CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES

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WHY DO WE NEED TO CLASSIFY ELEMENTS•GENESIS OF PERIODIC CLASSIFICATION•MODERN PERIODIC LAW AND THE PRESENT FORM OF THE PERIODIC•NOMENCLATURE OF ELEMENTS WITH ATOMIC NUMBERS > 100•ELECTRONIC CONFIGURTIONS OF ELEMENTS ANDTHE PERIODIC TABLE•ELECTRONIC CONFIGURATIONSAND TYPES OF ELEMENTS: s-, p-, d-, f- BLOCKS•PERIODIC TRENDS IN PROPERTIES OF ELEMENTS•

Chapter outline

CLASSIFICATION OF ELEMENTSAND

PERIODICITY IN PROPERTIES

CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES

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GENESIS OF PERIODIC CLASSIFICATION

PERIODIC CLASSIFICATION OF ELEmENTS

OBJECTIVES

Electronsarefilledinvariousshellsandsubshellsinafairlyregularfashion.Therefore,propertiesofelementsarerepeatedperiodically.Suchtrendsintheirphysicalandchemicalpropertieswerenoticedbychemistsinthenineteenthcenturyandattemptsweremadetoclassifyelementsontheirbasislongbeforestructureofatomwasknown.

In this lessonweshall studyabout theearlierattempts forclassification, thefirstsuccessfulclassificationwhichincludedall theknownelementsatthattimenamelyMendeleev’speriodictable,andabout the long formofmodernperiodic tablewhich isan improvementoverMendeleev’swork.

Aftercompletingthislesson,youwillbeabletostatetheimportanceofperiodicclassificationandperiodictable.

StatemainfeaturesofMendeleev’speriodictablestatemodernperiodiclaw.•Describethefeaturesofthelongformofperiodictable.•States,p,dandf-blocksandtheirproperties.•Definevariousperiodicproperties.•Discussthetrendsinvariousperiodicpropertiesintheperiodictable.•understandlanthanidecontractionandactinidecontraction.•

CONCEPT OF GROuP ELEmENTS BASED ON ThEIR PROPERTIES

Thereareabout111 known elements and 7 elementsyettobeconfirmed.Amongthese118 elements, 92 elementsareavailableintheelementalform.Remaining26 elements are manmade elements.Classificationof theseelements is very important tounderstandcommonpropertiesandperiodictrendsamongthese118elements.ScientistslikeJohnnDobereiner(1829),JohnAlexanderNewlands(1865)andLotharMayer(1869)gavedifferentkindsofclassifications.But theywerenotbecomepopular.

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Basedonhisownchemicalpropertiesandexperiments,helistedtheelementsintheincreasingorderofatomicmassesandshowedtheperiodictrends.

mendeleevassignedeachelementanumbercalleditsatomicnumber.Thisnumberisusefultodeterminethepositionoftheelementinaseriesofincreasingatomicmasses.Theelementsarearrangedinhorizontal rows called “periods” and vertical columns called “groups”. ThefirstthreeperiodsoftheMendeleev’stablearecalledasshort periods. And theotherperiodsareknownaslong periods.ThegroupsaresubdividedintosubgroupAandsubgroupB.

wehavelearntabouttheMendeleev’speriodicclassification.Althoughitwasaverysuccessfulclassificationbutitalsohadsomedefectsinit.

mODERN PERIODIC LAW AND ThE PRESENT FORm OF ThE PERIODIC TABLE

Element

Lithium, Li

Sodium, Na

Potassium, K

Atomic mass

7

23

39

Dobereiner

mendeleev

DOBEREINER’S TRIADS

In1829,Dobereiner,aGermanscientistmadesomegroupsofthreeelementseachandcalledthemtriads.Allthreeelementsofatriadweresimilarintheirproperties.Heobservedthattheatomicmassofthemiddleelementofatriadwasnearlyequaltothearithmeticmeanofatomicmassesofothertwoelements.Also,samewasthecasewiththeirotherproperties.Letustaketheexampleofthreeelementslithium,sodiumandpotassium.TheyformaDobereiner’striad.

Meanoftheatomicmassesofthefirst(Li)andthethird(K)elements:7+39by2=23.Theatomicmassofthemiddleelement,sodium,Naisequalto23.Dobereneir’sideaofclassificationofelementsintotriadsdidnotreceivewideacceptanceashecouldarrangeonlyafewelementsinthismanner.ThenextbreakthroughinclassificationofelementscameintheformofMendeleev’swork.

mENDELEEV’S PERIODIC LAW

“The properties of the elements and their compounds are a specific function of their atomic weights”.

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mODERN PERIODIC TABLE

henry moseley

Periodic table

modern periodic law“Thephysicalandchemicalpropertiesoftheelementsareperiodicfunctionsoftheiratomicnumbers”.

henry moseley, anEnglishphysicistdiscoveredintheyear1913thatatomicnumber,isthemostfundamentalpropertyofanelementandnotitsatomicmass.

Atomic number,(Z), of an element is the number of protons in the nucleus of its atom.

Thenumberofelectronsintheneutralatomisalsoequaltoitsatomicnumber.Thisdiscoverychangedthewholeperspectiveaboutelementsandtheirpropertiestosuchanextentthataneedwasfelttochangetheperiodiclawalso.Nowweshalllearnaboutthechangesmadeintheperiodiclaw.

The periodic table based on themodern periodic law is called theModernPeriodicTable.ManyversionsofthisperiodictableareinusebuttheonewhichismostcommonlyusedistheLongFormofModernPeriodicTable.

Lookatthelongformofthemodernperiodictable.

Thepropertiesofelementsareduetothedistributionofelectronsinorbitalsoftheatom.ThelongformofperiodictableisbasedontheBohr’smodelofatom.Itisthegraphicalrepresentationofaufbauprinciple.Itsuccessfullyexplainstheperiodicitiesofpropertiesofelements.

Nowletuslearnthemainfeaturesofthisperiodictable.Itcontains7 horizontal rows called ‘periods’ and 18 vertical columns called ‘groups’.Letusstudythedetailsofperiodsfirst.

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NOmENCLATuRE OF ELEmENTS WITh ATOmIC NumBERS > 100

Periodic Table showing different Group of Elements

INTRODuCTION

Periodic Table

Thelongformofperiodictableclearlyindicatestheelectronicconfigurationsoftheelements,similaritiesinphysicalandchemicalpropertiesanddifferencesintheseproperties.Whentheelementsarearrangedaccordingtotheiratomicnumbersortheelectronicconfigurations,agradualchangeintheirpropertiescanbeseen.Thegradationisveryusefulinderivinginformationabouttheelementsandtheircompounds.

PERIODICITY

In theperiodic table, thepropertiesofelementschangegraduallywithachange in theirelectronicconfigurations.This trend repeats itself at regular intervals.This repetition of a character is called“periodicity”andsuchpropertiesarecalledperiodicproperties.As theatomicnumber increases thepropertiesofelementsrepeatedatregularintervals.

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Example of periodicity

Forexample: Frompotassium(K19)toKrypton(Kr36)atomicnumberincreases.AgainfromRubidium(Rb37)toXenon(Xe54)samepropertiesofaboveelementsarerepeated.

Reason: Theperiodicityisduetothesimilarouterelectronicconfiguration.Potassium(19)generalelectronicconfigurationisns1.Krypton(36)electronicconfigurationisns2 np6.AgainfromRubidium(37)ns1 and Xenon(54)ns2 np6sameconfigurationisrepeatedandhencepropertiesalsorepeated.

Periodic properties “Anypropertywhichisperiodicinnatureiscalledperiodicproperty”.

Usesofperiodicproperties: Wecanpredict thenatureofchemicalbonds formedby theelementsandcompare their reactivity.Molecularshapesandcrystalstructurescanbeidentifiedeasily.

ImportantperiodicProperties:Someoftheimportantperiodicpropertiesare:Atomic size and ionic sizeElectron affinityIonization potentialElectro negativityValencymetallic natureReducing (or) Oxidizing natureElectro positivityNature of OxidesOxidation states

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Internuclear Distance

Atomic radius

ATOmIC SIZE

Atomic&ionicradiicalculatedfrominternucleardistance.

Inter-nuclear distance“The distance between two nuclei of neighboring atoms in a compound is called inter-nuclear distance”.

Inter-nucleardistancearemeasuredwithX-raydiffractionmethods(or)spectroscopicmethods.Atomic&ionicradiiareinfluencedby: TypeofchemicalbondOxidationstatesNumberofbondsformedCo-ordinationnumber

ATOmIC RADIuS

Theatomicradiusdependsonmanyfactorslikenumberofbondsformedbytheatom,natureofbonding,oxidationstateoftheatom.Types of atomic radii:Depending on the type of bond, three types of atomicradiiarethere1. Covalent radius 2. metallic or Crystal radius 3. Vander Waal’s radius 4. Ionic radius

“The distance between the centre of the nucleus and the electron cloud of outer most energy level”.

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Covalent Radius

No. of bonds

C - C

C = C

C ≡ C

Bondlength Ao Covalent Radius

1.54 AO 0.77 AO

0.67 AO

0.6 AO

1.34 AO

1.20 AO

metal

K

Ba

Zr

Atomic radius Ao Covalent Radius Ao

2.31 AO 2.03 AO

1.98 AO

1.45 AO

2.17 AO

1.57 AO

Non - metal

C

p

S

Atomic radius Ao Covalent Radius Ao

0.77 AO 0.77 AO

1.10 AO

1.04 AO

1.10 AO

1.04 AO

COVALENT RADIuS

“ half the equilibrium distance between the nuclei of two atoms held together by a covalent bond is covalent radius”.

Considerchlorinemolecule.Theinter-nucleardistancebetweentwochlorineatomsis1.98A.(1.98angstroms).1.98Aisalsocalledasbondlength.Covalentradiusofchlorineis1.98dividedby2=0.99A.Therefore,covalentradiusofchlorineis0.99A.

Characteristics:1.Itisapplicabletohomo-atomicmoleculeslikeCl2, H2 ,Br2etc.2.Itchangeswithtypeofbonds.

Examples:ForCarbon-Carbonsinglebond-Covalentradiusofcarbonis0.77Ao

ForCarbon-Carbondoublebond-Covalentradiusofcarbonis0.67Ao

ForCarbon-Carbontriplebond-Covalentradiusofcarbonis0.6Ao

3.Formetals,atomicradiusisslightlymorethancovalentradius.

4.Fornon-metals,atomicradiusisequaltocovalentradius.

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metallic Radius

mETALLIC OR CRYSTAL RADIuS

“half the inter-nuclear distance between two adjacent metal atoms in a metallic crystal”.

Considersodiumcrystal.Theinter-nucleardistancebetweentwosodiumatomsis3.72A°(angstroms)andmetallicradiusofsodiumis3.72/2=1.86A°.Therefore,Metallicradiusofsodiumatomis1.86A.

Characteristics: 1.Itisapplicableformetalatoms.2.Atomsaretreatedasspheres.

VANDER WAAL’S RADIuS

“half the equilibrium distance between the nuclei of two atoms bound by Vander Waal’s forces”.ConsiderChlorineatomsoftwodifferentmolecules.Thechlorineatomsnotformchemicalbonds.Whentheatomsareclosetoeachother,someweakforceofattractiondevelopsbetweenthem(atoms),thatforceisknownasVander Waal’s force.Thedistancebetweentwoadjacentchlorineatomsindifferentmoleculesis3.6A°.VanderWaalsradiusofchlorine=3.6/2=1.8A°.

VanderWaal’s Radius

Characteristics: 1.Itisobservedonlyinsolidmolecularsubstances.2.Itis40°largerthancovalentradius.

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ELECTRONIC CONFIGuRTIONS OF ELEmENTS ANDThE PERIODIC TABLE

Periods

There areseven rows in the periodic table.Each row is called a period. The periods have beennumberedfrom1to7(Arabicnumerals).Ineachperiodanewshellstartsfillingup.Theperiodnumberisalsothenumberofshellwhichstartsfillingupinit.

IONIC RADIuS

“The distance from the nucleus of the ion up to the point where its influence of electron cloud ceases”.Itisdeterminedbyx-raydiffractionofioniccrystals.Characteristics: 1.Fornegativeions,sizeofatomincreaseswithcharge;soionicradiusalsoincreases.For example:1.TheatomicradiusofChlorineatom=0.99A°.TheionicradiusofChlorineioncl-=1.81A°.Increaseinsize=0.82A°.Asthenumberofelectronsgainedincreases,theionicradiusincreasesproportionally.

2.Atomicradiusofoxygen=0.66A°.IonicradiusofO-2=1.40A°.Forpositive ionssizeofatomdecreaseswithcharge;so ionic radiusdecreases.As thenumberofelectronsremoved fromtheatom increases,cationic radiusdecreasesmore i.e. thecation(cat-ion)becomessmaller.Seethedifferentkindsofatomicradiiandtheirimportantproperties.

PERIODS

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For example:Inelementsof3rdperiod,thethirdshell(Mshell)startsfillingupaswemovefromlefttoright.Thefirstelementofthisperiodsodium Na (2,8,1)hasonlyoneelectroninitsvalenceshell(thirdshell)whilethelastelementofthisperiod,argon Ar (2,8,8)haseightelectronsinitsvalenceshell.Thegradualfilingofthethirdshellcanbefromtheabovetableandillustrations.Eachperiodstartswithanalkalimetalandendswithanoblegaselement.

1st period:Itcontainstwoelements-hydrogen & helium. Itistheshortestperiodanddiscontinuousperiod.

2nd period: ItcontainseightelementsfromLithium(3) to Neon (10). Itisfirstshortperiod.

Example of Periods (a)Sodium(Na)valenceshell(b)Argon(Ar)valenceshell

(a) (b)

3rd period:ItalsocontainseightelementsfromSodium, Na(11)to Argon, Ar (18). Itsecondshortperiod.Thisperiodelementsarecalledtypicalelements.

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4th period: Itcontains18elementsfromPotassium, K (19) to Krypton, Kr (36). Itisfirstlongperiod.Itcontainsfirsttransitionseriesscandium(21)tozinc(30).

5th period: Italsocontains18elementsfromRubidium (37) to Xenon (54). ItcontainssecondtransitionseriesfromYttrium(Y)(31)toCadmium(Cd)(48). Itissecondlongperiod.

6th period:Itcontain32elementsfromCesium, Cs (55) to Radon, Rn (86). Itisthelongestperiod.Itcontains14rareearthelements. ItcontainslanthanidesfromCerium,Ce(58)toLutetium(lew-tee-shee-əm)Lu(71).

7th period:Itisincompleteperiod&mostoftheelementsareradioactive. TheelementsfromFrancium (fran-see-əm) Fr (87) to Hahnium, Ha (105)belongsto thisgroup. ItcontainsactinidesThorium, Th (90) to Lawrencium, Lw (103).

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Thereare18 vertical columnsintheperiodictable.Each column is called a group. Thegroupshavebeennumberedfrom1to18(inArabicnumerals)fromlefttoright.

GROuPS

Groups showing (a)Alkalimetals(b)Noblegases

1 GROuP Alkalimetals

(Li,Na,K,Rb,Cs,Fr)

(a)

18 GROuP Noblegases

(He,Ne,Ar,Kr,XeandRn)

(b)

Group1onextremeleftpositioncontainsalkali metals(Li,Na,K,Rb,CsandFr)Group18onextremerightsidepositioncontainsnoble gases(He,Ne,Ar,Kr,XeandRn).

Allelementspresentinagrouphavesimilarelectronicconfigurationsandhavesamenumberofvalenceelectrons.Youcanseeincaseofgroup1(alkalimetals)andgroup17elements(halogens)thatasonemovesdownagroup,moreandmoreshellsareadded.Groupsarefurtherclassifiedintoa,bandzerogroupelements.

A GROuP ELEmENTS

1st 2nd & 13th to 17th columnsarecalled‘A’ group elements.Thisgroupcontains‘sandpblockelements’.sandpblocksexcludingzerogrouparecalledrepresentativeelements.

B GROuP ELEmENTS

3rd to 12th columns are called ‘B’ group elements.Thisgroupcontainsd-blockelements.Thesearecalled transition elements.

ZERO GROuP ELEmENTS

Therearenoblegases.Chemicallynonreactive.

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Periodic Table showing different Group of Elements

A-Group Elements

B-Group Elements

Zero Group Elements

Lanthanides

Actinides

INNER TRANSITION ELEmENTS

LANThANIDES ELEmENTS

14elementswithatomicnumbers58to71(CeriumtoLutetium(lew-tee-shee-əm))arecalledlanthanidesandtheyareplacedalongwiththeelementlanthanum(La),atomicnumber57inthesameposition(group3inperiod6)becauseofverycloseresemblancebetweenthem.However,forconveniencesaketheyareshownseparatelybelowthemainperiodictable.

ACTINIDES ELEmENTS

14elementswithatomicnumbers90to103(ThoriumtoLawrencium)arecalledactinidesandtheyareplacedalongwiththeelementactinium(Ac),atomicnumber89inthesameposition(group3inperiod7)becauseofverycloseresemblancebetweenthem.Theyareshownalsoseparatelybelowthemainperiodictablealongwithlanthanides.

ADVANTAGES OF mODERN PERIODIC CLASSIFICATION

Elementsarearrangedintheincreasingorderoftheiratomicnumber,whichisfundamentalfeatureofallelements.

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E.g.Argon(Ar40),Potassium(K39),andCopper(Cu59),Nickel(Ni58).Tellurium(Te128),Iodine(I127)anomalybehaviorisrectified.

Theelementofagroupresemblescloselywitheachotherinproperties.8thgroupgetssufficientplaceinthetable.Tableclearlyindicatesmetails,activemetals,transitionalmetals,non-metals,metalloids,lanthanides&actinides.

LImITATIONSThepositionofhydrogenstillremainsuncertain.•Theinnertransitionelementsareplacedseparatelybelowthetable.•The14lanthanidesdifferfromtheusualpatternofelectronicconfiguration.•

ELECTRONIC CONFIGuRATIONS AND TYPES OF ELEmENTS: s, p, d, f BLOCKS

INTRODuCTION

Basedon theelectronicconfigurationsanddifferentiating

electroni.e.electronintheoutermostorbit,theelementsin

theperiodictableareclassifiedinto4blocks.Theyare:

1. s block elements.

2. p block elements.

3. d block elements.

4. f block elements.

See thes,p,dand fblocks in the long formofperiodic

table.

Electron in the outermost orbit

s, p, d and f block eements

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S-block elements (a) ns1 Group I A (b) ns2 Group II A P-block elements

S-Blockelementsns1 GROuP I A

S-Blockelementsns2 GROuP II A

(a) (b)

s-blockelementsareplacedat the left sideof theperiodic table,p-block isat the rightsideandthed-blockinbetweenthes-andp-blocks.f-blockisplacedseparatelyatthebottomofthemaintable.

Elementswithoneelectronintheiroutershellshavetheconfigurationofns1.Theybelongtogroup1elements(hydrogen,alkalimetals).Elementswithtwoelectronsintheiroutershellshavetheconfiguration of ns2.They belong to group 2 elements (alkaline earthmetals). Elementswith threeelectrons(twoin‘s’orbitalandonein‘p’orbital)havetheconfigurationofns2 np2.Theybelongtogroup3elements.Inasimilarwaytheelementshavingfour,five,six,sevenandeightelectronsintheiroutershellshavethegeneralconfigurationns2npx(wherex=2,3,4,5or6)andbelongto4th,5th,6th,7th and Zerogrouprespectively.

S-BLOCK ELEmENTS

“The differentiating electron in an element enters into s - sub shell”.1A,2Agroupelementsbelongtothisblock.Thegeneralelectronicconfigurationis ns1 and ns2

1A GROuP ELEmENTS

“One differentiating electron is present in s-sub shell”.Generalelectronicconfigurationns1

Elements areLithium (Li)Sodium (Na)Potassium (K)Rubidium (Rb) Cesium (Cs) Francium (Fr) 1 A Group elements

Elements Electrons Atomic No.

3 4

3 + 8 12

11 + 8 20

19 + 18 38

37 + 18 56

55 + 32 88

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2 A Group elements

Elements Electrons Atomic No.

4 4

4 + 8 12

12 + 8 20

20 + 18 38

38 + 18 56

56 + 32 88

S block elements

2 A GROuP ELEmENTS

“Two differentiating electrons are present in the s - sub shell”.

Seethe1Agroupelementsandtheirelectronicconfiguration.Theoxides,hydroxidesof1AGrouparestrongalkalies,sothesearecalled“alkali metals”.

Seethe2Agroupelementsandtheirelectronicconfiguration.Theoxidesandhydroxidesarealkalineand found in thesurfaceof theearth.So thesearecalled “alkaline earth metals”.

Generalelectronicconfigurationns2

Elements areBeryllium (Be)magnesium (mg) Calcium (Ca)Strontium (Sr) Barium (Ba) Radium (Ra)

PROPERTIES OF S-BLOCK ELEmENTS

Thesearehighlyelectropositiveandlowelectro-negativeelements.They are highly reactivemetals.Hence, they are not available freely innaturebutareavailableastheircompounds.For example: Sodiumisavailableas“Sodiumchloride”(NaCl).Thechemicalreactingandmetallicnatureincreasesinagroupwithincreaseinatomicmass.

Thesemetalsarehavinglowestionizationenergy.Thesearepowerfulreducingagents.Theyposses+1,+2oxidationstates.Theyexhibitflamecolorationtests.

Example:Lithium-Crimsonred

Sodium-Goldenyellow

Potassium-Lilaccolor

Cesium-SkyBlue.

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P block elements

3 A Group elements

Boron(B)

Alluminium(Al)

Gallium(Ga)

Indium(In)

Thallium(Tl)

BoronFamily

IIIAGroup

4 A Group elements

Carbon(C)

Silicon(Si)

Germanium(Ge)

Tin(Sn)

Lead(Pb)

CarbonFamily

IVAGroup

P-BLOCK ELEmENTS

Thedifferentiating electronenters into p - sub shell.Asthep-sublevelcanaccommodateamaximumof6electrons,thereare6groupsofelements.13thto18th groupelementsbelongtothisblock.Thegeneralelectronicconfigurationns2 np1-6

3A GROuP ELEmENTS (13Th GROuP BORON FAmILY)

Onedifferentiatingelectron ispresent in thep - subshell.

Generalelectronicconfiguration ns2 np1

TheelementsareBoron (B) Alluminium (Al)Gallium (Ga)Indium (In)Thallium (Tl)

Seethe13thgroupelementsandtheirelectronicconfiguration.

4A GROuP ELEmENTS (14Th GROuP CARBON FAmILY)

Twodifferentiatingelectronsarepresentinthep-subshell.Generalelectronicconfigurationns2 np2

TheelementsareCarbon (C)Silicon (Si)Germanium (Ge)Tin (Sn) Lead (Pb)Seethe14thgroupelementsandtheirelectronicconfiguration.

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5A GROuP ELEmENTS (15Th GROuP NITROGEN FAmILY)

Threedifferentiatingelectronsarepresentinthep-subshell.Generalelectronicconfigurationns2 np3.TheelementsareNitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb) Bismuth (Bi)Seethe15thgroupelementsandtheirelectronicconfiguration.

5 A Group elements

NitrogenFamily

Nitrogen(N)

Phosphorus(P)

Arsenic(As)

Antimony(Sb)

Bismuth(Bi)

VAGroup

FourdifferentiatingelectronsarepresentintheP-subshell.Generalelectronicconfigurationns2 np4

TheelementsareOxygen (O)Sulphur (S)Selenium (Se) Tellurium (Te) Polonium (Po)Seethe16thgroupelementsandtheirelectronicconfiguration.

6A GROuP ELEmENTS (16Th GROuP OXYGEN FAmILY)

OxygenFamily

Oxygen(O)

Sulphur(S)

Selenium(Se)

Tellurium(Te)

Polonium(Po)

VIAGroup

6 A Group elements

7A GROuP ELEmENTS (17Th GROuP hALOGEN FAmILY)

FivedifferentiatingelectronsarepresentintheP-subshell.GeneralelectronicConfigurationns2 np5

TheelementsareFluorine (F) Chlorine (Cl)Bromine (Br)Iodine (I) Astatine (At)Seethe17thgroupelementsandtheirelectronicconfiguration.

VIIAGroup

HalogenFamily

Fluorine(F)

Chlorine(Cl)

Bromine(Br)

Iodine(I)

Astatine(At)

7 A Group elements

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VIIIAGroup

NobelGases

Helium(He)

Neon(Ne)

Argon(Ar)

Krypton(Kr)

Xenon(Xe)

Radon(Rn)

8 A Group elements

8A GROuP ELEmENTS (ZERO GROuP NOBEL GASES)

Theseelementshavingoctetofelectronsinvalenceshell.Generalelectronicconfigurationns2 np6

Thesearechemicallyinactiveastheirvalenceshellarecompletelyfilledwithns2 np6configuration.Thesearehelium (he)Neon (Ne)Argon (Ar)Krypton (Kr) Xenon (Xe)Radon (Rn)Seethenoblegaselementsandtheirelectronicconfiguration.

PROPERTIES OF P-BLOCK ELEmENTS

Theseelementsaremetals,non-metals,andmetalloids.•Theyshowvariableoxidationstates.•Theydonotimpartanycolortotheflame.•Theseelementsareplacedattherightsideoftheperiodictable.•Both s-block and p-block elements are referred as “representative elements” or “main group•elements”.

D-BLOCK ELEmENTS

Theseareelementsofgroup3 to12 in theperiodic table.Theelements inwhich thedifferentiatingelectronentersthepenultimateor(n-1)shelloftheatomoftheelementi.e.[(n-1)dsubshell]arecalledd-blockelements.Thed-blockelementsarecalled“transition elements” astheyareplacedbetweens-blockandp-blockelements.Thegeneralelectronicconfiguration(n-1)d1 to 10 ns1 to 2

Ithasfourseries:3d series: From Scandium(Z=21)toZinc(Z=30)inthe4thperiod.4d series: From Yttrium(Z=39)toCadmium(Z=48)inthe5thperiod.5d series: From Lanthanum(Z=57)andhafnium(Z=72)toMercury(Z=80). Theyformthe6thperiodoftheperiodictable.6d Series:In-completeseries.ItstartsfromActinium(Z=89). Theseelementsappearintheseventhperiodoftheperiodictable.

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D-block Elements

F-block Elements

PROPERTIES OF D-BLOCK ELEmENTS

Theyareallmetals.•Theyformalloys.•Theyaregoodconductorsofheat&electricity.•Theseelementsformcomplexcompounds.•TheyexhibitvariablevalenceandshowPara-magneticnatureintheiroxidationstates.•

F-BLOCK ELEmENTS

The two rows of elements present at the bottom of the periodic table are f - block elements. Thedifferentiatingelectronenterstof-orbitalofantipenultimate(n-2)shellofatom.Thesearecalled“innertransitionelements”.Thegeneralelectronicconfiguration(n-2) f1-14 (n-1) d0-1 ns1-2, where n = 6 or 7.Ithas2seriesandeachserieshas14 elements.4f - series or Lanthanides: Fromcerium(Z=58)toLutetium(Z=71).TheelementsofthisseriesarecalledLanthanidesorrareearths.5f series or Actinides: FromThorium(Z=90)toLawrencium(Z=103)Theelementsofthisseriesarecalledactinides.

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Periodic trends in properties of elements

ELECTRON AFFINITY

“The amount of energy released when an electron is added to a neutral isolated gaseous atom in its ground state”.

Equation:Atom(gaseousstate)+electron(e-)→Anion(gaseousstate)+Energy(E)

X (g) + e- → x- (g) + Energy (E) ( Where X = Atom , x- = Anion , E = Energy )

units:Electronvolts/(per)atom(or)KiloJoules/mole(or)Kilocalories/mole.Electronaffinitydependsonsizeandeffectivenuclearcharge.Note:Itcannotbemeasureddirectly.ItcanbemeasuredindirectlyusingBorn-HaberCycle.

SECOND ELECTRON AFFINITY

“The energy absorbed when an electron is added to uni-negative gaseous ion”.Equation:

x- (g) + e- → x2-(g) + Energy (Endothermic reaction)

(Endothermic reaction)

Reason for absorption of energy:

Repulsionbetweennegativelychargedionandelectronrequiressomeenergytoabsorbwhichcausestheendothermicreaction.Example:Firstelectronaffinityofoxygenis33.9Kilocaloriespermole-Hereenergyisreleased.

O (g) + e- → O- (g) + 33.9 Kcal

O -(g) + e- → O2- (g) + 119 Kcal

(Exothermic reaction)

Secondelectronaffinityofoxygenis119Kcal/moleenergyisabsorbed.

Factors influencing electron affinity: Sizeofatom

NuclearCharge

ElectronicConfiguration

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VARIATION OF ELECTRON AFFINITY

Groups: Onmoving down the group, electron affinity decreases as the atomic size increases. Inrepresentativeelementsthefirstelementofeverygrouphaslowerelectronaffinitythansecondelement.Theorderisasfollows: Fluorine < Chlorine, Oxygen < Sulphor, Nitrogen < Phosphorous etc.

F(g) + e- → F- + Energy

Element At.No Electron Affinity

9F 3.62

17Cl 3.78

35Br 3.54

53I 3.08

Reason:The repulsionbetweenaddedelectronandelectronsalreadypresentismore.Note: Why fluorine is powerful reducing agent thanchlorine?Because fluorine has less electron affinity and highbonddissociationenergy.

Periods: On moving from left to right in a period,electronaffinity increasesduetodecrease inatomicsize and increase in nuclear charge. Beryllium,Nitrogen, Neon elements has low electron affinityvalues.Astheyhavestableelectronicconfiguration.

Element

Electron Affinitykj/mole

Li Be B C N O F

57 -66 15 121 -31 142 333

Zerogroupelementshavenoelectronaffinity.Becausezerogroupelementshascompletedvalenceshellandsodoesnotacceptelectrons.Henceelectronaffinityvalueistakenaszero.Hencecalledzerogroupelements.

ELECTRO NEGATIVITY

ThisconceptwasproposedbyPaulingin1932.“The tendency of an atom of an element to attract the shared electron pairs of more towards itself in diatomic molecule or in a polar covalent bond”.Electronegativitydependson:1.Thechargeofnucleus2.Thedistanceoftheouterelectronsfromthenucleus.3.Shieldingeffectand4.Natureofbondedatomsasitisapropertyofbondedatoms.

Scales to measure electro-negativity: Therearetwoscalestomeasuretheelectro-negativity.1.MullikenScale.2.Pauling’sScale.

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muLLIKEN SCALE

ItwasproposedbyR.S.Mullikenin1934.Thismethodisapplicableonlyformonovalentatom.Accordingto thisscale,electro-negativity (E.N)ofanelement is theaverageof ionizationenergyandelectronaffinity.

E.N = (I1 + E1 ) / 2. Where I1 = Ionization Energy, E1 = Electron Affinity

Electronegativevaluesmeasuredonthisscaleare2.8timesmorethanvaluesmeasuredonPaulingscale.Limitation: Thedifficultyinthemeasurementofelectronaffinityvalues.WhenionizationenergyandelectronaffinityvaluesareinKiloJoulespermole,thenuseE.N = (I.P + E.A) divided by 544

PAuLING’S SCALE

ItwasproposedbyPaulingin1931.Itisbasedonbondenergyvalues.Expression:LetA-Bmolecule.ThebondenergyofmoleculeA-Btheoretically, E A-B=halfinto(EA-A+EB-B)ThebondenergyofA-BmoleculeexperimentallyE1

A-B.Thisbondenergyexceedstheoreticalvalue.Thedifferenceinbondenergiesisgivenby∆(delta)

∆=E1A-B - EA-B

Where ∆ → Ionic - Covalent Resonance Energy → It depends upon the electro chemical nature of atoms A and B. → It is measured in Kilo Joules per mole.Now, XA → Electro-negativity of atom A XB → Electro-negativity of atom BPaulingRelationis

XA - XB = 0.208 √∆

Note: Hecalculatedelectro-negativitiesofelementswithreferencetofluorine.OnPaulingscalefluorinehashigherelectronegativevalueof4.0.

uses of Electro-negativity:Intheidentificationofnatureofbondi.e.Ifelectro-negativedifferenceis1.7orgreaterthan1.7,then1.thebondisionic.Ifitislessthan1.7,thenthenatureofbondiscovalent.Metallicornon-metallicnatureoftheelementscanbeidentified.2.Toassigntheoxidationstate.(i.e.-veor+ve)3.Towrite the formulaof thecompound i.e.moreelectro-negativeshouldbewrittenonrighthand4.side.

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