Wednesday,September27th,2017

APChemistryDay12

Do-Now:TakeoutyourFRQpacketandturntoFRQ#4:1.   Usetheanswerkeytoreviewyour

response2.   Keepinmind:APFRQkeysare

guidelinestellinggraderswhattolookfor.Theyarenotgivingyoucompleteresponses.

3.   GiveyourselfanapproximatescoreforeachsecHon,andgiveyourselfatotaloutof6points

Do-Now:– Now,wewillcompleteanFRQanalysis.– Usethekeyandyourresponsetocompletetheworksheet.

– Discusswithyourgroupifneeded– Evenifyouthinkyoureceivedfullpoints,thinkabouthowyoucouldrewriteyouranswertoexpressyourideasclearly,concisely,andinalogicalflow.

Announcements• UnitTest

– Bringcalculatorsandreferencesheets– FRQ/ResponsesecKononFriday– MCsecKononTuesday

•  Labnextweek•  Tradeindojopoints

CW/HWAssignments15.  FRQMeta-Analysis9/2716. MassSpecNotes+Packet9/27

PLANNER •  StudyfortestJJJ•  Getallstamps•  FinishFRQMeta-AnalysisandMassSpec.packet

FLT•  Iwillbeableto:– UsedatafrommassspectrometrytoidenKfytheelementsandthemassesofindividualatomsofaspecificelement

– JusKfytheselecKonofaparKculartypeofspectroscopytomeasureproperKesassociatedwithvibraKonalorelectronicmoKonsofmolecules

•  Bycomple1ngMassSpecNotes

MassSpectrometry

Recall

PhotoelectronSpectroscopy(PES)

•  UsingPES,wecanidenKfyspecificelementsandalsocomparetheirionizaKonenergiesforspecificelectrons

IdealizedPESspectrumofphosphorus

IdealizedPESspectraofboronandfluorine

PhotoelectronSpectroscopy(PES)

Isotopes

Isotopes•  AreallatomsofagivenelementidenKcal?• Whileatomsareneutralandhaveequivalentnumbersofprotonsandelectrons...

•  Thenumberofneutronsmaydiffer•  Becauseatomsmayhavevaryingnumbersofneutrons,theirmassmayalsodiffer

Isotopes•  FrederickSoddy(1877-1956)proposedtheideaofisotopesin1912

•  Isotopes=atomsofthesameelementhavingdifferentmasses,duetovaryingnumbersofneutrons.

•  SoddywontheNobelPrizeinChemistryin1921forhisworkwithisotopesandradioacKvematerials.

Isotopes

• Elements occur in nature as mixtures of isotopes.

AverageAtomicMass

Atomic Mass§ Whatisthemassofanatomofoxygen?§ Itdepends,becausetherearedifferentkindsofoxygenatoms.

§ Wearemoreconcernedwiththeaverageatomicmass.

§ Averageatomicmass=weightedaverageoftheisotopesofagivenelementbasedontheabundance(%)innature

Atomic Mass• Each isotope has its own atomic

mass, thus we determine the average from percent abundance.

Calculating Atomic Mass•  MulKplytheatomicmassofeachisotopebyitsabundance(expressedasadecimal),thenaddtheresults.

Example•  Calculatetheaverageatomicmassofoxygen

Trythisoneinyourgroups:

SoluKon• a):

• Letx=abundanceofNe-20• 19.99x+21.00(1-x)=20.18• x=0.905• %abundaceNe-20=90.5%,Ne-22=9.5%

Average Atomic mass•  ButhowdoscienKstsdeterminepercentabundanceandaverageatomicmass?

MassSpectrometry

MassSpectrometry•  MassspectrometryprovidesmasstochargeraKoandprovidesuswithinformaKontodeterminethemolecularmassofatoms/moleculesinasample.

•  High-energyelectronsbombardthesample,causingittoionize

•  AnelectricfieldseparatestheionsbasedontheirmasstochargeraKoàthisdataiscompiledintoamassspectrum

•  (itseparatesisotopesbymass)

MassSpectrometry

MassSpectrometry•  LikePES,therelaKvesizeofthepeaksindicatestherelaKvenumberofparKcles

MassSpectrometry•  Basedonthisspectrum,whatisthemostcommonisotopeofzirconiuminoursample?

•  Zr-90hasthehighestintensity(tallestpeak),soitisthemostcommon

MassSpectrometry•  GivenZr-90is89.905amu,Zr-91is90.906amu,Zr-92is91.905amu,Zr-94is93.906amu,andZr-96is95.908amu,calculatetheaverageatomicmassofzirconium.

•  Seehowcloseyougetto91.22

BasedonthemassspectrumofatomY,whichofthefollowingstatementsisfalse?

a.peakAandpeakDcomefromatomsthathavethesamenumberofelectronsb.therearesevenisotopesofatomYc.peakCcomesfromthemostabundantisotopeofatomYd.peakDcomesfromanatomwith4moreprotonsthantheatomthatgavepeakB

Theiden1tyofcompoundYis:a.  Zirconiumb.  Molybdenumc.  Americiumd.  Einsteinium

Whichpeakcomesfromanatomwiththegreatestnumberofneutrons?a.  Ab.  Cc.  Dd.  Allpeakshavethesamenumberofneutrons

CW•  MassSpecpacket

– ThispacketgoesbeyondthelevelofunderstandingrequiredontheAP

– FocusoninterpreKng/explaining/calculaKngmorethanunderstandinghowitworks

– AjemptallquesKons

•  Studyforquiz