COVALENT BONDING

Online Classes : Megalecture@gmail.com1893 Chemical bondingThis topic introduces the different ways by which chemical bonding occurs and theeffect this can have on physical properties.3.2 Covalent bonding and co-ordinate (dative covalent) bondingCOVALENT BONDINGBILAL HAMEEDCOVALENT BONDINGwww.youtube.com/megalecture

Cambridge International AS and A Level Chemistry 9701 syllabus Syllabus contentOnline Classes : Megalecture@gmail.com3 Chemical bonding190This topic introduces the different ways by which chemical bonding occurs and the effect this can have3bondingonChemicalphysical properties.This topic introduces the different ways by which chemical bonding occurs and the effect this can haveon physical properties.Learning outcomesCandidates should be able to:3.1 Ionic bondingLearning outcomesCandidatesbe able to:a) describeshouldionic bonding,as in sodium chloride, magnesium oxide andcalcium fluoride, including the use of ‘dot-and-cross’ diagrams3.1 Ionic bonding3.2 Covalent bondingand co-ordinate(dative covalent)3.2 s covalent)of simple(dativemoleculesbondingincludingshapes of simplemoleculesa) describe ionic bonding, as in sodium chloride, magnesium oxide andincludinguse of ‘dot-and-cross’diagramsa) calciumdescribe,fluoride,includingthe usetheof ‘dot-and-cross’diagrams:(i) covalent bonding, in molecules such as hydrogen, oxygen, chlorine,a) describe,includingthe carbonuse of de, methane,ethene(i)bonding,moleculessuch assuchhydrogen,oxygen,chlorine,(ii) covalentco-ordinate(dativeincovalent)bonding,as in theformationof ion andcarbonin the uchas in theformationof theb) (ii)describecovalentbondingin termsof orbitaloverlap,givingσ and π23ammoniumin the dconcepttoformsp,spandsp26orbitals (seealso Sectionb) describecovalentbonding14.3)in terms of orbital overlap, giving σ and πtheof,conceptof hybridisationto form sp,sp2 andc) bonds,explain includingthe shapesand bondangles in, moleculesby usingthesp3orbitals(seealso Section14.3) repulsion (including lone pairs), usingqualitativemodelof electron-pairas simpleCO2 in,(linear),CH4 (tetrahedral),3 (trigonal),c) explaintheexamples:shapes of,BFandbond anglesmoleculesby using theNH3(pyramidal),modelH2O (non-linear),SF6 (octahedral),PF5 (trigonalbipyramidal)qualitativeof electron-pairrepulsion (includinglone pairs),usingsimpleCO2 in,(linear),CH4 (tetrahedral),NH3d) aspredicttheexamples:shapes of,BFandbond anglesmoleculesand ions analogous3 (trigonal),SF6also(octahedral),PF5 (trigonal bipyramidal)(pyramidal),H2O (non-linear),to those specifiedin 3.2(b) (seeSection 14.3)3.3 Intermolecularforces,electronegativity3.3 Intermolecularand bond propertiesforces,electronegativityand bond propertiesd) predict the shapes of, and bond angles in, molecules and ions analogousthose specified3.2(b) (seealsoSection and14.3)water as simplea) todescribehydrogeninbonding,usingammoniaexamples of molecules containing N–H and O–H groupsa)hydrogenbonding,ammoniawater as simpleb) describeunderstand,in simpleterms,usingthe conceptof andelectronegativityand applyexamplesofthemoleculescontainingN–H andO–Hgroupsit to explainpropertiesof moleculessuchas bondpolarity (seealso Section eb) negativitybehaviourofoxideswithwater(9.2(c))it to explain the properties of molecules such as bond polarity (seeSection3.3(c)),the energy,dipole momentsof molecules(3.3(d)) andc) alsoexplainthe termsbondbond lengthand bond polarityand theusebehaviourof oxideswater (9.2(c))them to comparethewithreactivitiesof covalent bonds (see also Section5.1(b)(ii))the terms bond energy, bond length and bond polarity and usec) explaind) themdescribeintermolecularforces (vander Waals’forces),onto comparethe reactivitiesof covalentbonds(seebasedalso Sectionpermanent and induced dipoles, as in, for example, CHCl 3(l); Br2(l) and5.1(b)(ii))theliquidintermolecularGroup 18 elementsd) describeforces (van der Waals’ forces), based on3.4 Metallic bonding3.4 Metallic bonding3.5 Bonding andphysical properties3.5 Bonding andphysical propertiespermanent and induced dipoles, as in, for example, CHCl 3(l); Br2(l) andtheliquid metallicGroup 18elementsa) describebondingin terms of a lattice of positive ionssurrounded by delocalised electronsa) describe metallic bonding in terms of a lattice of positive ionsby delocalisedelectronsa) surroundeddescribe, interpretand predictthe effect of different types of bonding(ionic bonding, covalent bonding, hydrogen bonding, other intermolecularinteractions,metallicbonding)on thephysicalpropertiesofofsubstancesa) describe,interpretandpredict theeffectof differenttypesbondingb) (ionicdeducethe typeof bondingpresentfrom nding,other intermolecularmetallic ofbonding)on reactionsthe physicalpropertiesof substancesc) interactions,show understandingchemicalin termsof energytransfersassociatedbreakingpresentand makingchemicalbondsb) deducethe withtype theof bondingfrom ofgiveninformationc) show understanding of chemical reactions in terms of energy transfersassociated with the breaking and making of chemical bondsBack to contents pageBack to contents pageBILAL 19COVALENT BONDINGwww.youtube.com/megalecture

Online Classes : Megalecture@gmail.com191O OCHEMICAL BONDING C H E MIC A L BON DING AWhenN D S T RtwoU C T UorR Emore atoms form a chemicalO OOONote that in this Lewis structure of O2 there are a total of fbondingpairstheof electrons(the heldlone pairs) and two boncompound,atoms arepairs of electrons.together in a characteristic arrangement by attractive forces.of a covalent bondnd is formed by thettraction between a sharedns and the positivelyi. According to IUPAC (theUnion of Pure and Appliedcovalent bond is a region ofelectron density betweenses at least partly fromelectrons and gives risee force and characteristicistance.Covalent bondingNitrogen, N2TheInchemicalbondis howthe atomsforcecanofeitherattractionbetweenatomsaionic bondingwe sawlose or gainelectronsinNitrogenis inanygrouptwo15, sohas fiveinvalenceelectrons. Hencorder to attain a noble gas electron configuration. Aacquiringsecond typeofthree more electrons nitrogen would achieve a ncompound.Theattractionthe repulsion ofchemical bondexists,however, isin thewhichforceatoms thatshare overcomeselectronseachelectron withconfigurationwith a complete octet of electrons.in order chargedto attain a noblegas electronThis type ofthe otherpositivelynucleiof the configuration.two atoms.If two nitrogen atoms each share three electrons with each oth bonding is covalent bonding, and it usually occurs between non-metals.electron configuration can be achieved and results in the formaIn order to lookat this typeof bondingin detail, itareis usefulfirstto siblefor thechemicalcovalentbondthe twonitrogen atoms. This covalentintroduce the idea of a Lewis symbol, which is a simpleandconvenienttriple bond and the three shared pairs can be represented bybond.Weofshallfocus ourattentiontheseelectronsand the electronmethodrepresentingthe valence(outeronshell)electronsof an element.In sub-topic 4.3 we shall develop this further into what weNtermthe NN Narrangementof atoms both before and after bond formation.Lewis (electron dot) structure of a compound, based on a systemdevised by the US chemist, Gilbert N. Lewis (1875–1946).NNIn a Lewis symbol representation, each element is surrounded by a Noteelectronsthat in thisLewis structure of N2 there are a total of tnumber of dots (or crosses), which represent the valenceof the1bondingpairsofelectrons (the lone pairs) and three boelement. Some examples are given in figure 1.pairs of electrons.NLet us consider the presence of covalent bonding in four differentspecies, F2, O2, N2, and HF.Hydrogen fluoride, HFFluorine is in group 17, so has seven valence electrons. Henceacquiring one4 . 2 moreC O V A electron,L E N T B O NfluorineD I N G would attain a noble gaconfigurationwith a complete octet of electrons. Hydrogen isFluorine is in group 17, so has seven valence electrons.Hence byhas justacquiring one more electron, fluorine would attain1,asonoblegas one valence electron. Hence by acquiring just onelectron,hydrogenwould attain the noble gas configurationelectron configuration with a complete octet of electrons. Fluorine, F2Cl O OO ONote that hydrogen does not acquire an octet (the octet ruis historical in nature, and the key point to remember hereO Ohydrogen is the formation of a noble gas electron configurF Note that in this Lewis structure of O2 there areatotal of four non theThesharedLewis symbolsforpairhydrogenand fluorine are:When electrons are shared rather than transferred,electronis referredbonding pairs of electrons (the lone pairs) and two bonding r,eachxbond.Hpairs of electrons.ure 1 Lewis symbols of three to as a covalentfluorine atom gains one more electron to attain a complete octet ofments. Nitrogen has five valenceelectrons,whichtoresultsthe formationa covalentbetweento gain or loseCovalentbondsNtendform inbetweenatomsofwithsimilarbondFtendenciesctrons, chlorine has isasinglebondand the2ence electrons, and boron has electrons. The most obvious examples are the diatomic molecules2, N2, O2, Fsymbols2, Cl2, (a cross and a dot) f resentedbyaline:ee valence electronselectronseach ofthe two Lewis symbols to signify differentthree more electrons nitrogen wouldachieve ina noblegasBr2, and acquiringI2.forelectrons.the two elements.electron configuration with a complete octet of The Lewis symbol for fluorine is: COVALENT BONDINGB deduce the number ofrons of an element you cannumber from the periodicnts. For example, sodiumgroup 1, so has one valenceum (also s-block) is in groupvalence electrons. For thents you simply drop the ‘1’umber to find the number ofons: silicon (p-block) is inas four valence electrons.p-block) is in group 17, soence electrons, and so on. F FO OF FO OachieveIf two nitrogen atoms each share three electrons withToeachother,noblethis gas configurations, fluorine and hydrogenshare oneofelectronwith each other, forming a covalenelectron configuration can be achieved and results ineachthe formationaF two nitrogenFO Obond and the shared pair cacovalentcovalent bond between theatoms. ThisThiscovalentbondbondis a is a singlerepresenteda Lewisline. structure of O there are a total oftriple bond and the three shared pairs can be representedby threelines: Note thatin bythis2Note that in this Lewis structure of F2 there are a total of six nonbondingpairsofelectrons(thelonepairs) and two box onebonding pairs(often called lone pairs) andxFN of electronsN NNHFpairsHof electrons.bonding pair of electrons.Oxygen, O2NNNitrogen, N2HFis in group 15, so has five valence electrons. HenNote thatin groupthis Lewisstructureof N2 thereare a Nitrogentotalof two Oxygenis in16, sohas six valenceelectrons.Henceby non2acquiringthree more electrons nitrogen would achieve abondingtwopairsof electronslonewouldpairs)attainand threebondingacquiringmoreelectrons, (theoxygena noblegaselectronconfigurationwith a complete octet of electrons.pairs ofconfigurationelectrons. with a complete octet of electrons.electron If two nitrogen atoms each share three electrons with each ot If two oxygen atoms each share two electrons with each other, thiselectron configuration can be achieved and results in the formHydrogenfluoride,HFelectron configuration can be achieved and results in the formation of acovalentbondthe two nitrogen atoms. This covalent Fluorinebondis in group17,theso hasvalenceHenceby s.This covalentbondis atriplebondandthethreeshared pairs can be represented byacquiringone andmoreelectron,fluorinea noblebygastwoelectrondoublebondthetwo sharedpairswouldcan beattainrepresentedlines.configuration with a complete octet of electrons. Hydrogen is in groupBILAL HAMEEDCOVALENT moreNN N BONDINGN one1, so has just one valence electron. Hence by acquiring justelectron, hydrogen would attain the noble gas configuration of helium. www.youtube.com/megalectureNN