Study Guides (380,000)
US (220,000)
UCLA (3,000)
LIFESCI (200)
Study Guide

[LIFESCI 2] - Final Exam Guide - Ultimate 51 pages long Study Guide!


Department
Life Sciences
Course Code
LIFESCI 2
Professor
Khankan
Study Guide
Final

This preview shows pages 1-3. to view the full 51 pages of the document.
UCLA
LIFESCI 2
FINAL EXAM
STUDY GUIDE

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

2SmallMoleculesandtheChemistryofLife
Oxygenhastwonaturallyoccurringisotopes;theyhavethesamechemicalpropertiesbutdifferentweights
becausetheirnucleihavedifferentnumbersofneutrons.BothisotopesofOareincorporatedintothebodiesof
animalsthatconsumetheisotopesinwaterandfood.
Thehardsurfaceofteeth,calledenamel,ismadeuplargelyofcalciumphosphate.Calciumphosphatehasalot
ofoxygen,andtheisotopiccompositionoftheoxygeninenamelvariesdependingonwhereananimalwasliving
whentheenamelwasmade.Whenwaterevaporatesfromtheocean,itformscloudsthatmoveinlandand
releaserain.WatermadeupoftheheavierisotopeofOisheavier,andtendstofallmorereadilythanwater
containingthelighterisotope.Regionsoftheworldclosertotheoceanreceiveraincontainingmoreheavywater
thanregionsfurtheraway,andthesedifferencesarereflectedinthebodiesofanimalsthatdwellinthese
regions.
Thispropertyhasrevealedafactaboutdinosaurs150millionyearsago.oxygenisotopesintheenamel
ofCamarasaurusfossilsfoundtwokindsofteeth:Somehadtheheavyoxygencontenttypicalofrains
androcksinthebasinregion.othershadalowerproportionofheavyoxygen,indicatingthattheanimals
hadlivedathigherelevationsγ00kmtothewest.Thisindicatesforthefirsttimethatdinosaursmigrated
alongwayfromwesttoeast.
2.1 HowDoesAtomicStructureExplainthePropertiesofMatter?
Allmatteriscomposedofatoms.Atomsaretiny.Eachconsistsofadense,positivelychargednucleus,around
whichnegativelychargedelectronsmove.Thenucleuscontainsoneormorepositivelychargedprotonsand
maycontainoneormoreneutronswithnoelectriccharge.Atomsandtheirparticleshavevolumeandmass,
characteristicsofallmatter.Massisameasureofthequantityofmatterpresent;thegreaterthemass,the
greaterthequantityofmatter.
Themassofaprotonservesasastandardunitofmeasurecalledthedalton.Asingleprotonorneutron
hasamassof1dalton(Da),whichis1.7×10−β4grams,butanelectronistinierat9×10−β8g(0.0005
Da).themassofanelectronisnegligiblecomparedwiththemassofaprotonoraneutron,sothe
contributionofelectronstothemassofanatomcanbeignoredwhenmeasurementsandcalculations
aremade.Itiselectrons,however,thatdeterminehowatomswillcombinewithotheratomstoform
stableassociations.
Chargesthataredifferentattracteachother,whereaschargesthatarealikerepeleachother.Generally,atoms
areelectricallyneutralbecausethenumberofelectronsinanatomequalsthenumberofprotons.
Anelementconsistsofonlyonekindofatom
Anelementisapuresubstancethatcontainsonlyonekindofatom.Theatomsofeachelementhavecertain
characteristicsthatdistinguishthemfromotherelements.Thesephysicalandchemical(reactive)properties
dependonthenumbersofsubatomicparticlestheatomscontain.
94elementsinnatureandβ4madeinphysicslaboratories.sixmostcommonelementsinlivingthingsare
carbon,hydrogen,oxygen,nitrogen,phosphorus,andsulfur.Sodiumandpotassiumfornervefunction;calcium
asabiologicalsignal;iodineacomponentofavitalhormone;andmagnesiumisboundtochlorophyllinplants.
Eachelementhasauniquenumberofprotons
Anelementdiffersfromotherelementsbythenumberofprotonsinthenucleusofeachofitsatoms;thenumber
ofprotonsisdesignatedtheatomicnumber.Thisatomicnumberisuniquetoeachelementanddoesnot
change.Sincethenumberofprotons(andelectrons)determineshowanelementbehavesinchemicalreactions,
itispossibletoarrangetheelementsbysimilarchemicalproperties.Thisistheperiodictable.
Themassnumberofanatomisthetotalnumberofprotonsandneutronsinitsnucleus.
symbolforanelementwiththeatomicnumberatthelowerleftandthemassnumberattheupperleft,both
precedingthesymbol.
Thenumberofneutronsdiffersamongisotopes
Differentisotopesofthesameelementhavethesamenumberofprotonsbutdifferentnumbersofneutron.
isotopesareformedwhenatomscombineand/orreleaseparticles(decay).Thenaturalisotopesofcarbon,
find more resources at oneclass.com
find more resources at oneclass.com
You're Reading a Preview

Unlock to view full version

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

areC(sixneutronsinthenucleus),C(sevenneutrons),and14C(eightneutrons).MostcarbonatomsareC,
1.1%areC,andatinyfraction14C.Allhavethesamechemicalreactivity,animportantpropertyfortheirusein
experimentalbiologyandmedicine.
Anelement’satomicweightistheaverageofthemassnumbersofarepresentativesampleofatomsofthat
element,withalltheisotopesintheirnormallyoccurringproportions.Itistheratiooftheaveragemassperatom
oftheelementto1/1βofthemassofanatomofC.Becauseitisaratio,atomicweightisadimensionless
physicalquantity—notexpressedinunits.Theatomicweightofhydrogenis1.00794.Thisnumberisfractional
becauseitistheaverageofthecontributingmassesofalloftheisotopes,butsomeisotopescontributemore.
Somewaterhasmoreoftheheavyisotopes,soatomicweightsasranges.Ex.H:1.0078–1.0081.
Mostisotopesarestable.Butsome,calledradioisotopes,areunstableandspontaneouslygiveoffenergyinthe
formofα(alpha),(beta),or(gamma)radiationfromtheatomicnucleus.Knownasradioactivedecay,this
releaseofenergytransformstheoriginalatom.
typeoftransformationvariesontheradioisotope,butsomeresultinadifferentnumberofprotons,sothat
theoriginalatombecomesadifferentelement.
scientistscanusethereleasedradiationtodetectthepresenceofradioisotopes,usingasimpledetector
calledaGeigercounter.Mostatomsinorganismsareorganizedintostableassociationscalled
molecules.Ifaradioisotopeisincorporatedintoamolecule,itactsasatag,allowingaresearcherto
trackthemoleculeinanexperiment.Radioisotopesareusedtodatefossils.
alowdoseofradiationhasthepotentialtodamagemoleculesandcells.thesedamagingeffects
aresometimesusedtoouradvantage;theradiationfromcobalt60isusedintokillcancercells.
Thebehaviorofelectronsdetermineschemicalbondingandgeometry
Thenumberofelectronsinanatomdetermineshowitwillcombinewithotheratoms.Itexplainshowchemical
reactionsoccur.Chemicalreactionsaltertheatomiccompositionsofsubstancesandtheirproperties.
Reactionsinvolvechangesinthedistributionofelectronsbetweenatoms.
Thelocationofagivenelectroninanatomatanygiventimeisimpossibletodetermine.canonlydescribea
regionofspacewheretheelectronisfound90percentofthetime:theelectron’sorbital.Orbitalshave
characteristicshapesandorientations,andagivenorbitalcanbeoccupiedbyamaxoftwoelectrons.Aswe
movefromlightertoheavieratomsintheperiodictable,theorbitalsarefilledinaspecificsequence,inaseries
ofwhatareknownaselectronshells,orenergylevels,aroundthenucleus.
Firstshell:Theinnermostelectronshellconsistsofoneorbital,ansorbital.Ahydrogenatomhasone
electroninitsfirstshell;heliumhastwo.Atomsofallotherelementshavetwoormoreshellsto
accommodateorbitalsforadditionalelectrons.
Secondshell:containsfourorbitals(ansorbitalandthreeporbitals)andholdsuptoeightelectrons.
sorbitalshavetheshapeofasphere,whereasporbitalsareorientedatrightanglestooneanother.The
orientationsoftheseorbitalsinspacecontributetotheγDshapesofmoleculeswhenlinkedtoothers.
Additionalshells:Elementswithmorethantenelectronshavethreeormoreelectronshells.Thefarther
ashellisfromthenucleus,thehighertheenergylevelisforanelectronoccupyingthatshell.
ElectronOrbitals
Thesorbitalsfillwithelectronsfirst,andtheirelectronshavethelowestenergylevel.Subsequentshellshave
differentnumbersoforbitals,buttheoutermostshellsholdonlyeightelectrons.Inanyatom,theoutermost
electronshell(thevalenceshell)determineshowtheatomcombineswithotheratoms.
Whenavalenceshellwithfourorbitalscontainseightelectrons,therearenounpairedelectronsandthe
atomisstable—leastlikelytoreactwithotheratoms.Ex.helium,neon,andargon.
atomsthathaveunpairedelectronsintheiroutershellsarecapableofreactingwithotheratoms.They
areunstableandwillundergoreactionstofilltheiroutermostshells.Reactiveatomscanattainstabilityby
sharingelectronswithotheratomsorbylosing/gainingelectrons.Thetendencyofatomstoform
stablemoleculessothattheyhaveeightelectronsintheiroutermostshellsisknownastheoctetrule.
Anexceptionishydrogen,whichattainsstabilitywhentwoelectronsoccupyitssingleshell.
find more resources at oneclass.com
find more resources at oneclass.com
You're Reading a Preview

Unlock to view full version