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CBSEClass12Chemistry

QuickRevisionNotes

Chapter1

TheSolidState

Solid:Solidisastateofmatterinwhichtheconstitutingparticlesarearrangedveryclosely.

Theconstituentparticlescanbeatoms,moleculesorions.

Propertiesofsolids:

1. Theyhavedefinitemass,volumeandshape.

2. Theyareincompressibleandrigid.

3. Intermoleculardistancesareveryshortandhencetheintermolecularforcesarestrong.

4. Theirconstituentparticleshavefixedposition.sandcanonlyoscillateabouttheirmean

positions.

Classificationofonthebasisofthearrangementofconstituentparticles:

Propertiesofcrystallinesolids:

Theyhaveadefinitegeometricalshape.

Theyhavealongrangeorder.

Theyhaveasharpmeltingpoint.

Theyareanisotropicinnaturei.e.theirphysicalpropertiesshowdifferentvalues

whenmeasuredalongdifferentdirectionsinthesamecrystal.

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Theyhaveadefiniteandcharacteristicheatoffusion.

Theyarecalledtruesolids.

Whencutwithasharpedgedtool,theysplitintotwopiecesandthenewlygenerated

surfacesareplainandsmooth.

Polymorphicformsorpolymorphs:

Thedifferentcrystallineformsofasubstanceareknownaspolymorphicformsor

polymorphs.Forexample:graphiteanddiamond.

Characteristicsofamorphoussolids:

1. Theyhaveanirregularshape.

2. Theyhaveashortrangeorder.

3. Theygraduallysoftenoverarrangeoftemperature.

4. Theyareisotropicinnaturei.e.theirphysicalpropertiesarethesameinalldirections.

5. Whencutwithasharpedgedtool,theycutintotwopieceswithirregularsurfaces.

6. Theydonothavedefiniteheatoffusion.

7. Theyarecalledpseudosolidsorsupercooledliquids.Thisisbecausetheyhavea

tendencytoflow,thoughveryslowly.

Typesofcrystallinesolids:

A.MolecularSolids

ConstituentParticles:Molecules

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Typeof

solid

Constituent

Particles

Bonding/

AttractiveForces

Electrical

conductivity

physical

nature

Melting

pointExamples

Non-polar

solidsMolecules

Dispersionor

LondonforcesInsulator Soft

Very

low

Ar,CCl4,

H2,l2,CO2

Polar

solidsMolecules

Dipole-dipole

interactionsInsulator Soft low

HCl,solid

SO2,solid

NH3

Hydrogen

bondedMolecules

Hydrogen

bondingInsulator Hard low H2O(ice)

B.IonicSolids

ConstituentParticles:Ions

Bonding/AttractiveForces:CoulombicorElectrostatic

ElectricalConductivity:Insulatorsinsolidstatebutconductsinmoltenstateandin

aqueoussolutions

PhysicalNature:Hardbutbrittle

MeltingPoint:High

Examples: ,ZnS,MgO,NaCl

C.MetallicSolids

ConstituentParticles:Positiveionsinaseaofdelocalizedelectrons

Bonding/AttractiveForces:Metallicbonding

ElectricalConductivity:Conductorsinsolidstateaswellasinmoltenstate

PhysicalNature:Hardbutmalleableandductile

MeltingPoint:Fairlyhigh

Examples:Fe,Cu,Ag,Mg

D.CovalentorNetworkSolids

ConstituentParticles:Atoms

Bonding/AttractiveForces:Covalentbonding

ElectricalConductivity:BadConductorsinsolidstateaswellasinmoltenstate

PhysicalNature:Hardbutmalleableandductile

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MeltingPoint:Fairlyhigh

Examples: ,(quartz),SiC,C(diamond),C(graphite)

Crystallattice:Aregularorderedarrangementofconstituentparticlesinthree

dimensionsiscalledcrystallattice.

Latticepointsorlatticesites:thefixedpositionsonwhichtheconstituentparticles

arepresentarecalledlatticepointsorlatticesites.Agroupoflatticepointswhich

whenrepeatedoverandoveragainin3dimensionsgivethecompletecrystallattice.

Unitcell:Itisdefinedasthesmallestrepeatingunitinspacelatticewhichwhen

repeatedoverandoveragaingeneratesthecompletecrystallattice.Thecrystalcan

consistofaninfinitenumberofunitcells.

Parameterswhichcharacterizeaunitcell:

1. Dimensionsoftheunitcellalongthethreeedges,a,bandc:theseedgesmayormaynot

bemutuallyperpendicular.

2. Inclinationoftheedgestoeachother:thisisdenotedbytheanglebetweentheedges , ,

andrespectively. istheanglebetweentheedgesbandc, istheanglebetweentheedgesa

andc,and istheanglebetweenaandb.

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Sevencrystalsystems:

1. Cubic: = = =90°,a=b=c

2. Tetragonal: = = =90°;a=b c

3. Orthorhombic: = = =90°;a b c

4. Monoclinic: = =90°, 90°;a b c

5. Hexagonal: = =90°, =120°;a=b c

6. Rhombohedralortrigonal: = = 90°;a=b=c

7. Triclinic: 90°;a b c

Typesofunitcells:

1. Primitiveorsimpleunitcellshaveconstituentparticlesonlyatitscorners.

2. Centeredunitcellsarethoseunitcellsinwhichoneormoreconstituentparticlesare

presentatpositionsinadditiontothosepresentatthecorners.

Typesofcenteredunitcells:

1. Facecenteredunitcell:Itconsistsofoneconstituentparticlepresentatthecentreofeach

faceinadditiontothosepresentatthecorners.

2. Bodycenteredunitcell:Itconsistsofaoneconstituentparticleispresentatitsbody

centreinadditiontothosepresentatthecorners.

3. Endcenteredunitcell:Itconsistsofoneconstituentparticlepresentatthecentreofany

twooppositefacesinadditiontothosepresentatthecorners.

Numberofparticlesatdifferentlatticepositions:

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Facecentre:ifanatomispresentatthecentreoftheface,itissharedbytwounit

cells.So,onlyhalfoftheatomactuallybelongstotheunitcell.

Bodycentre:ifanatomispresentatthebodycentre,itisnotsharedbyanyotherunit

cell.So,thatoneatomcompletelybelongstothesameunitcell.

Endcentre:fanatomispresentattheedgecentre,itissharedbyfourunitcells.So,

onlyonefourthofanatombelongstotheunitcell.

Numberofatomsindifferentunitcells:

1. Primitiveunitcellhave1atom

2. Facecenteredunitcellhave3atoms

3. Bodycenteredunitcellhave2atoms

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Coordinationnumber:Coordinationnumberisthenumberofnearestneighboursof

aparticle.

Closepackedstructures:

Closepackingintwodimensions:Itisgeneratedbystackingtherowsofclosepacked

spheresintwoways:

i)Squareclosepackingandii)Hexagonalclosepacking.

Closepackinginthreedimensions:Theycanbeobtainedbystackingthetwo

dimensionallayersoneabovetheother.Itcanbeobtainedintwoways:

i)Squareclosepackedlayersandii)Hexagonalclosepackedlayers.

Squareclosepacking:Here,thespheresofthesecondrowwareplacedexactly

abovethoseofthefirstrow.Thiswaythespheresarealignedhorizontallyaswellas

vertically.ThearrangementisAAAtype.Thecoordinationnumberis4.

Hexagonalclosepacking:Here,thesespheresofthesebondrowareplacedabove

thefirstoneinastaggeredmannerinsuchawaythatitsspheresfitinthedepression

ofthefirstrow.ThearrangementisABABtype.Thecoordinationnumberis6.

Threedimensionalclosepackingfromtwodimensionalsquareclosepacked

layers:Here,thespheresoftheupperlayerareplacedexactlyoverthefirstlayer

suchthespheresofthelayersareperfectlyalignedhorizontallyandvertically.Ithasa

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AAAAtypepattern.Thelatticeissimplecubiclattice.

Threedimensionalclosepackingfromtwodimensionalhexagonalclosepacked

layers:Therearetwostepsinvolvedas:

1. Placingthesebondlayeroverthefirstlayer

2. Placingthethirdlayeroverthesecondlayer

Therearetwopossibilities:

Coveringtheoctahedralvoids:Here,octahedralvoidsofthesebondlayermaybe

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coveredbythespheresofthethirdlayer.ItgivesrisetoABCABCABCtypepattern.The

threedimensionalstructureiscalledcubicclosepackedstructureorfacecentered

cubicstructure.Thecoordinationnumberis12.Example:Cu,Ag.

Typesofvoids:

Octahedralvoid-Itisformedatthecentrewhensixspheresarejoinedintheformof

anoctahedron.

Inhexagonalclosepackingorcubicclosepackingarrangement,theoctahedraland

tetrahedralvoidsarepresent.Thenumberofoctahedralvoidspresentinalatticeis

equaltothenumberofclosepackedparticles.Thenumberoftetrahedralvoidsis

twicethenumberofoctahedralvoids.

Forexample:

Ifthenumberofclosepackedparticles=n

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Numberofparticlespresentinoctahedralvoids=n

Then,thenumberofparticlespresentintetrahedralvoids=2n

Packingefficiency:Itisthepercentageoftotalspaceoccupiedbyconstituentparticles

(atoms,moleculesorions).

Packingefficiencyforfacecenteredunitcell=74%

Packingefficiencyforbodycenteredcubicunitcell=68%

Packingefficiencyforsimplecubicunitcell=52.4%

Radiusratioinanoctahedralvoid:Foranatomtooccupyanoctahedralvoid,its

radiusmustbe0.414timestheradiusofthesphere.

Radiusratiofortetrahedralvoid:Foranatomtooccupyatetrahedralvoid,itsradius

mustbe0.225timestheradiusofthesphere.

Densityofaunitcellissameasthedensityofthesubstance.

Relationshipbetweenradiusofconstituentparticle(r)andedgelength(a):

1. Simplecubicunitcell:a=2r

2. Facecenteredunitcell:a=

3. Bodycenteredunitcell:a=

Volumeofaunitcell=(edgelength)3=

1. Simplecubicunitcell:Volume=

2. Facecenteredunitcell:Volume=

3. Bodycenteredunitcell:Volume=

Numberofatomsinaunitcell(z):

1. Simplecubicunitcell:z=1

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2. Facecenteredunitcell:z=4

3. Bodycenteredunitcell:z=2

Densityofunitcell=

Crystaldefectsarebasicallyirregularitiesinthearrangementofconstituentparticles.

Typesofdefects:

1. Pointdefects-Pointdefectsaretheirregularitiesordeviationsfromidealarrangement

aroundapointoranatominacrystallinesubstance.

2. Linedefects-Linedefectsaretheirregularitiesordeviationsfromidealarrangementin

entirerowsoflatticepoints.

Differenttypesofpointdefects:

Differenttypesofstoichiometricdefectsfornon-ionicsolids:

Interstitialdefect:Acrystalissaidtohaveinterstitialdefectwhensomeconstituent

particles(atomsormolecules)occupyaninterstitialsite.Thisdefectresultsin

increaseindensityofthesubstance.

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Differenttypesofstoichiometricdefectsforionicsolids:

Frenkelordislocationdefect:Inthisdefect,thesmallerion(usuallycation)is

dislocatedfromitsnormalsitetoaninterstitialsite.Itcreatesavacancydefectatits

originalsiteandaninterstitialdefectatitsnewlocation.Itdoesnotchangethe

densityofthesolid.Frenkeldefectisshownbyionicsubstanceinwhichthereisa

largeddifferenceinthesizeofions.ItincludesZnS,AgCl,AgBrandAgI.

Differenttypesofnon-stoichiometricdefects:

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Metaldeficiency:Thisdefectarisesbecauseofabsenceofmetalionsfromitslattice

sites.Theelectricalneutralityismaintainedbyanadjacentionhavingahigher

positivecharge.

Reasonsforthecauseofmetalexcessdefect:

a)Anionicvacancies:Acompoundmayhaveanextrametalionifthenegativeionisabsent

fromitslatticesite.Thisemptylatticesiteiscalledahole.Tomaintainelectricalneutrality

thissiteisoccupiedbyanelectron.Theholeoccupiedbyanelectroniscalledf-centreor

Farbenzentercentre.TheF-centreisresponsibleforthecolourofthecompound.

b)Presenceofextracations:Acompoundissaidtohaveextracationsifacationispresent

intheinterstitialsite.Anelectronispresentintheinterstitialsitetomaintaintheelectrical

neutrality.

Classificationofsolidsbasedontheirelectricalconductivities:

a)Conductors:Thesolidswithconductivitiesrangingbetween to are

calledconductors.

b)Insulators:Thesearethesolidswithverylowconductivitiesrangingbetween to

.

c)Semi-conductors:Thesearethesolidswithconductivitiesintheintermediaterangefrom

to .

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b)Incaseofinsulators,theforbiddengapisverylargeandtheelectronsareunabletoexcite

totheconductionband.

c)Incaseofsemiconductors,forbiddengapissmall.Therefore,someelectronsmayjumpto

conductionbandandshowsomeconductivity.Electricalconductivityofsemiconductors

increaseswithriseintemperature,sincemoreelectronscanjumptotheconductionband.

Typesofsemiconductors:

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a)Intrinsicsemiconductors:Thesearethosesemiconductorsinwhichtheforbiddengapis

small.Onlysomeelectronsmayjumptoconductionbandandshowsomeconductivity.They

haveverylowelectricalconductivity.Example:Silicon,germanium.

b)Extrinsicsemiconductors:Whenanappropriateimpurityisaddedtoanintrinsic

semiconductor,itiscalledextrinsicsemiconductors.Theirelectricalconductivityishigh.

Doping:Theprocessofaddinganappropriateamountofsuitableimpurityto

increasetheconductivityofsemiconductorsisknownasdoping.

a)Then-typesemiconductors:Theyareformedwhensiliconisdopedwithelectronrich

impuritylikegroup15elements.Theincreaseinconductivityisduetothenegatively

chargedelectrons.

b)Thep-typesemiconductors:Theyareformedwhensiliconisdopedwithelectron

deficientimpuritylikegroup13elements.Theincreaseinconductivityisduetothe

positivelychargedholes.

Typesofextrinsicsemiconductors:

Diode:Itisacombinationofn-typeandp-typesemiconductorsandisusedasa

rectifier.

Transistors:Theyaremadebysandwichingalayerofonetypeofsemiconductor

betweentwolayersoftheothertypeofsemiconductor.Thenpnandpnptypeof

transistorsareusedtodetectoramplifyradiooraudiosignals.

The12-16compounds:Thesecompoundsareformedbythecombinationofgroup12

andgroup16compounds.Theypossessanaveragevalencyof4.Examples-

ZnS,CdS,CdSeandHgTe.

The13-15compounds:Thesecompoundsareformedbythecombinationofgroup13

andgroup15compounds.Theypossessanaveragevalencyof4.Examples-InSb,AlP

andGaAs.

Everysubstancehassomemagneticpropertiesassociatedwithit.Theoriginofthese

propertiesliesintheelectrons.

Eachelectroninanatombehaveslikeatinymagnet.Itsmagneticmomentoriginates

fromtwotypesofmotions:

(i)itsorbitalmotionaroundthenucleusand

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(ii)itsspinarounditsownaxis.

Classificationofsubstancesbasedontheirmagneticproperties:

1. Paramagneticsubstances:Thesearethosesubstanceswhichareweaklyattractedbythe

magneticfield.Itisduetopresenceofoneormoreunpairedelectrons.

2. Diamagneticsubstances:Diamagneticsubstancesareweaklyrepelledbyamagnetic

field.Diamagnetismisshownbythosesubstancesinwhichalltheelectronsarepaired

andtherearenounpairedelectrons.

3. Ferromagneticsubstances:Thesearethosesubstanceswhichareattractedevery

stronglybyamagneticfield.

4. Antiferromagneticsubstances:Theyhaveequalnumberofparallelandantiparallel

magneticdipolesresultinginazeronetdipolemoment.

5. Ferrimagneticsubstances:Theyhaveunequalnumberofparallelandantiparallel

magneticdipolesresultinginanatdipolemoment.