CBSE Class 12 Chemistry - Education Observer

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Material downloaded from myCBSEguide.com . 1 / 16 CBSE Class 12 Chemistry Quick Revision Notes Chapter 1 The Solid State Solid: Solid is a state of matter in which the constituting particles are arranged very closely. The constituent particles can be atoms, molecules or ions. Properties of solids: 1. They have definite mass, volume and shape. 2. They are incompressible and rigid. 3. Intermolecular distances are very short and hence the intermolecular forces are strong. 4. Their constituent particles have fixed position. sand can only oscillate about their mean positions. Classification of on the basis of the arrangement of constituent particles: Properties of crystalline solids: They have a definite geometrical shape. They have a long range order. They have a sharp melting point. They are anisotropic in nature i.e. their physical properties show different values when measured along different directions in the same crystal.

Transcript of CBSE Class 12 Chemistry - Education Observer

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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.