Focus on local effectsLook at BondsBeH2 H-Be-H2 Steric number: 2 …sp …Bond angle should be 180 degreesBe[He]2s2 [He]2s12p1 hybridization [He](sp)2 forms 2 bonds at 180 degrees. Each better than s or pBF3 steric number is 3…is sp2B [He]2s22p1 [He]2s12p2Hybrid [He]2(sp2)3Ch4 steric number is 4… sp3
Lecture 17: 10/27/1114:12Review of Lecture 16:Mos – solutions to schrodinger equation for the system H2+ describing the electron density over the whole moleculeMos for H2+ come in bonding and antibonding forms; Bonding if the probability desnsity is enhanced in space between nuclei,Antibonding if it is loweredCorresponding to lower and higher energyMos can be envisioned as created fro Aos of individual atomsMO does not tell you about geometry – no shit PCl5 [Ne]3s23p3 (promote) [Ne]3s13p33d1 (hybridize) [Ne] 3(sp3d)5 sp3dSf4? S[Ne]3s23p4 [Ne]3s13p43d1 [Ne] 3 (sp3d)6one filled hybrid and 4 sigma bondsSp3d2could be [Ne]3s13p33d2 [Ne] 3(sp3d2)66 sigma bonds to 6 half filled hybrids
Lecture 17: 10/27/1114:12Ethene C2H4C [He] 2s22p2 [He]2s12sp3 [He] 2 (sp3)4 SN4Or [He] 2 (sp2)3 2p1 SN3Or [He] 2 (sp)2 2p2 SN 2 Basically C can hybridize in sp, sp2, or sp3 Sigma bonds establish skeleton pattern and geometry Then leftover electrons if half filled make pi orbitals There electrons manage to avoid interfering too much w/ other electrons 2nd carbon bond is above and below the C-C sigma bondHF H: 1sF: 1s22s22p5Bond from 1sHydrogen to 2pfluorine From 2px 2py to 1 s nonbonding…Which things bond = based on how much it has more constructive interference MO looks more like F orbital in bonding orbital b/c F is greedyMO looks more like H orbital in antibonding orbital b/c H starts off at a higher energy…MOs look like AOs except where the energies are similarNonbonding.. localized ..dont count Relative position of energy levels corresponds to electronegativity: Lower energy = more electronegative MO in polyatomic molecules : BeH2Extend over whole molecule !
Lecture 18: 11/01/1114:12Review Lecture 17:
Lecture 18: 11/01/1114:12Valence bond theory – envisions the molecule as composed of pairwise AOs with bond overlap. Better for understanding local effects, eg geometry, hybridization of AOs to give geometry of VSEPR unique chemical features best explained by VbHeteronuclear MOs need to assess which orbitals are available for bonding, which are non bonding.Resonance best described by hybrid of MO and VB theory Review session Baker 200, sat 2:00 pm and sun 5:30 pm MO’s on moleculeLowest E MO’s in BeH22s (we don’t care about the nonvalence orbitals)
Lecture 18: 11/01/1114:12Ions [noble gas] nd^xMultiple oxidation states, eg +3,+4, etc Most metals M from transition metals M(L)m+ or m- nL=ligandProvides e-: Ce-, OH-, NH3, CN-, SCN-N=2,4,6Colored complexes There are low energy MO to MO transitions 6 coordinate structures:octahedral electrons prefer their own orbitalselectrons prefer lower E orbitals Delta O about equal to pairing energies
Lecture 18: 11/01/1114:12Pairing energy depends on (L)igandFe(Cl)Fe3+ d5high spin