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Unformatted text preview: Advanced Theories of Chemical Bonding
Chapter 10 1 Two Theories of Bonding
• MOLECULAR ORBITAL THEORY — Robert Mullikan (18961986) • valence electrons are delocalized • valence electrons are in orbitals (called molecular orbitals) orbitals) spread over entire molecule. 2 Two Theories of Bonding
• 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. 3 Atomic Orbitals Molecules Sigma Bond Formation by Orbital Overlap
Two s orbitals overlap 4 Sigma Bond Formation
Two s orbitals overlap 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 8 9 Bonding in BF3
• How to account for 3 bonds 120o apart using apart a spherical s orbital and p orbitals that are 90o apart? • Pauling said to modify VB approach with Bonding in BF3
2s hydridize orbs. 2p rearrange electrons Bonding in BF3 3
• The three hybrid orbitals are made The from 1 s orbital and 2 p orbitals 3 sp2 sp hybrids. 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 three sp 2 hybrid orbitals unused p orbital
• 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 Bonding in BF3 3 10 11 Bonding in CH4
How do we account for 4 C—H sigma bonds 109o apart? apart? Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 12 109o 109o An orbital from each F overlaps one of the sp2 hybrids to form a B-F bond. hybrids bond.
F F F F B B F F Need to use 4 atomic orbitals — s, px, py, and pz — to form 4 new to hybrid orbitals pointing in the correct direction. 4 C atom orbitals hybridize to form 3 four equivalent sp 3 hybrid atomic orbitals. orbitals. Page 2 Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals 13 14 15 Bonding in CH 4 Orbital Hybridization
Figure 10.5 Figure 10.5 BONDS 2 4 C atom orbitals 4 C atom hybridize to form hybridize to form four equivalent sp 3 four equivalent sp 3 hybrid atomic hybrid atomic orbitals. orbitals. orbitals.
Figure 10.6 SHAPE linear trigonal planar HYBRID REMAIN sp sp2 2 p’s 1p none 3 4 tetrahedral sp 3 16 17 18 Bonding in Glycine
3 Bonding in Glycine
3 H •• HN sp
3 O sp 2 H •• HN sp
3 O sp 2 C HH C •• OH •• sp
3 C HH C •• OH •• sp 3 Page 3 19 20 21 Bonding in Glycine
3 Bonding in Glycine
2 Bonding in Glycine
2 H •• HN sp
3 O sp 3 sp H •• HN sp
3 O C sp sp 3 H •• HN sp
3 O C sp 2 C HH C •• OH •• sp
3 C HH •• OH •• sp 3 C HH •• OH •• sp 3 Multiple Bonds
Consider ethylene, C 2H4 22 23 23 24 Sigma Bonds in C2H4
H H C H C H sp
2 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
10.9) H 120˚ H C C H sp H
2 120˚ 2s 2p 3 sp 2 hybrid orbitals p orb. for bond Page 4 25 26 27 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. 10.9) (See Multiple Bonding in C2H4 and and Bonding in C2H4 Figure 10.11 28 29 and and Bonding in CH2O CH and and Bonding in C2H2 Consequences of Multiple Bonding
There is restricted rotation around C=C bond. 30 Figure 10.13 Figure 10.12 Figure 10.14 Page 5 Consequences of Multiple Bonding
Restricted rotation around C=C bond. 31 32 Double Bonds and Vision See Butene.Map in ENER_MAP in CAChe models. Butene.Map
See Screen 10.13, Molecular Orbitals and Vision See also Chapter Focus 10, page 380 Page 6 ...
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This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.
- Fall '08