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Biology12 Chapter2.1-2.2:IntrotoChemistry Matter Matterisanythingthattakesupspaceandhasmass—consistsofchemicalelements,whichare composedofatoms.Only92naturallyoccurringelementsserveasthebuildingblocksofall matter. • TheprimaryelementsinEarth’scrustareSi,Al,andO • TheprimaryelementsinorganismsareO,N,C,andH;withSandP,theseelements makeupbiologicalmolecules. AtomicStructure Sub-atomicparticlesthatmakeupatoms include • protons(inthenucleus,positivecharge) • electrons(inthenucleus,uncharged) • neutrons(shellsurroundingthenucleus, negativecharge) • Allatomsofanelementhavethesame numberofprotons,calledtheatomic number. • Eachatomhasitsownmassnumber. • massnumber=numberofprotons+ numberofneutrons Isotopes Isotopesareatomsofthesameelementthathavethesamenumberofprotonsbutdifferent numbersofneutrons,and,therefore,adifferentmassnumber. These are different isotopes of carbon. Unstableisotopeschangeovertimeintostableisotopes,releasingvarioustypesofenergyin theformofraysandsubatomicparticlesduringtheprocess.Thesearecalledradioactive isotopes. Radioactivity Radioactiveisotopeshavedifferentuses,dependingontheirlevelofradioactivity. • Lowradiationlevels:Becausetheseisotopeshavethesamechemicalbehaviorasstable isotopes,theycanbeusedastracersinmedicaltestingandimaging. Biology12 HighLevelsofRadioactivity • Highradiationlevels:Becauseradiationcandamagecells,itcanbeusedforsterilizing medicalanddentalproducts. • RadiationcanalsodamageDNAandcausecancer,howeveritsabilitytokillcellscanbe appliedtocancercells. MoleculesandCompounds Whenatomsoftwoormoredifferentelementsbondtogether,acompoundforms.Twotypes ofbondsthatformare • ionicbonds:electronstransferbetweenatomstoformioniccompounds • covalentbonds:electronsaresharedbetweenatomstoformmolecules Moleculesalsoformwhentwoormoreofthesameatomarecovalentlybonded(e.g.,H2,O2, O3). IonicBonding Ionsarechargedparticlesthatformwhenelectronstransferfromoneatomtoanother. • Forexample,NadonateselectronsandClacceptselectrons Ioniccompoundsareheldtogetherbyattractionbetweenthepositiveandnegativeions,called anionicbond. CovalentBonding Acovalentbondformswhentwoatomsshareelectrons. • Acommonwaytoshowacovalentbondisalinebetweenatoms(a) • Adoublecovalentbondistwosharedpairsofelectrons(b) • Atriplecovalentbondisthreesharedpairsofelectrons(c) Biology12 ShapesofMolecules • Allmoleculeshavethree-dimensional shapes. • Moleculesconsistingoftwoatomsare alwayslinear.Moleculessuchas methane,withfiveatomsandfour singlecovalentbonds,havea tetrahedralshape. • Three-dimensionalshapesofbiological moleculesarerelatedtotheir structuralandfunctionalroles. NonpolarandPolarCovalentBonds • Whensharingofelectronsbetweenatomsisequal,thebondisanonpolarcovalent bond.(Allbondsonthepreviousfigurearenonpolar.) • Insomecompounds,suchaswater,thesharingisnot equal.Oxygenhasgreaterelectronegativitythan hydrogen(itattractselectronstoagreaterextent). • Unequalsharingofelectronsresultsinapolar covalentbond. • Themoreelectronegativeatomwillhaveapartial negativecharge;the otheratomwillhaveapartialpositivecharge. HydrogenBonding • Polaritywithinawatermoleculecauseshydrogenatomsofonemoleculetobe attractedtotheoxygenatomofanothermolecule.Thisattractioniscalledahydrogen bond. • Hydrogenbondsareweakerthanionicandcovalentbondsandareoftenrepresentedas adottedline.Manyhydrogenbondscancollectivelybeverystrong. • Hydrogenbondingoccursinmanybiologicalmolecules,whichhavepolarcovalent bondsbetweenhydrogenandoxygenornitrogen.
