Dr. S. M. Condren Chapter 10 Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals.
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Dr. S. M. Condren
Chapter 10
Bonding and Molecular Structure:
Orbital Hybridization and Molecular Orbitals
Dr. S. M. Condren
Advanced Theories of Chemical Bonding
Atomic OrbitalsAtomic Orbitals MoleculesMolecules
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
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.
Dr. S. M. Condren
Sigma Bond Formation by Orbital Overlap
Two s orbitals Two s orbitals overlapoverlap
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
Dr. S. M. Condren
Using VB Theory
Bonding in BFBonding in BF33
planar triangleplanar triangleangle = 120angle = 120oo
F
F F
Boron configuration
2p2s1s•• ••
••••
••
•• ••
••••
B
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
Dr. S. M. Condren
Bonding in BF3
rearrange electronshydridize orbs.
unused porbital
three sp2 hybrid orbitals
2p2s
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
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
Dr. S. M. Condren
BF3, Planar Trigonal
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
Dr. S. M. Condren
Bonding in CH4
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.
Dr. S. M. Condren
Dr. S. M. Condren
O
CO H
H
H
NH
Hsp3
sp3
sp3
sp2
••
••••C
Bonding in Glycine
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
Dr. S. M. Condren
C
H
H
H
H
sp2120Þ C
Multiple Bonds
Consider ethylene, CConsider ethylene, C22HH44
Dr. S. M. Condren
C
H
H
H
H
sp2120Þ C
Sigma Bonds in C2H4
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
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.
Dr. S. M. Condren
Multiple Bondingin C2H4
Dr. S. M. Condren
and π Bonding in C2H4
Dr. S. M. Condren
and π Bonding in CH2O
Dr. S. M. Condren
and π Bonding in C2H2
Dr. S. M. Condren
and π Bonding in C2H2
Dr. S. M. Condren
Consequences of Multiple BondingThere is restricted rotation around C=C bond.There is restricted rotation around C=C bond.
Dr. S. M. Condren
Consequences of Multiple Bonding
Restricted rotation around C=C bond.Restricted rotation around C=C bond.
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
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
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
+
Dr. S. M. Condren
1s 1snonbonding
AOB
AOB
MOB2
2s 2s
2p 2p
Dr. S. M. Condren
Molecular Orbital Diagram
side-by-side
end-to-end
bonding MO
bonding MO
antibonding MO
antibonding MO
Dr. S. M. Condren
1s 1snonbonding
AOC
AOC
MOC2
2s 2s
2p 2p
Dr. S. M. Condren
1s 1snonbonding
AOO
AOO
MOO2
2s 2s
2p 2p
Dr. S. M. Condren
Ene
rgy
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