Intermolecular Forces and Liquids and Solids

Chapter 12

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A

________

is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.

2 Phases Solid phase - ice Liquid phase - water 12.1

Intermolecular Forces

____________ forces

are attractive forces

between

molecules.

____________ forces

hold atoms together in a molecule.

Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (

____________

) • 930 kJ to break all O-H bonds in 1 mole of water (_______) Generally,

inter

molecular forces are much _________ than

intra

molecular forces.

“Measure” of intermolecular force boiling point melting point D H vap D H fus D H sub 12.2

Intermolecular Forces

Dipole-Dipole Forces

Attractive forces between ____________

molecules

Orientation of Polar Molecules in a Solid 12.2

Intermolecular Forces

Ion-Dipole Forces

Attractive forces between an ______ and a ________ molecule Ion-Dipole Interaction 12.2

12.2

Dispersion Forces

Intermolecular Forces

Attractive forces that arise as a result of

temporary

______________

induced

in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction 12.2

Induced Dipoles Interacting With Each Other

12.2

Intermolecular Forces

Dispersion Forces Continued

_____________________

is the ease with which the electron distribution in the atom or molecule can be distorted.

• • Polarizability increases with: greater number of electrons more diffuse electron cloud Dispersion forces usually increase with molar mass.

12.2

What type(s) of intermolecular forces exist between each of the following molecules?

HBr CH 4 SO 2 S 12.2

Intermolecular Forces

____________ Bond The

____________ bond

is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

A H…B or A A & B are N, O, or F H…A 12.2

12.2

Hydrogen Bond

Why is the hydrogen bond considered a “special” dipole-dipole interaction?

Decreasing molar mass Decreasing boiling point 12.2

Properties of Liquids

______ ________

is the amount of energy required to stretch or increase the surface of a liquid by a unit area.

Strong intermolecular forces High surface tension 12.3

Properties of Liquids

________

is the intermolecular attraction between like molecules

________

is an attraction between unlike molecules Adhesion Cohesion 12.3

Properties of Liquids

________

is a measure of a fluid’s resistance to flow.

Strong intermolecular forces High viscosity 12.3

Ice is less dense than water Water is a Unique Substance Maximum Density 4 0 C Density of Water 12.3

A

________ solid

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

An

________ solid

does not possess a well-defined arrangement and long-range molecular order.

A

________ ________

is the basic repeating structural unit of a crystalline solid.

Unit Cell lattice point Unit cells in 3 dimensions • • • At lattice points: Atoms Molecules Ions 12.4

12.4

12.4

12.4

12.4

Shared by 8 unit cells Shared by 2 unit cells 12.4

1 atom/unit cell (8 x 1/8 = 1) 2 atoms/unit cell (8 x 1/8 + 1 = 2) 4 atoms/unit cell (8 x 1/8 + 6 x 1/2 = 4) 12.4

12.4

When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver.

d

=

m V V

=

a

3 = (409 pm) 3 = 6.83 x 10 -23 4 atoms/unit cell in a face-centered cubic cell cm 3

m

= 4 Ag atoms 107.9 g x mole Ag x 1 mole Ag 6.022 x 10 23 atoms =

d

=

m V

= 7.17 x 10 -22 g 6.83 x 10 -23 cm 3 = 12.4

12.5

Extra distance = BC + CD = 2

d

sin q =

n

l (Bragg Equation) 12.5

X rays of wavelength 0.154 nm are diffracted from a crystal at an angle of 14.17

0 . Assuming that

n

= 1, what is the distance (in pm) between layers in the crystal?

n

l = 2

d

sin q

n

= 1 q = 14.17

0 l = 0.154 nm = 154 pm

d

=

n

l 2sin q = 1 x 154 pm 2 x sin14.17

= 314.0 pm 12.5

• • • •

Types of Crystals

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 CaF 2 12.6

• • • •

Types of Crystals

Crystals Lattice points occupied by atoms Held together by covalent bonds Hard, high melting point Poor conductor of heat and electricity carbon atoms diamond graphite 12.6

• • • •

Types of Crystals

Crystals Lattice points occupied by molecules Held together by intermolecular forces Soft, low melting point Poor conductor of heat and electricity 12.6

• • • •

Types of Crystals

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 12.6

Crystal Structures of Metals

12.6

Types of Crystals

12.6

An

________________ solid

does not possess a well-defined arrangement and long-range molecular order.

A

________________

is an optically transparent fusion product of inorganic materials that has cooled to a rigid state

without crystallizing

Crystalline quartz (SiO 2 ) Non-crystalline quartz glass 12.7

Chemistry In Action:

High-Temperature Superconductors

Chemistry In Action:

And All for the Want of a Button T < 13 0 C white tin grey tin stable weak

T 2 > T 1 Least Order Greatest Order 12.8

The

_________ _________ _________

is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation H 2 O (

l

) H 2 O (

g

) Dynamic Equilibrium Rate of condensation = Rate of evaporation 12.8

Before Evaporation At Equilibrium 12.8

________________________________

( D

H

vap ) is the energy required to vaporize 1 mole of a liquid at its boiling point.

Clausius-Clapeyron Equation D

H

vap ln

P

= +

C RT P

= (equilibrium) vapor pressure

T

= temperature (K)

R

= gas constant (8.314 J/K • mol)

Vapor Pressure Versus Temperature

12.8

The

________ ________

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

The

_________ _________ _________

is the temperature at which a liquid boils when the external pressure is 1 atm.

12.8

The

__________ temperature

(

T

c ) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure.

The

____________

pressure

(

P

c ) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature.

12.8

The Critical Phenomenon of SF 6

T < T c T > T c T ~ T c T < T c 12.8

H 2 O (

s

) H 2 O (

l

) The

________ point

of a solid or the

________ point

of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium 12.8

Molar ___________ of ___________

( D

H

fus ) is the energy required to melt 1 mole of a solid substance at its freezing point.

12.8

Heating Curve

12.8

H 2 O (

s

) H 2 O (

g

) (

Molar heat of ___________

D

H

sub ) is the energy required to sublime 1 mole of a solid.

D

H

sub = D

H

fus + D

H

vap ( Hess’s Law) 12.8

A

________ ________

summarizes the conditions at which a substance exists as a solid, liquid, or gas.

Phase Diagram of Water

12.9

Phase Diagram of Carbon Dioxide

CO 2 At 1 atm (

s

) CO 2 (

g

) 12.9

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

12.9

Chemistry In Action:

Liquid Crystals