MOLECULAR STRUCTURE & COVALENT BONDING
THEORIES
Chapter 8
Two Simple Theories of Covalent Bonding Valence Shell Electron Pair Repulsion
Theory__________R. J. Gillespie - 1950’s
Valence Bond Theory__________ __________L. Pauling - 1930’s & 40’s
VSEPR Theory
regions of __________ electron density around the central atom are as far apart as possible to __________ repulsions
__________ basic shapesbased on # of regions of high electron density
several __________ ____of these five basic shapes will also be examined
VSEPR Theory
1st shape: _____regions of high electron density
VSEPR Theory
2nd shape: _____ regions of high electron density
VSEPR Theory3rd shape: _____ regions of high electron density
VSEPR Theory
4th shape: _____ regions of high electron density
VSEPR Theory
5th shape: _____ regions of high electron density
VSEPR Theory _____ ________ _______– the arrangement of the
valence shell electrons around the central atomdetermined by the locations of regions of high electron density
around the central atom(s) (includes both elements and lone pairs of electrons)
_____ __________ _____- determined by the arrangement of atoms around the central atom(s)What the molecule really looks like (only elements)
_____ __________ __________ __________ __________ __________ __________ __________
VSEPR Theory CH4 vs. H2O
CH4 - methane
electronic geometry_____ _____
molecular geometry _____ _____
bond angles = 109.5o
VSEPR Theory _____ _____of electrons (unshared pairs) require
more volume than shared pairs
there is an ordering of _____ _____of electrons around central atom
H2O - water
electronic geometry _____ _____
molecular geometry_____ __________ _____
bond angle = 104.50
VSEPR Theory
1. lone pair to lone pair repulsion is _____ _____
2. lone pair to bonding pair repulsion is _____ _____
3. bonding pair to bonding pair repulsion is _____ ___
lone pair to lone pair repulsion is why bond angles in water are _____ _____109.50
Valence Bond Theory covalent bonds are formed by _____ _____of
atomic orbitals
atomic orbitals on the _____ _____atom can mix and exchange their character – _____ __________ _____
_____ __________ _____
pink flowers, mules, corn, grass
Hybrid orbitals
From orbital diagrams Hybridization - CP
s + p orbitals
s + p + p orbitals
s + p + p + p orbitals
s + p + p + p + d orbitals
s + p + p + p + d + d orbitals
helps describe the same shapes as VSEPR – (hybridization – mixing of orbitals)
Name of orbital – number of pairs on central atom (Regions of high e- density around the central atom)
Shape (name) of orbital
sp - 2
sp2 - 3
sp3 - 4
sp3d - 5
sp3d2 - 6
Molecular Geometry Terminology
In the next sections the following terminology will be usedA = central atom
B = bonding pairs around central atom
U = lone pairs around central atom
For example:AB3U designates that there are _____ _____
pairs and _____ __________ _____ around the central atom (_____ __________ ____)
AB2 Molecules - No Lone Pairs on A -
Linear Molecules
Ex. _____ _, BeBr2, BeI
2, HgCl
2, CdCl
2
~ all are _____ ___, _____ ___molecules
Dot Formula Electronic Geometry
180o - linear
BeCl Cl··
····
····
··
BeCl Cl··
····
····
····
··
AB2 Molecules - No Lone Pairs on A -
Linear Molecules
VSEPR Polarity
bondspolar very
3.5 51. 3.5 activitiesElectroneg
Cl - Be - Cl
0.22.0
180o-linear
BeCl Cl····
moleculenonpolar
symmetric are dipoles bond
Cl---Be---Cl
AB2 Molecules - No Lone Pairs on A -
Linear Molecules
Molecular Geometry
same as electronic geometry
__________ __________
Molecular Geometry
AB3 Molecules - No Lone Pairs on A -
Trigonal Planar Molecules
Examples: BF3, _____ __
all are _____ __________ _____,
_____ ____ molecules Dot Formula Electronic Geometry··
B
Cl
Cl Cl··
····
··
···· ··
····
·· ··
B··
··
··
120-trigonal planar
AB3 Molecules - No Lone Pairs on A -
Trigonal Planar Molecules
VSEPR Polarity
120-trigonal planar
BClCl
Cl
bondspolar ery v
3.0 1.5 ativitiesElectroneg
Cl - B
1.5
BClCl
Cl
bond dipoles are symmetric nonpolar molecule
AB3 Molecules - No Lone Pairs on A -
Trigonal Planar Molecules
Molecular Geometrysame as electronic geometry, symmetrical & nonpolar
Molecular Geometry
AB4 Molecules - No Lone Pairs on A -
Tetrahedral Molecules
Ex. _____ ___, CF4, CCl
4,
SiH
4,
SiF
4
all are _____ _____, _____ ___molecules~ as long as they have the same 4 _____ _____
Dot Formula Electronic Geometry
C
H
H
H H......
.. C
....
..
..
tetrahedral109.5o bond angles
AB4 Molecules - No Lone Pairs on A -
Tetrahedral Molecules
VSEPR Polarity
CH H
H
H
tetrahedralbondspolar slightly
2.1 2.5 ativitiesElectroneg
H- C
0.4
symmetric dipolesnonpolar molecule
CH H
H
H
AB4 Molecules - No Lone Pairs on A -
Tetrahedral Molecules
Molecular Geometrysame as electronic geometry, symmetrical & nonpolar
Molecular Geometry
AB3U Molecules - One Lone Pair -
Pyramidal Molecules
examples NH
3, NF
3
first example of _____ _____on the central atomelectronic and molecular geometry are differentall 3 substituents can be the same but molecule is _____
_____
NH3 and NF
3 are _____ _____, _____ molecules
AB3U Molecules - One Lone Pair -
Pyramidal Molecules
Dot Formulas Electronic Geometry
NH H
H..
.... ..
.. ....NF F
F..
..
..
....
....
.
..... tetrahedral
N
..
....
..
Molecular Geometry - different from the electronic geometry, _____ __________ __________ _____
Molecular Geometry
AB3U Molecules - One Lone Pair -
Pyramidal Molecules
VSEPR Polarity
1 lone pair
pyramidal
NF F
F
..
1 lone pair
pyramidal
NH H
H
..
bondspolar ry ve
4.0 3.0 ativitiesElectroneg
F-N
bondspolar y ver
2.1 3.0 ativitiesElectroneg
H-N
1.0
0.9
AB3U Molecules - One Lone Pair -
Pyramidal Molecules VSEPR Polarity
1 lone pair
pyramidal
NF F
F
..
1 lone pair
pyramidal
NH H
H
..
NF F
F
..bond dipolesoppose effect of lone pair
asymmetrical dipoles polar molecule=0.2 D
NH H
H
..
asymmetrical dipoles polar molecule=1.5 D
bond dipolesreinforce effect of lone pair
AB2U2 - Two Lone Pairs - V-Shaped Molecules Example H2O water is an angular, _____ __________ __,
_____ _____molecule
Dot Formula Electronic Geometry
O H
H
····
···· O
··
····
··
tetrahedralMolecular Geometry - different from electronic geometry, asymmetrical & polar
Molecular Geometry
AB2U2 - Two Lone Pairs - V-Shaped Molecules
VSEPR Polarity
OH
H
··
··
2 lone pairs
bent, angularor V-shaped
bondspolar y ver
2.1 3.5 ativitiesElectroneg
H- O
1.4
OH
H
··
··
bond dipolesreinforce lonepairs
asymetric dipolesvery polar molecule1.7 D
ABU3 - Three Lone Pairs - Linear Molecules
Hydrogen halides - ___, HCl, HBr, HI Dot Formula Electronic
Geometry
H F··
····
··
tetrahedral
FH
··
····
ABU3 - Three Lone Pairs - Linear Molecules
VSEPR Polarity
HF is a polar molecule.
linear
FH
··
····
3 lone pairs
Molecular Geometry - different from electronic geometry, _____ __________ __________ _____
Molecular Geometry
AB5- No Lone Pairs - Trigonal Bipyramidal Molecules
Ex. PF5, AsF5, PCl5, etc.
All are _____ __________ _____, _____ _____ molecules.
Dot Formula Electronic Geometry··
As
F
F
FF
F
··
··
··
····
··
····
····
····
··
··
··
··
··
·· ··trigonal bipyramidal
As
··
··
······
AB5- No Lone Pairs - Trigonal Bipyramidal Molecules
VSEPR Polarity
trigonal bipyramid
AsF
F
F
F
F
··
··
··
··
·· ··
··
··
····
··
····
····
bondspolar ry ve
4.0 2.1 ativitiesElectroneg
F- As
1.9
AB5- No Lone Pairs - Trigonal Bipyramidal Molecules
Polarity Molecular Geometry
symmetric dipoles cancel nonpolar molecule
AsF
F
F
F
F
··
··
··
··
·· ··
··
··
····
··
····
····
AB5- No Lone Pairs - Trigonal Bipyramidal Molecules
Valence Bond (Hybridization)
AB4U- One Lone Pair - Seesaw Molecules
For one lone pair an AB4U molecule results.
AB4U molecules have a _____ ____shaped
molecular geometry and are _____ ___.
SF4 is an AB4U molecule
_____ _____occupies an _____ _____position
AB4U- One Lone Pair - Seesaw Molecules
VSEPR Molecular Geometry
AB3U2 - Two Lone Pairs - T-shaped Molecules
For two lone pairs an AB3U2 molecule results
AB3U2 molecules have a _____ _____ molecular geometry and are _____ _____
IF3 is an AB3U2 molecule
_____ __________ _occupy _____ _____positions
AB3U2 - Two Lone Pairs - T-shaped Molecules
VSEPR Molecular Geometry
AB2U3 - Three Lone Pairs - Linear Molecules
For three lone pairs an AB2U3 molecule results
AB2U3 molecules have a _____ ___molecular geometry and are _____ _____
XeF2 is an AB2U3 molecule
_____ __________ __occupy _______ __positions
AB2U3 - Three Lone Pairs - Linear Molecules
VSEPR Molecular Geometry
AB6- No Lone Pairs - Octahedral Molecules
Ex. SF6, _____ __, SCl6, etc. These are _____ _____and _____ ___
molecules if all 6 substituents are the _____ ___
Dot Formula Electronic Geometry
Se
F
F
F
F
F
F
····
··
······
··
····
··
··
··
··
··
··
··
··
····
··
······
··
octahedral
Se
··
··
····
·· ··
Molecular Geometry
AB6- No Lone Pairs - Octahedral Molecules
VSEPR Polarity
octahedral
SeF
F
F
F
F
F
bondspolar ery v
4.0 2.4 ativitiesElectroneg
F- Se
1.6
symmetric dipoles cancel nonpolar molecule
SeF
F
F
F
F
F
AB6- No Lone Pairs - Octahedral Molecules
Valence Bond (Hybridization)
AB5U- One Lone Pair - Square Pyramidal Molecules
For one lone pair an AB5U molecule results.
AB5U molecules have a _____ _________
molecular geometry and are _____ __.
IF5 is an AB5U molecule
_____ _____occupies an _____ __position
AB5U- One Lone Pair - Square Pyramidal Molecules
VSEPR Molecular Geometry
AB4U2 - Two Lone Pairs - Square Planar Molecules
For two lone pairs an AB4U2 molecule results.
AB4U2 molecules have a ________ _____
molecular geometry and are _____ __.
XeF4 is an AB4U2 molecule
_____ lone pairs occupy _____ __positions
AB5U- One Lone Pair - Square Pyramidal Molecules
VSEPR Molecular Geometry
Summary of Electronic & Molecular Geometries
The structure of penicillin-G is shown below. What is the electron geometry, molecular geometry, and hybridization of each of the 10 indicated atoms in penicillin-G?
CH
C N
CH S
CH
C
CH3
CH3
OH
OO
NHO
CH2CCC
CC C
HH
H
HH
1
23 4
5 6
7
8910
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