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Chapter 9 Molecular Geometry & Molecular Geometry & Bonding Theories Bonding Theories

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Page 1: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Chapter 9

Molecular Geometry & Molecular Geometry & Bonding TheoriesBonding Theories

Chapter 9

Molecular Geometry & Molecular Geometry & Bonding TheoriesBonding Theories

Page 2: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Overview

Molecular Shapes VSEPR Model

Predicting Shapes Effect of Nonbonding Electrons

Polarity of Molecules Covalent Bonding

Page 3: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Hybrid Orbitals sp, sp2, sp3 hybrids containing d orbitals

Multiple Bonds sigma () & pi () localized & delocalized

Molecular Orbitals electron configurations & bond order diamagnetism & paramagnetism

Page 4: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Molecular Shapes & VSEPR

Shapes defined by bond angles linear, 180° angles trigonal planar, 120° angles tetrahedral, 109.5° angles

VSEPR Valence Shell Electron Pair Repulsion theory electron pairs are arranged symmetrically with

maximum separation

Page 5: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Two electron pairs 180° apart linear geometry

••••

180°

Page 6: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Three electron pairs 120° apart trigonal planar geometry

••

•• ••

120°

Page 7: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Four electron pairs 109.5° apart tetrahedral geometry

••

•• ••••

109.5°

Page 8: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Five electron pairs angles of 90° and 120° trigonal bipyramidal (TBP) geometry

••

••••

••••

120°

90°

Page 9: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Six electron pairs angles of 90° octahedral geometry

••

••

••

••

••

••

90°

Page 10: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Geometries

Electron pair geometry arrangement of electron pairs around a central

atom Molecular Geometry

arrangement of atoms around a central atom When all electron pairs are bonding pairs

electron pair geometry = molecular geometry When there are unshared electron pairs

electron pair geometry molecular geometry

Page 11: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

To determine electron pair geometry draw Lewis dot structure count shared & unshared electron pairs around central

atom• a multiple bond is counted as only one bonding pair when predicting geometry

determine electron pair geometry based on the number of electron pairs

• 2 pair = linear• 3 pair = trigonal planar• 4 pair = tetrahedral• 5 pair = trigonal bipyramidal• 6 pair = octahedral

Page 12: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Molecular Geometries with One or More Unshared Pairs

Two Pairs

electron pair geometry linear

bonding pairs 2

non-bonding pairs 0

molecular geometry linear

Page 13: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Two electron pairs

••••

180°

electron pair geometry

molecular geometry

Page 14: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Three Pairs

electron pair geometry trigonal planar

bonding pairs 3 2

non-bonding pairs 0 1

molecular geometry trig. pl. bent

Page 15: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Three electron pairs

••

•• ••

120°

••

trigonal planar

bent

electron pair geometry

molecular geometry

trigonal planar

Page 16: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Four Pairs

electron pair geometry tetrahedral

bonding pairs 4 3 2

non-bonding pairs 0 1 2

molecular geometry tet. trig. pyr. bent

Page 17: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Four electron pairs

••

•• ••••

109.5°

electron pair geometry

••

••

••

bent

trigonal pyramid

tetrahedral

molecular geometry

Page 18: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Five Pairs

electron pair geometry trigonal bipyramid

bonding pairs 5 4 3 2

non-bonding pairs 0 1 2 3

molecular geometry tbp seesaw T-shp. Lin.

Page 19: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Five electron pair

••

••••

••

••

120°

90°

electron pair geometrymolecular geometry

••

••

••

••••

••

TBP seesaw

T-shapedlinear

Page 20: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Six Pairs

electron pair geometry octahedral

bonding pairs 6 5 4 2

non-bonding pairs 0 1 2 4

molecular geometry oct sq.pyr. sq. pl. lin.

Page 21: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Six electron pairs

••

••

••

••

••••

90°

••

••

••

••

••

••

square pyramid

••

linear

square planar

octahedral

electron pair geometry

molecular geometry

Page 22: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Molecular Polarity

Molecules are always non-polar if all covalent bonds are non-polar N2, P4, Cl2

Molecules with polar bonds can be polar or non-polar H - Cl polar bond, polar molecular O=C=O two polar bonds but total molecule

is non-polar

Page 23: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

H Cl+

-

O C O

+- -

equal but opposite forces cancel out non-polar molecule

Page 24: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

O

H H+

+

-

are these dipole moments equal & opposite?

no

is this molecule polar? yes

Page 25: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

C

Cl Cl- -

+

Cl Cl--

are these bond dipole moments equal & opposite?

yes

is this molecule polar? no

Page 26: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

C

Cl Cl- -

H H+

+

are these bond dipole moments equal & opposite?

no

is this molecule polar? yes

Page 27: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Single and Multiple Bonds

(sigma) bonds always the first bond between two atoms single bonds are localized between two

atoms• orbitals from two atoms overlap, allowing electrons to be shared• electron density is on the internuclear axis

CC••

localized electrons

Page 28: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

(pi) bonds the second & third bonds between two

atoms bond electrons can be delocalized over

several atoms to form resonance structures• electron density is above & below the internuclear axis

CC CC internuclear axis

electron density above & below-- bond

CC CC

electron density can move or delocalize

••

••

Page 29: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Hybridization allows for greater number of bonds types of hybridization

sp mixing of one s orbital & one p orbital•

2s 2p sp p sp2 mixing of one s orbital & two p orbitals

• 2s 2p sp2 p

sp3 mixing of one s orbital & three p orbitals•

2s 2p sp3

Page 30: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

in sp hybridization the two sp hybrid orbitals form two bonds with linear geometry remaining two p orbitals form bonds

in sp2 hybridization the three hybrid orbitals form three bonds with trigonal planar

geometry the remaining one p orbital forms a bond

in sp3 hybridization the four hybrid orbitals form four bonds with tetrahedral geometry sp3 hybrid atoms can form no bonds as they have no unhybridized

p orbitals

Page 31: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

Molecular Orbitals

mathematical combinations of atomic orbitals delocalized over whole molecule n atomic orbitals produce n molecular orbitals

• ½ are bonding orbitals and ½ are antibonding orbitals

bond order # bonding electrons - # antibonding electron

2

Page 32: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

electron configuration of diatomic, homonuclear molecules

* * *

MO’s from s orbital combination

MO’s from p orbital combination

Page 33: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

electron configuration of diatomic, homonuclear molecules with interaction of the 2s and 2p orbitals

* * *

relative positions switched

Page 34: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

* * *

* * *

H2 N2

2 electrons 10 electrons

B.O. = 1 B.O. = 3

Page 35: Chapter 9 Molecular Geometry & Bonding Theories Chapter 9 Molecular Geometry & Bonding Theories

* * *

* * *

He2

4 electrons

B.O. = 0

O2

12 electrons

B.O. = 2