View
10
Download
0
Category
Preview:
Citation preview
Section11:ElectronConfigurationandPeriodicTrends
ThefollowingmapsthevideosinthissectiontotheTexasEssentialKnowledgeandSkillsfor
ScienceTAC§112.35(c).
11.01TheBohrModeloftheAtom• Chemistry (6)(A)
11.02OrbitalEnergiesandElectronConfigurations• Chemistry (6)(E)
11.03CondensedElectronConfigurationsandExceptions• Chemistry (6)(E)
11.04CategoriesofElectrons• Chemistry (6)(E)
11.05TrendsinAtomicRadii• Chemistry (5)(C)
11.06TrendsinIonizationEnergy• Chemistry (5)(C)
11.07ElectronConfigurationforIons• Chemistry (6)(E)
11.08TrendsinIonicRadii• Chemistry (5)(C)
Note:Unlessstatedotherwise,anysampledataisfictitiousandusedsolely
forthepurposeofinstruction.
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 1
11.01TheBohrModeloftheAtom
In1913,DanishphysicistNielsBohrproposedanewmodelofthehydrogenatom.Hismodel
hasthefollowingcharacteristics:
• Thehydrogenatomhasenergylevels(n)atwhichtheelectroncantravelinacircularorbitaroundthenucleus.Thesmallerthevalueofn,thesmallertheradiusoftheorbit
andthelowertheenergylevel.
• Anelectroninanatomdoesnotradiateenergywhileorbitingthenucleus.
• Theelectronwillmovetoanotherenergylevelonlyifitabsorbsoremitsaphotonthathasthesameenergyasthedifferencebetweenthetwoenergylevels.Inotherwords,ifanelectronisatenergylevel1(n1)andabsorbsaphoton,itcanmovetoenergylevel2
(n2),assumingthephotonaddedthesameamountofenergyasthedifferencebetween
n1andn2(n2–n1).
WhenstudyingtheBohrmodel,itisessentialtoknowafewkeyterms:
• Groundstate–whentheelectronisatthelowestenergyorbitalitcanoccupy(n=1forhydrogen)
• Excitedstate-whentheelectronisatahigherenergyorbitalthanthegroundstate(n=2,3,4,etc.forhydrogen)
• Ionize-theprocessbywhichanelectronisejectedfromanatom(nfinal=∞)
• Emission-atransitioninanatomwhereanelectroninahigherenergylevelreturnsto
alowerenergylevel(forexample,n=5ton=2)
• Absorption-atransitioninanatomwhereanelectroninalowerenergylevelmovesto
ahigherenergylevel(forexample,n=2ton=5)
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 2
Whenlightfromanelectricallyexcitedgaseousatomispassedthroughaslitandrefractedbya
prism,itcreatesalinespectrum.Thisconsistsofaseriesoffinelinesatspecificfrequencies,
separatedbyblackspaces.
Inahydrogenatom,anelectronundergoingemissioncanproducethreeseriesofspectrallines
thatareparticularlynoteworthy:
• Theultravioletspectrumisproducedwheretheelectrontransitionterminatesatn=1.Thewavelengthsofthelinesinthisseriesarebetween90and100nm.
• Thevisiblelightspectrumisproducedwheretheelectrontransitionterminatesatn=2.Thewavelengthsofthelinesinthisseriesarebetween400and750nm.
• Theinfraredseriesisproducedwhentheelectrontransitionterminatesatn=3.Thewavelengthsofthelinesinthisseriesareintherangeof1000sofnanometers.
1. Anelectroninahydrogenatomcanundergoanyofthetransitionsbelow,thuschangingits
energy.Whichtransitionisassociatedwiththeultravioletseries?
A. n=4ton=3B. n=1ton=2C. n=4ton=2D. n=3ton=1
2. Ofthetransitionsinthepreviousproblem,whichwillemittheradiationwiththeshortest
wavelength?
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 3
11.02OrbitalEnergiesandElectronConfigurations
Inamulti-electronatom,theelectronconfigurationisausefultoolfordeterminingthelocation
ofelectronsrelativetoothersastheyorbitthenucleus.Wecanthinkoftheelectron
configurationastheaddressoftheelectronsinanatom.
FourComponentsoftheAddress• Theprincipalenergylevel(n)describestheshellinwhichtheelectronorbitsthe
nucleus,accordingtotheBohrmodeloftheatom.Thevalueofnmustbeapositive
integer(1,2,3,...),andasthevalueincreases,theradiusoftheshellgrowslarger.
• Thedifferentenergylevelswithinaprincipalenergylevelarecalledthesubshellsorsublevels.Thesublevels,whichhavevaryingenergiesandshapes,aredenotedbytheletterss,p,d,andf.Thenumberofsublevelsinanygivenprincipalenergylevelisequal
ton.
• Theatomicorbitalisthethree-dimensionalvolumewithinasublevelwhereelectrons
havethehighestprobabilityofbeingfound.Everyorbitalcancontainamaximumof2
electrons.
o Thereis1sorbital,whichhasasphericalshape.
o Thereare3porbitals,eachhavingadumbbellshape.
o Thereare5dorbitals.Fourofthefivehaveadoubledumbbell(clover)shape.Onedorbitalhasadumbbellwithatorus(donut)shape.
o Thereare7forbitals,whoseshapesaremuchmorecomplexthanthoseofthedorbitals.
• Thespinofanelectronisapropertythatcanbedescribedaseitherclockwiseorcounter-clockwise.ThePauliExclusionPrinciplestatesthattominimizerepulsion,
electronsinthesameorbitalmusthaveopposingspins.
EnergyLevel(n) SublevelsPresent MaximumElectrons
1
2
3
4
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 4
1. Whichofthefollowingstatementsregardingenergylevelsandorbitalsisfalse?
A. Thenumberoforbitalsinthe5dsublevelis5.B. Theshapeofthe3sorbitalisspherical.C. Thereare3sublevelsinthen=3energylevel.D. Themaximumnumberofelectronsinann=3energylevelis9.
ConstructinganElectronConfiguration
Theaufbauprinciplestatesthatthelowestenergyorbitalsinanatomareoccupiedfirst.
Accordingly,whenwewriteanelectronconfiguration,westartfillingorbitalsinthelowest
valueenergylevel(n=1)andbuildupuntilwehaveaccountedforeveryelectronintheatom.
• Aneutralhydrogenatomhasoneelectron.Thelowestenergylevelisn=1anditcontainsonlyanssublevel,sotheelectronconfigurationforhydrogenis
1s1
Notethattheleadingnumberreferstothenvalue,theletter(s)referstothesubleveldesignation,andthesuperscriptdescribesthenumberofelectronsinthat
sublevel.
• Recallthatinthen=2energylevel,therearetwopossiblesublevels,sandp.Oncethessublevelisfilled,electronsbegintooccupythepsublevel.Considertheelectronconfigurationforcarbon:
1s22s22p2
• Writetheelectronconfigurationforneon,followingtheexamplegivenabove.
• Oncethessublevelandthepsublevelarecompletelyfull,wemuststartonthenext
energylevel,n=3,wherewecanmakeuseofs,p,anddorbitals.
• Hund’sRulestatesthateachorbitalinasublevelisassignedoneelectronbeforeanyorbitalisfilledwithasecondelectron.
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 5
2. Givetheelectronconfigurationsforthefollowingelements:
i. Boron
ii. Phosphorus
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 6
11.03CondensedElectronConfigurationsandExceptions
Foranatomwithmanyelectrons,wecanuseashortcuttoexpressitselectronconfiguration
usingthemostimmediatepreviousnoblegas.
• Forexample,theelectronconfigurationofcalciumis1s22s22p63s23p64s2.Usingtheshortcut,wecanexpressthisas[Ar]4s2.
• Writetheelectronconfigurationforchlorineusingtheshortcutdescribedabove.
FillingOrderofElectrons
Thedorbitalsofanenergylevelarefilledafterthesorbitalofthenextenergylevel.Forexample,the4ssublevelisfilledbeforethe3dsublevel.
Thediagrambelowillustratesthegeneralorderforfillingorbitals:
1s ®
2s ® 2p
3s ® 3p
4s ® 3d ® 4p
Writetheelectronconfigurationforvanadium,usingthenoblegasshortcut.
1. Theelectronconfigurationofanatomis1s22s22p63s23p64s23d5,whichreferstothegroundstateof
A. Mn.
B. Fe.C. Ca.
D. Ti.
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 7
ExceptionstotheAufbauPrinciple
Certainmetalswillviolatetheaufbauprinciplebecausetheyhaveincreasedstabilityduetoa
half-filledorfilleddsublevel.Theelectronconfigurationsofchromiumandcopper,two
exceptionstotheaufbauprinciple,areshownbelow:
Cr:1s22s22p63s23p64s13d5or[Ar]4s13d5
Cu:1s22s22p63s23p64s13d10or[Ar]4s13d10
2. Usetheperiodictabletogivethesymboloftheelementforeachofthefollowingelectron
configurations:
i. 1s22s
22p
5
ii. [He]2s22p
63s
1
iii. 1s22s22p63s23p64s13d10
iv. [Ar]4s23d5
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 8
11.04CategoriesofElectrons
Therearethreecategoriesofelectronsinanatom:
• Inner(core)electrons-Theelectronsinthelowerenergylevelsofanatomuptothe
mostimmediatepreviousnoblegas,plusanycompletedtransitionseries
Fe:[Ar]4s23d6®18innerelectrons
• Outerelectrons-Theelectronsinthehighestenergylevel(nvalue)ofanatom
Zn:[Ar]4s23d10®2outerelectrons
• Valenceelectrons-Theelectronsinvolvedincompoundformation
Formaingroupelements(1A–8A),thevalenceelectronsaretheouterelectrons.Forthetransitionmetals,allthe(n–1)delectronsarecountedaspartofthevalenceelectronsunlessthedsublevelisfilled.
Ge:[Ar]4s23d104p2®4valenceelectrons
Fe:[Ar]4s23d6®8valenceelectrons
Valenceelectrons=Totalelectrons-Innerelectrons
1. Selectthefalsestatementbelow.
A. TheVatomhas2outerelectrons.
B. ThePatomhas5valenceelectrons.
C. TheCuatomhas18innerelectrons.
D. TheNaatomhas10innerelectronsand1outerelectron.
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 9
11.05TrendsinAtomicRadii
Atomicradius–Whentwoatomsofthesameelementarejoinedtogether,onehalfofthe
distancebetweenthenucleiofthetwoatomsistheatomicradius.
• Theatomicradiusisthebestwaytopredictthesizeofanatom.
• Therearetwotrendsthathelppredictthesizeofanatom:
o Astheatomicnumberincreasesdownagroup,thechargeonthenucleus
increasesandthenumberofoccupiedenergylevelsincreases.
§ Thereisanincreaseinnuclearchargeandanincreaseinshielding,but
theshieldingeffectisgreaterthantheeffectoftheincreaseinnuclear
charge.
§ Thisresultsinanincreaseinsizedownagroup.
o Acrossaperiod,eachelementhasonemoreprotonandelectronthanthe
precedingelement.
§ Theshieldingeffectisconstantforallelementsinaperiod,whilethe
nuclearchargepullstheelectronsinthehighestoccupiedenergylevel
closertothenucleus.
§ Thisresultsinanincreaseinsize,righttoleft,acrossaperiod.
• Ingeneral,atomicradiiincreasefromtoptobottomwithinagroupandincreasefrom
righttoleftacrossaperiod.
1. Ineachpair,whichelementislarger?
i. Na,Rb
ii. Cl,Na
iii. Se,Br
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 10
11.06TrendsinIonizationEnergy
Ionizationenergy–Theenergyrequiredtoremoveanelectronfromanatom
• Ionizationenergyismeasuredwhentheatomisinitsgaseousstate.
Example:K(g)+energy(ionization)®K+(g)+e
-
• Thefirstionizationenergyistheenergyrequiredtoremovethefirstelectronfroman
atom.
• Ingeneral,thefirstionizationenergytrendistheoppositeoftheatomicradiustrend.
o Firstionizationenergytendstoincreasefrombottomtotopwithinagroupand
increasefromlefttorightacrossaperiod.
o Astheatomicnumberdecreasesfrombottomtotopinagroup,thevalence
electronsareclosertothenucleus,sotheyarehardertoremove.
o Asyougolefttorightacrossaperiod,theincreaseinnuclearchargecausesan
increaseintheattractionbetweenthenucleusandanelectron.
1. Usingonlytheperiodictable,ranktheelementsineachofthefollowingsetsinorderof
decreasingfirstionizationenergy:
i. P,Mg,O
ii. K,Ca,Sr
iii. I,Xe,Rb
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 11
11.07ElectronConfigurationforIons
• Anatomiselectricallyneutralbecauseithasanequalnumberofprotonsandelectrons.
Anionformswhenanatomorgroupofatomslosesorgainselectrons.
o Acation,orapositivelychargedion,isproducedwhenanatomlosesoneor
morevalenceelectrons.
o Ananion,oranegativelychargedion,isproducedwhenanatomgainsoneor
morevalenceelectrons.
• Thefirstelectronremovedbyanatomwillcomefromthehighestoccupiedenergylevel
(n)becausethoseelectronsexperiencelessnuclearcharge.
Ifthereismorethanonesubshellinthehighestoccupiedenergylevel,theatom
removeselectronsinthefsubshellfirst,thenthedsubshell,thenthepsubshell,andfinallythessubshell.
• Thefirstelectrongainedbyanatomwillgotothelowestunoccupiedenergylevelthat
hasroom.
Ifthereismorethanonesubshellinthelowestunoccupiedenergylevel,the
atomgainselectronsinthessubshellfirst,thenthepsubshell,thenthedsubshell,andfinallythefsubshell.
• Inbecominganion,anatomgainsorloseselectronstoreachanoblegasconfiguration.
Noblegaseshaveverylowreactivitybecausetheirhighestoccupiedenergylevelisfull
ofelectrons,whichmakesthemverystable.
• Somecationsdonotformcationswithanoblegasconfiguration;instead,theybecome
cationswithtwodifferentstableconfigurations:
o Pseudo–noblegasconfigurationoccurswhenanelementemptiesoutits
highestsandpsubshellstoleaveafilleddsubshellbehind.
o Inertpairconfigurationoccurswhenanelementemptiesoutitshighest
occupiedpsubshelltoleavefilledsanddsubshells.
1. Writetheelectronconfigurationforthefollowingions.
i. Al3+
ii. Se2-
iii. Ga3+
iv. Cr3+
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 12
2. Howmanyunpairedelectronsarepresentinthefullground-stateelectronconfigurationof
themonatomicionmostlikelytobeformedbyMg?
A. 1B. 2C. 3
D. Nounpairedelectrons
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 13
11.08TrendsinIonicRadii
• Theionicradiusistheapproximatedistancefromthecenterofaniontoitshighest
occupiedelectronorbital.Weobservethefollowingphenomena:
o Cationsaresmallerthantheparentatom–Whenelectronsareremoved,the
nuclearchargeincreases,sothesizeoftheatomdecreases.
Example:Na>Na+
o Anionsarelargerthantheparentatom–Whenelectronsaregained,thenuclear
chargedecreases,sothesizeoftheatomincreases.
Example:Cl->Cl
• Ionicradiifollowthetrendofatomicradii,increasingtoptobottomwithinagroupand
increasingrighttoleftacrossaperiod.
1. Ineachpair,whichionissmaller?
i. K+,Na
+
ii. Br-,Se
2-
iii. Fe2+,Fe3+
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 14
�
Copyright 2017 Licensed and Authorized for Use Only by Texas Education Agency 15
Recommended