orquantumtheory.
(a) Atomic size decreasesfrom Na to Cl in the periodic table.
Acrossthe periodictablefrom Na to Cl, the numberof electrons
in the s- and p- orbitalsof the valenceshellincreases,
as doesthe
numberof protonsin the nucleus.The addedelectronsonly
partiallyshieldthe addedprotons,resultingin an increased
effectivenuclearcharge.This resultsin a greaterattractionfor
the electrons,drawingthem closerto the nucleus,makingthe
atomsmaller.
One point is earnedfor indicating
the increasein nuclearcharse.
One point is earnedfor attributing
the sizedecrease
to the greater
attractionof the nucleusfor the
electronscausedby the increasein
nuclearcharge.
(b) Boroncommonlyforms moleculesof the type BXr. Thesemoleculeshavea trigonalplanarstructure.
Boronhasthreevalenceelectrons,eachof which can
form a singlecovalentbond with X. The threesingle
covalentbondsof the boron atom orientto minimize
electron-pairinteraction,resultingin bond anglesof
l20"and a trigonalplanarstructure.
One point is earned for describing the
valence electrons and the bonds.
One point is earned for a
correct VSEPR arsument.
(c) The first ionizationenergyof K is lessthanthat of Na.
Both Na and K havean s' valence-shell
electron
configuration(Na: [Ne] 3sl ; K: [Ar]4sl). The K atom
valenceelectronhasa highern quantumnumber,placingit
fartherfrom the nucleusthanthe Na atom valenceelectron
The greaterdistanceresultsin lessattractionto the nucleus.
Becauseits valenceelectronis lessattractedto its nucleus.
the K atomhasthe lower ionizationenergy.
I
I
I
One point is earnedfor the size
explanation.
I
I
One point is earnedfor describing
the attractionto the nucleus.
(d) Eachelementdisplaysa uniquegas-phase
emissionspectrum.
Eachelementhasa uniquesetof quantizedenergystatesfor
One point is earnedfor describing
its electrons(becauseof its uniquenuclearchargeand unique
the quantizedenergystatesand
electronconfiguration).As the electronsof an elementabsorb
emissionphenomenon.
quantaof energy,they changeto higherenergystates
(areexcited)- duringde-excitation,energyis releasedasEM
One point is earnedfor describingthe
radiationas the electronscascadeto lower energystates.
of the nucleus
Eachphotonof the EM radiationis associated
with a specific effectof the uniqueness
=
and/or
confisuration.
electron
wavelength(7" hclE), a flux of which producesthe lines of
theemissionsDectrum.
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13
2006 AP'CHEMISTRY
GeCla
FREE.RESPONSE OI'ESTIONS (FOrM B)
ICI;
SeClo
ICl4*
6. The speciesrepresentedaboveall have the samenumberof chlorine atomsattachedto the centralatom.
(a) Draw the Lewis structure(electron-dotdiagram)of eachof the four species.Show all valenceelectronsin
your structures.
(b) On the basisof the Lewis structuresdrawn in part (a), answerthe following questionsaboutthe particular
speciesindicated.
(i) What is the Cl -Ge-Cl
bond anglein GeClo?
(ii) Is SeClo polar?Explain.
(iii) What is the hybridization of the I atom in ICl4- ?
(iv) What is the geometricshapeformed by the atomsin ICl4+?
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tl
AP@CHEMISTRY
(Form B)
2006SCORINGGUIDELINES
Ouestion 6
GeCla
ICl4-
SeClo
ICl4+
6. The speciesrepresentedaboveall have the samenumber of chlorine atomsattachedto the centralatom.
(a) Draw the Lewis structure(electron-dotdiagram)of eachof the four species.Show all valenceelectrons
in vour structures.
'9lt
: C I : G eC: I :
."
.at.
[ 'i', l*
:Cl:
:Cl:
."
s* ,91'
..c1.
[';,,'.,t']
, I
l,fi,;..c1.
|
.
..
L :9'..
I
I
Onepoint is
earnedfor
eachcorrect
structure.
(b) On the basisof the Lewis structuresdrawn in part (a), answerthe following questionsaboutthe
particularspeciesindicated.
(i) What is the Cl -Ge-Cl
bond anglein GeClo?
109.5'
One point is earnedfor the correct angle.
(ii) Is SeClo polar?Explain.
Yes. The SeClo moleculeis polar becausethe lone pair of
nonbondingelectronsin the valenceshell of the seleniumatom
interactswith the bonding pairs of electrons,causinga spatial
asymmetryof the dipole momentsof the polar Se-Clbonds.
The resultis a SeCla moleculewith a net dipolemoment.
One point is earnedfor
the correct answer.
(iii) What is the hybridization of the I atom in ICI; ?
*tpt
One point is earnedfor the correct hybridization.
or sp3&
(iv) What is the geometricshapeformed by the atomsin ICl4* ?
See-saw(or distortedtetrahedralor disphenoidal)
|
One point is earnedfor the correct shape.
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12
2006 AP' CHEMISTRY FREE-RESPONSE OUESTIONS
Answer EITHER Question7 below OR Question8 printed on page 14. Only one of thesetwo questionswill be
graded.Ifyou startboth questions,be sureto crossout the questionyou do not want graded.The SectionII score
weightingfor the questionyou chooseis 15 percent.
7. Answer the following questionsaboutthe structuresof ions that containonly sulfur and fluorine.
(a) The compounds SFa and BF, react to form an ionic compoundaccordingto the following equation.
SF.+BF, + SFTBF.
(i) Draw a completeLewis structurefor the SF3* cation in SFrBFo.
(ii) Identify the type of hybridization exhibitedby sulfur in the SFr+ cation.
(iii) Identify the geometryof the SFr+ cation that is consistentwith the Lewis structuredrawn
in part (a)(i).
(iv) Predictwhetherthe F-S-F bond anglein the SF3+cation is larger than, equalto, or smaller
than 109.5".Justifyyour answer.
(b) The compounds SFo and CsF react to form an ionic compoundaccordingto the following equation.
SFo+ CsF -+ CsSF,
(i) Draw a completeLewis structurefor the SF5- anionin CsSF5.
(ii) Identify the type of hybridizationexhibitedby sulfur in the SFr- anion.
(iii) Identify the geometryof the SFr- anion that is consistentwith the Lewis structuredrawn
in part (b)(i).
(iv) Identify the oxidation numberof sulfur in the compound CsSF5.
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13
AP@CHEMISTRY
2006SCORINGGUIDELINES
Ouestion 7
7. Answerthe following questionsaboutthe structuresof ions that containonly sulfur andfluorine.
(a) The compoundsSFa and BF, reactto form an ionic compoundaccordingto the following equation.
SF*+BF, + SF3BF4
(i) Draw a completeLewis structurefor the SF3+cationin SFrBFo.
+
'''
S
One point is earnedfor the correctLewis
structure(the structuremustincludelonepairsof
electrons,which may be represented
asdashes).
:F:
.F.
|
(ii) Identify the type of hybridizationexhibitedby sulfur in the SF.,+cation.
One point is earnedfor the correcthybridization.
sp'
(iii) Identify the geometryof the SFr+ cationthat is consistentwith the Lewis structuredrawn
in part (a)(i).
One point is earnedfor the correctshape.
Trigonal pyramidal
(iv) Predictwhetherthe F-S-F bond anglein the SF3* cationis largerthan,equalto, or smaller
than 109.5'.Justifvvour answer.
The F-S -F bond anglein the SFr* cationis expectedto be slightly
smallerthan 109.5' becausethe repulsionbetweenthe nonbondingpair of
electronsand the S -F bondingpairsof electrons"squeezes"the F-S -F
One point is earnedfor
statingthat the angleis
smaller,with justification.
bond anglestogetherslightly.
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14
AP@CHEMISTRY
2006SCORINGGUIDELINES
Ouestion 7 (continued)
(b) The compounds SFa and CsF react to form an ionic compoundaccordingto the following equation.
SFo+ CsF -+ CsSF,
(i) Draw a completeLewis structurefor the SF5- anionin CsSF5.
.'i.
iF'.'j.'.
::: s :..
"f": rrtf
t
One point is earnedfor the correct Lewis structure
(the structuremust include lone pairs of electrons,which
may be representedas dashes).
(ii) Identify the type of hybridization exhibitedby sulfur in the SF5- anion.
sp3d2
One point is eamedfor the correct hybridization.
(iii) Identify the geometryof the SFr- anion that is consistentwith the Lewis structuredrawn
in part (bXi).
One point is earnedfor the correct shape.
Squarepyramidal
(iv) Identify the oxidation numberof sulfur in the compound CsSF5.
+4
One point is earnedfor the correct oxidation number.
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15
2005 Ap'CHEMTSTRY
FREE-RESPONSE Ot ESTTONS (Form B)
8. Use principlesof atomic structure,bonding,and intermolecularforces to answerthe following questions.Your
referredto in eachpart.
responsesmust include specific information aboutall substances
(a) Draw a completeLewis electron-dotstructurefor the CS, molecule.Include all valenceelectronsin your
structure.
(b) The carbon-to-sulfur
bond lengthin CSe2
bond lengthin CS2 is 160picometers.Is the carbon-to-selenium
expectedto be greaterthan, lessthan, or equalto this value?Justify your answer.
(c) Thebondenergyofthecarbon-to-sulfurbondin
CS2 is 577kJmol-l.Isthebondenergyofthecarbon-togreater
to
than,
lessthan,or equalto this value?Justifyyour answer.
seleniumbond in CSe, expected be
HHHO
tttrl
H- C-C -C -H
H/C \O/H
lll''
HHH
MethanoicAcid
Propane
(d) The completestructuralformulasof propane,CsHs, andmethanoicacid,HCOOH, areshownabove.In the
tablebelow, write the type(s)of intermolecularattractiveforce(s)that occur in eachsubstance.
Substance
Boiling Point
Propane
229 K
Methanoicacid
374K
IntermolecularAttractive Force(s)
(e) Use principlesof intermolecularattractiveforcesto explain why methanoicacid hasa higher boiling point
thanpropane.
ENDOF EXAM
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t4
AP@CHEMISTRY
(Form B)
2005SCORINGGUIDELINES
Question8
Useprinciplesof atomicstructure,bonding,and intermolecular
forcesto answerthe following questions.Your
responsesmust include specific information aboutall substances
referredto in eachpart.
(a) Draw a completeLewis electron-dotstructurefor the CS, molecule.Includeall valenceelectronsin your
structure.
:S=G=S:
One point is earnedfor the correctstructure.
(b) The carbon-to-sulfur
bond lengthin CSr is 160picometers.Is the carbon-to-selenium
bond lengthin CSe,
expectedto be greaterthan,lessthan,or equalto this value?Justifyyour answer.
The carbon-to-selenium
bond lengthin CSe, is greater
thanthe carbon-to-sulfur
bond lengthin CS2. Because
the valenceelectronsin Se are in a highershell (n = 4)
thanthevalenceelectrons
in S (n : 3), Se hasa
One point is earnedfor indicatingthat the
C-Se bond lengthis greaterthanthe C-S
bond length.
largeratomicradiusthan S has.Therefore,the carbonto-seleniumbond lengthis greaterthanthe carbon-to-
Onepoint is earnedfor indicatingthat Se is
larserthan S.
sulfurbond length.
(c) The bondenergyof the carbon-to-sulfur
bond in CS2 is 577 kJ mol-I. ls the bond energyof the carbon-togreater
seleniumbond in CSe2 expectedto be
than,lessthan,or equalto this value?Justifyyour answer.
The carbon-to-selenium
bondenergyin CSe, is lessthan
the carbon-to-sulfur
bond energyin CS2 becauseSe hasa
largeratomicradiusthan S . BecauseSe is a larger
atom,the orbitaloverlapbetweenthe Se and C will be
smallerthanthe orbital overlapbetween S and C.
Onepoint is earnedfor indicatingthat the
C-Se bond energyis lessthanthe C-S
bond energy.
Onepoint is earnedfor the explanation.
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AP@CHEMISTRY
(Form B)
2005SCORINGGUIDELINES
Question8 (continued)
HHHO
lllll
H-C_C_C-H
lii
i
H/-\o/"
HHH
Propane
MethanoicAcid
(d) The completestructuralformulasof propane,C3Hs,andmethanoicacid,HCOOH, areshownabove.In the
tablebelow,write the type(s)of intermolecularattractiveforces(s)that occurin eachsubstance.
Substance
Boiline Point
Propane
229K
Methanoicacid
374K
IntermolecularAttractive Force(s)
Propanehasdispersionforces.
Methanoicacid hasdispersionforcesand hydrogenbondingforces.
One point is earnedfor IMFs 1n
propane.
One point is earnedfor IMFs ln
methanoicacid.
(e) Useprinciplesof intermolecularattractiveforcesto explainwhy methanoicacid hasa higherboiling point
than propane.
Hydrogenbonding IMFs amongmethanoicacid moleculesare
muchstrongerthan dispersionforcesamongpropanemolecules.
I One point is earnedfor comparing
the strengthsof the IMFs.
The strongerthe IMFs, the more energyit takesto overcomethem. I
Therefore,methanoicacid hasa higherboiling point thanpropane.
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2OO5AP' CHEMISTRY FREE.RESPONSE OTIESTIONS
6. Answer the following questionsthat relateto chemicalbonding.
(a) In the boxesprovided, draw the completeLewis structure(electron-dotdiagram)for eachof the three
moleculesrepresentedbelow.
cF+
(b) On the basisof the Lewis structuresdrawn above,answerthe following questionsaboutthe particular
moleculeindicated.
(i) What is the F-C-F
bond anglein CF, ?
(ii) What is the hybridization of the valenceorbitals of P i n P F ?
(iii) What is the geometricshapeformed by the atomsin sF4 ?
(c) Two Lewis structurescan be drawn for the OPFI molecule,as shownbelow.
.ii.
..
:o:
tt ll
I
..1
:F_P _F:
"l
:F-P -F:
"I
'r'
I
I
rf,
2
Structure
StnrctureI
(i) How many sigmabondsand how many pi bondsare in structure1 ?
(ii) Which one of the two structuresbestrepresentsa moleculeof OPFI ? Justify your answerin termsof
formal charge.
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12
AP@CHEMISTRY
2OO5
SCORINGGUIDELINES
Question6
Answer the following questionsthat relateto chemicalbonding.
(a) In the boxesprovided,draw the completeLewis structure(electron-dotdiagram)for eachof the three
moleculesrepresented
below.
cF+
PFs
SF+
:fr:
:F:
.l
.r1..
:F-'S - F'
IF-C-F:
r'
|
t"
"
tHt
:F:
One point is eamedfor eachcorrectcompleteLewis structure.
Seediagramsabove.
Onepoint is deductedwhenstructuresare correct but nonbonding
electronsaround F atomsare missing.
(b) On the basisof the Lewis structuresdrawn above,answerthe following questionsaboutthe particular
moleculeindicated.
(i) What is the F{-F
bond angle in CFo ?
One point is earnedfor the correctbond angle.
109,5'(or within rangel09o-l l0)
|
Thebondanglegiven in thispart mustbe consistentwith the
Lewis structuredrawn in part (a).
(ii) What is the hybridization of the valenceorbitalsof P in PF. ?
One point is earnedfor the correcthybridization.
dtp3
Thehybridizationgiven in this part must be consistentwith
the Lewis structuredrawn in part h).
(iii) What is the geometricshapeformed by the atomsin SFo?
One point is eamedfor the correctmoleculargeometry.
Seesaw(or distortedtetrahedronor
asymmetricaltetrahedron)
Themoleculargeometrygiven in this part must be consistent
with the Lewis structure drawn in part (a).
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14
AP@CHEMISTRY
2OO5
SCORINGGUIDELINES
Question6 (continued)
(c) Two Lewis structurescan be drawn for the oPFl molecule,as shown below.
'o'
'6,
ill
,n-fl-n :
t""l
:i-i -it'
:F:
:F:
StructureI
Structure2
(i) How manysigmabondsandhowmanypi bondsarein structureI ?
One point is earnedfor the correctnumberof
sigmabonds.
One point is earnedfor the correctnumberof
pi bonds.
4 sigmabondsand I pi bond
(ii) Which one of the two structuresbestrepresentsa moleculeof OPF, ? Justiff your answerin termsof
formal charge.
Structure1 is the better structurebecauseall ofits
atomshavea formal chargeof zero.
One point is eamedfor choosingthe conect
structureand either (1) indicatingthat the formal
chargeis zeroon P or O, or (2) showingthe
calculationfor formal charge.
P: 5-5-0=0
F:7-l-6=0
O: 6-2-4:0
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2OO3AP@CHEMISTRY
FREE.RESPONSE
QUESTIONS
A' Hr'op
Compound
Name
Compound
Formula
Propane
cH3cH2cH3
19.0
CH?COCH?
32.0
Propanone
1-propanol
(kJ mol-r)
cH3cH2cH2oH
47.3
8. Using the information in the table above,answerthe following questionsaboutorganic compounds.
(a) Forpropanone,
(i) draw the completestructuralformula (showingall atomsand bonds);
(ii) predict the approximatecarbon-to-carbon-to-carbon
bond angle.
(b) For eachpair of compoundsbelow, explain why they do not havethe samevalue for their standardheatof
vaporization,L H ioo. (You mustincludespecificinformationaboutboth compoundsin eachpair.)
(i) Propaneand propanone
(ii) Propanoneand l-propanol
(c) Draw the completestructuralformula for an isomerof the moleculeyou drew in part (a) (i).
(d) Given the structuralformula for propynebelow,
Hr/
,
H_C_C=C_H
H
(i) indicatethe hybridization of the carbonatom indicatedby the arrow in the structureabove;
(ii) indicatethe total numberof sigma (o) bondsand the total numberof pi (n) bondsin the moldcule.
ENDOF EXAMINATION
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AP@CHEMISTRY
2OO3
SCORINGGUIDELINES
Question8
LHr"*
Compound
Name
Compound
Formula
Propane
cH3cH2cH3
r 9.0
Propanone
cH3cocH3
32.0
1-propanol
cH3cH2cH2oH
47.3
(kJ mol-r)
8. Usingthe informationin the tableabove,answerthe following questionsaboutorganiccompounds.
(a) For propanone,
(i) draw the completestructuralformula(showingall atomsand bonds);
H
o
H
I tl I
H - C -c - C - H
I
I
H
1 point for completeand correct structuralformula
H
(ii) predictthe approximatecarbon-to-carbon-to-carbon
bond angle,
The C-C-C
bondansleis l20o
I point for bond angle
(b) For eachpair of compoundsbelow,explainwhy they do not havethe samevaluefor their standard
heatof vaporization,Lffro,. (You mustincludespecificinformationaboutboth compoundsin each
pair.)
(i) Propaneand propanone
The intermolecularattractiveforcesin propaneare
dispersionforcesonly. The IMFs in propanoneare
1 point for correctly identiffing the IMFs
dispersionand dipole-dipole.Sincethe intermolecular
for eachsubstance
the enthalpy
attractiveforces differ in the two substances,
of vaporizationwill differ.
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AP@CHEMISTRY
2OO3
SCORINGGUIDELINES
QuestionI (cont'd.)
(ii) Propanoneand 1-propanol
The intermolecularattractiveforces in 1-propanolare dispersion
forcesand hydrogen-bonding.The IMFs in propanoneare dispersion
and dipole-dipole.Sincethe intermolecularattractiveforcesdiffer in
the two substances,
the enthalpyof vaporizationwill differ.
I point for conectly
identifying the IMFs for each
substance
(c) Draw the completestructuralformula for an isomerof the moleculeyou drew in part (a) (i).
HH
tl
H_C-C
o
il
I point for correct,completestructural
formula
_C_H
tl
HH
(d) Given the structuralformula for propynebelow,
HJ
l/
H-C_C:C-H
I
H
(i) indicatethe hybridizationofthe carbonatom indicatedby the arrow in the structureabove;
I point for correcthybridization
sp hybridization
(ii) indicatethe total numberof sigma(o) bondsandthe total numberof pi (n) bondsin the
molecule.
6 sigmabonds
I point for correctnumberof sigmabonds
2 pi bonds
I point for correctnumberofpi bonds
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21
2003AP@CHEMTSTY
(Form B)
FREE-RESPONSE
QUESTTONS
(d) Of the compounds NaOH, CuS, and NaNO3, which one is appropriateto use in a salt bridge?Briefly
explain your answer,and for eachofthe other compounds,include a reasonwhy it is not appropriate.
(e) Another standardcell is basedon the following reaction.
zn + Pbz+ -> znz+ + Pb
If the concentrationof Zn2+ is decreasedfrom 1.0M to 0.25 M. whateffect doesthis haveon the cell
potential?Justify your answer.
Answer EITHER Question7 below OR Question8 printed on page 14. Only one of thesetwo questionswill be
graded.Ifyou startboth questions,be sureto crossout the questionyou do not want graded.The SectionII score
weightingfor the questionyou chooseis 15 percent.
7. Account for the following observationsusing principlesof atomic structureand/orchemicalbonding.In each
part, your answermust include specificinformation aboutboth substances.
(a) The Ca2+ and Cl- ions are isoelectronic,but their radii are not the same.Which ion hasthe largerradius?
Explain.
(b) Carbonand lead are in the samegroup of elements,but carbonis classifiedas a nonmetaland leadis
classifiedas a metal.
(c) Compoundscontaining Kr have beensynthesized,but thereare no known compoundsthat contain He .
(d) The first ionizationenergyof Be is 900 kJ mol -1, but the first ionizationenergyof B is 800 kJ mol -l .
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AP@CHEMISTRY
(FormB)
2003SCORINGGUIDELINES
Question 7
Total Score 8 points
7. Accountfor the following observations
usingprinciplesof atomicstructureand/orchemicalbonding.In
eachpart,your answermust includespecificinformationaboutboth substances.
(a) The C** and Cl- ions are isoelectronic,
but their radii arenot the same.Which ion hasthe larger
radius?Explain.
Both Ca2+and Cl- ions have l8 electrons.Their electron
configurationis1s22s22p63s23p6.
However,they differ by the
numberof protonsin the nucleus. Calciumhas20 protonsand
chlorinehas l7 protons.
I point for indicatingthat
chlorideion hasthe lareerionic
radius
The valenceelectronsare shieldedby the samenumberof
electronsin eachion (10), so the effectivenuclearcharge(ENC)
experienced
by the valenceelectronsin Ca2* is +10 andfor Cl+7.
the ENC is
The valenceelectronsin Cl- experiencea
smallerattractionto the nucleusdue to the smallernuclear
charge,so Cl- hasthe largerionic radius.
(The sameargumentis acceptablewhen comparingthe total
numberof protonsversustotal numberof electronsfor eachion.)
1 point for correctexplanation
(b) Carbonand leadare in the samegroupof elements,but carbonis classifiedas a nonmetaland leadis
classifiedasa metal.
Binary compoundsof carbonexhibit covalentcharacter(property
of a nonmetallicelement),whereasbinary compoundsof lead
exhibit ionic character(propertyof a metallicelement).
OR
Oxidesof carbon,when dissolvedin water,are acidic(property I
element),
whereas
oxides
ofanonmetallic
"i;;;il;;il;,"
water,arebasic(propertyof a metallicelement).
OR
Laroonrs a poorrnermarconoucror(properryoTa nonmera'lc
.
element),whereaslead is a very goodthermalconductor
(propertyof a metallicelement).
II cnaracterlstlc
ll:11t-Tl "::*lllgll:
ol eacn element
.
II and, the
differencein behavior
by the element,and
exhibited
;
thenrelatingthe behaviorto a
, metal nonmetal
I
or
Note: Studentsmay useotherexampleswherethe chemicalor
physicalpropertiesofcarbon and leaddiffer to distinguish
betweenthe two elements.)
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AP@CHEMISTRY
(FormB)
2003SCORINGGUIDELINES
Qr""tion 7 (cont'd.)
(c) CompoundscontainingKr have beensynthesized,but there are no known compoundsthat
containHe.
Helium has a filled shell (the first shell), so doesnot tend to lose
or gainelectrons.Therefore,helium doesnot react.
I point for filled shell for He
Krypton, while having filled 4s and4p sublevels,has empty4d
, I t point for indicating presence
and 4/sublevels. Theseempty orbitals affect the reactivity of Kr. of empty d orbitals in Kr
I
Note: Also acceptableis a comparisonof the ionizationenergies
of helium, and krypton and then the justification for krypton
beingmorereactive.
(d) The first ionizationenergyof Be is 900 kJ mol-I, but the first ionizationenergyof B is
800kJ mol-r.
The electronconfiguration for Be is ls22s2,whereasthe
The first electron
electronconfigurationfor B is 1s22s22p1.
removedin boronis in a 2p subshell,which is higherin energy
thanthe 2s subshell,from which the first electronis removedin
beryllium. The higherin energythe subshellcontainingthe
electronto be removed(ionized),the lower the ionizationenergy.
1 point for indicatingthe
differencein the subshellwhere
the first electronis removedfor
eachelement
I point for associatinghigher
energysublevelwith lower
ionization energy
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