Chapter 4 Molecular Geometry and Bonding Theories ExamplesDr.Harbi

Valence Shell Electron Pair Repulsion (VSEPR) Theory based on idea that regions of electron density in valence shell of central atom will be distributed in space such that electrostatic repulsions are minimizedbased on idea that regions of electron density in valence shell of central atom will be distributed in space such that electrostatic repulsions are minimized places regions of electron density as far apart as possibleplaces regions of electron density as far apart as possible produces molecular geometryproduces molecular geometry

Steps in Predicting Molecular Geometry draw Lewis structure of substancedraw Lewis structure of substance count regions of electron density on central atomcount regions of electron density on central atom draw electron pair shapedraw electron pair shape derive and draw molecular geometryderive and draw molecular geometry

Regions of Electron Density single covalent bondsingle covalent bond double covalent bonddouble covalent bond triple covalent bondtriple covalent bond lone pairlone pair unpaired electronunpaired electron

# Regions Shape 2linear 180°

Shape 2 3 linear trigonal planar 180° 120°

# Regions Shape 2 3 linear trigonal planar 4tetrahedral 180° 120° 109.5°

5 trigonal bypyramidal 90° 120°

5 6 octahedral 90° 90° 120°

Central Atoms Having Less than an Octet Relatively rare.Relatively rare. Molecules with less than an octet are typical for compounds of Groups 1A, 2A, and 3A.Molecules with less than an octet are typical for compounds of Groups 1A, 2A, and 3A. Most typical example is BF 3.Most typical example is BF 3. Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds.Formal charges indicate that the Lewis structure with an incomplete octet is more important than the ones with double bonds. Exceptions to the Octet Rule

Summary of VSEPR Molecular Shapes e-pairsNotationName of VSEPR shapeExamples 2AX 2 LinearHgCl 2, ZnI 2, CS 2, CO 2 3AX 3 Trigonal planarBF 3, GaI 3 AX 2 ENon-linear (Bent)SO 2, SnCl 2 4AX 4 TetrahedralCCl 4, CH 4, BF 4 - AX 3 E(Trigonal) PyramidalNH 3, OH 3 - AX 2 E 2 Non-Linear (Bent)H 2 O, SeCl 2 5AX 5 Trigonal bipyramidalPCl 5, PF 5 AX 4 EDistorted tetrahedral (see-sawed) TeCl 4, SF 4 AX 3 E 2 T-ShapedClF 3, BrF 3 AX 2 E 3 LinearI 3 -, ICl 2 - 6AX 6 OctahedralSF 6, PF 6 - AX 5 ESquare PyramidalIF 5, BrF 5 AX 4 E 2 Square PlanarICl 4 -, BrF 4 -

Examples Determine the electron-pair (Domain) and molecular geometries of each of the following. Draw and name each.

Beryllium Chloride

BeCl 2

Beryllium Chloride BeCl 2 1. Lewis structure

Beryllium Chloride BeCl 2 1. Lewis structure             Cl Be Cl

Beryllium Chloride BeCl 2 1. Lewis structure             Cl Be Cl 2. Count regions of electron density on central atom central atom

Beryllium Chloride BeCl 2 1. Lewis structure             Cl Be Cl 2. Count regions of electron density on central atom central atom 2

Beryllium Chloride BeCl 2 1. Lewis structure             Cl Be Cl 2. Count regions of electron density on central atom central atom 2 3. Draw and name electron-pair shape             Cl Be Cl linear

Beryllium Chloride BeCl 2 3. Draw and name electron-pair shape             Cl Be Cl linear 3. Derive and name molecular shape             Cl Be Cl linear

Carbon Dioxide

CO 2

Carbon Dioxide CO 2         O C O

Carbon Dioxide CO 2         O C O 2 regions

Carbon Dioxide CO 2         O C O 2 regions Electron-pair shape, linear        O C O

Carbon Dioxide CO 2         O C O 2 regions Electron-pair shape, linear        O C O Molecular shape, linear       O C O

Aluminum Bromide

AlBr 3

Aluminum Bromide AlBr 3 Al Br Br Br                  

Aluminum Bromide AlBr 3 Al Br Br Br                   3 regions

Aluminum Bromide AlBr 3 Al Br Br Br                   3 regions Electron-pair shape trigonal planar Al Br Br Br                  

Aluminum Bromide AlBr 3 Al Br Br Br                   3 regions Electron-pair shape trigonal planar Al Br Br Br                   Molecular shape trigonal planar Al Br Br Br                  

Nitrite Ion

NO 2 –

Nitrite Ion NO 2 –       ONO       –

Nitrite Ion NO 2 –       ONO       – 3 regions

Nitrite Ion NO 2 –       ONO       – 3 regions Electron-pair shape trigonal planar N O O             –

Nitrite Ion NO 2 –       ONO       – 3 regions Electron-pair shape trigonal planar N O O             –

Nitrite Ion NO 2 –       ONO       – 3 regions Electron-pair shape trigonal planar N O O             – Molecular shape bent bent N O O             –

Carbon Tetrabromide

CBr 4

Carbon Tetrabromide CBr 4 C Br Br Br                   Br      

Carbon Tetrabromide CBr 4 C Br Br Br                   Br       4 regions

Carbon Tetrabromide CBr 4 C Br Br Br                   Br       4 regions Electron-pair shape tetrahedral C Br Br Br                   Br      

Carbon Tetrabromide CBr 4 C Br Br Br                   Br       4 regions Electron-pair shape tetrahedral C Br Br Br                   Br       Molecular shape tetrahedral

Arsine

Arsine AsH 3

Arsine As H H H  

Arsine As H H H   4 regions electron-pair shape, tetrahedral

Arsine AsH 3 As H H H   4 regions electron-pair shape, tetrahedral As   H H H

Arsine AsH 3 As H H H   4 regions electron-pair shape, tetrahedral As   H H H molecular shape trigonal pyramid or tripod

Arsine AsH 3 As H H H   4 regions electron-pair shape, tetrahedral As   H H H molecular shape trigonal pyramid or tripod As H H H

Water H2OH2OH2OH2O

Water H2OH2OH2OH2O O   HH  

Water H2OH2OH2OH2O O   HH   4 regions electron-pair shape tetrahedral

Water H2OH2OH2OH2O O   HH   4 regions electron-pair shape tetrahedral O   HH  

Water H2OH2OH2OH2O O   HH   4 regions electron-pair shape tetrahedral O   HH   molecular shape bent

Water H2OH2OH2OH2O O   HH   4 regions electron-pair shape tetrahedral O   HH   molecular shape bent O HH

Phosphorus Pentafluoride

PF 5                 P F F F F F              

Phosphorus Pentafluoride PF 5                 P F F F F F               5 regions electron-pair shape trigonal bipyramidal                 F F F F F               P

Phosphorus Pentafluoride PF 5                 P F F F F F               5 regions electron-pair shape trigonal bipyramidal                 F F F F F               P molecular shape trigonal bipyramidal

Sulfur Tetrafluoride

SF 4

Sulfur Tetrafluoride SF 4           S F F F F                

Sulfur Tetrafluoride SF 4           S F F F F                 5 regions trigonal bipyramidal

Sulfur Tetrafluoride SF 4           S F F F F                 5 regions trigonal bipyramidal                 F F F F           S

Sulfur Tetrafluoride SF 4           S F F F F                 5 regions trigonal bipyramidal                 F F F F           S                 F F F F         S molecular shape distorted tetrahedral

Sulfur Tetrafluoride SF 4           S F F F F                 5 regions trigonal bipyramidal                 F F F F           S molecular shape see saw S F F F F

Chlorine Trifluoride

ClF 3

Chlorine Trifluoride ClF 3           F F F             Cl

Chlorine Trifluoride ClF 3           F F F             Cl 5 regions electron-pair shape trigonal bipyramidal

Chlorine Trifluoride ClF 3           F F F             Cl 5 regions electron-pair shape trigonal bipyramidal Cl   F F F                    

Chlorine Trifluoride ClF 3           F F F             Cl 5 regions electron-pair shape trigonal bipyramidal Cl   F F F                    

Chlorine Trifluoride ClF 3           F F F             Cl 5 regions electron-pair shape trigonal bipyramidal Cl   F F F                     molecular shape T-shape Cl   F F F                

Sulfur Hexafluoride

SF 6

Sulfur Hexafluoride SF 6 S F F F F F F                                    

Sulfur Hexafluoride SF 6 S F F F F F F                                     6 regions electron-pair shape octahedral S F F F F F F                                    

Sulfur Hexafluoride SF 6 S F F F F F F                                     6 regions electron-pair shape octahedral S F F F F F F                                     molecular shape octahedral

Bromine Pentafluoride

BrF 5

Bromine Pentafluoride BrF 5 Br F F F F F                                

Bromine Pentafluoride BrF 5 Br F F F F F                               6 regions electron-pair shape octahedral  

Bromine Pentafluoride BrF 5 Br F F F F F                               6 regions electron-pair shape octahedral Br F F F F F                                  

Bromine Pentafluoride BrF 5 Br F F F F F                               6 regions electron-pair shape octahedral Br F F F F F                                  

Bromine Pentafluoride BrF 5 Br F F F F F                               6 regions electron-pair shape octahedral Br F F F F F                                 molecular shape square pyramidal Br F F F F F                              

Xenon Tetrafluoride

XeF 4

Xenon Tetrafluoride XeF 4 Xe F F F F                            

Xenon Tetrafluoride XeF 4 Xe F F F F                             6 regions electron-pair shape octahedral

Xenon Tetrafluoride XeF 4 Xe F F F F                             6 regions electron-pair shape octahedral Xe F F F F                            

Xenon Tetrafluoride XeF 4 Xe F F F F                             6 regions electron-pair shape octahedral Xe F F F F                           

Xenon Tetrafluoride XeF 4 Xe F F F F                             6 regions electron-pair shape octahedral Xe F F F F                            Xe F F F F                         molecular shape square planar

Tribromide Ion Br 3 – Br 3 –

Tribromide Ion Br 3 – Br 3 – Br                   Br Br

Tribromide Ion Br 3 – Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bipyramidal

Tribromide Ion Br 3 – Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bipyramidal              Br Br      Br

Tribromide Ion Br 3 – Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bipyramidal              Br Br      Br

Tribromide Ion Br 3 – Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bipyramidal              Br Br      Br molecular shape linear             Br Br Br

Polarity of Molecules molecules in which dipole moments of the bonds do not cancel are polar moleculesmolecules in which dipole moments of the bonds do not cancel are polar molecules molecules that do not contain polar bonds or in which all dipole moments cancel are non-polar moleculesmolecules that do not contain polar bonds or in which all dipole moments cancel are non-polar molecules

CO 2 vs H 2 O C O O O H H

C O O O H H  +  –  +  –

CO 2 vs H 2 O C O O O H H  +  –  +  –

CO 2 vs H 2 O C O O O H H  +  –  +  – 0

CO 2 vs H 2 O C O O O H H  +  –  +  – 0

CO 2 vs H 2 O C O O O H H  +  –  +  – 0yx yx

CO 2 vs H 2 O C O O O H H  +  –  +  – yx y x

CO 2 vs H 2 O C O O O H H  +  –  +  – nonpolar polar

Study and Know 9.2 Polarity of Molecules

VSEPR Theory only explains molecular shapes says nothing about bonding in molecules Enter Valence Bond (VB) Theory atoms share electron pairs by allowing their atomic orbitals to overlap

+ H H

+ H H  bond

+ H H 1s E H

+ H H 1s E H H

+ F F F2F2F2F2

+ F F F2F2F2F2

1s 2s 2p E F

1s 2s 2p F E F

Methane CH 4 1s 2s 2p E C

Methane 1s 2s 2p E C H H

Methane 1s 2s 2p E C H H H+H+H+H+

Methane 1s 2s 2p E C H H H+H+H+H+ H–H–H–H–

Methane 1s 2s 2p E C H H H+H+H+H+ H–H–H–H– C H H H H 90° 90°

Methane C H H H H 109.5° Tetrahedral Geometry 4 Identical Bonds 4 Identical Bonds

Problem and Solution C must have 4 identical orbitals in valence shell for bonding solution: hybridization

Methane CH 4 1s 2s 2p E

Methane 1s 2s 2p E 1s 2s 2p E

Methane 1s 2s 2p E 1s 2s 2p E

Methane 1s 2s 2p E 1s 2s 2p E

Methane 1s 2s 2p E 1s E sp 3

– p 2s

– = 2p 2s an sp 3 hybrid orbital

4 identical sp 3 hybrid orbitals

tetrahedral geometry

4 identical sp 3 hybrid orbitals tetrahedral geometry

4 identical sp 3 hybrid orbitals tetrahedral geometry

Methane CH 4 1s 2s 2p E 1s E sp 3 H H H H

Hybridization vs Shape (e – pair) sp linearsp linear sp 2 trigonal planarsp 2 trigonal planar sp 3 tetrahedralsp 3 tetrahedral sp 3 d trigonal bipyramidalsp 3 d trigonal bipyramidal sp 3 d 2 octahedralsp 3 d 2 octahedral

Predict the Hybridization of the Central Atom in tribromide ion in tribromide ion

Predict the Hybridization of the Central Atom in tribromide ion in tribromide ion Br 3 –

Predict the Hybridization of the Central Atom in tribromide ion in tribromide ion Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bypyramidal

Predict the Hybridization of the Central Atom in tribromide ion in tribromide ion Br 3 – Br                   Br Br 5 regions electron-pair shape trigonal bypyramidal sp 3 d

Predict the Hybridization of the Central Atom in carbon dioxide in carbon dioxide CO 2

Predict the Hybridization of the Central Atom in carbon dioxide in carbon dioxide CO 2         O C O 2 regions Electron-pair shape, linear

Predict the Hybridization of the Central Atom in carbon dioxide in carbon dioxide CO 2         O C O 2 regions Electron-pair shape, linear sp

Predict the Hybridization of the Central Atom in aluminum bromide in aluminum bromide

Predict the Hybridization of the Central Atom in aluminum bromide in aluminum bromide Al Br Br Br                 3 regions Electron-pair shape trigonal planar  

Predict the Hybridization of the Central Atom in aluminum bromide in aluminum bromide Al Br Br Br                 3 regions Electron-pair shape trigonal planar   sp 2

Predict the Hybridization of the Central Atom in xenon tetrafluoride in xenon tetrafluoride

Predict the Hybridization of the Central Atom in xenon tetrafluoride in xenon tetrafluoride Xe F F F F                             6 regions electron-pair shape octahedral

Predict the Hybridization of the Central Atom in xenon tetrafluoride in xenon tetrafluoride Xe F F F F                             6 regions electron-pair shape octahedral sp 3 d 2

Consider Ethylene, C 2 H 4

C C H H H H

C C H H H H 3 regions trigonal planar

Consider Ethylene, C 2 H 4 C C H H H H 3 regions trigonal planar sp 2

Consider Ethylene, C 2 H 4 C C H H H H 3 regions trigonal planar sp 2

1s 2s 2p E

1s 2s 2p E 1s 2s 2p E

1s 2s 2p E 1s 2p E

2p

2p

 bond framework

 bond

Consider Acetylene, C 2 H 2 C C H H

C C H H 2 regions linear

Consider Acetylene, C 2 H 2 C C H H 2 regions linear sp

Consider Acetylene, C 2 H 2 C C H H 2 regions linear sp

1s 2s 2p E 1s 2s 2p E

1s 2s 2p E 1s sp 2p E

sp sp 2p 2p

 bond framework

 bonds

Generally single bond is a  bondsingle bond is a  bond double bond consists of 1  and 1  bonddouble bond consists of 1  and 1  bond triple bond consists of 1  and 2  bondstriple bond consists of 1  and 2  bonds

Molecular Orbital (MO) Theory when atoms combine to form molecules, atomic orbitals overlap and are then combined to form molecular orbitals orbitals are conserved a molecular orbital is an orbital associated with more than 1 nucleus like any other orbital, an MO can hold 2 electrons consider hydrogen atoms bonding to form H 2

+ H H

add subtract

add subtract bonding antibonding

add subtract bonding antibonding  * 1s  1s

1s 1s  * 1s H H H2H2H2H2 E E

1s 1s  1s  * 1s H H H2H2H2H2 E E

1s 1s  1s  * 1s H H H2H2H2H2 E E

1s 1s  1s  * 1s H H H2H2H2H2 E E

1s 1s  1s  * 1s H H H2H2H2H2 E E (  1s ) 2

1s 1s  1s  * 1s H H H2H2H2H2 E E (  1s ) 2 total spin = 0

Diamagnetic: slightly repelled by a magnetic fieldDiamagnetic: slightly repelled by a magnetic field total spin = 0 paramagnetic: attracted to a magnetic fielsparamagnetic: attracted to a magnetic fiels total spin not 0 Bond Order = 1/2 (bonding e – – antibonding e – )Bond Order = 1/2 (bonding e – – antibonding e – )

1s 1s  1s  * 1s H H H2H2H2H2 E E (  1s ) 2 total spin = 0 diamagnetic

1s 1s  1s  * 1s H H H2H2H2H2 E E BO = 1/2 ( 2 – 0) = 1

Consider He 2

1s 1s  1s  * 1s He He He 2 E E

1s 1s  1s  * 1s He He He 2 E E

1s 1s  1s  * 1s He He He 2 E E (  1s ) 2 (  * 1s ) 2

1s 1s  1s  * 1s He He He 2 E E diamagnetic

1s 1s  1s  * 1s He He He 2 E E BO = 1/2 ( 2 – 2 ) = 0

Combination of p Atomic Orbitals

2p 2p

subtract add

bonding MO antibonding MO subtract add

bonding MO antibonding MO  * 2p  2p subtract add

2p 2p

subtract add

antibonding MO bonding MO subtract add

 2p  * 2p subtract add

 2p  * 2p subtract add

Consider Li 2

2s 2s  2s  * 2s Li Li Li 2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s Li Li Li 2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s Be Be Be 2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s Be Be Be 2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s B B B2B2B2B2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s B B B2B2B2B2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s C C C2C2C2C2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s N N N2N2N2N2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s O O O2O2O2O2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s F F F2F2F2F2 E E 2p  2p  * 2p 2p  2p  * 2p

2s 2s  2s  * 2s Ne Ne Ne 2 E E 2p  2p  * 2p 2p  2p  * 2p