1 Five Basic Geometries Linear Trigona l Octahedral Trigonal bipyramidal Tetrahedra l
Jan 23, 2016
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Five Basic Geometries
LinearTrigonal
Octahedral
Trigonal bipyramidal
Tetrahedral
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SeF6, IF5, and XeF4
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SeF6: Octahedron
All bond angles are 90°
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IF5 and XeF4
IF5 XeF4
Square Pyramidal
Square Planar
The 1st lone pair can occupy any site
The 2nd lone pair is arranged opposite to the 1st
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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
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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
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BeH2
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
BeH H
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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
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BeH2
Be: 1s22s2s22
sp - hybridization
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BeH2
H H+ +Be1s
1s
sp sp
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BF3
BF
F
F
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BF3
B: 1s22s2s222p2p11
sp 2 - hybridization
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BF3
+
B
3 F2p
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CH4 and CF4
109.5°
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C: 1s22s2s222p2p22
sp 3 - hybridization
CH4 and CF4
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CH4
+
4
C
H
1s
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CF4
+
4 F
C
2p
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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
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N: 1s22s2s222p2p33 sp 3 - hybridization
NH3 and NF3
N
Four sp 3
orbitals
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+
3
N
H
1s
NH3 and NF3
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NH4+
+
H+
1s +
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PF5
P: [Ne]3s3s223p3p33
sp 3d - hybridization
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PF5
Trigonal bipyramidal electronic geometry is achieved by sp
3d - hybridization
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SF6
S: [Ne]3s3s223p3p44
sp 3d
2 - hybridization
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SF6
Octahedral electronic geometry is achieved by sp
3d 2 - hybridization
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VB vs. VSEPR Theories
Regions of High
Electron Density
Electronic Geometry
Hybridization
2 Linear sp
3 Trigonal planar
sp2
4 Tetrahedral sp3
5 Trigonal bipyramidal
sp3d
6 Octahedral sp3d2
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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
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Two sp 2 hybridized C atoms plus p -orbitals in
proper orientation to form a C=C double bond
Double Bond: C2H4
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Double Bond: C2H4
The portion of the double bond formed from the head-on overlap of the sp
2 hybrids is designated as a bond
The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a bond
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A bond results from the head-on overlap of two sp hybrid orbitals
Triple Bond: C2H2
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The unhybridized p orbitals form two bonds
Note that a triple bond consists of one and two bonds
Triple Bond: C2H2
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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)