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Unformatted text preview: VB theory VB = V alence B ond tries to explain how bonds form predicts which orbitals / hybrid orbitals* are used Hybrid orbitals : created from s,p,d orbitals as required . Bonding (VB Theory) Use the H atom orbitals, superimposed and filled using Aufbau and Pauli Principles and Hunds Rule. VB Theory: A bond occurs when a HALF filled orbital from one atom overlaps with another HALF filled orbital on another atom. What if the orbitals dont have the right geometry? What if there are not enough halffilled orbitals? Use HYBRIDIZATION: Mixing of orbitals to make new hybrid orbitals. ALWAYS MAKE THE SAME NUMBER OF HYBRID ORBITALS AS ATOMIC ORBITALS YOU START WITH!! Each hybrid orbital has its own equation, so has its own shape. Hybridization (VB Theory) sp Hybridization (for 2 RHED) s p HYBRIDIZE sp + sp sp sp sp Hybridization (for 2 RHED) = position of nucelus Actual orientation: Angles: 180 sp 2 Hybridization (for 3 RHED) s p HYBRIDIZE + p + sp 2 sp 2 sp 2 sp 2 sp 2 sp 2 = position of nucelus sp 2 Hybridization (for 3 RHED) Actual orientation: Angles: 120 sp 3 Hybridization (for 4 RHED) s p HYBRIDIZE + p + p + sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 sp 3 = position of nucelus Actual orientation: sp 3 sp 3 Hybridization (for 4 RHED) Angles: 109.5 sp 3 d Hybridization (for 5 RHED) s p HYBRIDIZE + p + p + sp 3 d + d sp 3 d sp 3 d sp 3 d sp 3 d sp 3 d = position of nucelus sp 3 d Hybridization (for 5 RHED) sp 3 d sp 3 d sp 3 d sp 3 d Actual orientation: Angles: 90, 120, 180 sp 3 d 2 Hybridization (for 6 RHED) s p HYBRIDIZE + p + p + sp 3 d 2 + d + d sp 3 d 2 sp 3 d 2 sp 3 d 2 sp 3 d 2 sp 3 d 2 = position of nucelus sp 3 d 2 sp 3 d 2 sp 3 d 2 sp 3 d 2 Actual orientation: sp 3 d 2 sp 3 d 2 sp 3 d 2 Hybridization (for 6 RHED) Angles: 90, 180 Peripheral atoms Note that we also hybridize these. Same procedure as for the central atoms... there will be more lone pairs. RHED ELECTRONIC GEOMETRY HYBRIDIZATION OF CENTRAL ATOM # lone pairs MOLECULAR GEOMETRY ANGLES (lone pairs may distort these slightly) 2 linear sp linear 180 3 trigonal planar sp 2 trigonal planar 120 3 trigonal planar sp 2 1 bent 120 4 tetrahedral sp 3 tetrahedral 109.5 4 tetrahedral sp 3 1 trigonal pyramidal 109.5 4 tetrahedral sp 3 2 bent 109.5 5 trigonal bipyramidal sp 3 d trigonal bipyramidal 90, 180, 120 5 trigonal bipyramidal sp 3 d 1 seesaw 90, 180, 120 5 trigonal bipyramidal sp 3 d 2 T shape 90, 180 5 trigonal bipyramidal sp 3 d 3 linear 180 6 octahedral sp 3 d 2 octahedral 90, 180 6 octahedral sp 3 d 2 1 square pyramidal 90, 180 6 octahedral sp 3 d 2 2 square planar 90, 180 6 octahedral sp 3 d 2 3 T shape 90, 180 6 octahedral sp 3 d 2 4 linear 180 VSEPR AND VB FULL SUMMARY An empty table is posted on BB to help you practice.. SIGMA BOND: formed by end to end overlap of orbitals (all hybrids, s and p orbitals can overlap this way) ALL SINGLE BONDS ARE SIGMA BONDS...
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 Fall '07
 Fakhreddine/Lyon
 Chemistry, Atom, Valence

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