Five Basic Geometries
Linear
Trigonal
Tetrahedral
Octahedral
Trigonal bipyramidal
1
SeF6, IF5, and XeF4
2
SeF6: Octahedron
All bond angles are 90°
3
IF5 and XeF4
 The 1st lone pair can occupy any site
 The 2nd lone pair is arranged opposite to the 1st
IF5
XeF4
Square
Pyramidal
Square
Planar
4
Octahedral Electronic
Geometry

If lone pairs are incorporated into
the octahedral structure, there are
2 possible new shapes
 1 lone pair – Square pyramid
 2 lone pairs – Square planar
5
Chemical Bonding


How are the chemical bonds formed?
Formation of a chemical bond usually
involves pairing of unpaired electrons
from the atoms being bound

Example – H2 molecule
H· + ·H  H:H
6
BeH2
H


Be
H
The Be atom has 2 paired electrons
How does it form 2 equivalent bonds?

To answer questions like this, the
valence bond theory was proposed
7
Valence Bond Theory





When an atom is nearby other atoms,
its outer shell orbitals can mix and
get modified
They form a new set of orbitals that
are more appropriate for bonding
This process is called hybridization
The new orbitals are therefore
called hybrid orbitals
Hybrid orbitals are arranged in the
same way as predicted by VSEPR
8
BeH2
Be: 1s22s2
sp - hybridization
9
BeH2
sp
1s
H
+
sp
Be
1s
+
H
10
BF3
F
F
B
F
11
BF3
B: 1s22s22p1
sp 2 - hybridization
12
BF3
B
+
3
F
2p
13
CH4 and CF4
109.5°
14
CH4 and CF4
C: 1s22s22p2
sp 3 - hybridization
15
CH4
C
+
4
H
1s
16
CF4
C
+
4
F
2p
17
NH3 and NF3
NH3
NF3
107.3°
102.1°
 Just like in CH4 and CF4, the orbitals are
arranged in the tetrahedral fashion which
means that the sp 3 hybridization takes place
 One of the orbitals, however, contains a pair
of electrons and is not used for bonding
18
NH3 and NF3
N: 1s22s22p3
sp 3 - hybridization
N
Four sp 3 orbitals
19
NH3 and NF3
N
+
3
H
1s
20
NH4+
1s
H+
+
+
21
PF5
P: [Ne]3s23p3
sp 3d - hybridization
22
PF5
Trigonal bipyramidal
electronic geometry
is achieved by
sp 3d - hybridization
23
SF6
S: [Ne]3s23p4
sp 3d 2 - hybridization
24
SF6
Octahedral electronic
geometry is achieved by
sp 3d 2 - hybridization
25
VB vs. VSEPR Theories
Regions of
High Electron
Density
2
3
4
5
6
Electronic
Geometry
Hybridization
Linear
Trigonal
planar
Tetrahedral
Trigonal
bipyramidal
Octahedral
sp
sp2
sp3
sp3d
sp3d2
26
Double Bond: C2H4

An sp 2 hybridized C atom has one
electron in each of the three sp 2 lobes
Top view of
the sp 2 hybrid
Side view of the sp 2 hybrid
+ the unhybridized p orbital
27
Double Bond: C2H4

Two sp 2 hybridized C atoms plus p -orbitals in
proper orientation to form a C=C double bond
28
Double Bond: C2H4


The portion of the double bond formed
from the head-on overlap of the sp 2
hybrids is designated as a s bond
The other portion of the double bond,
resulting from the side-on overlap of
the p orbitals, is designated as a p bond
29
Triple Bond: C2H2
A s bond results from the head-on overlap
of two sp hybrid orbitals
30
Triple Bond: C2H2


The unhybridized p orbitals form two p bonds
Note that a triple bond consists of
one s and two p bonds
31
Assignments & Reminders

Go through the lecture notes

Read Chapter 8 completely


Homework #5 covers Chapters 7 & 8
and is due by Oct. 31
Monday (10/31) and Tuesday (11/1) –
lecture quiz #5 (Chapter 8)
32