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Lecture April 3
1
HW Chap. 10 - Due April 8Quiz Chap. 10 - Due April 10
More Valence Bond TheoryLook and the figures in the text!
Summary Table 10.3
Next Exam April 10:acid-base reactions, oxidation-reduction
(Chap. 4)
Chap. 9 and 10
MO Theory Sec. 10.8
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sp2Hybrids
2
CH2CO formaldehyde
O
CH
H
Determining thegeometry - countthe #!bonds and
the #lone pairs
about the atom
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Review Multiple Bonds
3
CO2
linear
sp hybrid
CO32-
carbonate ion
trigonal planarsp2hybrid
2 sigma bonds
3 sigma bonds1 "bond
2 "bonds
leaves 2 porbitals free
central C is sp hybridized
central C is sp2hybridized
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More Multiple Bonds
4
CH2Cl-CH2Cl CHCl=CHCl
OR
C-C rotates freely rigid C=Ctwo distinct structures
cis trans
sp3 sp2
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C6H12 vs C6H6
5
cyclohexane
sp3
flexible - boat andchair geometries
sp2
rigid planar geometry
benzene
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Resonance - Benzene
6
The !bonds aredelocalized
O3ozoneO=O-O
O-O=O
2 !and 1 "See p. 445
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Molecular Orbitals
7
We will start with the individual orbital shapesLinear
Combination of Atomic Orbitals (LCAO)
bonding - energy islower than the
individual orbitals
but have to end upwith the same energy
you started with sosomething has to also
be higher
sum oforbitals
di#erence
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Complete Energy Diagram
8
!1s
!*1s
Figure p.435
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9
Creating MO Bonds
1) Create the MO energy level diagram (given)2) Fill in the
number of valence electrons -
starting with the lowest energy and still
filling UNPAIREDfirst3) Find the BOND ORDER=
1/2 (# bonding electrons-#antibonding electrons)
From H2find BO = 1/2(2) = 1
A BO = 0 means that no energetic advantageto being bound
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Another Example
10
BO = 1/2 (2-1) = 1/2So conclude He2+is bound and exists
But He2does NOT BO=0
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The p Orbitals
11
px orbital in the!
orientation
pzorbital in the"orientation
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MO Diagrams with p orbitals
1210
"2p
!2p
"*2p
"2p
!2p
orderinverted
!*2p !*2p
"*2p
order NOTinverted
B2, C2, N2O2, F2, Ne2
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1311
Paramagnetic
unsharedelectrons
O2
$% %$
$%
$%
$% $ $ $%$ $
%
%%
% %
$
$
$
BO=1/2(6-2) = 2
Example with ps
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Summary of 2s-2p MOs
14
Bondenergy
increaseswith BO
Bondlength
decreases
with BO
1 2 3 2 1 0
Figure 10.15
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Quiz of the Day
15
Give the number of !and "bonds in thefollowing molecule. Give
your answer with ,
between and NO spaces.
O
C
H
O H
H
H
CCH3-COOH
acetic acid
Answer: 7,1
