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7.pBlockElements
Pointstoremember:
Thegeneralvalenceshellelectronicconfigurationofpblockelementsns2np16
GROUP15ELEMENTS:
Group15elements;N,P,As,Sb&Bi
Generalelectronicconfiguration:ns2np3
PhysicalProperties:
Dinitrogenisadiatomicgaswhileallothersaresolids. N&Parenonmetals.As&Sbmetalloids&Biisametals.thisisduetodecreaseinionization
enthalpy&increaseinatomicsize.
Electronegativitydecreasesdownthe group.Chemicalproperties:
o Commonoxidationstates: 3,+3&+5.o Duetoinerteffect,thestabilityof+5statedecreasesdownthegroup&stabilityof+3state
increases.
o InthecaseofNitrogenallOxidationstatesfrom+1to+4tendtodisproportionateinacidsolution,e.g.: 3HNO3H2O+2NO
Anamalous behaviorofNitrogen: duetoitssmallsize,highelectronegativity,highionization
enthalpyandabsenceofdorbital.
N2hasuniqueabilitytoppmultiplebondswhereastheheavierofthisgroupdonotform p
p becausethereatomicorbitalsaresolarge&diffusethattheycannothaveeffective
overlapping.
Nitrogenexistsasdiatomicmoleculewithtriplebondbetweenthetwoatomswhereasother
elementsformsinglebondsinelementalstate.
Ncannotformdp duetothenonavailibilityofdorbitalswhereasotherelementscan.
TrendsInProperties:
Stability NH3>PH3>AsH3>SbH3>BiH3
BondDissociationEnthalpy NH3>PH3>AsH3>SbH3>BiH3
Reducingcharacter NH3>PH3>AsH3>SbH3>BiH3
Basiccharacter NH3>PH3>AsH3>SbH3>BiH3
Acidiccharacter N2O3>P2O3>As2O3>Sb2O3>Bi2O3
Dinitrogen:
Preparation
CommercialpreparationBytheliquification&fractionaldistillationofair. LaboratorypreparationBytreatinganaqueoussolutionNH4Clwithsodiumnitrate.
NH4Cl+NaNO2N2+2H2O+NaCl
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ThermaldecompositionofammoniumdichromateolsogiseN2.(NH4)2Cr2O7 N2+4H2O+Cr2O3
ThermaldecompositionofBariumorSodiumazidegivesverypureN2.PROPERTIES
Athightemperaturenitrogencombineswithmetalstoformionicnitride(Mg3N2)&withnon
metals,covalentnitride.
AMMONIAPREPARATION
InlaboratoryitispreparedbyheatingammoniumsaltwithNaOHorlime.2NH4Cl+Ca(OH)22NH3+2H2O+CaCl2
InlargescaleitismanufacturedbyHaberprocessN2+3H2=2NH3
H0= 46.1kJ/mol
Acc.toLechateliersprinciplethefavourableconditionsforthemanufactureofNH3are:
Optimumtemperature:700K
Highpressure:200atm
Catalytst:IronOxides
Promoter:K2O&Al2O3
PROPERTIES
Ammoniaisacolorlessgaswithpungentodour.
Highlysolubleinwater.
Insolids&liquidstatesitexistsasanassociatedmoleculeduetohydrogenbondingwitchaccountsfor
highmelting&boilingpointsofNH3
TrigonalPyramidalshapeNH3molecule.
AqueoussolutionofammoniaisweaklybasicduetotheformationofOHion.
ZnSO4+2NH4OHZn(OH)2+(NH4)2SO4
Ammoniacanformcoordinatebondsbydonatingitsloneonnitrogen,ammoniaformscomplexes.
CuSO4+4NH3[Cu(NH3)4]2SO4
Name Formula Oxidationstate Chemicalnature
Nitrousoxideor
Laughinggas
N2O +1 Neutral
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Nitricoxide NO +2 Neutral
Dinitrogentrioxide N2O3 +3 Acidic
Dinitrogentetraoxide N2O4orNO2 +4 Acidic
Dinitrogenpentaoxide N2O5 +5 Acidic
NITRICACID
PREPARATION:ostwaldsproceesitisbaseduponcatalyticoxidationofammoniabyatmospheric
oxidation.Themainstepsare
1) 4NH3+5O2PT500K,9BAR 4NO+6H2O2) 2NO+O22HNO3+NO
PROPERTIES:
(i)conc.HNO3isastrongoxidizingagent&attacksmostmetalsgold&Pt..
(ii)Cr&AldonotdissolveHNO3becauseoftheformationofapositivefilmofoxideonthesurface.
(iii)itoxidisesnonmetalslikeI2toHNO3,CtoCO2,StoH2so4
(iv)brownringtesisusedtodetectNO.
PHOSPHOROUS:
ALLOTROPICFORMS:White,red black&black.
WhitephosphorousismorereactiveredphosphorousbecausewhitePexistsasdiscreteP4molecules.
inredPseveralP4moleculesarelinkedtoformedpolymericchain.
PHOSPHINE
Preparation:ItispreparedinlaboratorybyheatingwhitePwithconcentratednaohsolutioninan
InertatmosphereofCO2[P4+3NaOH+3H2O PH3+3NaH2PO2]Phosphoroushalides
PhosphorousformstwotypesofhalidesPX3&PX5(X=F,I,Br)
Trihalideshavepyramidalshapeandpentahalideshavetrigonalbipyramidalstructure.
OXOACIDSOFPHOSPHOROUS
Theacidsin+3oxidationstatedisproportionatetohigher&loweroxidation.4H3PO33H3PO4+PH3
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AcidswhichcontainsPHbondhavestrongreducingproperties.EX:H3PO2Areionisableandcausethebasicity.
HydrogenatomwhichareattachedwithoxygeninPOHformareionisable
GROUP16ELEMENTS(CHALCOGENS)
Grouo16Elements:O,S,SE,TE,PO
Generalelectronicconfiguration:ns2np4
Element Occurence
Oxygen Comprises20.946%byvolumeoftheatmosphere.
Sulphur AssulphatessuchasgypsumCaSO4.2H2O,EpsomsaltMgSO4.7H2Oandsulphides
SuchasgalenaPbS,zincblendeZnS,copperpyritesCuFeS2
Asmetalselenidesandtelluridesinsulphideores.
Se&Te asadecayproductofthoriumanduraniumminerals.
ATOMIC&PHYSICALPROPERTIES
Ionisationenthalpydecreasesfromoxygentopolonium. OxygenatomhaslessnegativeelectrongainenthalpythanSbecauseofthecompactnatureoftheoxygenatom.HoweverfromtheSonwardsthevalueagainbecomesless
negativeuptopolonium. Electronegativitygraduallydecreasesfromoxygentopolonium,metalliccharacterincreasesfromoxygentopolonium.
Oxygen&Sarenonmetals,seleniumandteleriumaremetalloids.Poisaradioactivemetal.
OxygenisadiatomicgaswhileS,Se&TeareoctaatomicS8,Se8&Te8moleculeswhichhaspuckeredringstructure.
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CHEMICALPROPERTIES
Commonoxidationstate: 2,+2,+4&+6. Duetoinerteffect,thestabilityof+6 decreasesdownthegroupandstabilityof+4increases.
Oxygenexhibits+1stateinO2F2,+2inOF2.
Anamolousbehaviorofoxygenduetoitssmallsize,highelectronegativityandabsenceofd
orbitals.
TRENDINPROPERTIES
AcidiccharacterH2OH2Te
ReducingcharacterH2SI
HALIDES
DIHALIDES:sp3
hybridisationbutangularstructure.
TETRAHALIDES:sp3hybridisationseesawgeometry
HEXAHALIDES:sp3d2,octahedralSF6
DIOXYGEN
Preparedbyheatingoxygencontainingsaltslikechlorates,nitrares
2KClO3heat
2KCl+3O2
2Fe3+
+SO2+2H2O2Fe2+
+SO42
+4H+
5SO2+2MnO4+2H2O5SO42+4H++2Mn2+
SO2moleculeisangular.
OXIDES
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Abinarycompoundofoxygenwithanotherelementiscalledoxide.Oxidescanbeclassified
onthebasisofnature
AcidicOxides: Nonmetallicoxides.Aqueoussolutionsareacids.Neutralizebasestoformsalts.Ex:So2,Co2,N2O5etc.
BasicOxides:metallicoxides.Aqueoussolutionsarealkalis.Neutralizeacidstoformsalts.Ex:Na2O,K2o,etc.
Amphotericoxides:somemetallicoxidesexhibitadualbehavior.Neutralizebothacids&basestoformsalts.
Ex:Al2O3,SbO2,SnO,etc..
OZONE
PREPARATION
Preparedbysubjectingcold,dryoxygentosilentelectricdischarge.
3O22O3
PROPERTIES
Duetotheeasewithwhichitliberatesatomsofnascentoxygen,itactsasapowerful
oxidizingagent.Foreg: itoxidisesleadsulphidetoleadsulphateandiodideionsto
iodine.
PbS+4O3PbSO4+4O2
SULPHURDIOXIDE
PREPARATION
BurningofSinair
S+O2SO2
Roastingofsulphideminerals
(Ironpyrites)
4FeS2+11022Fe2O3+8SO2
(Zincblend)2ZnS+3O22ZnO+2SO2
PROPERTIES
HighlysolubleinwatertoformsolutionofsulphurousacidSO2+H2OH2SO3
SO2reactswithCl2 toformsulphurylchlorideSO2+Cl2SO2Cl2
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ItreactswithoxygentoformSO3inpresenceofV2O5catalyst2SO2+O22SO3
MoistSO2behavesasareducingagent.ItconvertsFe(III)ionstoFe(II)ions&decolourisesacidifiedpotassiumpermanganate(VII)solution(Itisthetestforthe
gas).
SULPHURICACID
PREPARATION
Itismanufacturedbycontactprocesswhichinvolves3steps
1. BurningofSorSulphideoresinairtogenerateSO2.2. ConversionofSO2toSO3inpresenceof V2O5catalyst3. AbsorptionofSO3inH2SO4togiveoleum.PROPERTIES
1. Inaqeoussolutionitionizesin2stepsH2SO4+H2OH3O++HSO4HSO4
+H2OH3O++SO422. ItisastrongdehydratingagentEg:charringactionofsugar
C12H22O11H2SO4
12C+11H2O
3. Itisamoderatelystrongoxidizingagent.Cu+2H2SO4(conc.)CuSO4+SO2+2H2O
C+2H2SO4(conc.)CO2+2SO2+2H2O
GROUP17ELEMENTS(HALOGENS)
Group17elements:F,Cl,Br,I,At
Generalelectronicconfiguration:ns2np5
Element Occurence
Fluorine
Cl.Br,I
Asinsolublefluorides(fluorsparCaF2,Cryoliteand
fluoroapattie)
Seawatercontainschlorides,bromidesandiodides
of
Sodium,potassiummagnesiumandcalcium,butis
mainlysodiumchloridesolution(2.5%bymass).
Certainformsofmarinelife(variousseaweeds)
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ATOMIC & PHYSICAL PROPERTIES
i. Atomic & ionic radii increase from fluorine to iodine.ii. Ionization enthalpy gradually decreases from fluorine to iodine due to increase in atomic size.iii. Electron gain enthalpy of fluorine is less than that of chlorine. It is due to small size of fluorine &
repulsion between newly added electron &electrons already present in its small 2p orbital.
iv. Electronegativity decreases from fluorine to iodine. Fluorine is the most electronegative elementin the periodic table.
v. The color of halogens is due to absorption of radiations in visible region which results in theexcitation of outer electrons to higher energy level.
vi. Bond dissociation enthalpy of fluorine is smaller than that of chlorine is due to electron-electronrepulsion among the lone pair in fluorine molecules where they are much closer to each other
than in case of chlorine. The trend: Cl-Cl>Br-Br>F-F>I-I.
CHEMICAL PROPERTIES
OXIDATION STATES:-1.However, chlorine, bromine &iodine exhibit +1, +3, +5, +7 oxidation
states also.
Fluorine forms two oxides OF2 and O2F2. These are essentially oxygen fluorides because of the
higher electronegativity of fluorine than oxygen.
Anomalous behavior of fluorine- due to its small size, highest electronegativity, low F-F bond
dissociation enthalpy and absence of d-orbitals.TRENDS IN PROPERTIES
Oxidizing property F2>Cl2>Br2>I2Acidic strength- HFHI
Stability of oxides of halogens- I>Cl>Br
Ionic character of halides MF>MCl>MBr>MI
CHLORINE
PREPARATION
1. MnO2 +4HClMnCl2+Cl2+2H2O2. 4NaCl+MnO2+4H2SO4MnCl2+4 NaHSO4+2H2O+Cl23. 2KMnO4+16HCl2KCl+2MnCl2+8H2O+5Cl24. DEACONS PROCESS
4HCl+O2CuCl22Cl2+2H2O
5. By electrolysis of brine solution. Cl2 is obtained at anode.
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PROPERTIES
i. With cold and dilute Cl2 produces a mixture of chloride and hypochlorite butwith hot and concentrated alkalis it gives chloride and chlorate.
2NaOH+Cl2NaCl+NaOCl+H2O
6NaOH+3Cl25NaCl+NaClO3+3H2O
ii. With dry slaked lime it gives bleaching powder.2Ca (OH)2+2Cl2Ca (OH)2+CaCl2+2H2O
iii. It is a powerful bleaching agent; bleaching action is due to oxidationCl2+H2O2HCl+(O)
Colored substance+(O)colorless substance
iv. Action of concentrated H2SO4on NaCl give HCl gas.NaCl+H2SO4420KNaHSO4+HCl
3:1 ratio of conc. HCl & HNO3 is known as aquaregia & it is used for dissolving
noble metals like Au and Pt.
OXOACIDS OF HALOGENS (SEE TABLE 7.10& FIG.7.8)
Interhalogen compounds are prepared by direct combination of halogens.
Ex: ClF, ClF3, BrF5, IF7
They are more reactive than halogens because X-X is weaker than X-X bonds in
halogens (except F-F).
TY PE STRUCTURE
XX3 Bent T-shaped
XX5 Square pyramidal
XX7 Pentagonal bipyramidal
GROUP 18 ELEMENTS
GROUP 18 ELEMENTS: He, Ne, Ar,Kr,Xe &Rn
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General electronic configuration:ns2np6
Atomic radii- large as compared to other elements in the period since it
corresponds to Vander Waal radii.
Inert due to complete octet of outermost shell, very high ionization enthalpy &
electron gain enthalpies are almost zero.
The first noble compound prepared by Neil Bartlett was XePtF6&Xenon.
O2+PtF6
-.led to the discovery of XePtF6 since first ionization enthalpy of
molecular oxygen (1175kJmol-1) was almost identical with that of xenon
(1170kJmol-1).
PROPERTIES
Xe+F2--------673K, 1bar--XeF2
Xe (g) +2F2 (g) ----873k, 7barXeF4(s)
Xe (g) +3F2 (g) ----573k, 6070barXeF6(s)
XeF6+MFM+[XeF7]
-
XeF2+PF5[XeF]+[PF6]
-
XeF6+2H2OXeO2F2+4HF(partial hydrolysis)
SOLVED QUESTIONS
1 MARK QUESTIONS
1. Ammonia has higher boiling point than phosphine. Why?-AMMONIA FORMS INTERMOLECULAR H-BOND.
2. Why BiH3 the strongest reducing agent amongst all the hydrides of group 15 elements ?3. Why does PCl3 fume in moisture ?
In the presence of (H2O) , PCl3 undergoes hydrolysis giving fumes of HCl .
PCl3 +3H2O H3PO3+ 3HCl
4. What Happens when H3PO3 is Heated ?It disproportionate to give orthophosphoric acid and Phosphine .
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4H3PO3 3H3PO4 PH3
5. Why H2S is acidic and H2S is neutral ?The S---H bond is weaker than O---H bond because the size of S atomis bigger than
that of O atom . Hence H2S can dissociate to give H+Ions in aqueous solution .
6. Name two poisonous gases which can be prepared from chlorine gas ?Phosgene (COCl2) , tear gas (CCl3NO2)
7. Name the halogen which does not exhibit positive oxidation state .Flourine being the most electronegative element does not show positive oxidation state .
8.
Iodine forms I3-
but F2 does not form F3-
ions .why?
Due to the presence of vacant D-orbitals , I2 accepts electrons from I-ions to form I3-
ions , but because of d-orbitals F2 does not accept electrons from F-ions to form F3 ions.
9. Draw the structure of peroxosulphuric acid .10.Phosphorous forms PCl5 but nitrogen cannot form NCl5. Why?
Due to the availability of vacant d-orbital in p.
2MARKQUESTION(SHORTANSWERTYPEQUESTION)
1.WhyisHFacidstoredinwaxcoatedglassbottles?
ThisisbecauseHFdoesnotattackwaxbutreactswithglass.ItdissolvesSiO2
presentinglassforminghydrofluorosilicicacid.
SiO2+6HFH
2SiF
6+2H
2O
2.Whatislaughinggas?Whyisitsocalled?Howisitprepared?
Nitrousoxide(N2O)iscalledlaughinggas,becausewheninhaleditproduced
hystericallaughter.Itispreparedbygentlyheatingammoniumnitrate.
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NH4NO3N2O+2H2O
3.Givereasonsforthefollowing:
(i)Conc.HNO3turnsyellowonexposuretosunlight.
(ii)PCl5behavesasanionicspeciesinsolidstate.
(i)ConcHNO3decomposetoNO2whichisbrownincolour &NO2dissolvesin
HNO3toit yellow.
(ii)Itexistsas[PCl4]+[PCl6]
insolidstate.
4.WhathappenswhenwhitePisheatedwithconc.NaOHsolutioninan
atmosphereofCO2?Giveequation.
Phosphorusgaswillbeformed.
P4+3NaOH+3H2OPH3+3NaH2PO2
5.Howisozoneestimatedquantitatively?
Whenozonereactswithanexcessofpotassiumiodidesolution
Bufferedwithaboratebuffer(Ph9.2),Iodideisliberatedwhichcanbetitrated
againstastandardsolutionofsodiumthiosulphate.Thisisaquantitativemethod
forestimatingO3gas.
6.AreallthefivebondsinPCl5moleculeequivalent?Justifyyouranswer.
PCl5hasatrigonalbipyramidalstructureandthethreeequatorialPClbondsare
equivalent,whilethetwoaxialbondsaredifferentandlongerthanequatorial
bonds.
7.NO2iscolouredandreadilydimerises.Why?
NO2containsoddnumberofvalenceelectrons.Itbehavesasatypicalodd
molecules.Ondimerization;itisconvertedtostableN204moleculewitheven
numberofelectrons.
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8.WritethebalancedchemicalequationforthereactionofCl2withhotand
concentratedNaOH.Isthisreactionadispropotionationreaction?Justify:
3Cl2+6NaOH5NaCl+NaClO3+3H2O
Yes,chlorinefromzerooxidationstateischangedto 1and+5oxidationstates.
9.Accountforthefollowing.
(i)SF6islessreactivethan.
(ii)0fthenoblegasesonlyxenonchemicalcompounds.
(i)InSF6thereislessrepulsionbetweenFatomsthanInSF4.
(II)Xehaslowionisationenthalpy&highpolarisingpowerduetolargeratomic
size.
10.WithwhatneutralmoleculeisClOIsoelectronic?IsthatmoleculeaLewis
base?
CiF.Yes,itisLewisbaseduetopresenceoflonepairofelectron.
3MARKQUESTIONS
1(i)whyisHeusedindivingapparatus?
(ii)Noblegaseshaveverylowboilingpoints.Why?
(iii)WhyisIClmoereactivethanI2?
(I)Itisnotsolubleinbloodevenunderhighpressure.
(ii)Beingmonoatomictheyhaveweakdispersionforces.
(ii)IClbondisweakerthanllbond
2.Completethefollowingequations.
(i)XeF4+H2O
(ii)Ca3P2+H2O
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(iii)AgCl(s)+NH3(aq)
(i)6XeF4+12H2O4Xe+2XeO3+24HF+3O2
(ii)Ca2P2+6H2O3Ca(OH)2+2PH3
(iii)AgCl(s)+2NH3(aq)[Ag(NH3)2]Cl(aq)
3.(i)HowisXeOF4prepared?Drawitsstructure.
(ii)WhenHCLreactswithfinelypowderediron,itformsferrouschlorideandnot
ferricchloride.Why?
(i)PartialhydrolysisofXeOF4
XeF6+H2OXeOF4+2HF
Structuresquarepyramidal.SeeFig7.9
(ii)Itsreactionwithironproducesh2
Fe+2HClFeCl2+H2
Liberationofhydrogenpreventstheformationofferricchloride.
5MARKQUESTION
1.Accountforthefollowing.
(i)NoblegasformcompoundswithF2&O2only.
(ii)Sulphurshowsparamagneticbehavior.
(iii)HFismuchlessvolatilethanHCl.
(iv)Whitephosphorousiskeptunderwater.
(v)Ammoniaisastrongerbasethanphosphine.
(i)F2&O2arebestoxidizingagents.
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(ii)InvapourstatesulphurpartlyexistsasS2moleculewhichhastwounpaired
electronsintheantibondingpi*orbitalslikeO2and,hence,exhibit
paramagnetism.
(iii)HFisassociatedwithintermolecularHbonding.
(iv)Ignitiontemperatureofwhitephosphorousisverylow(303K).Thereforeon
explosuretoair,itspontaneouslycatchesfireformingP4O10.Thereforetoprotect
itfromair,itiskeptunderwater.
(v)DuetothesmallersizeofN,lonepairofelectronsisreadilyavailable.
2.WhenConc.H2SO4wasaddedtoanunknownsaltpresentinatesttube,a
browngas(A)wasevolved.Thisgasintensifiedwhencopperturningswereadded
intotesttube.Oncoolinggas(A)changedintoacolourlessgas(B).
(a)IdentifythegasesAandB
(b)Writetheequationsforthereactionsinvolved
ThegasAisNO2whereasBisN2O4.
XNO3+H2SO4XHSO4+HNO3
Salt (conc.)
Cu+4HNO3(Conc.)Cu(NO3)2+2NO2+2H2O
Blue Brown(A)
2NO2(oncooling)N2O4
Colourless(B)
3.Arrangethefollowingintheincreasingorderofthepropertymentioned.
(i)HOCl,HClO2,HClO3,HClO4(Acidicstrength)
(ii)As2O3,ClO2,GeO3,Ga2O3(Acidity)
(iii)NH3,PH3,AsH3,SbH3(HEHbondangle)
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(iv)HF,HCl,HBr,HI(Acidicstrength)
(v)MF,MCl,MBr,MI(ioniccharacter)
(i)Acidicstrength:HOCl
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2)Whydonoblegaseshavecomparativelylargeatomicsizes?
3)ArrangeindecreasingorderofIoniccharacter
MF,MCl,MBr,MI
4)Phosphinicacidbehavesasamonoproticacid
5)Arrangethefollowingintheorderofpropertyindicated:
a)AS2O3,ClO2,GeO2,Ga2O3__Increasingacidity
b)H2O,H2S,H2Se,H2Te__Increasingacidstrength.
6)Arrangeindecreasingorderofbondenergy:
F2,Cl2,Br2,I2
7)Completethefollowing:
i)HNO3+P4O10
ii)IO3+I
+H
+
8)Givethechemicalreactionsinsupportoffollowingobservations:
a)The+5oxidationstateofBiislessstablethan+3oxidationstate.
b)Sulphurexhibitsgreatertendencyforcatenationthanselenium.
9)Howwouldyouaccountforfollowing?
i)EnthalpyofdissociationofF2ismuchlessthanthatofCl2.
ii)Sulphurinvapourstateexhibitsparamagnetism.
10)Drawstructuresoffollowing:
a)PreoxomonasalphuricacidH2SO5
b)XeF4
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LevelIII
1.Completeandbalance:
i)F2+H2OCold
ii)BrO3+F2+OH
iii)Li+N2(cold)
iv)NH3+NaOCl
2)DespitelowerelectronaffinityofF2,isstrongeroxidisingagentthanCl2.
Explain.
3)Givereasons:
a)Nitricoxidebecomesbrownwhenreleasedinair.
b)PCl5isionicinnatureinthesolidstate.
4)WhichofthetwoismorecovalentSbCl3orSbCl5?
5)AdditionofCl2toKlsolutiongivesifbrowncolourbutexcessatifturnsit
colourless.Explain.
IdentifyhybridizationstateofcentralatomanduseconceotofVSEPRtheory.also
itsshape(geometry)anddrawthestructure.
PCl3 sp3 bp=3 lp=1
PCl5 sp3d bp=5 lp=0
BrF3 sp3d bp=3 lp=2
XeF2 sp3d bp=2 lp=3
XeF4 sp3d2 bp=4 lp=2
XeOF4 sp3d2 bp=5 lp=1XeO3 sp
3 bp=3 lp=1
XeF6 sp3d3 bp=6 lp=1
SF4 sp3d bp=4 lp=1
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