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Today’sblogpostandpodcastareonthetopicofusefultopicsfromhighschoolchemistryfor reviewpriortobeginningChem1210.ManyofthetopicsofChemistry1210willlikelybethings you’vealreadylearnedaboutinhighschool.APchemistryisoftenverysimilarincontenttoour classandevenregularhighschoolchemistrycoversmostofthemaintopicsoftenthoughwith alittlelessdepth.OneparticularwayChem1210mightbemoreadvancedthanthesehigh schoolcoursesisthatwehaveastrongfocusontheideasandconceptsthatyoumust understandforsuccessinlatercourses,likeChem1220,Chem2310/2510/2520/2540/2550 (organicchemistrycourses),andupperlevelbiochemistry,genetics,andmaterialsscience courses. Asameanstoreviewand/orintroducesomeofthemaintopicsforthecourse,thisblogpost willreviewsomeofthekeytermsandideasfromthefirst11chaptersofourtextbook. Chapter1: Chemistry:Propertiesandreactionsofmatter. Chemicalreactions:transformationofasubstanceorsubstancestonewsubstances.Wewill discusswhatachemicalsubstancemeansanddefinitionsofelements,compounds,and moleculesinchapter1. Significantfigures:Oneofthemorechallengingconceptsofhowtoapply,butthissystemhelps knowhowtoroundresultsofmathematicalcalculationsinvolvingmeasurements. Measurementsalwayshavesomefundamentallimitationonhowwelltheyareknown.Likea scaleinyourbathroommightweightouttothenearest1poundormaybetothenearest0.1 pound.Mostobjectscouldbedescribedbyamuchmoreprecisemassthanthis,thoughthis bathroomscalewouldbelimitedtoonlytheplaceholdersshownonitsdisplay.Oftenyoufind toolsthishavesomeuncertaintyinthatlastplaceholder–youmightseesomefluctuationand youwouldtryyourbesttotakethemassastheaverageofthesevalueswhenpossible.When youdoacalculationonanumberlike123,youordinarilywouldthinkthismeans123.00000000 butif123representsthenumberofpoundsreadfromascale,itwouldreallymean123±1.The truemassoftheobjectisverylikelybetween122.5and123.5andwecannotknowitsmassany betterthanthisrange.Thisfundamentallimitationwilllimitthenumberofplaceholdersthat aresignificantincalculationsofthisvalue,likeaddition/subtraction,multiplication/division, naturallogs,etc.Wewillgoovertheserulesinthefirstweekoflecture. Precisionvsaccuracyofameasurement:Precisionistherepeatabilityofameasurementand accuracyishowcloseameasurementistoatruevalue.Accuracycanonlybetestedby comparisontoaknownvalue,likeusinganexactly1.00000±0.000001kgobjecttotestthemass ofabalance.Thetopicofsignificantfigureshasmoretodowithprecisionofameasurement,in whichamoreprecisemeasurementisonethatcontainsmoresignificantdigits.Amass recordedonabalanceof125.5poundsismoreprecisethananotherbalancewhichreadsits masstobe126pounds.Bothmeasurementsareessentiallyjustasaccurateaseachother though.Weeithertestatoolinthelaborwewilljustassumeagiventoolisaccurateitsgiven numberofplaceholders. Rulesofsignificantfigures,whichwewilldiscussthoroughlyinlecture,aregeneralizedrulesfor statisticalanalysiswhendealingwithmeasuredquantitiesthatyoumightlearnmoreaboutin anintroductorystatsclass.Significantfiguresareakeyitemofdiscussioninchapter1sowe willexplorethistopicinlecture,sothisisnotatopicIexpectmostofyoutohavemuch knowledgeaboutfromhighschoolchemisty. Onefinaltopicfromchapter1isdimensionalanalysis.Youlikelyrecallthatthismethodisoften usedtoconvertunitsforproblemslikefiguringouthowmanysecondsarein1year.Wecan alsousedimensionalanalysisasageneralmeansofsolvingproblemsanytimeequalitiesare known.Oneequalitythatcaneasilybeusedindimensionalanalysisisdensity,likethedensity ofwateris1.00g/mL.Ifyouhave55.0mLofwater,itwouldofcoursehaveamassof55.0g becausethedensitysaysyouhave1.00gpereverymL.Wehardlyneedanymethodtosolve thatproblem.Butwhatifwe’retalkingaboutethanol,whichhasadensityof0.789g/mL,what isthemassof55mLofethanol?Well,nowwemightrightthisoutmorecarefully: #g=55mLx0.789g/mL=43.4g AllweneedtoknowtosetthisproblemupisthatthemLmustcancelout,sowemust thereforemultiplybythedensityandthenthiscalculationresultsinourdesiredunitofgrams beinginthenumerator.Wecouldhaveinsteadusedtheformulafordensity,whichisd=m/V, rearrangedform,andpluggedandchugged.Thisproblemsolvingmethodistotallycorrecttoo, butwedidhavetorememberanequationtousethatmethodandwedidn’thavetoremember muchofanythingtousedimensionalanalysis.Wewilloftenusedimensionalanalysisinthis coursetosolveavarietyofproblemsinwaysthatoughttomakethesolutionssimplerthan othermethods. Ididn’tmentionthisdetailinthepodcast,butthereisreallyneveranywhereonexamsor recitationswhereyouhavetoshowwork(recitationsarejustattendancepointsandexamsare allmultiplechoice).Sohowyousolveyourhomeworkproblemsismostlyirrelevant,provided youultimatelygettheanswerright!Ialwaysrecommendthoughthatyouwriteoutunitsin yourworkthoughasthisprocesswillhelpeliminatemistakes. Topicsinchapter2includemodernatomictheory,atomicandmolecularweights,andsome examplesofcommoncompoundsandrulesfornamingclassesofcompounds.Thefirsttwo sectionsdiscusstheoriesaboutthediscoveryofthesubatomicparticlesliketheelectron (negativeparticle),proton(positiveparticle),neutron(neutralparticle),andhowthetheoryof thenuclearatomwasdiscovered.Wewillbrieflydiscusstheperiodictableandit’sstructure basedonincreasingsizeandgroupingofelementsbysimilarproperties. Eachoftheelementsdifferbythenumberofprotonswithinthenucleusoftheatoms comprisingtheelement.Hydrogenatomshave1protonintheirnucleus,carbonatomshave6. Thenumberofprotonshencedefinestheidentityoftheatomsoit’scalledtheatomicnumber. Theneutronisaneutralparticleandatomsofsomeelementscandifferinhowmanyneutrons theycontain.Atomsofthesameelementwithdifferentnumberofneutronsareisotopes. Carbonforexamplemostcommonlyexistsascarbon-12andcarbon-13.Thenumberafterthe elementisthemassnumber,thesumoftheprotonsandneutrons(socarbon-12has6protons and6neutrons,about99%naturalabundanceofcarbon,andcarbon-13has6protonsand7 neutrons,whichisabout1%naturalabundanceofcarbon).Theseisotopesoftenbehavevery similarlyandtheyareonlydifferentbythesmalldifferenceinmass.Electronsarenotcounted inthemassnumberprimarilybecausetheirmassisverylow,around1/1000ththemassofa protonorneutron.Theelectronsbeingsolightareonereasonwhytheydonotcoexistamong theprotonsandneutronsbutinsteadspinaroundthepositivelychargednucleus.Theproton andelectronhavethesamemagnitudeofcharge,justoppositeincharge.Soaneutralcarbon atomcontains6electrons.Afluorineatom(9protons)with10electronshasachargeof-1and hencethisisanion.Na+istheionofsodiumwith11protonsand10electrons.Wewillsee oftenatomsneartheendsoftheperiodictablecanloseelectrons(ontheleftside)orgain electrons(ontherightside)sothattheyarriveatastablenoblegascountofelectrons.Wewill seelaterinchapter6howelectronconfigurationsandshellsplayarole. Metallicelementsonlyloseelectronstoformcationsandtheywillnevergainelectronsand formanions.Metallicelementsaswewillseeinchapter7havelowionizationenergies. Sodium’sgroup(thealkalifamily)willloseoneelectrontoform+1cations,calcium’sgroup (alkalinefamily)willlosetwoelectronstoform+2cations.Thetransitionmetalscanoftenlose avariablenumberofelectronsthatisnotverypredictable,thoughtheywouldneverloseany electronspastthenearestnoblegascount(forexample,titaniumcanformtheTi4+cationasits highestchargedcationsinceitwouldhave18electronslikeargon).Inorderforametal(orany atom)toloseelectrons,anotheratommustbeabletoacceptthoseelectrons.IfNa(s)andCl2 (g)wereallowedtoreacttogether,twosodiumatomswouldloseoneelectroneachandtheCl atomsinaCl2moleculewouldgainoneelectroneachandthecompoundNaClwouldresult. Thiscompoundisanioniccompound,Na+andCl–ionswouldbepresentandtheirelectrostatic attractionkeepsthesaltcrystalheldtogether. Wewillseecommoncompoundsandnamingconventionsintheendofchapter2.Wewillalso seesomebasicsofformulasandchargesofionsincommonioniccompounds. Chapter3dealswithchemicalreactions,suchaswriting,balancing,andsolvingproblems relatedtobasicchemicalreactions.Achemicalreactionshowsthereactantsontheleftside andthenewsubstancesthatresultintheproducts.Achemicalreactionisnotreallyan equality,ratheritismuchbetterthoughtofasa‘beforeandafter’.Achemicalreactionnever changestheidentitiesoftheelements,ratheronlynewcompoundsareformedfrom rearrangingtheatomsintonewsubstancesintheproducts.Asanexample,CH4(methane) reactswithO2(oxygengas)toformcarbondioxide(CO2)andwater(H2O).Allofthecarbonin methanewillendasallofthecarbondioxide(CO2).Allofthehydrogeninmethaneendsupin thewatermoleculesthatform.If1moleculeofmethanearereacted,then1moleculeofCO2 andtwomoleculesofH2OmustformtobalancetheCatomsandHatoms.TwomoleculesofO2 mustthereforebepresentinthereactants.Reactionsmustalwayshaveanequalnumberof atomsinthereactantandproductsidesofthereaction: CH4+2O2àCO2+2H2O Subscriptsareneverchangedtobalanceareaction.Subscriptsrelatethenumberofatomsof anelementinamoleculeorunitofthecompound.Anoxygenmoleculecontainstwooxygen atoms.“2O2”intheabovereactionimpliestwooxygenmolecules.O4wouldbeatotally differentmolecule,whichdoesnotevenexist.Afewothermoleculeexamplestogetasenseof thecomplexityothermoleculeshave,methanolisCH3OH,youcouldwritethisasCH4Obut CH3OHisimplyingsomethingaboutthemolecularstructureofthemoleculethatwewilllater seemoreaboutinchapters8and9.Methanolisamolecularcompoundandasampleof methanolwouldcontainmanymoleculesofmethanol.Ifyouweretoboilmethanol,individual moleculesofmethanolwouldescapefromtheliquidsurfaceintogaseousvapors(justlike watermoleculesevolvefromboilingwater).SulfateionisSO42–.PotassiumsulfateisK2SO4(and thisisanexampleofanioniccompound,withanoverallneutralcompoundcomprisedofions). Stoichiometryisanotherkeytopicchapter3,whichisthebookkeepingsystemforreactions.So sayif3.0gramsofmethanereactswithexcessoxygen,stoichiometrywillhelpusfigureout howmuchCO2andH2Owouldform.Themoleisacommonunitwewilluse.Amoleofan objectrefersto6.02214179x1023ofthatobjectsoamoleofmethanolcontains6.02x1023 methanolmolecules(roundingtothreesigfigs).Theperiodictableliststheaverageatomic weightsofalloftheelements,oftenroundedto4-5sigfigsbutyoucanlookmoresigfigsupin theCRCifeverneeded.Theaverageatomicweightaccountsfortheabundanceofeachisotope ofanelementanditsatomicweightanditsumsupallofthesequantitiesfortheaverageatom ofeachelement.Forcarbon,carbon-12isdefinedtohaveamassofexactly12atomicmass units(amu),sothinkofitsmassas12.000000000000·····amu.Moreonthissystemina moment,butthemassofcarbon-13isabout13amu(wewillseeapreciseexampleinclass).If yourecallcarbon-12isabout99%naturalabundanceandcarbon-13isabout0.01,sotake0.99 times12plus0.01x13=12.01.Sotheaverageatomicweightofcarbonisjustalittleoverthe massoftheisotopethat~99%oftheatomshaveamassof,thatmakessenseIhope!Togeta senseofamorepreciseatomicweight,we’dhavetoplugintheexactmassandabundanceof thecarbon-13isotope.Backtotheamuacale,socarbon-12’smasswasdefinedtobeexactly12 amu.Ifyoutakeasexactmassof12gramsofcarbon-12asyoucanfindabalancetomeasure (about9sigfigsispossible)andstartcountingatoms,you’dcomeupwithabout 6.02214179x1023atoms(Avogadrofiguredthisout).Whatthismeansisthateachatomweights 12.0000000g/6.02214179x1023atoms=1.992···x10–23g.Thisthenalsomeansthat12amu= 1.992x10–23g,orthat1amu=1.660····x10–24g,orthat1g=6.022···x1023amu.OK,ifyoucan followallofthat,that’sgreat!Wewilltalkaboutthatderivationinclass,butthereisasimple conclusionwecaneitherdrawfromthisorjusttakeforgranted,thatisthattheperiodictable tabulatedthemassesofeachatom,eitherintheunitofamuperaverageatomoringramsper moleoftheelement.Sooxygenontheperiodictablesays15.9994.Thismeanseitheran averageoxygenatomhasamassof15.9994amuorthatonemoleofoxygenhasamassof 15.9994g.Wecouldcallthemolarmassofoxygento15.9994g/mol.Wecanthenusethe periodictabletodeterminemolarmassesofcompoundsjustbyaddingupalloftheaverage molarmassesofitselements,soCH4=12.01+1.008*4=16.04g/mol. GoingbacktotheCH4+2O2àCO2+2H2Oreaction,thereactantsandproductscanberelated intermsofmoleculesormoles:1moleculeofCH4reactswith2moleculesofO2toform1 moleculeofCO2and2moleculesofH2OOR1moleofCH4reactswith2moleofO2toform1 moleofCO2and2moleofH2O.If3.00gramsofCH4reactswithexcessO2,andwewantedto knowhowmuchCO2forms,wecouldconvertgramsofCH4tomoles,molesofCH4canthenbe convertedtomolesofCO2,andthenthemolarmassofCO2(44.01g/mol)canbeusedto convertmolesofCO2togramsofCO2;8.23gramsofCO2wouldform. Stoichiometryalsogetsintowhichreactantlimitstheamountofproductformationandwhich mightbepresentinexcess,orwhatthepercentyieldisofareaction.Chapter4getsinto reactionstakingplaceinwater,suchasacid-basereactionsandmetathesisreactions(whichare reactionswhereyoutaketwowater-solubleioniccompounds,likeNaCl(aq)andAgNO3(aq) whenmixedleadtoAgClforming,whichisawhitesolid,whichwouldappeartoformas snowflakesinthesolutionandultimatelysettleonthebottomofthereactionflask.AgClforms asasolidbecausethecompoundisinsolubleinwater.Solubilitytrendsofionswillbediscussed sowecanproductwhenmetathesisreactionswilloccur.Chapter4alsodiscussesoxidationreductionreactions,whicharereactionswhereelectronsaregained(i.e.reduction)andlostby atoms(i.e.oxidation)duringthereaction.Chapter4wrapsupwithsolutionstoichiometry problems,suchastitrations. Chapter5discussesheatcapacity,likehowmuchheatmustwaterabsorbtoraiseits temperature,andenthalpychangesofchemicalreactions.AlaterchapterinChem1220would getintootherthermodynamicstopics. Chapter6dealswithpropertiesofelectronsinatoms,startingwiththehydrogenatomin greaterdetailandthenelectronconfigurationsforlargeratomstowardstheendofthechapter (e.g.youmightrecallthegroundstateelectronconfigurationofcarbonis1s22s22p2). Chapter7dealswithnuclearandperiodictrends.Onesuchperiodictrendisionizationenergy, whichmostlyincreasesfromlefttorightacrossarowoftheperiodictablebutdecreasesfrom toptobottomdownagroup.Wewilldiscusswhy,aswellwewilldiscussothertrendslike atomicsize,ionicsize,andelectronaffinitytrends.Thesetrendscanhelpusunderstandsimple bondingtrendsinioniccompounds,likesodiumshouldhasarelativelylowionizationenergy, sonotmuchenergyisrequiredfortheatomtoloseanelectron.Chlorineontheotherhandhas amuchhigherionizationenergy.SoifyouareconsideringtheionicstructuretobeeitherNa+Cl– vs.Na–Cl+,thelatterwouldtakemoreenergytoformCl+thanitwouldtakeforsodiumtolose anelectron,soNa–Cl+isunlikelytoformwiththosecharges.Additionally,theelectronaffinity ofClismorenegative,aselectronaffinitydecreases(becomesmorenegativeandhencemore favorableforanatomtoabsorbanelectron)fromlefttoright.SoClisenergeticallymore favoredtoacceptanelectronthanNa.SowecanconcludethatNaClformsthestructurewe havethoughtallalong,Na+Cl–. Chapter8startswithadescriptionofionicbondstrengthsasarelationshiptothelatticeenergy oftheions.Asionsaremorehighlychargedinmagnitude,thelatticeenergyincreaseshence theionicbondstrengthisstronger,andthenanassociatedtrendlikemeltingpointshould increase.Forexample,wecancompareNaCl(mp~800˚C)toMgO(mp2850).MgOhashigher chargedionsofMg2+O2–,sotheattractionoftheseionsismuchgreater.Thecompoundhasa latticeenergyaboutfourtimesthatofNaClandlikewiseitsmeltingpointismuchgreater. Thesecondhalfofchapter8iscenteredaroundLewisstructuresofmolecularcompounds. Molecularcompoundsresultbetweennon-metallicelementslikeC,H,N,O,Cl,etc.These elementsbynaturehavehigherionizationenergiesandmanyhavelessnegativeelectron affinities.Sothesecompoundsarenotabletogainandloseelectronslikemetalsandnonmetalsareableto.Instead,theseelementsmustshareelectronswitheachotherinorderto gainstability,throughbondscalledcovalentbonds.Covalentbondsarenotasstrongasionic bonds.ALewisstructureisadepictionofallofthebondsandbondtypes(suchassingle, double,triple,etc)inamolecule.Hydrogenmolecule,H2,hasasinglebondbetweenitstwoH atoms,H–H.EachHatomhastwoelectronsnearit,allowingeachtohaveanelectroncountlike He–it’snearestNoblegaselement.Twooxygenatoms,eachwith6valenceelectrons,can adoptaconfigurationof8valenceelectronsbyformingtheoxygenmoleculewithadouble bond:O=O.CH3OHforexamplehasthreesinglebondsbetweenCandH,asinglebondbetween aCandOatom,andasinglebondbetweenOandH.Throughsomesimplerulesandideas,we cangetintosomebiggermoleculestowardtheendofchapter8. Electronegativityandbondpolarityisdiscussedinchapter8andwediscussmolecularpolarity inchapter9.Wealsotalkaboutthreedimensionalmolecularshapeinchapter9.Chapter9also discussesmolecularshape.Organicchemistrybuildsoffmanyoftheideasfromchapters8and 9. Chapter10isonthetopicofgasesandbeginswiththeidealgaslaw.Inthislaw,gasesare describedasnon-interactingparticles.Notmuchchemistryhappensbetweennon-interacting particles!However,allgaseswilleventuallycondense,hencetheirparticlesmustatsomelow temperaturebegintointeract.TheseinteractionscanbedescribedbythevanderWaals equationtowardtheendofchapter10andthesubsequentliquidstateisdiscussedinchapter 11. Chapter11discussesmanyimportantfactorsofliquids,suchasintermolecularforcesof dispersionforces(forcepresentinliquidsofnonpolarsubstances),dipole-dipoleforces(force presentinliquidsofpolarsubstances),hydrogenbonding(forcepresentinliquidsofpolar substanceswhereHisdirectlybondedtoanN,O,orFatom).Theseintermolecularforcesare weakerthancovalentbondsbuttheyarestillveryimportantforunderstandingpropertiesof liquids.Manypropertiesandtrendsofaliquidcanbeinferredfromitstypesofintermolecular forces,andtheseforcescanbeimpliedfromknowledgeoftheshapeandstructureofa molecule.Chapter12completesadiscussionofthephaseofsubstancesbydiscussingsolids. ThisismuchlongerthanIthoughtitwouldbe!Ihopethisgivesasenseofwhatthiscourseis aboutandthatyouprobablyhaveheardmanyofthesewordsandideasbefore.Wewillexpand upontheseideasandfocusonproblemsolvinginourlectures. Thereisanotherhandoutyoucanreadonsomeofthesetopics.It’spostedbelowontheblog– checkitoutifyouwanttoreadmore. ThisisthelastblogentryoftopicsIhadplannedbeforeourclassstartsup.Ifyouhave questions,keepthemcomingasIcoulddomorepostsonFAQsiftherearestillquestions.Ialso plantokeepthebloggoingthroughoutthetermthoughI’mexactlysurehowIplantodothis. MyplanatthemomentisIcouldprovidepreand/orpostchaptersummariestohelpintroduce topicsandtohelpreviewmaterial.Ifyouhaveideasforfutureblogtopics,letmeknow!