Secondary 3 Chemical Bonding Notes - Pure Chemistry

Chemical BondingSyllabusLearningObjectives/ Notes 3.1IonicBonding (a)describetheformationofionsbyelectronloss/gainandthattheseionsusuallyhavetheelectronicconfigurationofanoblegas(b)describe,includingtheuseof‘dot-and-cross’diagrams,theformationofionicbondsbetweenmetalsandnon-metals,e.g.NaCl;MgCl2 (c)statethationicmaterialscontainagiantlatticeinwhichtheionsareheldbyelectrostaticattraction,e.g.NaCl(studentswillnotberequiredtodrawdiagramsofioniclattices)(d)relatethephysicalproperties(includingelectricalproperty)ofioniccompoundstotheirlatticestructure(seealso3.4(g)) 3.2Covalent Bonding (a)describetheformationofacovalentbondbythesharingofapairofelectronsandthattheatomsinthemoleculesusuallyhavetheelectronicconfigurationofanoblegas(b)describe,using‘dot-and-cross’diagrams,theformationofcovalentbondsbetweennonmetallicelements,e.g.H2 ;O2 ;H2 O;CH4 ;CO2 (c)deducethearrangementofelectronsinothercovalentmolecules(d)relatethephysicalproperties(includingelectricalproperty)ofcovalentsubstancestotheirstructureandbonding(seealso3.4(g)) 3.3MetallicBonding (a)describemetalsasalatticeofpositiveionsina‘seaofelectrons’(b)describethegeneralphysicalpropertiesofmetalsassolidshavinghighmeltingandboilingpoints,malleable,goodconductorsofheatandelectricityintermsoftheirstructure(seealso3.4(g)) 13.4StructureandPropertiesof Materials (b)describeanalloyasamixtureofametalwithanotherelement,e.g.brass;stainlesssteel(c)identifyrepresentationsofmetalsandalloysfromdiagramsofstructures(d)explainwhyalloyshavedifferentphysicalpropertiestotheirconstituentelements(e)comparethestructuresofthefollowingsubstancesinordertodeducetheirproperties:(i)simplemolecularsubstances,e.g.methane,iodine(ii)macromolecules,e.g.poly(ethene)(iii)giantcovalentsubstances,e.g.sand(silicondioxide),diamond,graphite(seealso3.4(g))(f)comparethebondingandstructuresofdiamondandgraphiteinordertodeducetheir

propertiessuchaselectricalconductivity,lubricatingorcuttingaction(studentswillnotberequiredtodrawthestructures)(g)deducethephysicalandchemicalpropertiesofsubstancesfromtheirstructuresandbondingandviceversa(seealso3.1(d),3.2(d),3.3(b)and3.4(e)) 4.1FormulaeandEquationWriting (a)statethesymbolsoftheelementsandformulaeofthecompoundsmentionedinthesyllabus(c)deducetheformulaeofsimplecompoundsfromtherelativenumbersofatomspresentandviceversa(d)deducetheformulaeofioniccompoundsfromthechargesontheionspresentandviceversa 2IonicBonding 1. Formationof IonsBigidea1: TheStableElectronicConfigurationof aNobleGas 1.TheelementsfoundinGroup0ofthePeriodicTableareknownasnoblegases.Someexamplesofthenoblegasesarehelium,neon,argon,krypton,xenonandradon. 2.Noblegasesarestableandunreactive.Theyaremonatomicandexistassingleatoms.

3.Noblegasesarestablebecausetheyhavefullyfilledoutershells.Heliumhasadupletconfigurationwhileallothernoblegaseshaveanoctetconfiguration.(thusareinert anddonotreactwithotheratoms.) 4.Atomsofotherelementsarereactivebecausetheiroutershellsarenotfullyfilled.Theseatomslose,gainorshareouterelectronstoachievecompletevalenceshellconfiguration(thestablenoblegasconfiguration). 2. Whyatomsformions?Bigidea2: Atomsformionstoachievestableelectronicstructurewithfull electronshells. 1.Toachievethestableelectronicstructure,(a)atomsofmetalsloseelectronstoformpositiveions(cations);(b)atomsofnon-metalsgainelectrontoformnegativeions(anions).2.Ions withtwoormorecovalentlybondedatomsarecalledpolyatomicions. Examplesofsuchionsaretheammoniumion(NH4 + ),carbonateion(CO3 2– )andthesulfateion(SO4 2– )(Note:structureofpolyatomicionsisnotrequired). 3. Formationof IonicBond: TransferringElectrons 1.Ionicbondsareformedbetweenmetalsandnon-metals. Examplesofmetals:Sodium,potassium, calcium,magnesium Examplesofnon-metals: Fluorine, chlorine, oxygen,sulfur 2.Intheformationofanionicbond,themetalatomtransferselectronstothenon-metalatomtoformpositiveions(cations)andnegativeions(anions). 3.Theoppositely-chargedionsareheldtogetherbystrongelectrostaticforcesofattractioncalledionicbonds. 3Example1:Intheformationofsodiumchloride, (a)sodiumatom(2.8.1)loses1electrontoformNa + ion,achievingstableelectronicstructure(2.8).

(b)chlorineatom(2.8.7)gains1electrontoformCl - ,achievingstableelectronicstructure(2.8.8).(c)Thereisatransferofelectronsfromsodiumtochlorinetoformsodiumchloride. Formula Na Cl Na + Cl - Name Sodiumatom Chlorineatom Sodiumion Chlorideion Electronicconfiguration 2,8,1 2,8,7 2,8 2,8,8 (d)TheformulaofthecompoundformedisNaCl. Example2:Intheformationofmagnesiumchloride, (a)magnesiumatom(2.8.2)loses2electronstoformMg 2+ ,achievingstableelectronicstructure.(b)chlorineatom(2.8.7)gains1electrontoformCl - ,achievingstableelectronicstructure(2.8.8).(c)Thereisatransferof2electronsfrommagnesiumtotwochlorineatoms,formingmagnesiumchloride. Cl Mg Cl Formula Mg Cl Cl - Mg 2+ Cl - Name Magnesiumatom Chlorineatom Chlorideion Magnesiumion Chlorideion Electronicconfiguration 2,8,2 2,8,7 2,8,8 2,8 2,8,8

(d)TheformulaofthecompoundformedisMgCl2 . 44. Physical Propertiesof IoniccompoundsProperty Explanation(Specifytheidentityof theionswhereapplicable.) Have very high melting andboiling points (for reference:m.p. ~ few hundred to fewthousanddegreesCelsius). Anioniccompoundhasagiantioniccrystallatticestructure.Alargeamountofenergyisrequiredtoovercomethestrongforcesofelectrostaticforcesofattractionbetweenthenegativeandpositiveions.(Ioniccompoundsareusuallysolidatroomtemperatureduetothesamereason.) Usuallysolubleinwaterbut insolubleinorganicsolvents. Dissolve to form a solution(aqueousstateandthesymbolis(aq)). Notrequiredtoexplain Conductelectricityintheaqueousandmoltenstatesbutnotinthesolidstate. In solidstate,theionsareheldinfixedpositionsbystrongelectrostatic forces of attraction between the positive andnegative ions. As there are no freemobileionstocarrycharges, ionic compoundscannotconductelectricityinthesolidstate. In moltenor aqueousstates,thestrongelectrostaticforcesofattractionhavebeenovercome,hencetherearemobileionstocarrycharges. Hardandstrong Alargeamountofenergyisrequiredtoovercomethestrongforcesofelectrostaticforcesofattractionbetweenthenegativeandpositiveions. 5. Chemical Formulaeof IonicCompounds 1.Thenameofthenon-metalionusuallyendswith–ide(mostlymonatomic),–ite(polyatomic)or–ate(polyatomic) 2.Nameandformulaeofcomplex(polyatomic)ions[needtoremember theformula]Name Formula hydroxide OH -

sulfate SO4 2- nitrate NO3 - carbonate CO3 2- ammonium NH4 + phosphate PO4 3- 53.Someexamplesofchemicalformulaeofioniccompounds:Chemical formula Name NaCl sodiumchloride CaO calciumoxide NH4 F ammoniumfluoride Ca(OH)2 magnesiumhydroxide BaS bariumsulfide Zn3 N2 zincnitride K2 S potassiumsulfide BaSO4 bariumsulfate 4.Todeterminetheratioofpositivetonegativeions: (a)Thechargesmustbebalancedforthecompoundtobestable(i.e.overallchargemustbe0).(b)Forinorganiccompounds,thesymbolofthemetallicelementwillgofirst.(c)Morethanoneioncanbeinvolvedinformingthecompound.Thenumberofeachionisindicatedbyasubscriptnumberafterthechemicalsymboloftheion.Theratioshouldbethesimplestratio.“1”isbydefaultanddoesnotneedtobeindicatedinthechemicalformula.(d)Polyatomicionscannotbesplitupandshouldbeconsideredasawhole.Bracketsarerequiredtogroupthem. 5.Somecommonacidsandtheirchemicalformulae:Substance Chemical formula Hydrochloricacid HCl

Nitricacid HNO3 Sulfuricacid H2 SO4 Phosphoricacid H3 PO4 6Covalent Bonding 1. Covalent Bond: SharingElectrons 1.Covalentbondinginvolvesthesharingofelectronswithnotransferormovementofelectronsbetweentwoatoms.Moleculesareformed,notions. 2.Thistypeofbondingoccurswhennon-metalatomsbondtogethersoastoachievethestableelectronicconfigurationofanoblegaswithfullelectronshells. 3.Covalentcompoundscanbecategorisedintosimplemolecules(simplemolecularstructure)andgiantmolecules(giantmolecularstructure). (a)Exampleofsimplemolecules:chlorine,methane,carbondioxideandwater(b)Exampleofgiantmolecules:diamond,graphiteandsilicondioxide 2. SimpleMolecules 1.Simplecovalentcompoundsexistassimple,discretemolecules.2.Atomsareheldtogetherbystrongcovalentbonds.3.Moleculesareheldtogetherbyweakintermolecula