What

1
Whats coming up???

• Oct 25 The atmosphere, part 1 Ch. 8
• Oct 27 Midterm No lecture
• Oct 29 The atmosphere, part 2 Ch. 8
• Nov 1 Light, blackbodies, Bohr Ch. 9
• Nov 3,5 Postulates of QM, p-in-a-box Ch. 9
• Nov 8,10 Hydrogen and multi e atoms Ch. 9
• Nov 12 Multi-electron atoms Ch.9,10
• Nov 15 Periodic properties Ch. 10
• Nov 17 Periodic properties Ch. 10
• Nov 19 Valence-bond Lewis structures Ch. 11
• Nov 22 VSEPR Ch. 11
• Nov 24 Hybrid orbitals VSEPR Ch. 11, 12
• Nov 26 MO theory Ch. 12
• Nov 29 MO theory Ch. 12
• Dec 1 bonding wrapup Ch. 11,12
• Dec 2 Review for exam

2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
COMBINING ORBITALS TO FORM HYBRIDS
HYBRIDIZATION
the combination of two or more native atomic
orbitals on an atom to produce hybrid orbitals
the number of atomic orbitals that are combined
must equal the number which are formed
RULE
All resulting hybrid orbitals are identical.
6
(No Transcript)
7
HYBRIDIZATION
Combine one s and one p
a sp- hybrid

ADD the orbitals

?2s ?2p
8
The positive part adds to positive part
CONSTRUCTIVE INTERFERENCE
?2s ?2p
9
Combine one s and one p to give
an sp- hybrid
?2s ?2p

REMEMBER IF WE MIX TWO WE MUST GET TWO BACK
The other combination is s - p
10
The positive part adds to positive part
?2s- ?2p
CONSTRUCTIVE INTERFERENCE
The positive part cancels negative part
DESTRUCTIVE INTERFERENCE
11
?2s- ?2p

We get two equivalent sp orbitals
ORIENTED AT 1800
12
sp-HYBRIDIZATION
The s and p orbitals
The two sp-hybrids
Directed at 1800
13
COMBINE one s-orbital and two p-orbitals
Get three sp2 - orbitals oriented at 1200
The s and p orbitals
The three sp2-hybrids
Directed at 1200
14
COMBINE one s-orbital and three p-orbitals
Get three sp3- orbitals oriented at 109.50
Back to methane
15
METHANE CH4
four hybrid orbitals needed to form four bonds
s px py pz
4 sp3 hybrids
An atom with sp3 hybrid orbitals is said to be
sp3 hybridized
The four sp3 hybrid orbitals form a tetrahedral
arrangement.
16
When orbitals are hybridized they have the same
energy
HYBRIDIZE
2p
sp3
E
E
2s
Orbitals in free C atom
Hybridized orbitals of C atom in methane
The FOUR sp3 hybrids are DEGENERATE.

sp3 hybridization.
17
sp3 HYBRIDS
sp3 orbitals
Now form the bonds to the H-atoms...
18
Each bond in methane results from the overlap of
a hydrogen 1s orbital and a carbon sp3 orbital.
Hydrogen 1s orbital
Carbon sp3 orbitals
H
Form a chemical bond by sharing a pair of
electrons.
H
H
H
19
VALENCE BOND MODEL
Hybrid orbital model
Step 1 Draw the Lewis structure(s)
Step 2 Determine the geometry of the electron
pairs around each atom using VSEPR picture of
molecular shapes
Step 3 Specify the hybrid orbitals needed
to accommodate the electron pairs on each atom
20
AMMONIA NH3
N
H
H
H
Electron pair geometry is tetrahedral
Need sp3 hybrids
21
sp3 hybrids on N in AMMONIA
22
WATER
Overlap of two of oxygen sp3 hybrids with ..
Lone pairs in two of the sp3 hybrids.
H atom 1s orbitals.
To form two ? bonds.
Think about H3O !!!
23
HYDRONIUM ION.
ISOELECTRONIC WITH ..?
NH3
H ion empty 1s orbitals.
H
24
Ethylene C2H4
25
FORMATION OF sp2 hybrids
GROUND STATE C atom
sp2 hybridized orbitals of C
HYBRIDIZE
This leaves one p orbital unhybrized.
26
An sp2 hydridized C atom
sp2 - hybrid orbitals
UNHYBRIDIZED p- orbital
The unhybridized p orbital is perpendicular to
sp2 plane.
27
BONDING IN ETHYLENE
s bond
z
z
y
y
C
C
x
x
OVERLAP the sp2 hybrids from the two carbons to
form a sigma bond between them.
28
The two unhybridized p orbitals are left over to
form a ..
z
z
H
H
y
y
H
H
x
x
pi bond (p bond)
29
H
H
C
C
H
H
30
BONDING SCHEME IN ETHYNE
pC(2p)-C(2p) TWO OF THESE!!
s H(1s)-C(sp)
s H(1s)-C(sp)
sC(sp)-C(sp)
What does this look like????
31
OVERLAP the C sp hybrids with H 1s to form sigma
bonds
z
z
C
y
y
H
H
C
x
x
32
LATERAL OVERLAP of p orbitals to form pi bonds.
z
z
y
y
H
H
C
C
x
x
two pi bonds (p bonds)
33
What about molecules with more than an octet
around the central atom?
Examples PCl5, or SF4 or SiF62- etc..
Four orbitals
Four pairs needs
Five orbitals
Five pairs needs
six pairs needs
six orbitals
So??????
34
PCl5
We ignore the chlorine atoms and just describe
central atom.
Need five hybrid orbitals on the phosphorus
to fit the trigonal bipyramidal electron pair
geometry
d s px py pz
5 dsp3 hybrids
5 effective electron pairs
dsp3 hybridization
Five equivalent orbitals..
35
dsp3 - hybrid orbitals
TRIGONAL BIPYRAMID
900
1200
overlap with orbitals on chlorine to form 5 s
bonds.
36
We ignore the chlorine atoms and just describe
central atom.
SF6
We need six hybrid orbitals on the sulfur
6 d2sp3 hybrids
d d s px py pz
d2sp3 hybridization
6 effective electron pairs
SIX equivalent orbitals..
37
d2sp3 - hybrid orbitals
900
900
overlap with orbitals on flourine to form 6 s
bonds.
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
EXAMPLES
Describe the molecular structure and bonding in
XeF2 and XeF4
F
F
36 electrons 8 bonding
Xe
F
F
4 x 6 on the F atoms 32 used so 4 more on Xe
6 electron pairs about Xe octahedral
Square planar
d2sp3 hybrids
42
EXAMPLES
Describe the molecular structure and bonding in
XeF2 and XeF4
Xe
F
F
5 electron pairs . Trigonal bipyrimid
Molecule is linear
dsp3 hybrids