8/6/2019 Chap 11 smr 11

1/8

7/5/201

1

Intermolecular Forces andLiquids and Solids

Chapter 11

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2

Phase: homogeneous part of the system in contact with otherparts of the system but separated from them by a well-definedboundary.

3

Forces

Intermolecular forcesare attractive forces between molecules.

Intramolecular forceshold atoms together in a molecule.

Intermolecular vs Intramolecular

41 kJ to vaporize 1 mole of water (inter)

930 kJ to break all O-H bonds in 1 mole of water ( intra)

Generally, intermolecular

forces are much weakerthan intramolecular forces.

Measure of intermolecular force

boiling point

melting point

DHvap

DHfus

DHsub 4

Intermolecular Forces

Dipole-Dipole Forces

Attractive forces between polar molecules

Orientation of Polar Molecules in a Solid

5

Intermolecular Forces

Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

Ion-Dipole Interaction

6

in solution

EX: Interaction Between Water and Cations

8/6/2019 Chap 11 smr 11

2/8

7/5/201

7

Intermolecular Forces

Dispersion Forces

Attractive forces that arise as a result of temporarydipoles induced in atoms or molecules

ion-induced dipole interaction

dipole-induced dipole interaction

Neutral

molecule

8

Induced Dipoles Interacting With Each Other

9

Intermolecular Forces

Dispersion Forces Continued:

Polarizability: the ease with which the electron distribution inthe atom or molecule can be distorted

Polarizability increases with:

greater number of electrons

more diffuse electron cloud

Dispersion forces usually

increase with molar mass

10

S

EX:What type(s) of intermolecular forces existbetween each of the following molecules?

HBrHBr is a polar molecule: dipole-dipole forces. There arealso dispersion forces between HBr molecules.

CH4CH4 is nonpolar: dispersion forces.

SO2SO2 is a polar molecule: dipole-dipole forces. There arealso dispersion forces between SO2 molecules.

11

Intermolecular Forces

Hydrogen Bond : a special dipole-dipole interaction betweenthe hydrogen atom in a polar N-H, O-H, or F-H bond and anelectronegative O, N, or F atom.

A HB A HAor

A & B are N, O, or F

12

Hydrogen Bond

HCOOH and water

8/6/2019 Chap 11 smr 11

3/8

7/5/201

13

Why is the hydrogen bond considered a special

dipole-dipole interaction?

Decreasing molar massDecreasing boiling point

14

Properties of Liquids

Surface tension: the amount of energy required to stretchor increase the surface of a liquid by a unit area.

Strongintermolecular

forces

Highsurfacetension

15

Properties of Liquids

Cohesion:the intermolecular attraction between likemolecules

Adhesion:an attraction between unlikemolecules

Adhesion

Cohesion

16

Properties of Liquids

Viscosity: a measure of a fluids resistance to flow

Strongintermolecular

forces

Highviscosity

17

Density of Water

Maximum Density40C

Ice is less dense than water

Water is a Unique Substance3-D Structure of Water

18

crystalline solidpossesses rigid and long-range order. In acrystalline solid, atoms, molecules or ions occupy specific(predictable) positions.

amorphous soliddoes not possess a well-defined

arrangement and long-range molecular order.

unit cellis the basic repeating structural unit of a crystallinesolid.

latticepoint

Unit Cell Unit cells in 3 dimensions

At lattice points:

Atoms

Molecules

Ions

8/6/2019 Chap 11 smr 11

4/8

7/5/201

19

An Arrangement for Obtaining the X-ray Diffraction Patternof a Crystal.

20

Types of Crystals

Ionic Crystals Lattice points occupied by cations and anions

Held together by electrostatic attraction

Hard, brittle, high melting point

Poor conductor of heat and electricity

CsCl ZnS CaF2

21

Types of Crystals

Covalent Crystals Lattice points occupied by atoms

Held together by covalent bonds

Hard, high melting point

Poor conductor of heat and electricity

diamond graphite

carbonatoms

22

Types of Crystals

Molecular Crystals Lattice points occupied by molecules

Held together by intermolecular forces

Soft, low melting point

Poor conductor of heat and electricity

water benzene

23

Types of Crystals

Metallic Crystals Lattice points occupied by metal atoms

Held together by metallic bonds

Soft to hard, low to high melting point Good conductors of heat and electricity

Cross Section of a Metallic Crystal

nucleus &inner shell e-

mobile sea

of e-

24

Crystal Structures of Metals

8/6/2019 Chap 11 smr 11

5/8

7/5/201

25

Types of Crystals

26

A glassis an optically transparent fusion product of inorganicmaterials that has cooled to a rigid state without crystallizing

Crystallinequartz (SiO2)

Non-crystallinequartz glass

27

Chemistry In Action: High-Temperature Superconductors

MgB2

28

Chemistry In Action: And All for the Want of a Button

white tin grey tinT < 13 0C

stable weak

29GreatestOrder

LeastOrder

Phase Changes

30

T2 > T1

Effect of Temperature on Kinetic Energy

8/6/2019 Chap 11 smr 11

6/8

7/5/201

31

Equilibrium vapor pressureis the vapor pressuremeasured when a dynamic equilibrium exists between

condensation and evaporation

H2O (l) H2O (g)

Rate ofcondensation

Rate ofevaporation

=

Dynamic Equilibrium

32

BeforeEvaporation

AtEquilibrium

Measurement of Vapor Pressure

33

Molar heat of vaporization(DHvap) is the energy required tovaporize 1 mole of a liquid at its boiling point.

ln P= -DHvap

RT+ C

Clausius-Clapeyron Equation

P= (equilibrium) vapor pressure

T= temperature (K)

R= gas constant (8.314 J/Kmol)

Vapor Pressure Versus Temperature

34

Alternate Forms of the Clausius-Clapeyron Equation

At two temperatures

or

35

boiling pointis the temperature at which the (equilibrium)vapor pressure of a liquid is equal to the external pressure.

The normal boiling pointis the temperature at which a liquidboils when the external pressure is 1 atm.

36

The critical temperature(Tc) is the temperature above whichthe gas cannot be made to liquefy, no matter how great theapplied pressure.

The critical pressure(Pc) is the minimumpressure that must beapplied to bring about

liquefaction at thecritical temperature

8/6/2019 Chap 11 smr 11

7/8

7/5/201

37

The Critical Phenomenon of SF6

T < Tc T > Tc T ~ Tc T < Tc

38

H2O (s) H2O (l)

The melting pointof a solidor the freezing pointof aliquid is the temperature atwhich the solid and liquidphases coexist in equilibrium

Solid-Liquid Equilibrium

39

Molar heat of fusion(DHfus) is the energy required to melt1 mole of a solid substance at its freezing point.

40

Heating Curve

41

H2O (s) H2O (g)

Molar heat of sublimation(DHsub) is the energy requiredto sublime 1 mole of a solid.

DHsub = DHfus + DHvap( Hesss Law)

Solid-Gas Equilibrium

42

A phase diagramsummarizes the conditions at which asubstance exists as a solid, liquid, or gas.

Phase Diagram of Water

8/6/2019 Chap 11 smr 11

8/8

7/5/201

43

Phase Diagram of Carbon Dioxide

At 1 atmCO2 (s) CO2 (g)

44

Effect of Increase in Pressure on the Melting Pointof Ice and the Boiling Point of Water

45

Chemistry In Action: Ice Skating