Atomic Structure and The Periodic Table · PDF fileThe Structure of an Atom •Atoms are...
Transcript of 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.