Bonding in diatomic moleculesCH101 Fall 2012Boston UniversityBoston University Slideshow Title Goes HereFigures on slides 4‐6, 8, 9, 18, 19, 22 and 32−34 are used with permission from Clayden et al., Organic Chemistry (Oxford University Press, 2000), © 2007 Oxford University Press.Figures on slides 7, 14‐16, 0, 23 and 24 are used with permission from Mahaffy et al., Chemistry: Human Activity, Chemical Reactivity (Nelson, 2011), © 2011 Nelson Education Ltd.Figure on slides 26 are used with permission from Laird, University Chemistry (McGraw‐Hill, 2009), © 2009 The McGraw‐Hill Companies.Bonding in diatomic molecules2Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereAtoms interact by merging wavesAO + AO  2 MOsBonding in diatomic molecules3Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereRelative AO phase determines MO character Bonding in diatomic molecules4Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Hereσ MO’s have cylindrical symmetryBonding in diatomic molecules5Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here1sσ and 1sσ*Bonding in diatomic molecules6Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here1sσ and 1sσ*Mahaffy et al., Figure 10.20Bonding in diatomic molecules7Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here1sσ (lower) and 1sσ* (upper)Bonding in diatomic molecules8Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Hereσ is “bonding” and σ*is “antibonding”Bonding in diatomic molecules9Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereBonding PE , KE and total EAttractive (< 0) PE is opposed by repulsive (> 0) KE.Molecular size is at minimum of total E.Bonding in diatomic molecules10Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereAntibonding PE , KE and total ERepulsive (> 0) PE enhanced by repulsive (> 0) KE. No minimum of total E ‐‐‐ atoms fly apart!Bonding in diatomic molecules11Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereBonding and antibonding total EWhat matters are the total bonding and antibonding E at the bonding minimum versus the AO energies‐‐‐the energy at infinite separation.Bonding in diatomic molecules12Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereCorrelation diagrams …… summarize bonding and antibonding effectsBonding in diatomic molecules13Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereFilling of MO’s  H2MO configurationMahaffy et al., Figure 10.20Bonding in diatomic molecules14Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereFilling of MO’s  He2MO configurationMahaffy et al., Figure 10.21Bonding in diatomic molecules15Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereFilling of MO’s  Li2MO configurationMahaffy et al., Figure 10.22Bonding in diatomic molecules16Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereBond order(bonding e‐’s – antibonding e‐’s)/2Division by two is because a single bond shares a pair of electronsH2+= H∙H+ bond order = 1/2H2= H:H  bond order = 1He2 bond order = 0He2+ bond order = …?Bonding in diatomic molecules17Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here1s (and 2s) σ and σ*Bonding in diatomic molecules18Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here2pzσ and 2pzσ*Bonding in diatomic molecules19Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here2pzσ and 2pzσ*Mahaffy et al., Figure 10.23Bonding in diatomic molecules20Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here2pzσ (lower) and 2pzσ* (upper)Bonding in diatomic molecules21Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here2pxπ and 2pxπ*Bonding in diatomic molecules22Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes Here2pxπ and 2pxπ*Mahaffy et al., Figure 10.24Bonding in diatomic molecules23Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereHomonuclear diatomics, up to N2Mahaffy et al., Figure 10.25Bonding in diatomic molecules24Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereHomonuclear diatomics, after N2Bonding in diatomic molecules25Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereHomonuclear diatomicsLaird, University Chemistry, Figure 3.4Bonding in diatomic molecules26Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereHomonuclear diatomicsChallenge: Of H2, Li2, and Be2, which is/are most stable?Challenge: In Li2, what contribution to bonding is due to MO’s made from 1s AO’s?Challenge: N2, O2, F2, Ne2TurningPoint lesson: Homonuclear diatomic moleculeshttp://goo.gl/404yQ Bonding in diatomic molecules27Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereWhich AO’s combine?SOE: Symmetry, Overlap, Energy Symmetry: Which AO’s can combine to form MO’s? Overlap: Which AO’s combine with the greatest bonding/antibonding effect? Energy: How does relative AO energy affect composition of MO’s?Bonding in diatomic molecules28Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereSymmetry: Net overlap or not? For a pair of AO’s to give a (bonding/antibonding) pair of MO’s, there must be net overlap (in‐phase or net out‐of‐phase). If in‐phase and out of phase overlap exactly balance, the AO’s remain uncombined, as nonbonding orbitals.Bonding in diatomic molecules29Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereOverlap: Greater the better The more net overlap, the greater the bonding/antibonding effect. Core AO’s have least overlap Valence AO’s have greatest overlap Bonding due to MO’s made from valence AO’sBonding in diatomic molecules30Copyright © 2012 Dan Dill [email protected] University Slideshow Title Goes HereEnergy: Closer the better The closer AO’s are in energy, the greater the bonding/antibonding effect. If AO’s have same energy (identical atoms, homonuclear