AP Notes Chapter 12 & 13Intermolecular Forces, Liquids and SolidsIntermolecular Forces, Liquids and Solids

1. Ion - Ion

Dissociation Energy of Alkali Halides

500600700800900

10001100

Li Na K Rb Cs

Hdi

ssoc

(kJ/

mol

)

F

Cl

Br

I

Dissociation Energy

Opposite of Lattice Energy

MX (s) M+(g) + X-

(g)

1. Ion - Ion2. Ion - Permanent Dipole

Hydrated IonsA particle that is only weakly polar but is much larger than ion alone

The number of waters of hydration depends on size of ion and strength of charge to be stabilized (typically less than 5)

1. Ion - Ion2. Ion - Permanent Dipole3. Dipole - Dipole

Occurs between molecules with

permanent dipoles (SO2 , CHCl3 , etc)

Hydrogen-Bonding

Relatively strong attraction between a hydrogen atom in one molecule and a highly electronegative atom (F, O, N) in a different molecule

Hydrogen-Bonding

Strong enough to produce a phase

change in a compound that should be more

random at that temperature(about 1.5 kJ)

Dimer ofAcetic Acid

Hydrogen-Bonding

How and why of bonding is not clear - most likely due to strong attraction between e- cloud of the highly EN atom and the nucleus of the H atom

QUESTIONIs the hydrogen bond

a “true” chemical bond or is it just a

very strong electrostatic attraction?

1. Ion - Ion2. Ion - Dipole3. Dipole – Dipole4. Dipole-Induced Dipole

1. Ion - Ion2. Ion - Dipole3. Dipole – Dipole4. Dipole-Induced Dipole5. Dispersion Forces

Dispersion Forces

Process of distorting an electron cloud by

electrostatic forces of attraction and

repulsion.Weakest of the

intermolecular forces.

Non-polarmolecules

Momentary attractions

& repulsions

Temporarydipoles

established

Dispersion forces also called

van der Waal’s forces

LIQUIDS & SOLIDS

Cohesive Forcesvarious

intermolecular forces holding a liquid together

Vaporization Process in which a Process in which a

substance in the liquid substance in the liquid state becomes a gas.state becomes a gas.

Vaporization requires Vaporization requires energy since it involves energy since it involves separation of particles separation of particles that are attracted to one that are attracted to one another. another.

Standard Molar Enthalpy of

Vaporization, Hºvap Energy required to convert one Energy required to convert one

mole of liquid to one mole of the mole of liquid to one mole of the corresponding gas at the BP.corresponding gas at the BP.

Always endothermic, Always endothermic, HHvapvap is is positive.positive.

Liquids having greater attractive Liquids having greater attractive forces have higher forces have higher HHvapvap

2mv2

1 KE

Opposite of Evaporation

Condensation -- Exothermic

Condensation

Viscosity

a measure of the resistance to

flow of a liquidEthylene Glycol & EtOH

Surface Tension

the force that causes the surface of a

liquid to contract

Paper Clip

Adhesive Forces

the forces of attraction between a

liquid and a surface

Capillary Action Meniscus

SOLIDS

Amorphous Solids

Arrangement of particles lacks an ordered internal

structure. As temp is lowered, molecules

move slower and stop in somewhat random

positions.

Crystalline SolidsAtoms or ions are held

in simple, regular geometric patterns

IonicMolecular

Atomic

Atomic SolidsNoble Gases

NetworkMetallic

X-ray Crystallography

How do you determine the spacing and

position of atoms in an organized

solid like a crystal?

X-ray Crystallography

Bragg discovered that nuclei of atoms or

ions in a crystal will defract x-rays and form a pattern on

photofilm that can be analyzed using simple trig &

geometry

X-ray CrystallographyUse the fact that x-rays

are part of the electromagnetic

spectrumNuclei in crystalline solids are in layers that can act as a diffraction grating to the x-ray wavelength

Crystalline Solids Diffract X-rays

Let = “extra” distance that i’ must travel so

that r’ is in-phase with r

= xy + yzor = 2xy

Using trigonometry:

sin dxy

d

xysin

sin d 2

But for constructive interference

But for constructive interference

= nn = 2d sin

BRAGG EQUATION

1. X-rays from a copperx-ray tube ( = 154 pm)were diffracted at an angle of 14.220 by acrystal of Si. What isthe interplanar spacingin silicon?

Solids

Types of Solids

1. Atomic (Metals)

2. Molecular (Ice) 3. Ionic (NaCl)

Structures of Metals

The unit cell is the smallest

representation of the building block of the

regular lattice

Unit CellOnly 23 different unit

cells have been defined

Called Brave’ LatticesPatterns are determined by crystallography

Coordination NumberCN is related to net

atoms found within the unit cell

CN is the number of atoms closest to any

given atom in a crystal

There are three Cubic Unit Cell TypesThere are three Cubic Unit Cell Types

(pc) primitive cubic or simple cubic(pc) primitive cubic or simple cubic(8 corners of cube) x (1/8 each corner in cell) = 1 net atom in cell(8 corners of cube) x (1/8 each corner in cell) = 1 net atom in cell

CN = 6CN = 6

(bcc) body centered cubic(bcc) body centered cubic(1 atom in cube) + (1 atom in cube) +

[(8 corners of cube) x (1/8 each corner in cell)] = 2 net atoms in [(8 corners of cube) x (1/8 each corner in cell)] = 2 net atoms in cellcell

CN = 8CN = 8

(fcc) face centered cubic(fcc) face centered cubic[(6 faces of cube) x (1/2 of atom in cell)] + [(6 faces of cube) x (1/2 of atom in cell)] +

[(8 corners of cube) x (1/8 each corner in cell)] = 4 net atoms in [(8 corners of cube) x (1/8 each corner in cell)] = 4 net atoms in cellcell

oror CN = 12CN = 12 (1 atom in cube) +(1 atom in cube) + [(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell[(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell

CN = 12CN = 12

1 Atom per Cell

CN = 6

l = 2r

l

2 Atoms per Cell

CN = 8l

22 2 r42

3

r4

4 Atoms per Cell

CN = 12

l

2 22 r4

2r2

Summary

Unit Cell

Atoms

Per Cell

C.N.

LengthOf Side

Cubic 1 6 2rBCC 2 8

FCC 4 12

34r

22r

Face-centered cubicPrimitive cubic

Structures of Metals

Closest Packing

Structures of Metals

Closest Packing 1. Hexagonal 2. Cubic

A-B A-B-C

(Primitive cubic)

2. Al crystallizes as a face centered cube. The atomic radius of Al is 143 pm. What is

the density of Al in g/cm3?

3. What is the percent of empty space in a body

centered unit cell?

VAPORPRESSURE

Evaporationand equilibrium

Vapor Pressure

pressure in space above a liquid in a CLOSED container

PROPERTIES1. closed container2. temperature dependent

3. subject to all laws of partial pressures

4. dynamic system

Vapor Pressure temperature dependent

P

T

To plot in a linear fashion, must transform the

variables.

ln P

1/T (K)

y = mx + b

& R = 8.314 J/K mol

R

H m :where vap

therefore:

bT

1

R

H- P ln vap

ln P

1/T (K)

define 2 points

1

2

bT

1

R

H- P ln

bT

1

R

H- P ln

2

vap2

1

vap1

Subtract: ln P1 - ln P2

bT

1

R

H--

bT

1

R

H-

2

vap

1

vap

Collect terms & factor:

Clausius-ClapeyronEquation

12

vap

2

1

T

1

T

1

R

H

P

Pln

SUMMARY OF IDEAS TO BE CONSIDERED:1. vapor pressure - temperature dependent2. volume determines time needed to establish vapor pressure - NOT final pressure

3. H (condensation) = -H (vaporization)

4. Critical Point - (T,P) above which vapor cannot be liquefied - regardless of pressure5. Boiling: temperature where vapor pressure of liquid is the same as atmospheric pressure

4. The temperature inside a pressure

cooker is 1150C. What is the vapor pressure

of water inside the pressure cooker?

PHASE DIAGRAMS

PHASE DIAGRAMPHASE DIAGRAM

A representation of the A representation of the phases of a substance in phases of a substance in

a closed system as a a closed system as a function of temperature function of temperature

and pressureand pressure

Normal Boiling PointNormal Boiling Point

Temperature at which Temperature at which the vapor pressure of the vapor pressure of the liquid is exactly 1 the liquid is exactly 1

atmosphereatmosphere

Normal Melting Normal Melting PointPoint

Temperature at which Temperature at which the solid and liquid the solid and liquid

states have the same states have the same vapor pressure when vapor pressure when

the total P = 1 atmthe total P = 1 atm

Triple PointTriple Point

The point on a phase The point on a phase diagram at which all diagram at which all

three states of a three states of a substance are presentsubstance are present

Critical TemperatureCritical Temperature

Temperature above Temperature above which vapor cannot be which vapor cannot be liquified no matter what liquified no matter what

pressure is appliedpressure is applied

Critical PressureCritical Pressure

Minimum pressure Minimum pressure required to produce required to produce

liquefaction of a liquefaction of a substance at the substance at the

critical temperaturecritical temperature

Critical PointCritical Point

Ordered pair ofOrdered pair of

Critical TemperatureCritical Temperature

& Critical Pressure& Critical Pressure

CO2

H2O

sulfur