chapter 9 molecular geometries - lamar university · coverage of chapter 9 9.1 all 9.2 all 9.3 all...
TRANSCRIPT
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Chapter 9
Molecular Geometries
and Bonding Theories
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Coverage of Chapter 9
9.1 All
9.2 All
9.3 All
9.4 All
9.5 Omit Hybridization Involving d Orbitals
9.6 All
9.7 and 9.8 Omit ALL
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MOLECULAR SHAPES
• The shape of a molecule plays an important
role in its reactivity.
• By knowing the number of bonding and
nonbonding electron pairs we can predict the
shape of the molecule.
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Two (2) Theories forMOLECULAR GEOMETRY
1. Valence Shell Electron Pair Repulsion
(VSEPR)(VSEPR)(VSEPR)(VSEPR) THEORY
&
2. The Valence Bond
(VB) THEORY
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Lewis Structures
&
Formal Charge
Formal charge is a charge assigned to each
atom in a Lewis structure that helps to
distinguish among competing structures.
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What is the correct formula for
Hypo Chlorous Acid
HClO (aq)
H – Cl – O
or
H – O – Cl
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Hypo chlorite ion
ClO -
Number of Valence e-
Number of Nonbonding e-
½ Number of Bonding e-
Formal Charge
| O – Cl |
6 7
- 6 - 6
- 1 - 1
-1 0
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Where does the H go on HClO?
| O – Cl – H or H – O – Cl |
Valence e-
Nonbonding
e-
½ Bonding e-
O Cl O Cl
6 7 6 7
-6 -4 -4 -6
-1 -2 -2 -1
-1 -1 0 0
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• Electron pairs are refered to as electron domains
• Single, double or triple bonds all count as one electron domain.
The atom A in this molecule, has four electron domains.
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The First
MOLECULAR GEOMETRY theory
(VSEPR)
Valence Shell Electron Pair
Repulsion theory
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VSEPRVSEPR TheoryTheory
1. To predict molecular shape, assume the
valence electrons repel each other
2. The electrons adopt an arrangement in
space to minimize e- e- repulsion
3. The molecule adopts whichever 3D
geometry minimized this repulsion.
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What Determines the Shape of a Molecule?
Four electron domains on N
3 bonding and 1 nonbonding
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What Determines the Shape of a Molecule?
Electrons, whether they be bonding or non-
bonding, repel each other. So electrons are
placed as far as possible from each other
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Two (2) Different “Types” of
Molecules
1. Molecules with NO nonBonding electrons
on the central atom
2. Molecules with nonBonding electrons on
the central atom
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Electron Domains &
NonBonding Electrons
Example 1 CO2
| O = C = O |
How many electron domains on C
How many NonBonding electrons on C
2
0
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Electron Domains &
NonBonding Electrons
Example 2 H2O..
H – O– H
How many electron domains on O
How many NonBonding electrons on O
4
4
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There are five fundamental geometries :
1. Linear
2. Trigonal Planar
3. Tetrahedral
4. Trigonal bepyramidal
5. Octahedral
Molecular Geometries for molecules with
no nonbonding electrons on central atom
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Only consider Three in detail
1. Linear
2. Trigonal Planar
3. Tetrahedral
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In order to determine geometry
First Draw Lewis Dot Formula
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MOLECULES IN WHICH THE
CENTRAL ATOM HAS NO LONE PAIRS
ZINC CHLORIDE
Zn Cl2
Zn (30) [Ar] 3d10 4s2
Cl – Zn - Cl
B – A – B
AB2 = LINEAR
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AB2 Molecules Such as CO2 are Linear
(Molecules With NO UnPaired Electrons On
the Central Atom)
. . . .
: O = C = O :
B – A – B
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Molecular Shape and Molecular Shape and
Molecular PolarityMolecular Polarity
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AB3 Molecules Such as BF3 are Planar
(Molecules With NO UnPaired Electrons On
the Central Atom)
Formula B F3
Number of Valence e- 3 21 = 24 total
• Lewis Structure F – B – F
F
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AB3 (Molecules With NO UnPaired Electrons
On the Central Atom) Such as BF3 are Planar
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AB4 Molecules Such as CH4 are Tetrahedral
(Molecules With NO UnPaired Electrons On
the Central Atom)
• Formula C H4
• Number of Valence e- 4 4 = 8 total
H
• Lewis Structure H – C – H
H
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AB4 Such as CH4 are Tetrahedral
(Molecules With NO UnPaired Electrons On the Central Atom)
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AB4 Molecules Such as CCl4 are Tetrahedral
Carbon Carbon TetraChlorideTetraChloride
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AB5 Such as PCl5 are Triangular bipyramidal
• Name ?
• Number of Bonds ?
• Lewis dot structure ?
Cl
Cl – P – Cl
Cl Cl
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AB6 Such as SF6 are Octahedral
• Name ?
• Number of Bonds ?
• Lewis dot structure ?
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Molecules With NO UNPaired e-
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Molecules with NO unpaired e- on
Central Atom
1. 2 Bonds ………AB2 or AX2 e.g. CO2
2. 3 Bonds ……... AB3 or AX3 e.g. BF3
3. 4 Bonds ………AB4 or AX4 e.g. CH4
4. 5 Bonds ……... AB5 or AX5 e.g. PCl5
5. 6 Bonds ……... AB6 or AX6 e.g. SF6
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Polarity
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Part 2. of VSEPR TheoryPart 2. of VSEPR Theory
CENTRAL ATOM HAS
LONE PAIRS
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Molecules With UnPaired Electrons On
the Central Atom
Class Example
• AB2E SO2 & O3
• AB2E2 H2 O
• AB3E NH3
Geometry
Bent
Bent
Trigonal pyramidal
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1. AB2E OZONEOZONEOZONEOZONE
2. AB2E2 WATER
O
OO
O
OO
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AB2E2 (Molecules With UnPaired Electrons
On the Central Atom) Such as H2O are Bent
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3. AB3E AMMONIA
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AB3E (Molecules With UnPaired Electrons On the
Central Atom) Such as NH3 are NOT Planar
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Predict Molecular Shapes
1. SiCl4
2. CH2Cl2
3. GeCl2
4. OF2
5. NH3
6. PH3
_________
_________
_________
_________
__________
___________
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Give the
electron domain and molecular geometries for
(a) N2O
(b) SO3
(c) PCl3
(d) NH2Cl
electron domain molecular geometry
____________ ________________
____________ ________________
___________ ________________
___________ ________________
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Examples of AB2 molecules
• Linear AB2 How many bonds
CO2
• Bent AB2E How many “bonds”
SO2 and NO2-
• Bent AB2E2 How many “bonds”
H2O
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Examples of AB3 molecules
• Planar AB3 How many bonds
BF3
• Pyramidal AB3E How many “bonds”
NH3
• T shape AB3E2 How many “bonds”
ClF3
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Two (2) Theories forMOLECULAR GEOMETRY
1. Valence Shell Electron Pair Repulsion
(VSEPR)(VSEPR)(VSEPR)(VSEPR) THEORY
Now consider
2. The Valence Bond
(VB) THEORY
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Method
uses molecular orbitals
not Atomic Orbitals
WHAT IS A MOLECULAR ORGITAL?
Orbitals used in bonding of Molecules
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CH4 as an EXAMPLE
Ground State Electron Configuration
C (6 e- ) 1s2 2s2 2p2 = ( ↑↓) (↑↓) (↑) (↑ ) ( )
Only place for two bonds to form
Therefore would predict CH2 formation
and not CH4
But CH2 does not exist while CH4 does
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C (6 e- ) 1s2 2s2 2p2 = ( ↑↓) (↑↓) (↑) (↑ ) ( )
Only place for two bonds to form
Excited State Electron Configuration
C (6 e- ) 1s2 2s1 2p3 = (↑↓ ) (↑ ) (↑ ) (↑) (↑)
Now a place for four bonds
One electron from H goes into an s orbital
and Three from H go into the p orbitals
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The BONDS in CH4
are ALL the SAME!
One electron in an s orbital and Three in p
orbitals would create different bonds.
Since All the Bonds are Equal, this cannot
be correct
INTRODUCE THE CONCEPT OF
HYBRIDIZATION
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Hybridization
In order to made All Bonding sites equal,
we must create NEW Orbitals.
s, p, d, f are ATOMIC ORBITALS
MOLECULAR ORBITALS are formed
from Atomic orbitals
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VALENCE SHELL ORBITALS
HYBRIDIZE
THE ORIENTATION OF ALL
HYBRID VALENCE SHELL
ORBITALS DETERMINES THE
GEOMETRY OF THE MOLECULE
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are formed from ATOMIC ORBITALS
Atomic Orbitals
one S + one P
one S + two P
one S + three P
Molecular Orbitals
Two (2) SP
Three (3) SP2
Four (4) SP3
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They are called
SP
SP2
SP3
SP3d and
SP3d2
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sp3 HYBRIDIZATION
TETRAHEDRAL
Bond Angles
109½o
Methane CH4
Four σ Bonds
on C
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sp2 HYBRIDIZATION
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sp HYBRIDIZATION
one S orbital + one P orbital
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Carbon is NOT The Only Element That
Undergoes sp3 HYBRIDIZATION
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In CH3COOH, there are three (3)
hybridized atoms.
Geometry is assign about each
hybridized atom separately.