chapter 6 section 5 molecular geometry pages 197-207 1 modern chemistry chapter 6 chemical bonding...

Chapter 6 Section 5 Molecular Geometry pages 197-207

1

Modern ChemistryChapter 6

Chemical Bonding

Sections 1-5Introduction to Chemical Bonding

Covalent Bonding & Molecular CompoundsIonic Bonding & Ionic Compounds

Metallic BondingMolecular Geometry


2

Chapte

r V

oca

bula

ryVSEPR theoryHybridizationHybrid orbitalsDipoleHydrogen bonding London dispersion

forces


3

Section 5

Molecular Geometry


4

VSEPR Theory•Valence-Shell

Electron-Pair Repulsion

• Repulsions between the set of valence-level electrons surrounding an atom causes these sets to be oriented as far apart as possible.


5

VSPR

E &

Mole

cula

r G

eom

etr

yp.

xx


6

Geom

etr

y &

Lone P

air

s


7

Molecular GeometryLINEAR

Example formula: BeF2

Type of molecule: AB2 Bond angle: 180° Shared pairs on the central atom: 2Unshared pairs on the central atom:

0

- Be -

F::F: :

: :


8

TRIGONAL PLANAR

Example formula: BF3

Type of molecule: AB3 Bond angle: 120° Shared pairs on the central atom: 3Unshared pairs on the central atom:

0

Molecular Geometry

F:::

:F::

:F::

B


9

Molecular GeometryTETRAHEDRAL

Example formula: CH4

Type of molecule: AB4 Bond angle: 109.5° Shared pairs on the central atom: 4Unshared pairs on the central atom:

0

CHH

H

H


10

Molecular GeometryANGULAR

Example formula: H2O

Type of molecule: AB2E2

Bond angle: 105° Shared pairs on the central atom: 2Unshared pairs on the central atom:

2

HO

H

::


11

Molecular GeometryTRIGONAL PYRAMIDAL

Example formula: NH3

Type of molecule: AB3EBond angle: 107° Shared pairs on the central atom: 3Unshared pairs on the central atom:

1

H H

N

:

H


12

Molecular Geometry• Unshared pairs occupies more

space around the central atom than shared pairs

• Unshared pairs repel other electrons more strongly than shared pairs

• Multiple bonds are treated the same as single bonds

• Polyatomic ions are treated like molecules.


13

Molecular Geometry• Try

– CO2

– ClO3 1-

• Practice Problems page 201• Try

– CF4

– NO3 1-


14

Hybridization• The mixing of two or more atomic

orbitals of similar energies on the same atom to produce new hybrid atomic orbitals of equal energy

• Example CH4

C = _ _ __ 1s 2s 2p _ _ _ _ 1s sp3


15

Hybridization• s and p orbitals have different

shapes• The 2s & 2p hybridize to make

four identical orbitals– named sp3

– The 3 is from the three p orbitals used

– But the 1 is not written for the s


16

Hybridization• All sp3 orbitals have the same

energy– Higher than 2s but– Lower than 2p

• Hybrid orbitals – orbitals of equal energy produced by the combination of two or more orbitals.


17

HybridizationN = _ _ _ 1s 2s 2p _ _ _ 1s sp3

O = _ _ 1s 2s 2p _ _ 1s sp3


18

HybridizationBe = 1s 2s _ _ __ 1s spB = _ __ __ 1s 2s 2p _ _ _ __ 1s sp2

Uses one p orbital

Uses two p orbitals


19

Hyb

rid

izati

on

p.

xx


20

Hybri

d O

rbit

al A

nim

ati

on

p. x

x


21

Comparing Molecular & Ionic Compoundsp

. xx


22

Molecule Polarity

• Dipole: created by equal but opposite charges that are separated by a short distance

H - ClLower EN

Higher ENpolar bond =

dipole

2.1

3.0

δ+ δ-


23

Molecule Polarity• Molecule polarity for

compounds with more than one bond depends on …

bond polarity and

molecule geometry.


24

Molecule Polarity1. Draw the Lewis Structure true

to shape. Example NH3

NH

HH

:


25

Molecule Polarity2. Find all the partial positive and

negatives for each atom in the molecule

HH

H

Look at each bond.High EN = δ- Low EN = δ+

δ-

δ+

δ+

δ+

2.1

3.0N

:


26

Molecule Polarity3. Look at around the “outside” of

the molecule.

NH

HH

:

All the same δ = NP; Different δ = P

δ-

δ+

δ+

δ+


27

Molecule Polarity1. Draw the Lewis Structure true

to shape. Example CH4

CH

HH

H


28

Molecule Polarity2. Find all the partial positive and

negatives for each atom in the molecule

Look at each bond.High EN = δ- Low EN = δ+

δ+

δ+

δ+

δ+

2.1

2.5C

HH

H

H

2.12.

1

2.1

δ-


29

Molecule Polarity3. Look at around the “outside” of

the molecule.

δ+

δ+

δ+

δ+

CH

HH

H

δ-

All the same δ = NP; Different δ = PCarbon is not on the “outside”.


30

Intermolecular Forces• The force of attraction between

molecules to make (solids or) liquids

• Boiling point is a good measure of the strength of intermolecular forces

• Weaker than covalent bonds, ionic bonds and metallic bonds


31

Molecule Polarity

Dipole-dipole force: the force of attraction between polar molecules

H - Clδ+ δ-

H - Clδ+ δ-


32

Dip

ole

Dip

ole

Anim

ati

on

p. x

x


33

Comparing Dipole Dipole Forcesp

. xx


34

Hydrogen Bonding• H-F, H-O or H-N bonds have a

large electronegativity difference

• These bonds are very polar.• Molecules with these bonds

have very strong dipole-dipole forces


35

Hyd

rog

en

Bon

din

g

p.

xx


36

Hydrogen Bonding• The intermolecular force in

which a Hydrogen atom that is bonded toNitrogen or Oxygen or Fluorineis attracted to an unshared pair of electronsof the N, O or F of another molecule


37

Hydrogen Bonding• Compare

PH3 & NH3 H2O & H2S Page 204


38

Dip

ole

Induce

d D

ipole

p. x

x


39

Induced Dipole• Polar molecules cause a dipole

in a nonpolar molecule

O

H

H

δ+

δ- O O::

::

::

δ+ δ

+δ-


40

London Dispersion Forces• Nonpolar molecules don’t have

dipoles• However at any instance the

electron distribution may be uneven.

• An instantaneous dipole can occur and induce dipoles in other molecules


41

London D

ispers

ion F

orc

ep.

xx


42

London Dispersion Forces• London dispersion forces – the

intermolecular attraction resulting from the constant motion of electrons and the creation of instantaneous dipoles

• Very weak intermolecular forces• London forces increase with

increasing atomic or molar mass.


43

Lew

is S

truct

ure

s Pra

ctic

e

• C2H4

• BeF2

• AsH3

• IBr

• CHCl3• CN 1-

• N2O2


44

Lew

is S

truct

ure

s Pra

ctic

e

• C2Cl4• SCl2• AsF5

• CI2Cl2• BF3

• NO 1-

• CH2O

• IO3 1-


45

Section 5 Homework

Chapter 6 Section 5 Worksheet

chapter 6 section 5 molecular geometry pages 197-207 1 modern chemistry chapter 6 chemical bonding...

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