CBSEClass11ChemistryImportantQuestions

Chapter11

Thep-BlockElements

1MarksQuestions

1.Howmanygroupsarethereinp-block?

Ans.Therearesixgroupsofp-blockelementsintheperiodictablenumberingfrom13to18.

2.Whatis‘inertpaireffect’?

Ans.Theoccurrenceofoxidationstatestwounitlessthanthegroupoxidationstatesare

sometimesattributedtothe‘inertpaireffect’.

3.Howdoesmetallicandnon-metalliccharactervaryinagroup?

Ans.Thenon-metalsandthemetalsexistonlyinthep-blockoftheperiodictable.Thenon-

metalliccharacterofelementsdecreasesdownthegroup.Infacttheheaviestelementin

eachp-blackgroupisthemostmetallicinnature.

4.Whydothird–periodelementsexpandtheircovalenceabovefour?

Ans.Thethird–periodelementsofp-groupsincludedd-orbital,whichcanbeutilizedto

formbondandexpandoctet.

5.Whydoheaverelementsformπ–bonds?

Ans.Theheavierelementsofp-blockelementsformsπ–bondsbecauseofthecombined

effectofsizeandavailabilityofd-orbital’sconsiderablyinfluencestheabilityofthere

elementstoformπ–bonds.

6.Wheredoesmetalloidsandnon–metalsexist?

1

Ans.Itisinterestingtonotethatthenon-metalsandmetalloidsexistonlyinthep-blockof

theperiodiclabels.

7.Givethechemicalformulaofinorganicbenzene.

Ans.

8.Givetwoexamplesofelectrondeficientmolecules.

Ans.BF3,B2H6.

9.Arrangethefollowinghalidesofboronintheincreasingorderofacidiccharacter:

BF3,BCl3,BBr3,BI3.

Ans.BF3<BCl3<BBr3<BI3.

10.Whyisboricacidconsideredasaweakacid?

Ans.BoricacidisnotabletoreleaseH+ionsonitsown.ItreceiveOH-ionsfromwater

moleculestocompleteitsoctetandinturnreleaseH+ions.

11.Whyisboronmetalloid?

Ans.Because,boronresemblesbothwithmetalsandnon-metals,thereforeboronis

metalloid.

12.Whydoboronhaveunusualhighmeltingpoint?

Ans.Duetoverystrongcrystallinelattice,boronhasunusuallyhighmeltingpoint.

13.WhydoesBF3actasLewisacids?

Ans.Boroninitshalideshasonlysixelectronsinitsvalenceshell.Therefore,itcanaccepta

pairofelectronsfromanyelectron-richmolecule.Therefore,itactsasanelectron–acceptor

2

andcalledLewisacid.

14.WhatistheelectronicconfigurationofGroup-14elements?

Ans.Theelectronicconfigurationisns2np2.

15.NamethemetalloidfoundinGroup14element?

Ans.Germaniumisametalloidfoundingroup–14.

16.Whichofthefollowingreactswithwaterandaqueoussolutionbecomesacidic:SiCl4

orCCl4?

Ans.SiCl4.

17.WhyCCl4behavesasanelectronprecisemolecule?

Ans.CarboninCCl4,thenumberofelectronsaroundthecentralatominamoleculeiseight

andthusiselectronprecisemolecule.

18.Whyisleadunaffectedbywater?

Ans.Leadisunaffectedbywater,probablebecauseofaprotectiveoxidefilmformation.

19.Whatisthecommonnameofrecentlydevelopedallotropeofcarboni.e.C60

molecule?s

Ans.Fullerene.

20.Howarefullerenesobtained?

Ans.Fullerenesaremadebytheheatingofgraphiteinanelectricarcinthepresenceofinert

gasessuchasheliumorargon.

3

21.Diamondisthehardestsubstanceknown.Why?

Ans.Diamondisthehardestsubstanceontheearthbecauseitisverydifficulttobreak

extendedcovalentbonding.

22.Whatiswatergas?

Ans.ThemixtureofCOandH2isknownaswatergasorsynthesisgas.

23.Silicondioxideistreatedwithhydrogenfluoride.Explain?

Ans.

24.Whataresilicones?

Ans.Simplesiliconesconsistsof chainsinwhichalkalylorphenyl

groups

occupytheremainingbondingpositiononeachsilicon.Theyarehydrophobicinnature.

25.Whatisdryice?

Ans.SolidCO2isknownasdryice.

26.Whataresilicates?

Ans.ThestructuralunitofsilicatesisSiO44-inwhichsiliconatomisbondedtofouroxygen

atomsintetrahedronfashion.

27.Writetheresonancestructuresofcarbondioxide.

Ans.

4

Resonancestructuresofcarbondioxide.

28.Whatissilica-gelusedas?

Ans.Silicagelisusedasadryingagentandasasupportforchromatographicmaterialsand

catalysts.

5

CBSEClass12Chemistry

ImportantQuestions

Chapter11

Thep-BlockElements

2MarksQuestions

1.Whytheelementsofgroup13arecalledp-blockelements?

Ans.Group13elementsarecalledp-blockelementsbecausethelastelectronispresentinthe

p-orbital(np1).ThevalenceshellconfigurationsareB(2s22p1),Al(3s2,3p1),Ga(4s2,4p1),In

(5s25p1)Tl(6s26p1)

2.TheelementsB,Al,Ca,InandTlareplacedinthesamegroupoftheperiodictable.

Givereason.

Ans.TheelementsB,Al,Ga,InandTlareplacedinthesamegroupoftheperiodictable

becauseeachonehasthesamenumberofelectrons(ns2np1)initsvalanceshell.

3.Aluminiumforms innotformedwhy?

Ans.Duetopresenceofvacantd-orbital’s,Alcanexpanditsoctettoformbondswithsix

fluorideionswhereasBcannot.Borondoesnothaved-orbital’s.

4.TheatomicradiusofCaislessthanthatofAl.Why?

Ans.Thisisduetothevariationintheinnercoreoftheelectronicconfiguration.The

presenceofadditional10d-electronsofferonlypoorscreeningeffectfortheouterelectrons

fromtheincreasednuclearchargeingallium.

5.CandSarealwaystetravalentbutGe,SnAndPbshowdivalency.Why?

Ans.Inertpairismoreprominentaswemovedownthegroupinp–blockelements.Ge,Sn

6

andPbshowdivalencyduetoinertpaireffect.

6.Somehalidesofgroup14elementsformcomplexesofthetype .Givereason.

Ans.Thehalidesoftheelementshavingvacantd-orbital’scanformcomplexeslike

becauseinsuchacasethecentralatomcanincreaseits

coordinationnumberfrom4to6duetoavailabilityofvacantd–orbital’s.

7. isleadknownwhereas not.Givereason.

Ans.Themainreasonsarethat

(i) SixlargechlorideionscannotbeaccommodatedaroundSi4+duetolimitationofitssize.

(ii) InteractionbetweenlonepairofchlorideionandSi4+isnotverystrong.

8.PbI4doesnotexist.Why?

Ans.PbI4doesnotexistbecausePb–Ibondinitiallyformedduringthereactiondoesnot

releaseenoughenergytounpair6s2electronsandexciteoneofthemtohigherorbitalto

havefourunpairedelectronsaroundleadatom.

9.Whyiscarbondifferentfromothermemberofthegroup?

Ans.Carbondiffersfromrestofthemembersofitsgroupduetoitssmallersize,higher

electronegativity,higherionizationenthalpyandunavailabilityofd-orbital’s.

10.Whydoesthecovalenceofcarbonnotexpandbeyondfour?

Ans.Incarbon,onlysandporbital’sareavailableforbondingandthereforeitcan

accommodateonlyfourpairsofelectronsaroundit.Thislimitthemaximumcovalenceto

fourwhereasothermemberscanexpandtheircovalenceduetothepresenceofd-orbital’s.

7

11.Whydoescarbonshowdifferentallotropicforms?

Ans.Duetopropertyofcatenationandpπ-pπbondformationCarbonisabletoshow

differentallotropicforms.

12.Siliconhasnoallotropicformanalogoustographite.Why?

Ans.Duetolargesize.Sihaslittleornotendencyforpπ–pπbonding.Whereascarbonatom

formseasilypπ–pπbondsduetosmallersizeingraphitestructure.Hence,Sidoesnot

exhibitgraphitestructure.

13.Whydoesgraphiteconductelectricity?

Ans.Graphiteformshexagonalringandundergoessp2hybridization.Theelectronsare

delocalizedoverthewholesheet.Electronsaremobileandthereforegraphiteconducts

electricityoverthesheet.

14.Graphiteisusedaslubricant.Givereason.

Ans.Graphitehassp2hybridizedcarbonwithalayerstructureduetowideseparationand

weakinter–layerbondsthetwoadjacentlayerscaneasilyslideovereachother.Thismakes

graphiteactasalubricant.

15.Howaresiliconesmanufactured?

Ans.Theyaremanufacturedbyhydrolysisofchlorosilanes–

whereRisamethylorphenylgroup.

8

16.WhydoesCO2havealinearshapewithnodipolemoment

Ans.InCO2moleculecarbonatomundergoessphybridization.Twosphybridizedorbitalof

carbonatomoverlapwithtwop-orbital’sofoxygenatomstomaketwosigmabondswhile

othertwoelectronsofcarbonatomareinvolvedinpπ–pπbondingwithoxygenatom.This

resultsinitslinearshape[withbothc-obondofequallength(115pm)]withnodipole

moment.

9

CBSEClass12Chemistry

ImportantQuestions

Chapter11

Thep-BlockElements

3MarksQuestions

1.Whycarbondoesnotformioniccompounds?

Ans.Theelectronicconfigurationofcarbonatomis1s22s22px12py1andhasfourvalence

electrons.Inordertoformioniccompound,ithastoeitherlosefourelectronsorgainfour

electrons.Sinceveryhighenergyareinvolvedindoingso.Carbondoesnotformionic

compounds.Itcompletesitsoctetbysharingofelectronsandformscovalentcompounds.

2.Whydoestheheavierelementsdonotformpπ–pπmultiplebondascarbondo?

Ans.Carbonhastheuniqueabilitytoformpπ–pπmultiplebondwithitselfandwithother

atomsofsmallsizeandhighelectronegativitywhereasheavierelementsdonotfrompπ–

pπbondsbecausetheiratomicorbital’saretoolargeanddiffusetohaveeffective

overlapping.

3.WhyisCOconsideredpoisonous?

Ans.ThehighlypoisonousnatureofCOarisesbecauseofitsabilitytoformacomplexwith

haemoglobinwhichisabout300timesmorestablethantheoxygen–haemoglobincomplex.

Thispreventshaemoglobinintheredbloodcorpusclesfromcarryingoxygenroundthebody

andultimatelyresultingindeath.

10