AtomicTheory&ThePeriodicTable

AtomicTheory

TheBeginningofAtomicTheory

•  440BC–Greekphilosopher,DemocritusthoughtallmaterialscouldbecutinhalfoverandoverunAltheyreachedthesizeofoneatom

•  Atom=Greekfor“notabletobedivided”

•  Democritus’Theory:allatomsaresmall,hardparAclesmadeofonematerialformedintodifferentshapesandsizes

Dalton’sAtomicTheory

•  JohnDalton–BriAshchemistandschoolteacher(late1700’s–early1800’s)

•  Wantedtoknowwhyelementsalwayscombineincertainways–  (HandOalwayscombinein

sameproporAonstomake water)

•  Hisexperimentsshowithappens becauseelementsaremadeof singleatoms

•  1803–Dalton’sTheory:– Allsubstancesaremadeofatoms.AtomsaresmallparAclesthatcan’tbecreated/destroyed.

– Atomsofthesameelementareexactlyalike,andatomsofdifferentelementsaredifferent

– Atomsjoinwithotheratomstomakenewsubstances

Dalton’sTheory:BilliardBallAtomicModel

NotQuiteRight

•  Dalton’stheoryhadsomegoodparts,butasmorediscoveriesweremade,somepartsdidn’tfit

•  SothesearchconAnues….

J.J.Thomson’sAddiAons

•  J.J.Thomson–BriAshscienAstinthe1800’s•  ShowedthatDalton’stheoryhadaflaw–atomshaveparts!

•  ExperimentedwithacathoderayandshowedthatraysbendundertheinfluenceofamagneAcfield,showinganegaAvecharge

•  NegaAveparAcleswerelaternamedelectrons

Thomson’sNewModel

•  HethoughttheatomhadanoverallposiAvechargewithsomeelectrons,negaAvecharge,floaAngaround.

•  ThisiscalledthePlumPuddingmodeloftheatom.(itlookedlikeacommondessert…youmightcallitchocolatechipicecreammodel)

Dalton J.J.Thomson

EarnestRutherford

•  FormerstudentofJ.J.Thomson

•  1909‐TestedThomson’stheorybystudyingthepartsofanatominthe“GoldFoilExperiment”

•  GoldFoilExperiment:•  PosiAveparAclesareshotat

anelement(gold)•  IfThompson’smodelwas

right,allparAcleswouldbeevenlydeflectedsincetherewere+/‐chargesspreadthroughouttopush/pulltheposiAveparAcles

Rutherford’sConclusions&NewModel‐1911

1.  SincemostoftheparAclespassedthroughthefoilundeflected,thereforemostoftheatomisempty.

2.  SmallanglesofdeflecAonshowthatposiAvelychargedparAcleswereajractedbyelectrons.(nega7vea9ractsposi7ve)

3.  LargeanglesofdeflecAonshowthatthereisamassiveposiAvelychargedbodypresentin theatomcalledanucleus (posi7vestronglyrepulsesposi7ve)

Bohr’sElectronLevels

•  NielsBohr–DanishscienAst;workedwithRutherford– Studiedthewayatomsreacttolight– Thoughtelectronsmovearoundthenucleusinspecificpaths(energylevels)

– Helpedpredictatomicbehavior,butwassAllflawed

NewEvidenceforElectrons

ErwinSchrodinger(Austrianphysicist)&WernerHeisenberg(Germanphysicist)‐explainedhowelectronsreallybehave– Electronsdon’thaveadefinitepath,butregionswheretheyarelikelytobe(electronclouds)

StructureofanAtom

Atomshave3parts:1.  Protons–posiAvelychargedparAcleinnucleus2.  Neutrons–neutralparAcleinnucleus3.  Electrons–negaAvelychargedparAclesorbiAng

outsidethenucleus

**Electronsarefoundinmanyorbitsaroundthenucleus,calledorbitals

CurrentAtomicTheory

1.Elementsaremadeofsmallatoms.

2.AllatomsofagivenelementhavethesamechemicalproperAesandcontainthesamenumberofprotons.

3.Compoundsaremadebycombiningtwoormoredifferentatoms.

4.Atomsaretheunitsofchemicalchange.

ThePeriodicTableofElements:TrendsExplainedbyAtomicTheory

BuildingthePeriodicTable

•  1869–DmitriMendeleevarrangedthe63knownelementsintotheperiodictable

•  Elementsareinascendingorder(smalltobig)byatomicweightandgroupedbysimilarproperAes

•  Hepredictedtheexistenceofelementsthathadyettobediscoveredandcorrectedacceptedatomicweightsthatwerewrong

ElementsasBuildingBlocks•  PeriodicTableisorganizedlikeabiggrid•  Elementsareplacedinspecificplacesbecauseofhowtheylookandact.

•  Therearerows(leotoright)andcolumns(upanddown)

•  Rowsandcolumnsmeandifferentthings

Periods(Rows)•  Alloftherowsgole?toright(evenifthere’sbiggapsintherow)

•  Eachrowisadifferentperiod.

•  Elementsinthesameperiodhavethesamenumberoforbitals.

1stand2ndPeriod•  Period1:Hydrogen&Helium

•  1orbital

•  Period2:Lithium,Beryllium,Boron,Carbon,Nitrogen,Oxygen,Fluorine,Neon•  2orbitals

•  elementsinaperiodhavethesamenumberofatomicorbitals

•  Therownumber(1‐7)tellsyouhowmanyorbitalstheyhave

PeriodicGroups(Columns)•  Whenacolumngoesfromtop

tobojom,it’scalledaGROUP

•  Groupshaveacommonproperty:numberofouter(valence)electrons

•  ValenceElectron:thenumberofelectronsintheoutermostorbital–  Group1(redstripe)has1valence

electron

–  Group3(yellowstripe)has3valenceelectrons

–  Group8(purplestripe)has8valenceelectrons

**TransiAonelements(clearblocks)areanexcepAon

SpecialGroupNames:Families•  Severalgroupshavespecialnamesandarecalledfamilies–  Group1:AlkaliMetals–  Group2:Alkaline‐EarthMetals–  Group7:HalogenGases–  Group8:NobleGases–  Groups1B‐8B(middle):TransiAonMetals

•  FamiliesaregroupedbytheirchemicalproperAes‐ReacAvity ‐ValenceElectrons ‐RadioacAvity

RuleBreakers:Hydrogen&Helium

•  HydrogenandHeliumarespecialelements

•  Hydrogencanhavethetalentsandelectronsoftwogroups:1and7–  It’sseenashavingoneextraelectron(likegroup1)ormissingone(likegroup7)

•  Heliumisdifferentfromallotherelements.Itonlyhastwovalenceelectrons,butisgroupedwithnoblegases

RuleBreakers:TransiAonMetals•  TransiAonMetals– Theyliveinthecenteroftheperiodictable– Theyhavespecialelectronrules,whichallowsthemtobindwithmoreelements

Metals•  Almost75%ofelementsaremetals•  Notallofthemareshinylikegoldandsilver!•  WhatarecharacterisAcsofmetals?

–  Goodconductorsofelectricity(Ag,Cu)–  ReacOve(formcompoundseasily)(Na,K)–  Solidatroomtemperature–  Formalloys(combine2+metals)(steel,bronze)

Nonmetals•  Foundjustabovethe“staircase”inGroups4through8.

•  Notgoodconductorsofelectricityorheat.

•  Foundonlyasagasorsolidatroomtemperature.

•  Examples:– Hydrogen,Nitrogen,Oxygen,Sulfur,etc.

Metalloids•  Foundalongthe“staircase”onthePeriodicTable.

•  ShareproperAesofbothmetalsandnonmetals.

Family:AlkaliMetals•  NoAcethatHydrogenisNOTpartofthisfamily.It’singroup1,butit’sNOTanalkalimetal

•  FamilyMembers:•  Lithium(Li),Sodium(Na),Potassium(K),Rubidium(Rb),Cesium(Cs)andFrancium(Fr).

• TheseareVERYreacOvebecausetheyhaveoneelectronintheiroutershell.

• That’soneawayfromhavingafullshell.Whenyouarethatclosetohavingafullshell,youwanttobondwithotherelementsandlosethatelectron.• Increaseddesiretobond=greaterreacOvity

Family:AlkalineEarthMetals

•  SecondmostreacOvegrouponthetable(alkalimetalsarefirst)

•  Theyhavetwoelectronsintheiroutershellthattheywanttogiveuptohaveafullshell

• Theyliveingroup2• FamilyMembers:

Beryllium(Be),Magnesium(Mg),Calcium(Ca),StronAum(Sr),Barium(Ba),andRadium(Ra).

Family:Halogens•  Theyliveinthesecondcolumn fromtheright

•  Halo=salt,gen=maker•  Familymembers:

Fluorine(F),Chlorine(Cl),Bromine(Br),Iodine(I),andAstaAne(At).

•  Commonality:theyarealloneelectronshyofafullshell.–  Theyaresoclosetobeinghappywithfullshells,thattheyhaveatendencytobondwithmanydifferentelementstoformcompounds(typicallysalts)

–  ThatmeansthattheyarereacOve

Family:Noble(Inert)Gases

•  Locatedonthefarrightcolumn•  FamilyMembers:

–  Helium(He),Neon(Ne),Argon(Ar),Krypton(Kr),Xenon(Xe),andRadon(Rn)

•  Theyarethemoststableofall(don’treactwithmuch)becausetheyhavefullshells–  Theydon’twanttogiveuportakeanymoreelectronsthantheyalreadyhave

•  Glowwhengivenelectricity