dr. s. m. condren chapter 10 bonding and molecular structure: orbital hybridization and molecular...
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Dr. S. M. Condren
Chapter 10
Bonding and Molecular Structure:
Orbital Hybridization and Molecular Orbitals
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Dr. S. M. Condren
Advanced Theories of Chemical Bonding
Atomic OrbitalsAtomic Orbitals MoleculesMolecules
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Dr. S. M. Condren
• MOLECULAR ORBITAL THEORY — —
• Robert Mullikan (1896-1986)Robert Mullikan (1896-1986)
• valence electrons are valence electrons are delocalizeddelocalized
• valence electrons are in valence electrons are in orbitals (called molecular orbitals (called molecular orbitals) spread over entire orbitals) spread over entire molecule.molecule.
Two Theories of Bonding
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Dr. S. M. Condren
Two Theories of Bonding
• VALENCE BOND THEORY — Linus — Linus PaulingPauling
• valence electrons are valence electrons are localized between atoms localized between atoms (or are lone pairs).(or are lone pairs).
• half-filled atomic orbitals half-filled atomic orbitals overlap to form bonds.overlap to form bonds.
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Dr. S. M. Condren
Sigma Bond Formation by Orbital Overlap
Two s orbitals Two s orbitals overlapoverlap
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Dr. S. M. Condren
Two s Two s orbitals orbitals overlapoverlap
Two p Two p orbitals orbitals overlapoverlap
Sigma Bond Formation
One s One s and one p and one p orbitalorbitaloverlapoverlap
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Dr. S. M. Condren
Using VB Theory
Bonding in BFBonding in BF33
planar triangleplanar triangleangle = 120angle = 120oo
F
F F
Boron configuration
2p2s1s•• ••
••••
••
•• ••
••••
B
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Dr. S. M. Condren
• How to account for 3 bonds 120How to account for 3 bonds 120oo apart using a apart using a spherical s orbital and p orbitals that are 90spherical s orbital and p orbitals that are 90oo apart?apart?
• Pauling said to modify VB approach with Pauling said to modify VB approach with
ORBITAL HYBRIDIZATION• — — mix available orbitals to form a new set mix available orbitals to form a new set
of orbitals — of orbitals — HYBRID ORBITALS — that — that will give the maximum overlap, in the will give the maximum overlap, in the
correct geometry.correct geometry.
Bonding in BF3
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Dr. S. M. Condren
Bonding in BF3
rearrange electronshydridize orbs.
unused porbital
three sp2 hybrid orbitals
2p2s
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Dr. S. M. Condren
• The three hybrid orbitals are made from 1 The three hybrid orbitals are made from 1 s orbital and 2 p orbitals s orbital and 2 p orbitals 3 sp 3 sp22 hybrids. hybrids.
• Now we have 3, half-filled HYBRID orbitals Now we have 3, half-filled HYBRID orbitals that can be used to form B-F sigma bonds.that can be used to form B-F sigma bonds.
Bonding in BF3
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Dr. S. M. Condren
An orbital from each F overlaps one of the An orbital from each F overlaps one of the spsp22 hybrids to form a B-F hybrids to form a B-F bond. bond.
B
F
F
F
B
F
F
F
B
F
F
F
B
F
F
F
Bonding in BF3
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Dr. S. M. Condren
BF3, Planar Trigonal
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Dr. S. M. Condren
Bonding in CH4
How do we account for 4 CHow do we account for 4 C
—H sigma bonds 109—H sigma bonds 109oo
apart? apart?
Need to use 4 atomic Need to use 4 atomic
orbitals — s, porbitals — s, pxx, p, pyy, and , and
ppzz — to form 4 new — to form 4 new
hybrid orbitals pointing in hybrid orbitals pointing in
the correct direction.the correct direction.
109o109o
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Dr. S. M. Condren
Bonding in CH4
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Dr. S. M. Condren
Bonding in a Tetrahedron — Formation of Hybrid Atomic Orbitals
4 C atomic orbitals 4 C atomic orbitals hybridize to form hybridize to form four equivalent spfour equivalent sp33 hybrid atomic hybrid atomic orbitals.orbitals.
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Dr. S. M. Condren
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Dr. S. M. Condren
O
CO H
H
H
NH
Hsp3
sp3
sp3
sp2
••
••••C
Bonding in Glycine
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Dr. S. M. Condren
BONDSBONDS SHAPESHAPE HYBRID HYBRID
REMAINREMAIN
22 linearlinear sp sp 2 p’s2 p’s
33 trigonaltrigonal sp sp22 1 p1 pplanarplanar
44 tetrahedral sptetrahedral sp33 nonenone
Orbital Hybridization
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Dr. S. M. Condren
C
H
H
H
H
sp2120Þ C
Multiple Bonds
Consider ethylene, CConsider ethylene, C22HH44
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Dr. S. M. Condren
C
H
H
H
H
sp2120Þ C
Sigma Bonds in C2H4
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Dr. S. M. Condren
π π Bonding in C2H4
The unused p orbital on each The unused p orbital on each C atom contains an C atom contains an electron and this p orbital electron and this p orbital overlaps the p orbital on overlaps the p orbital on the neighboring atom to the neighboring atom to form the π bond.form the π bond.
p orb.for šbond
3 sp 2
hybrid orbitals
2p2s
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Dr. S. M. Condren
π Bonding in C2H4
The unused p orbital on each C atom contains an The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital electron and this p orbital overlaps the p orbital
on the neighboring atom to form the π bond.on the neighboring atom to form the π bond.
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Dr. S. M. Condren
Multiple Bondingin C2H4
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Dr. S. M. Condren
and π Bonding in C2H4
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Dr. S. M. Condren
and π Bonding in CH2O
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Dr. S. M. Condren
and π Bonding in C2H2
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Dr. S. M. Condren
and π Bonding in C2H2
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Dr. S. M. Condren
Consequences of Multiple BondingThere is restricted rotation around C=C bond.There is restricted rotation around C=C bond.
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Dr. S. M. Condren
Consequences of Multiple Bonding
Restricted rotation around C=C bond.Restricted rotation around C=C bond.
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Dr. S. M. Condren
Diatomic MoleculesAO MO AO
H H2 H
1s
ENERGY
1s
B - AB 2 - 0B.O. = ------------ = -------- = 1 2 2all electrons are paired, thus diamagnetic
B => bonding electrons
AB => antibonding electrons
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Dr. S. M. Condren
Diatomic MoleculesAO MO AO
He He2 He
1s
ENERGY
1s
B - AB 2 - 2B.O. = ------------ = -------- = 0 2 2
Zero bond order means it does not exist
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Dr. S. M. Condren
Diatomic MoleculesAO MO AO
He He2 He+
1s
ENERGY
1s
B - AB 2 - 1B.O. = ------------ = -------- = 1/2 2 2
One unpaired electron, thus, paramagnetic
+
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Dr. S. M. Condren
1s 1snonbonding
AOB
AOB
MOB2
2s 2s
2p 2p
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Dr. S. M. Condren
Molecular Orbital Diagram
side-by-side
end-to-end
bonding MO
bonding MO
antibonding MO
antibonding MO
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Dr. S. M. Condren
1s 1snonbonding
AOC
AOC
MOC2
2s 2s
2p 2p
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Dr. S. M. Condren
1s 1snonbonding
AOO
AOO
MOO2
2s 2s
2p 2p
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Dr. S. M. Condren
Ene
rgy