CH 12: Intermolecular Forces and Liquids and Solids

I. States of Mattera) Kinetic Energy vs. Attractive Forces

II. Intermolecular Forces (Attractive, van der Waal Forces)a) Dipole-Dipole--- (Polar Molecules)

i. Hydrogen Bonding

b) Dispersion (London) Forces--- (NonPolar Molecules)

c) Attractive Forces Involving Ions

Intermolecular Forces and Liquids and Solids

III. Properties of Liquidsa) Viscosityb) Meniscus Formationc) Surface Tensiond) Capillary Action

IV. Phase Changesa) Equilibrium Vapor Pressure

i. Normal boiling point

b) Phase Diagrams

Intermolecular Forces and Liquids and Solids

V. Crystalline Structure of Solidsa) Unit Cells (Simple Cubic, BCC, FCC)

i. Coordination Number

ii. # Lattice Points in a Unit Cell

VI. Radius vs. Unit Cell Edge Length,aa) Density

VII. Types of Crystalline Solidsa) Ionic, Molecular, Covalent, and Metallic

States of Matter

Part I

Three States of Matter

1.5

Factors in Determining State of Matter

I. Kinetic Energy

II. Intermolecular Forces; Attractive Forces between different molecules• neglible in gases

• important in solids, liquids

GAS-Effect of Kinetic Energy Overwhelms Attractive Force

Liquid – Molecules have Enough Kinetic Energy to Slide Past One Another.

Liquid – Molecules have Enough Kinetic Energy to Slide Past One Another.

Solid – Molecules Kinetic Energy is NOT Strong Enough to Allow

Molecules to Slide Past One Another

Intermolecular Forces(Attractive Forces, van der Waal

Forces)

Part II

Intermolecular Forces

11.2

Interermolecular forces; attractive forces between diff. Moleculeswhich bring the molecules in contac with eac other

Intraramolecular forces hold 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 weaker than intramolecular forces.

“Measure” of intermolecular force

boiling point

melting point

Hvap

Hfus

Hsub

Types of Intermolecular Forces

1. Dipole/ Dipole Forces (Polar Molecules)

• Hydrogen Bonds

2. London/ Dispersion Forces (NonPolar Molecules)

Intermolecular Forces

I. Dipole-Dipole Forces

Attractive forces between polar molecules

Orientation of Polar Molecules in a Solid

11.2

Intermolecular Forces

II. Dispersion Forces

Attractive forces that arise as a result of temporary dipoles induced in atoms or nonpolar molecules

11.2

Polarizability

• Ease at which the electron distribution in an atom or molecule can be distorted and a temporary dipole induced

– More electrons (greater Molar Mass) leads to greater polarizability.

Formation of Temporary Dipoles

1. Random movement of electrons

2. ion-induced dipole interaction

3. dipole-induced dipole interaction

SO

O

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

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

CH4

CH4 is nonpolar: dispersion forces.

SO2

SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.

11.2

Boiling Point- Temperature at which there is enough Kinetic Energy to Overcome Intermolecular Forces

Liquid

Has Intermolecular Forces

Gas

No Intermolecular Forces

Boiling Point Increases with..

1. Stronger Intermolecular Force

2. If same Intermolecular Force;• increasing Molar Mass, higher boiling point

Explain why the Higher Molar Mass Compound, CF4, has a Lower

Boiling Point than H2Se

CF4

• Boiling Point; -150.0°C• Molar Mass ~ 88 g/mole

H2Se• Boiling Point; -42.0 °C• Molar Mass ~ 81 g/mole

Intermolecular Force; Dispersion Force

Intermolecular Force; Dipole-Dipole Force

Boiling Points of Polar Hydrogen Compounds

Approximate Molar Mass;

g/mole

Boiling Point;

°C

H2O 18 + 100

H2S 34 -60

H2Se 81 -42

H2Te 130 -2

Hydrogen Bond

• Strong Type of Dipole-Dipole Force. This Type of Intermolecular Force Happens When H is directly bonded to O, N, or F.

High Strength of H- bond

1. Large electronegativity difference between H and N, O, or F.

2. Small size of H atom allows it to get close to another molecule

Hydrogen Bond

O-H Covalent Bond that Makes H-bonding Possible

Which of the Two Polar Molecules Has a Higher Boiling Point ?

diethyl ether

C

H

H

H O C

H

H

H

C

H

H

H C

H

H

O H

ethanol

Importance of H-Bonds in H2O

1. Very high boiling point for water (H2O(l)) for its Molar Mass.

2. The solid form of the material is less dense than liquid form

• Ice Floats on liquid water.• Water expands as it freezes

Ice Cubes float on water (Left)Solid benzene sinks to the bottom of

liquid benzene (right)

Importance of H-Bonds in H2O

1. Very high boiling point for water (H2O(l)) for its Molar Mass.

2. Ice floats on liquid water. • The solid form of the material is less dense

than liquid form• Water expands as it freezes

3. High specific heat of Water

Determining Type of Intermolecular Force

Polar Molecules ?

Dispersion/London Forces

H Directly Bonded to O, N, or F ?

Dipole/Dipole Force

Hydrogen Bonding

Increasing Strength of Intermolecular Force

NO

YES

NO YES