atomic structure and the periodic table · pdf filethe structure of an atom •atoms are...

AtomicStructureandThePeriodicTable

Unit3

Lesson1:AtomsUnit5:AtomicStructure&ThePeriodicTable

Atoms

• Howsmallcanthingsget?Ifyoubreakastonewallintosmallerandsmallerpieces,youwouldhaveapileofsmallerstones.Ifyoucouldbreakthesmallerstonesintothesmallestpiecespossible,youwouldhaveapileofatoms.• Anatom isthesmallestunitofmatter.• GreekphilosophersproposedthefirstatomictheoryofmatterinthefifthcenturyBC.Thisideathatatomsarethebasicbuildingblockshasbeenconfirmedbymodern-erascientists.• Atomsaresosmall– asingleteaspoonofwatercontainsapprox.500,000,000,000,000,000,000,000atoms!

History

• About2400yearsago,GreekphilosophersproposedthateverythingonEarthwasmadeofonly4things:air,water,fire,andearth.Everythingelsewasamixtureofthesefourbasicsubstances.• Astimewenton,chemistscametorealizethattherehadtobemorethanfourbasicsubstances.• Todaychemistsknowthatabout100 basicsubstances– orelements–accountforeverythingweseeortouch.• Sometimestheseelementsappearbythemselves.However,mostoften,theyappearincombinationwithotherelementsandcompounds.

Elements

•Anelement isasubstancethatcontainsonlyasingletypeofanatom.•Thenumberofatomsisnotimportant,aslongasalltheatomsareofthesametype.•Youcannot separateanelementintoothersubstances.•Examples:silver,oxygen,hydrogen,helium,aluminum,gold•Therearemorethan100elements.

ChemicalSymbols

•Eachelementhasitsownuniquesymbol,referredtoasitschemicalsymbol.•Forsome,it’sthefirstletterofitsname.• Examples:hydrogen(H),carbon(C)

•Forothers,it’sthefirstletterplusoneotherletteroftheelement’sname.• Examples:aluminum(Al),platinum(Pt)

CompositionofElements

•Eachelementismadeoftinyparticlescalledatoms.•Allatomsofaparticularelementareidentical,butdifferent fromatomsofallotherelements.•Forexample,everyatomofsilverissimilartoeveryotheratomofsilver.Butitisdifferentfromanatomofiron.

ElectricCharges

•Atomscontainsubatomicparticlesthathaveelectriccharges.•Aparticle’schargecanbeeitherpositiveornegative.•Subatomicparticleswiththesamechargerepeleachother.•Subatomicparticleswithdifferentchargesattracteachother.

TheStructureofanAtom

•Atomsarecomposedofthreetypesofsubatomicparticles.• Aproton isapositivelychargedparticle• Aneutron isaneutralparticle.Neutral meansthatisneithernegativelyorpositivelycharged;thereisnocharge.• Anelectron isanegativelychargedparticle.

• Theprotonsandneutronsmakeupthenucleus oftheatom.Thenucleus isthecentralregionofanatom,wheremostoftheatom’smassisfoundinprotonsandneutrons.• Theelectronsmovearoundtheoutside oftheatom.

TheSizeofanAtom

•Itwouldtakeyouabout500yearstocountthenumberofatomsinonegrainofsalt.•Electronsaremuchlessmassivethanprotonsorneutrons.Therefore,mostoftheatom’smassisinthenucleus.•Thenegativeelectronsstickaroundthenucleusbecausetheyareattracted tothepositivelychargedprotons.

AtomicNumbers

•Theidentityofanatomisdeterminedbythenumberofprotonsinitsnucleus,calledtheatomicnumber.•Example:Everyhydrogenatomhasexactly1 protoninitsnucleus.Therefore,itsatomicnumberis1.•Example:Everygoldatomhasexactly79 protonsinitsnucleus.Therefore,itsatomicnumberis79.

AtomicMassNumbers

•Remember,mostoftheatom’smassisinthenucleus.•Thetotalnumberofprotonsandneutronsinanatom’snucleusiscalleditsatomicmassnumber.•AtomicMassNumber=Protons +Neutrons

AtomicMassNumber

FindingtheNumberofNeutrons

Inordertofindthenumberofneutrons:1. Roundtheatomicmassnumbertothenearestwholenumber.2. Subtracttheatomicnumberfromtheatomicmassnumber.

Checkpoint:Atoms

1.Drawamodelofanatom.Labelthepartsoftheatom.

Lesson2:Elements,Compounds,andMixtures

Unit5:AtomicStructure&ThePeriodicTable

AtomicMassNumbers

•Theatomsofacertainelementalwayshavethesame numberofprotons.•However,theydonot alwayshavethesamenumberofneutrons.•Therefore,NOT allatomsofthesameelementhavethesameatomicmassnumber.

Isotopes

•Forexample,allchlorineatomshave17protons.•However,somechlorineatomshave18neutrons,whileotherchlorineatomshave20neutrons.•Thechlorineatomsthathave18or20neutronsarecalledchlorineisotopes.Anisotope isanatomofthesameelementthathasadifferentnumberofneutrons.

Isotopes

•Anisotopeisidentifiedbythenameoftheelement anditsatomicmassnumber.•Youcanfindthenumberofneutronsinanisotopebysubtractingtheatomicnumberfromtheatomicmassnumber.•Example:Chlorine-35indicatestheisotopeofchlorinethathas18neutrons(35– 17).

ValenceElectrons•Avalenceelectronisanelectroninanatomthatcanformachemicalbondwithanotheratom.•Avalenceelectronistypicallyfoundintheoutermost electronshell.•Valenceelectronscanonlybefoundinatomsthatdonothaveafulloutermostelectronshell.

SharingElectrons

Na=11protons

Cl =17protons

Ions• Aneutralatomhasanequal numberofelectronsandprotons.• Anion isanatomthathaslostorgainedoneormoreelectrons• Apositive ionhaslost anelectron.Itisrepresentedbythesymbolfortheelement,witharaisedplussign(+)toindicateapositivecharge.• Examples:Na+,Ca2+

• Anegative ionhasgained anelectron.Itisrepresentedbythesymbolfortheelement,witharaised negativesign(-)toindicateanegativecharge.• Examples:Cl-,O2-

PureSubstances

•Mattercanbepure,oritcanbetwoormoresubstancesmixedtogether.• Often,thedifferencebetweenpureandmixedsubstancesisapparentonlyontheatomic ormolecularlevel.• Apuresubstancehasonlyonetypeofcomponent.• Example:Purewatercontainsonlywatermolecules;puresilvercontainsonlysilveratoms.• Asubstanceisconsideredpureifitcontainsonlyasingletypeofatom,suchasgold,orasinglecombinationofatomsthatarebondedtogether,suchasawatermolecule.

• Anelement isatypeofapuresubstance.

Molecules

•Whentwoormoreatomsbondtogether,orcombine,theymakeaparticlecalledamolecule.• Amoleculecanbemadeofatomsthataredifferent oratomsthatarealike.• Example:A moleculeofwaterisacombinationofdifferentatoms–twohydrogenatomsandoneoxygenatom.H2O• Example:Hydrogengasmoleculesaremadeofthesameatoms– twohydrogenatomsbondedtogether.H2

• Amoleculeisthesmallestamountofasubstancemadeofcombinedatomsthatisconsideredtobeasubstance.

Compounds

• Acompound isasubstancethatconsistsoftwoormoredifferenttypesofatomsbondedtogether.• Sometypesofcompoundsaremadeofmolecules,suchaswater(H2O)andcarbondioxide(CO2).Othercompoundsaremadeofatoms thatarebondedtogetherinadifferentway,liketablesalt(NaCl).• Acompoundcanhaveverydifferentpropertiesfromtheindividualelementsthatmakeupthatcompound.Forexample,tablesaltisacombinationofsodiumandchlorine.Althoughtablesaltissafetoeat,theindividualelementscanbepoisonous.

CombiningAtoms

• Asubscript isanumberwrittenslightlybelowandtotherightofachemicalsymbolthatshowshowmanyatomsofanelementareinacompound.• Achemicalformulaisanexpressionthatshowsthenumberandtypesofatomsjoinedinacompound.

Mixtures

•Amixture isacombinationofdifferentsubstancesthatremainthesameindividualsubstancesandcanbeseparatedbyphysicalmeans.•Examples:Fruitsalad,trailmix

Compoundsvs.Mixtures

• Thesubstancesinmixturesremainthesame substances(physicalchange).Compoundsarenew substancesformedbyatomsthatbondtogether(chemicalchange).•Mixturescanbeseparatedbyphysical means.Compoundscanbeseparatedonlybybreakingthebondsbetweenatoms (chemicalchange).• Theproportionsofdifferentsubstancesinamixturecanvarythroughoutthemixtureorfrommixturetomixture.Theproportionsofdifferentsubstancesinacompoundarefixedbecausethetypeandnumberofatomsthatmakeupabasicunitofthecompoundarealwaysthesame.

Checkpoint:Atoms

1.Whatisthedifferencebetweenanelement,acompound,andamixture?

Lesson3:ThePeriodicTableUnit5:AtomicStructure&ThePeriodicTable

OrganizingElements

• Whatcharacteristicswouldyouusetoorganizeapileofallsortsofbuttons?• Onewayoforganizingelementsisbythemasses oftheiratoms.• Findingthemassofasingleatomisincrediblydifficult.Instead,chemistshadtofindthemassofaverylargenumberofatomsofacertainelement.Thentheycouldinferthemassofasingleoneofthem.

• Rememberthatnotalltheatomsofanelementhavethesameatomicmassnumber.Elementshaveisotopes.• Whenchemiststrytomeasurethemassofanatom,therefore,theyareactuallyfindingtheaveragemassofallitsisotopes.

• Theatomicmassistheaveragemassofalltheelement’sisotopes.

AtomicMassNumbers

•Remember,mostoftheatom’smassisinthenucleus.•Theaveragemassoftheatomsiscalleditsatomicmass.•Thetotalnumberofprotonsandneutronsinanatom’snucleusiscalleditsatomicmassnumber. Atomic

MassNumber

AtomicMass

Mendeleev’sPeriodicTable

• Intheearly1800sseveralscientistsproposedsystemstoorganizetheelementsbasedontheirproperties.Noneworkedverywell.• Finally,aRussianchemistnamedDmitriMendeleev cameupwithasysteminthe1860s.• Mendeleevmadeasetofelementscards;eachcardcontainedtheatomicmassofanatomoftheelementandinformationabouttheelement’sproperties.Hethensearchedforarelationshipbetweenthepropertiesandtheatomicmass.• Mendeleevproducedthefirstperiodictableoftheelementsin1869.• Periodic=repeatingpatternofpropertiesofelements

Rows:SimilarchemicalpropertiesColumns:Increasingatomicmasses

PredictingNewElements

•Mendeleevleftsomeemptyspaceswherenoknownelementsfitthepattern.Hepredictedthatnewelementswouldbediscovered.Heevendescribedsomeofthepropertiesoftheseunknownelements.• Atfirst,manychemistsfoundithardtoacceptMendeleev’spredictionofunknownelements.However,only6yearsafterhepublishedthetable,thefirstoftheseelementswasdiscovered.• Inthenext20years,twootherelementsMendeleevpredictedwerediscovered.

ModernPeriodicTable

•ThemodernperiodictablediffersfromMendeleev’sinseveralways:•Elementswithsimilarpropertiesarefoundincolumns (notrows).•Theelementsarearrangedbytheiratomicnumber,notbyatomicmasses.•Wecannowdefinetheperiodictableasatableoftheelements,arrangedbyatomicnumber,thatshowsthepatternsintheirproperties.

ReadingthePeriodicTable

• Eachsquareoftheperiodictablegivesparticularinformationabouttheatomsofanelement.

PeriodicTable

Groups

•Elementsinaverticalcolumnoftheperiodictablearesimilarinchemicalandphysicalproperties,knownasagroup.•Eachgroupisidentifiedbyanumber atthetopofthecolumn.Sometimesagroupiscalledafamily ofelements,becausetheseelementsarerelated.

HalogenFamily

• Group17iscommonlycalledthehalogengroup/family.• Theytendtocombineeasily withmanyotherelementsandcompounds,especiallywiththoseinGroup1andGroup2.• Theyhavesimilarchemical properties,soanelementthatcombineswithonehalogenwilllikelycombinewithanother.

NobleGases

• Group18iscommonlyreferredtoastheNobleGases.• Theyarecalled“inert”becausetheyareinactive.• Alloftheirenergyshellsarefull,sotheyarestable.

Periods

•Eachhorizontalrowintheperiodictableiscalledaperiod.•Propertiesofelementschangeinpredictablewaysfromoneendofaperiodtotheother.

ElectronArrangement

•Thechemicalpropertiesofanelementdependonthewaytheelectronsarearrangedaboutthenucleus.•Remember,wedon’tknowexactlywheretheelectronsare.Weonlyknowtheregion(theenergyshell,orelectronshell)iswheretheelectronsmove.

ElectronArrangement

•Theperiodsontheperiodictableend whenanenergyshellgetsfull ofelectrons.• Elementslocatedontheleft(lithium,sodium)haveoneelectronaddedtoanew energyshell.• Elementslocatedontheright(chlorine,iodine)areneartheendofaperiod.Therefore,theyhaveenergyshellsthatarealmostfull.

•Elementsinthesamegrouphavesimilar electronarrangement.

Checkpoint:PeriodicTable

1.Whatisthedifferencebetweenthegroupsandperiodsonaperiodictableofelements?Group:Elementsinaverticalcolumnoftheperiodictablearesimilarinchemicalandphysicalproperties.Period:Propertiesofelementschangeinpredictablewaysasyoumovethroughthehorizontalrow.

Lesson4:ClassificationUnit5:AtomicStructure&ThePeriodicTable

DistinctRegionsofthePeriodicTable

•Theperiodictableisakindofmapoftheelements.Ithas3distinctregions:•Metals=left•Nonmetals(excepthydrogen)=right•Metalloids=inbetween

Metals

•Ametal isanelementthatconductselectriccurrentandheatwellandhasashinyappearance.•Mostoftheelementsaremetals.•Propertiesofmetals:• Aresolidsatroomtemperature(exceptMercury)• Canbeshapedeasily• Shiny• Goodconductor

ReactiveMetals

•Anelement’spositiononthetablealsoindicateshowreactive itis.•Reactivemeanshowlikelyanelementistoundergoachemicalchange.• ElementsinGroups1and17arethemost reactive.• ElementsinGroup18arealmostcompletelyunreactive.

ReactiveMetals

•ThemetalsinGroup1arethealkalimetals.•Thesemetalsareveryreactive.•Whenexposedtoair,theseelementsreactrapidlywithoxygenandwatervapor.

•ThemetalsinGroup2arethealkalineearthmetals.•Thesemetalsareless reactivethanthealkalimetals,butmore reactivethanmostothermetals.

TransitionMetals

•ThemetalsinGroups3-12arecalledthetransitionmetals.• Thesemetalsaresomeoftheearliest knownelements,suchascopper,gold,silver,andiron.• Theyaregenerallyless reactivethanmostothermetals.• Forthousandsofyearsthesemetalshavebeenusedtomakejewelry andcoins.• Some,likesteel,iron,andcopper,arealsoimportantforindustry.• Theyremainrelativelyunchanged sincethetimetheyweremade.

RareEarthMetals

•Tworowsofelementsaresetbelowtheperiodictabletosavespace.Thetop rowistherareearthmetals.•ScientistsoncethoughttheywereavailableonlyintinyamountsinEarth’scrust.•Throughminingwehavelearnedthatarenotsorare,buthardtoisolateinpureform.

Nonmetals

•Anonmetal isanelementthatisnotametalandhaspropertiesgenerallyoppositetothoseofametal.•Propertiesofnonmetals:•Manyareagasatroomtemperature(Bromineisaliquid)• Dullsurfaces• Noteasilyshaped• Generallypoorconductors

Metalloids

•Ametalloidhaspropertiesofbothmetalsandnonmetals.•Theylieoneithersideofthezigzaglineseparatingmetalsfromnonmetals.•Themostcommonmetalloidissilicon,thesecondmostcommonelementinEarth’scrust.•Metalloidsareusedinsemiconductors foundinelectronics.Theyconductanelectriccurrentundersomeconditions,butnotunderothers.

ExpansionofthePeriodicTable

• Before1940,noonehadfoundanelementwhoseatomshadmorethan92protonsinitsnucleus.• Thatyear,scientistsEdwinMcMillanandPhilipAbelsonthoughttheymaybeabletomakeoneusingacyclotron.Acyclotroncanhurlprotonsandneutronstowardsthenucleiofotheratoms.Ifsomeoftheseparticlessticktoanucleus,thereisachanceadifferentelementcanform.Theyweresuccessfulinassemblinganelementwith93protons.• ThenextyearscientistGlennSeaborgassembledanelementswith94protons.Healsowentontopredictpropertiesofelementswithhighernumbersofprotons.

TrendsofthePeriodicTable

•Remember,agroupisonecolumnoftheperiodictable.Atomsoftheelementsinagrouphavethesamenumberofelectronsintheirouterenergyshells.•Thisgivestheelementssimilarchemicalproperties.• Italsogivestrendstotheperiodictable.

TrendsofthePeriodicTable:AtomicSize

• Wemeasurethesizeofanatombythesizeofitselectroncloud.• Thesizeoftheclouddependsonhowmanyelectronsitcontainsandhowstronglytheprotonsinthenucleuspullontheelectrons.• Ifthenucleusexertsastrongpullontheelectrons,theatomissmaller.• Ifthenucleuspullsonlyweaklyontheelectrons,theatomislarger.

Theelectroncloudsaroundthenucleusgrowsasmoreenergyshellsarefilled.

Eventhoughtherearemoreelectrons,thenucleuspullsmorestronglyontheseelectrons,sotheatomsaresmaller.

• Metalsusuallyloseelectronstoformpositiveions.• ThemetalsinGroup1loseoneelectroneasily.• Asyoumovefromlefttorightacrosstheperiodictable,moreenergyisrequiredtoremoveanelectron.• However,thefurtherdownacolumnyougo,thelessenergyisrequiredtoremoveanelectron.

TrendsofthePeriodicTable:Ions

• Nonmetalsusuallygainelectronstoformnegativeions.• ThenonmetalsinGroup17gainoneelectroneasily.• Atomsfarthertotherightoftheperiodictablegainelectronsmoreeasily.• Remember,NobleGasesnormallydonotformionsbecausetheirelectronshellsarefull.

TrendsofthePeriodicTable:Ions

• Density:Witheachperiod,theelementsareattherightandleftedges oftherowareleast dense.Theelementsinthemiddle oftherowarethemostdense.• Hardness:Denseelementstendtobehard.Hardnessmeansamaterialcan’tbescratchedordentedeasily.• Conductivity:Elementsontheright sideofthetable(nonmetals)tendtobepoorconductors.Elementsinthemiddleandleftsideofthetable(metals)tendtobegoodconductors.• Melting/BoilingPoints:Elementsontheright sideofthetable(nonmetals)tendtohavelowermeltingandboilingpoints.Elementsinthemiddleandleftside ofthetable(metals)tendtohavehighermeltingandboilingpoints.

TrendsofthePeriodicTable:PhysicalProperties

Checkpoint:Classification

1.Identifyandexplainatrendfoundontheperiodictable.