Book1Part04.docx

Book1Part04.docx

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Book1Part04

Part4BondingandStructure（Book1,p.320–p.325）

29.NeandAr:

simplemolecularstructurewithatomsattractedtogetherbyveryweakinstantaneousdipole-induceddipoleinteractions.Hence,bothNeandArhaveverylowmeltingpoints.

Thestrengthofintermolecularforcesincreaseswiththenumberofelectrons.

ArhasalargeratomicsizeandhasmoreelectronsthanNe.

ArhasahighermeltingpointthanNe.

H2O:

polarmolecule.StronghydrogenbondingexistsbetweenH2Omolecules.

Ice:

simplemolecularstructurewitheachH2Omoleculehydrogen-bondedtofourotherH2Omoleculestogiveanopennetworkstructure.

IceorH2O（s）hasalowmeltingpointcomparedwithionicsolidsorgiantcovalentcompounds.However,becauseofthepresenceofstronghydrogenbonding,itsmeltingpointishigherthanothersimplemolecularsubstanceswithsimilarmolecularmasses.

NaF:

giantionicstructure.Na+andF–areheldinlatticesitesbyverystrongionicbonds.

Alargeamountofenergyisrequiredtoseparatetheionsformeltingtooccurveryhighmeltingpoint.

Diamond:

giantcovalentstructurewithCatomscovalentlybondedtoeachother.EachCatomisstronglybondedtofourotherCatomstogiveagiantnetworkofCatoms.Therefore,infinitenumberofstrongcovalentbondsaretobebrokeninmeltingveryhighmeltingpoint.

30.Thelargerthemolecularsizeduetothegreaternumberofelectronsinthemolecule,thestrongertheintermolecularforces.Moreenergyisrequiredtoseparatethemoleculesduringboilingandhenceahigherboilingpointisexpected.BhasasmallermolecularsizethanA.Hence,Bisexpectedtohaveaboilingpointlowerthan17C.

C,havingalargermolecularsize（sinceithasmoreClatoms）,hasahigherboilingpointthanA.

31.（a）（i）

BE=bondenergy

IE1=firstionizationenergy

IE2=secondionizationenergy

EA1=firstelectronaffinity

LE=latticeenergy

（ii）Hf（CaF2（s））=Hat（Ca）+BE（FF）+IE1（Ca）+IE2（Ca）+2EA1（F）+LE（CaF2）

1220=+178+158+590+1150+2（328）+LE（CaF2）

LE（CaF2）=2640kJmol1

（b）（i）CaF2（s）+H2SO4（aq）2HF（g）+CaSO4（s）

（ii）

Hr=Hf（CaF2）Hf（H2SO4）+2Hf（HF）+Hf（CaSO4）

=（1220）（814）+2（271）+（1434）kJmol1

=+58kJmol1

（iii）Sincetheforwardreactionisendothermic,heatingthesystemhelpstodrivethereactionforwardsaccordingtoLeChatelier’sprinciple.

32.

（a）

Thereare3regionsofelectroncloudsaroundB.Tominimizeelectronicrepulsion,theyaredirectedinatrigonalplanarmanner.Sinceallarebondsandthereisnoloneelectronpair,BF3istrigonalplanar.

InbothCF4andNF3,thereare4regionsofelectroncloudsaroundCandNrespectively.Tominimizeelectronicrepulsion,theyaredirectedtetrahedrally.

InCF4,thereisnoloneelectronpair.Hence,CF4istetrahedral.

InNF3,thereisoneloneelectronpair.Hence,NF3istrigonalpyramidal.

Thereare6regionsofelectroncloudsaroundS.Tominimizeelectronicrepulsion,theyaredirectedoctahedrally.Sincethereisnoloneelectronpair,SF6isoctahedral.

（b）ThebondenthalpyofCClis340kJmol1,whichisweakerthanCFbond.Unlike

CClbond,CFisnoteasilybrokendowntogiveFatoms.Hence,replacingCF2Cl2byC2H2F4preventstheformationofreactivehalogenatomsandthereforehelpstoreduceozonedepletion.

33.（a）（i）A:

CH4,non-polarmolecule

Discretemoleculesareheldtogetherbyweakinstantaneousdipole-induceddipoleinteractionsverylowboilingpoint.

D:

SiH4similartoA

Weakintermolecularforces（instantaneousdipole-induceddipoleinteractions）

verylowboilingpoint.

SinceSiH4hasmoreelectronsthanCH4,thestrengthofintermolecularforcesisstronger.Therefore,theboilingpointofSiH4ishigherthanthatofCH4.

B:

NH3isapolarmoleculewithhighlyelectronegativeatomN.SincestronghydrogenbondingexistsbetweenNH3molecules,theboilingpointofBishigherthanthatofAandD.

C:

H2OisapolarmoleculehashighlyelectronegativeatomO.ThehydrogenbondingbetweenH2OmoleculesisstrongerthanthatbetweenNH3moleculesbecauseOismoreelectronegativethanN.Therefore,theboilingpointofH2OishigherthanthatofNH3.

（ii）BoilingpointofH2O>BoilingpointofHF>BoilingpointofNH3

（formsmorehydrogen（Fmore

bondsthanHF）electronegativethanN）

BoilingpointofGeH4>BoilingpointofSiH4

GeH4hasmoreelectrons,thereforestrongervanderWaals’forcesareformedbetweenthemolecules.

（b）

（i）

（ii）Hydrogenbonds

34.（a）CH4（g）C（g）+4H（g）H=4BE（CH）

Itistheaverageenergyrequiredtobreak1moleofCHbondsofmethane.

（b）（i）CH4（g）+H2O（g）

CO（g）+3H2（g）H1=+206kJmol1

H1=4BE（CH）+2BE（OH）BE（CO）3BE（HH）

260=4410+2460BE（CO）3436

BE（CO）=1046kJmol1

（ii）BE（CO）=360kJmol1

BE（C=O）=740kJmol1

Incarbonmonoxide,theCObondisatriplebond.ItisstrongerthanaC=OdoublebondandaCOsinglebond.

35.（a）（i）A:

Enthalpychangeofatomizationofsodium

B:

Firstionizationenergyofsodium

C:

Enthalpychangeofneutralization

（ii）D:

EnthalpychangeofhydrationofgaseoussodiumionandelectronaffinityofH+（aq）

（b）（i）B:

H=+494kJmol1

（ii）–58–494–107+HE=–850

HE=–191kJmol1

36.（a）InNH3,polarNHbondsarepresent.

InHCl,apolarHClbondispresent.

Inbothcases,thebondsareformedthroughthehead-onoverlapbetweenorbitals.

InCO2,C=Obondsarepresent.Thebondisformedthroughahead-onoverlap（bond）andaside-wayoverlap（bond）oforbitals.

BetweenNH3molecules,relativelystronghydrogenbondsexist.

Hence,itsboilingpointisthehighestamongthethree.

BetweenHClmolecules,permanentdipole-permanentdipoleinteractionsexistasaresultofthepolarityofHClmolecules.

TheseinteractionsarenotasstrongasthehydrogenbondsinNH3.Hence,itsboilingpointislower.

InCO2,instantaneousdipole-induceddipoleinteractionsexistbetweenthenon-polarmolecules.DuetoitslargermolecularsizethanHCl,suchinteractionsareslightlystrongerthanthoseinHCl.Hence,ithasaslightlyhigherboilingpointthanHCl.

（b）

37.

（a）

Aluminiumchloride

Ammonia

（b）AdativebondisformedbetweenNandAl.

（c）

Aluminiumchloride（trigonalplanar）

Ammonia

（trigonalpyramidal）

Theproduct（allthebondanglesareabout109.5）

（d）

（i）

（ii）

38.（a）Standardenthalpychangeofformationofacompoundistheenergychangewhen1moleofthatcompoundinthespecifiedstateisformedfromitsconstituentelementsatstandardstateat298Kand1atm.

（b）

（c）610=+338+4（+122）4BE（SiCl）

BE（SiCl）=+359kJmol1

（d）（i）SiCl3H+H2Si+3HCl

（ii）BE（SiH）=320kJmol1

Atahightemperature,theheatenergysuppliedissufficienttobreaktheSiHbondwhichdoesnothaveanextremelyhighbondenergy.

（iii）Puresiliconisusedinmakingsemi-conductors.

39.（a）（i）Na+（g）+Cl（g）NaCl（s）H=latticeenergy

Latticeenergyistheenergyreleasedwhen1moleofsolidcrystallineNaClisformedfromthecombinationof1moleofgaseousNa+and1moleofgaseousCl.

（ii）

Li+hasasmallercationicsize（

）thanNa+.Hence,LiClhasamoreexothermiclatticeenergy.

（b）（i）LiCl:

=

+

=0.074+0.181=0.255nm

（ii）NaCl:

=

+

=0.095+0.181=0.276nm

40.Asthemolecularsizeandthenumberofelectronspermoleculeincrease,thestrengthofvanderWaals’forcesbetweenthemoleculesalsoincrease.Moreenergyisrequiredtoseparatethemoleculesduringboiling.Hence,theboilingpointincreasesfromCH4toC20H42.

Withincreasingmasses,thedensityisexpectedtoincreasesincedensityisdefinedasmassperunitvolume.However,duetothelargervolumeofthemoleculesfromCH4toC20H42,theincreaseindensityisnotasdrasticastheincreaseinmass.

41.（a）BF3:

trigonalplanar

CF4:

tetrahedral

NF3:

trigonalpyramidal

（b）BF3hasavacantporbitalforoccupationbythelonepairofelectronofoxygeninwater;whilstNF3doesnothavesuchvacantorbital.

BF3+3H2OB（OH）3+3HF

（c）（i）MoleratioofK:

Sn:

Cl:

O:

H

=

:

:

:

:

=0.56:

0.28:

0.85:

0.85:

0.85

=2:

1:

3:

3:

3

Hence,theempiricalformulaisK2SnCl3O3H3.

（ii）[SnCl3（OH）3]2;octahedral

（iii）SnCl4+3KOHK2SnCl3（OH）3+KCl

42.（a）（i）ThehydrogenbondsbetweentheOHgroupsofglucosemoleculesarebroken.HydrogenbondsbetweentheOHgroupsofglucosemoleculesandwatermoleculesareformed.

（ii）

（b）CO2（aq）+H2O（l）

H2CO3（aq）

Covalentbond

43.Inpentane,weakvanderWaals’forcesexistbetweenthemoleculeswhilestronghydrogenbondsarepresentintheotherthreesubstances.Hence,theleastamountofenergyisrequiredtoseparatethemoleculesapartandpentanehasthelowestboilingpoint.Themoleculesarerelativelyfarapartandithasthelowestdensity.Sinceitcannotformhydrogenbondswithwatermolecules,itisinsolubleinwater.Ontheotherhand,theotherthreearesolubleinwatersincetheyareabletoformhydrogenbondswithwatermolecules.

Propanoicacidformsthemostextensivehydrogenbondsduetothepresenceof

groupandithastheshortesthydrocarbonchain.Hence,ithasthehighestboilingpointanditsmoleculesarerelativelyclosertoeachothercomparedtothealcoholandamine.Hence,ithasthehighestdensity.

Oxygenismoreelectronegativethannitrogen.Hence,thehydrogenbondsformed