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Covalent Bonding:Covalent Bonding: Orbitals
The Central Themes of VB Theory
Basic Principle
•A covalent bond forms when the orbitals of two atoms overlap and are occupied by a pair of electrons that have the highest probability of being located between the
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the highest probability of being located between the nuclei.
Themes
•These overlapping orbitals can have up to two electrons that must have opposite spins (Pauli principle).
•The valence orbitals in a molecule are different from those in isolated atoms.
Figure 12.18: Three representations of the hydrogen 1s
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Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance
between the nuclei of the hydrogen atoms.
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Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance
between the nuclei of the hydrogen atoms.
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Figure 12.19b: Representation of the 2p orbitals.
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Hydrogen, H2
3 WAYS TO FORM σMOLECULAR ORBITALS
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Hydrogen fluoride, HF
Fluorine, F2
What about The other 2Atomicp orbitals?
Figure 14.1: (a) Lewis structure of the methane molecule (b) the tetrahedral molecular geometry
of the methane molecule.
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Figure 14.2: valence orbitals on a free carbon atom
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Figure 14.1: (a) Lewis structure of the methane molecule (b) the tetrahedral molecular geometry
of the methane molecule.
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Figure 14.3: native 2s and three 2p atomic orbitals characteristic of a free carbon atome are combined to
form a new set of four sp3 orbitals.
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Carbon 1s22s22p2
Carbon could only make two bondsif no hybridization occurs. However,carbon can make four equivalent bonds.
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s
px py pz
sp3
hybrid orbitals
Ene
rgy
sp3
C atom of CH4 orbital diagram
B
A
BB
B
Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 321
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Figure 14.4: Cross section of an sp3 orbital
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The four sp3 hybrid orbitals in CH4
Promotion
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Figure 11.9 The bonds in ethane.
both C are sp3 hybridizeds-sp3 overlaps to bonds
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sp3-sp3 overlap to form a bondrelatively even
distribution of electron density over all
bonds (Greek sigma) bondshave axial symmetry andgood overlap
Rotation about C-Cbond allowed.
Figure 14.6: Tetrahedral set of four sp3
orbitals on the carbon atom
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Figure 14.7: The nitrogen atom in ammonia is sp3 hybridized.
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The four sp3 hybrid orbitals in CH4
Promotion
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The four sp3 hybrid orbitals in CH4
Promotion
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The four sp3 hybrid orbitals in NH3
Promotion
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N
The four sp3 hybrid orbitals in NH3
Promotion
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N
Figure 11.5 The sp3 hybrid orbitals in H2O
Lone pairs
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Diamond - sp3 hybridized C
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Figure 14.8: The hybridization of the s, px, and py atomic orbitals results in the formation of three
sp2 orbitals centered in the xy plane.
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NB: The remaining p orbital can be empty or serve another function
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The three sp2 hybrid orbitals in BF3
PromotionNote the single left overUnhybridized p orbital on B
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Region of overlap
Unhybridized p orbital on B
Hybrid Orbitals
2s 2p
Ground-state B atom
2s 2p
B atom with one electron “promoted”
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s
px py pzEne
rgy
sp2 2p
B atom of BH3 orbital diagram
hybridize
s orbital
p
sp2
hybrid orbitals
p orbitalssp2 hybrid orbitals shown together
(large lobes only)three sps hybrid orbitals
H
H
HB
Figure 14.10: When one s and two p oribitals are mixed to form a set of three sp2 orbitals, one p orbital remains unchanged and
is perpendicular to the plane of the hybrid orbitals.
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Figure 14.13: (a) The orbitals used to form the bonds in ethylene. (b) The Lewis structure for ethylene.
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The plastics shown here were manufactured with ethylene.
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Source: Comstock - Mountainside, NJ
Figure 14.11: The σ bonds in ethylene.
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Figure 14.12: A carbon-carbon double bond consists of a σ bond and a π bond.
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Figure 14.48: The benzene molecule consists of a ring of six carbon atoms with one hydrogen atom bound to
each carbon; all atoms are in the same plane.
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• Sp2 hybridized
FIGURE 14.49: Sigma BondingSystem in Benzene
FIGURE 14.50: (a) Pi MO System in Benzene, (b) Delocalized Pi MO Over Entire Ring of C
Atoms
N
O
N
O
N
O
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N
O O
N
O O
N
O O
FIGURE 14.51: (a) Pi BondingSystem in NO3
-, (b) Delocalized Electronsin the pi MO System of NO3
- Ion
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Graphite – sp2 hybridized C
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Fullerene-C60 and Fullerene-C70
What hybridization of C describes the structures?
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Figure 14.14: When one s orbital and one p orbital are hybridized, a set of two sporbitals oriented at 180 degrees results.
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The sp hybrid orbitals in gaseous BeCl2
Promotion
Promote to create two half filled orbitals that participate in
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Why are sp hybrids invoked? Because if Be made one bond with its2s and one bond with a 2p orbital, then the two Be-Cl bonds would have different strengths & lengths. But both bonds are identical.
participate in bond formation
Filled 2s orbital can’t bond to Cl
The two sp hybrid orbitals in gaseous BeCl2
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Note the two “leftover” p orbitals of BeRegion of overlap
Figure 14.15: The hybrid orbitals in the CO2 molecule
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Figure 14.16: orbital energy level diagram for the formation of sp hybrid orbitals of carbon.
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Figure 14.17: Orbitals of an sp hybridized carbon atom
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sp2 hybridization of an oxygen atom
4 atomicorbitals
s p
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1 trigonalBond with2 lone pairs+ 1 for a pi bond
sp2 px
4 hybridizedorbitals
sp2 px
Figure 14.18: Orbital arrangement for an sp2
hybridized oxygen atom
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Figure 14.19: (a) Orbitals predicted by the LE model to describe (b) The Lewis structure for carbon dioxide
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Hybrid Orbitals
Types of Hybrid Orbitals
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sp sp2 sp3 sp3d sp3d2
Shapes: linear triangular tetrahedral trig. bipyram. Octahedral# orbitals: 2 3 4 5 6
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The four sp3 hybrid orbitals in NH3
Promotion
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N
The four sp3 hybrid orbitals in NH3
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Promotion
Figure 14.20: (a) An sp hybridized nitrogen atom (b) The s bond in the N2 molecule (c) the two p bonds
in N2 are formed
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The conceptual steps from molecular formula to the hybrid orbitals used in bonding.
M l l h
Step 1 Step 2 Step 3
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Molecular formula
Lewis structure
Molecular shape and e- group arrangement
Hybrid orbitals
sp3 hybridization of a carbon atom
4 atomicorbitals
s p
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4 hybridizedorbitals
sp3
4 tetrahedralbonds
sp3
sp3 hybridization of a carbon atom
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sp3 hybridization of a nitrogen atom
4 atomicorbitals
s p
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3 tetrahedralbonds with1 lone pair sp3
4 hybridizedorbitals
sp3
sp3 hybridization of a nitrogen atom
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N
sp3 hybridization of a oxygen atom
4 atomicorbitals
s p
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2 tetrahedralbonds with2 lone pairs sp3
4 hybridizedorbitals
sp3
sp3 hybridization of a oxygen atom
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sp2 hybridization of a carbon atom
4 atomicorbitals
s p
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3 trigonalBonds+ 1 for a pi bond sp2 px
4 hybridizedorbitals
sp2 px
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sp2 hybridization of an oxygen atom
4 atomicorbitals
s p
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1 trigonalBond with2 lone pairs+ 1 for a pi bond
sp2 px
4 hybridizedorbitals
sp2 px
Figure 14.19: (a) Orbitals predicted by the LE model to describe (b) The Lewis structure for carbon dioxide
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sp hybridization of a carbon atom
4 atomicorbitals
s p
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4 hybridizedorbitals
sp
2 linearbonds+ 2 for pi bonds sp py
py
px
px
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sp hybridization of an nitrogen atom
4 atomicorbitals
s p
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4 hybridizedorbitals
sp
1 linearBonds with1 lone pair+ 2 for pi bonds
sp py
py
px
px
Figure 14.20: (a) An sp hybridized nitrogen atom (b) The s bond in the N2 molecule (c) the two p bonds
in N2 are formed
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Figure 14.21: A set of dsp3 hybrid orbitals on a phosphorous atom
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Hybridization Involving d Orbitals
3s 3p 3d 3s 3p 3d
promote
hybridizeunhybridized P atom
P = [Ne]3s23p3vacant d orbitals
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five sp3d orbitals 3dF
F
FP
F
F
Be
Be
Be
Ba
Ba
Trigonal bipyramidal
hybridize
degenerateorbitals
(all EQUAL)
[ ] p
Figure 11.6 The five sp3d hybrid orbitals in PCl5
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Figure 14.22: The orbitals used to form the bonds in the PCL5 molecule
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Figure 14.23: An octahedral set of d2sp3
orbitals on a sulfur atom
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Figure 11.7
The six sp3d2 hybrid orbitals in SF6
Figure 14.24: The relationship among the number of effective pairs, their spatial arrangement,
and the hybrid orbital set required
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Figure 14.24: The relationship among the number of effective pairs, their spatial arrangement,
and the hybrid orbital set required (cont’d)
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Figure 11.8
The conceptual steps from molecular formula to the hybrid orbitals used in bonding.
Molecular formula
Lewis structure
Molecular shape and e- group
t
Hybrid orbitals
Step 1 Step 2 Step 3
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formula structure arrangement orbitals
Figure 10.1 Figure 10.12 Table 11.1