Chapter 8. Two Simple Theories of Covalent Bonding Valence Shell Electron Pair Repulsion Theory...

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··

····

····

····

··


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


Linear Molecules

Molecular Geometry

same as electronic geometry

__________ __________

Molecular Geometry


Trigonal Planar Molecules

Examples: BF3, _____ __

all are _____ __________ _____,

_____ ____ molecules Dot Formula Electronic Geometry··

B

Cl

Cl Cl··

····

··

···· ··

····

·· ··

B··

··

··

120-trigonal planar



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



Molecular Geometrysame as electronic geometry, symmetrical & nonpolar

Molecular Geometry


Tetrahedral Molecules

Ex. _____ ___, CF4, CCl

4,

SiH

4,

SiF

4

all are _____ _____, _____ ___molecules~ as long as they have the same 4 _____ _____


C

H

H

H H......

.. C

....

..

..

tetrahedral109.5o bond angles



VSEPR Polarity

CH H

H

H

tetrahedralbondspolar slightly


H- C

0.4

symmetric dipolesnonpolar molecule

CH H

H

H



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


Pyramidal Molecules

Dot Formulas Electronic Geometry

NH H

H..

.... ..

.. ....NF F

F..

..

..

....

....

.

..... tetrahedral

N

..

....

..

Molecular Geometry - different from the electronic geometry, _____ __________ __________ _____

Molecular Geometry


Pyramidal Molecules

VSEPR Polarity

1 lone pair

pyramidal

NF F

F

..

1 lone pair

pyramidal

NH H

H

..

bondspolar ry ve


F-N

bondspolar y ver


H-N

1.0

0.9


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


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


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

··

··

······


VSEPR Polarity

trigonal bipyramid

AsF

F

F

F

F

··

··

··

··

·· ··

··

··

····

··

····

····

bondspolar ry ve


F- As

1.9


Polarity Molecular Geometry

symmetric dipoles cancel nonpolar molecule

AsF

F

F

F

F

··

··

··

··

·· ··

··

··

····

··

····

····


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


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


AB6- No Lone Pairs - Octahedral Molecules

Ex. SF6, _____ __, SCl6, etc. These are _____ _____and _____ ___

molecules if all 6 substituents are the _____ ___


Se

F

F

F

F

F

F

····

··

······

··

····

··

··

··

··

··

··

··

··

····

··

······

··

octahedral

Se

··

··

····

·· ··

Molecular Geometry


VSEPR Polarity

octahedral

SeF

F

F

F

F

F

bondspolar ery v


F- Se

1.6

symmetric dipoles cancel nonpolar molecule

SeF

F

F

F

F

F


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

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

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

Chapter 8. Two Simple Theories of Covalent Bonding Valence Shell Electron Pair Repulsion Theory...

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