Ch10_Hybrids

Ch10_Hybrids - Advanced Theories of Chemical Bonding 1...

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Unformatted text preview: Advanced Theories of Chemical Bonding 1 Chapter 10 Atomic Orbitals • MOLECULAR ORBITAL THEORY — Robert Mullikan (18961986) • valence electrons are delocalized • valence electrons are in orbitals (called molecular orbitals) spread over entire molecule. Molecules Sigma Bond Formation by Orbital Overlap Two Theories of Bonding 2 4 • VALENCE BOND THEORY — Linus Pauling • valence electrons are localized between atoms (or are lone pairs). • half-filled atomic orbitals overlap to form bonds. • See Screen 10.3 and Figures 10.1 and 10.2. Sigma Bond Formation Two s orbitals overlap Two s orbitals overlap Two Theories of Bonding 3 Two p orbitals overlap 5 6 Using VB Theory Bonding in BF3 • •• • •F• Boron configuration B •• • ••• F F ••• 2p 2s •• • 1s planar triangle planar angle = 120o Page 1 7 Bonding in BF3 8 Bonding in BF3 • How to account for 3 bonds 120o apart using a spherical s orbital and p orbitals that are 90o apart? • Pauling said to modify VB approach with hydridize orbs. Bonding in BF3 3 • The three hybrid orbitals are made The from 1 s orbital and 2 p orbitals 3 sp2 hybrids. 2p 2s 9 rearrange electrons ORBITAL HYBRIDIZATION • — mix available orbitals to form a new set of orbitals — HYBRID ORBITALS HYBRID — that will give the maximum overlap in the correct geometry. (See Screen 10.6) (See in three sp 2 hybrid orbitals unused p orbital 10 Bonding in BF3 3 11 Bonding in CH4 How do we account for 4 C—H sigma bonds 109o apart? An orbital from each F overlaps one of the sp2 hybrids to form a B-F bond. F F F F • Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds. See Figure 10.9 and Screen 10.6 B B F F Need to use 4 atomic orbitals — s, px, py, and pz — to form 4 new hybrid orbitals pointing in the correct direction. Page 2 109o 109o Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 4 C atom orbitals orbitals hybridize to form 3 four equivalent sp 3 hybrid atomic orbitals. orbitals. 12 Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 13 14 15 Orbital Hybridization Bonding in CH 4 Figure 10.5 Figure 10.5 BONDS 2 linear sp 2 p’s 3 trigonal planar sp2 1p 4 4 C atom orbitals 4 C atom orbitals hybridize to form hybridize to form four equivalent sp 3 four equivalent sp 3 hybrid atomic hybrid atomic orbitals. orbitals. SHAPE HYBRID REMAIN tetrahedral sp 3 none Figure 10.6 16 17 18 Bonding in Glycine sp 3 •• HN sp 3 Bonding in Glycine H C HH C •• OH •• sp Page 3 sp sp 2 O 3 3 •• HN sp 3 H C HH O sp 2 C •• OH •• sp 3 19 20 Bonding in Glycine sp •• HN sp 3 H C HH sp O C HH C sp sp 2 3 H O C HH C •• HN sp 3 sp 3 H C sp C H H H 2 2 •• OH •• 24 Bonding in C 2H4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the bond. (See Fig. (See form 10.9) 2s Page 4 sp sp 3 23 23 H C sp 2 •• OH •• 3 120˚ H H sp Sigma Bonds in C2H4 Consider ethylene, C 2H4 H H •• HN 3 Bonding in Glycine 3 22 Multiple Bonds C sp 2 C •• OH •• sp 120˚ Bonding in Glycine 3 O 21 2p 3 sp 2 hybrid orbitals p orb. for bond 25 26 Bonding in C 2H4 and and Multiple Bonding in C2H4 The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the neighboring atom to form the bond. (See Fig. 10.9) (See 27 Bonding in C2H4 Figure 10.11 28 and and Bonding in CH2O CH 29 and and Bonding in C2H2 Consequences of Multiple Bonding There is restricted rotation around C=C bond. Figure 10.13 Figure 10.12 Figure 10.14 Page 5 30 Consequences of Multiple Bonding 31 32 Double Bonds and Vision Restricted rotation around C=C bond. See Butene.Map in ENER_MAP in CAChe models. See See Screen 10.13, Molecular Orbitals and Vision and See also Chapter Focus 10, page 380 Page 6 ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Mcquade during the Fall '08 term at FSU.

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